Showing papers in "European Journal of Plant Pathology in 2020"
TL;DR: It is argued to approach latent postharvest diseases as complex problems that require multiple interventions at different stages of the disease process in a systems intervention approach for their control.
Abstract: Postharvest diseases of pome fruit are typically caused by a wide diversity of fungal pathogens, and the list of confirmed causal agents is still growing. There is considerable knowledge on the epidemiology of wound pathogens, such as Botrytis cinerea and Penicillium expansum. In contrast, knowledge on the occurrence of the different postharvest diseases caused after latent (quiescent) infections during long-term storage and their epidemiology is limited. Well-known pathogens causing postharvest losses after latent infections are Neofabraea spp. and Colletotrichum spp., but in many cases the causal agents that occur in a specific region remain unknown and their control relies on the routine use of fungicide applications. However, due to the growing concern over the use of synthetic fungicides, alternative control measures are highly desired. Over the past years the use of physical treatments, natural compounds, and biocontrol agents have been investigated as alternatives. However, no single method has emerged that can robustly and reliably control postharvest diseases of pome fruit in practice. In this review it is argued to approach latent postharvest diseases as complex problems that require multiple interventions at different stages of the disease process in a systems intervention approach for their control. Such approach requires a deep understanding of the epidemiology of the causal agents in the orchard, fruit defence mechanisms against pathogens, and the molecular biology of host-pathogen interactions in order to develop novel disease control methods in which the deployment of resistant cultivars can be a cornerstone.
49 citations
TL;DR: Results obtained in this study indicated that the beneficial effect of S. indica colonization on FocTR4 resistance of banana might be achieved, at least partly, through regulation of antioxidant enzyme activities.
Abstract: Serendipita indica is a root-colonizing basidiomycete that has received considerable attention in recent decades on account of its wide host range and the diverse benefits it imparts to host plants, including banana (Musa spp.). Banana is globally threatened by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc). In this study, to examine whether S. indica can improve the Foc resistance of banana, S. indica colonized (S+) and non-colonized (CK) ‘Tianbaojiao’ banana plants were inoculated with Foc tropical race 4 (TR4). Chlorophyll fluorescence parameters in leaves and antioxidant enzyme activities in roots of S+, CK, FocTR4-inoculated S+ plants (SF), and FocTR4-inoculated CK plants (F+) were determined and symptom appearance in corms of SF and F+ plants was observed. An analysis of antagonistic activity between S. indica and FocTR4 was performed and results showed that no significant differences in chlorophyll fluorescence parameters were displayed between CK and S+. No significant differences in Y(II) (effective quantum yield of photochemical energy in PSII) and Y(NPQ) (quantum yield of regulated energy dissipation in PSII) were exhibited among the four groups. However, the Fv/fm (ratio of variable to maximal fluorescence) values were significantly decreased (p < 0.01) in F+ and SF, and the Fv/fm value of SF was significantly improved than that of F+ (p < 0.05). The Y(NO) (quantum yield of non-regulated energy dissipation in PSII) was remarkable improved (p < 0.01) in F+ but not in SF. Although infection symptoms in SF were significantly alleviated compared with those of F+, no obvious antagonistic effect was observed between S. indica and FocTR4, indicating that the enhancement of FocTR4 resistance in banana was not directly induced by S. indica. Colonization by S. indica increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities in S+. After FocTR4 inoculation, SOD activity was significantly compromised in F+ but not in SF; POD activity was drastically increased in both F+ and SF, and that in SF was significantly higher than in F+; CAT activity was significantly improved in S+, but no obvious change was observed in F+ and SF when compared with CK. Moreover, APX and glutathione reductase (GR) activities were enhanced dramatically in SF but not in F+ compared with CK. Results obtained in this study indicated that the beneficial effect of S. indica colonization on FocTR4 resistance of banana might be achieved, at least partly, through regulation of antioxidant enzyme activities.
31 citations
TL;DR: Pathogenicity tests demonstrated that most of these fungi were pathogenic to inoculated almond, pistachio and walnut shoots, and specific management strategies should be included within the nut crops IPM management programs, with the aim of improving their sustainability.
Abstract: Branch and trunk canker diseases have become prevalent on nut crops in Iran. During 2015 to 2018, extensive field surveys were conducted on 58 almond, 43 pistachio and 80 walnut orchards in Iran to study fungal pathogens associated with symptomatic trees. One hundred and fifty-six representative fungal isolates were selected and identified based on morphological characteristics and by phylogenetic comparison of DNA sequence data. Fungal species found were Collophorina hispanica, Pleurostoma richardsiae, nine species of Phaeoacremonium (namely P. angustius, P. cinereum, P. italicum, P. fraxinopennsylvanicum, P. minimum, P. parasiticum, P. scolyti, P. tuscanum and P. viticola), 11 species of Botryosphaeriaceae (namely Botryosphaeria dothidea, Diplodia gallae, D. mutila, D. seriata, Dothiorella plurivora, Do. sarmentorum, Do. viticola, Lasiodiplodia citricola, L. mahajangana, L. theobromae and Neofusicoccum parvum), four species of Diatrypaceae (namely Cryptosphaeria pullmanensis, Diatrype whitmanensis, Eutypella citricola and E. vitis) and two non-identified Eutypella spp. (Eutypella sp. 1 and Eutypella sp. 2). Some of these species represent new reports in Iran and/or are reported for the first time in their respective hosts. Pathogenicity tests demonstrated that most of these fungi were pathogenic to inoculated almond, pistachio and walnut shoots. Therefore, more importance should be given to fungal trunk pathogens in Iran, and specific management strategies should be included within the nut crops IPM management programs, with the aim of improving their sustainability.
28 citations
TL;DR: A large regional and yearly variation in disease severity, distribution and impact on yield is verified, emphasizing the need to adapt fungicide applications to the actual need based on locally adapted risk assessment systems.
Abstract: Fungal plant diseases driven by weather factors are common in European wheat and barley crops. Among these, septoria tritici blotch (Zymoseptoria tritici), tan spot (Pyrenophora tritici-repentis), and stagonospora nodorum blotch (Parastagonospora nodorum) are common in the Nordic-Baltic region at variable incidence and severity both in spring and winter wheat fields. In spring barley, net blotch (Pyrenophora teres), scald (Rhynchosporium graminicola, syn. Rhynchosporium commune) and ramularia leaf spot (Ramularia collo-cygni) are common yield limiting foliar diseases. We analysed data from 449 field trials from 2007 to 2017 in wheat and barley crops in the Nordic-Baltic region and explored the differences in severity of leaf blotch diseases between countries and years, and the impact of the diseases on yield. In the experiments, septoria tritici blotch dominated in winter wheat in Denmark and southern Sweden; while in Lithuania, both septoria tritici blotch and tan spot were common. In spring wheat, stagonospora nodorum blotch dominated in Norway and tan spot in Finland. Net blotch and ramularia leaf blotch were the most severe barley diseases over large areas, while scald occurred more locally and had less yield impact in all countries. Leaf blotch diseases, with severity >50% at DC 73–77, caused an average yield loss of 1072 kg/ha in winter wheat and 1114 kg/ha in spring barley across all countries over 5 years. These data verify a large regional and yearly variation in disease severity, distribution and impact on yield, emphasizing the need to adapt fungicide applications to the actual need based on locally adapted risk assessment systems.
24 citations
TL;DR: The studies reinforce the view that the principles of anti-resistance management should be applied upon the launch of a new active ingredient to prolong the effective life of both the old and new products.
Abstract: Zymoseptoria tritici causes septoria tritici blotch (STB), the predominant fungal disease in wheat in Denmark and Sweden. Disease control is highly reliant on fungicides in the group of demethylation inhibitors (DMI). The use of DMIs has increased steadily since their introduction in the 1970s. Epoxiconazole and prothioconazole were the most widely used active ingredients in the last ten years. The goal of this investigation was to survey the resistance development of Z. tritici towards these two compounds. In total, EC50 values were determined for 3472 Z. tritici isolates from 2012 to 2019. Also, the field performance of the most used DMI compounds was tested in field trials. EC50 values of epoxiconazole and prothioconazole increased in the testing period. A significant shift was observed for epoxiconazole in 2016 and again 2018 with average EC50 values >1 ppm in Denmark. In Sweden, average EC50 values for epoxiconazole reached 1 ppm in 2017. The sensitivity towards prothioconazole remained stable at a high level. Following the decline in sensitivity in vitro, field efficacies of epoxiconazole and prothioconazole decreased from 80 - 90% to 30 - 40% in Denmark and Sweden. Currently, the Danish and Swedish Z. tritici populations are highly adapted to epoxiconazole and prothioconazole. At the same time, a recovery in the sensitivity of tebuconazole and metconazole is observed. Our studies reinforce the view that the principles of anti-resistance management should be applied upon the launch of a new active ingredient to prolong the effective life of both the old and new products.
22 citations
TL;DR: It is reported that DLA is a rapid, reliable technique to screen maize resistance to SCLB and use of this tool in maize breeding programs can speed up the process of identification of sources of resistance to multiple variants of SclB.
Abstract: Southern corn leaf blight (SCLB), caused by the fungus Bipolaris maydis, is a disease that significantly affects maize productivity across the globe. A detached leaf assay (DLA) was developed to rapidly assess maize resistance to SCLB. Several experiments were conducted to: (i) identify a highly virulent B. maydis isolate; and to determine the most appropriate (ii) phytohormone to maintain viability of maize leaf tissue, (iii) leaf age for the assay, and (iv) inoculum concentration. Once optimized, the DLA was compared with screenhouse and field experiments. Use of DLA required a maximum of 28 days for resistance assessment, in contrast to screenhouse and field tests at a minimum of 33 and 72 days, respectively. DLA positively correlated with screenhouse (r = 0.48, P = 0.08) and field experiments (r = 0.68, P = 0.008). Assessments of diverse B. maydis strains and host genotypes indicated that the DLA could be used to detect both highly virulent SCLB strains and highly resistant maize genotypes. Here we report that DLA is a rapid, reliable technique to screen maize resistance to SCLB. Use of this tool in maize breeding programs can speed up the process of identification of sources of resistance to multiple variants of SCLB.
22 citations
TL;DR: Inoculation trials of blueberry plants confirmed the pathogenicity of Lasiodiplodia and Neopestalotiopsis species and revealed differences in aggressiveness among species and isolates.
Abstract: The production of blueberry in Peru has been increasing over the last years. Dieback and stem blight of plants are the most prominent disease symptoms observed in blueberry orchards. This study evaluated the diversity and pathogenicity of Lasiodiplodia and Neopestalotiopsis species associated with dieback of blueberry plants in Peru. A collection of isolates was initially subjected to Microsatellite-primed PCR (MSP-PCR) fingerprinting and further characterised by sequence analyses of the rDNA internal transcribed spacer region (ITS), translation elongation factor 1-alpha (tef1-α) and β-tubulin (tub2). The phylogenetic analyses revealed the presence of Lasiodiplodia theobromae, L. laeliocattleyae and Neopestalotiopsis rosae. Lasiodiplodia laeliocattleyae and N. rosae are reported for the first time in blueberry plants associated with dieback and stem blight symptoms. Additionally, N. rosae is newly reported from Peru. Inoculation trials of blueberry plants confirmed the pathogenicity of Lasiodiplodia and Neopestalotiopsis species and revealed differences in aggressiveness among species and isolates.
22 citations
TL;DR: This loop-mediated isothermal amplification method can rapidly detect Pst-infected tissues without strain enrichment and complex DNA extraction, and hence, it is suitable for quarantine and field detection.
Abstract: Tomato bacterial speck, caused by Pseudomonas syringae pv. tomato (Pst), is one of the most devastating bacterial diseases in tomato worldwide. To establish a rapid amplification system for the detection of Pst, a loop-mediated isothermal amplification (LAMP) method, which includes two external primers (F3/B3), two internal primers (FIP/BIP) and one backward loop primer (B-Loop), was designed based on the hrpZ gene. The specificity of the LAMP primer set was widely validated on Pst and non-target strains. The conditions for LAMP detection of Pst were optimized to complete in 60 min at 63 °C. The amplification was confirmed through gel electrophoresis or visual inspection using calcein. In the sensitivity test, the detection limit of the LAMP assay was 1.61 × 10 fg μL−1 for genomic DNA and 1.05 × 103 CFU mL−1 for bacterial suspension without DNA extraction. The novel method was also applied for the detection of Pst in artificially and naturally infected tomato leaf and stem tissue samples, and even the early onset of disease could be detected by the assay. This method can rapidly detect Pst-infected tissues without strain enrichment and complex DNA extraction, and hence, it is suitable for quarantine and field detection.
21 citations
TL;DR: It was proved that cinnamon powder has potential to inhibit B. cinerea growth and also has a stimulating effect for tomato plants.
Abstract: In this study, the effects of organic powder of Cinnamomum zeylanicum on the development of Botrytis cinerea and its influence on tomato plants were evaluated. The cinnamon bark powder and its water suspensions and filtrates were used at 0.5 and 1% rates. After 6 days of the start of an in vitro experiment the mycelium growth was inhibited by both 0.5 and 1% cinnamon water filtrates - to a greater degree in the case of the higher concentration, by 54.4 and 81.4%, respectively. Spraying with cinnamon water filtrates positively influenced the growth of plants both in the greenhouse and the field. Antifungal activity of cinnamon was proved in the greenhouse tests - the disease symptoms of grey mould on infected tomato plants decreased. The fresh weight of non-inoculated tomato plants treated with cinnamon filtrates was significantly higher than control plants (17.17 g compared to 12.83 g) showing a stimulating effect of cinnamon filtrates. In the case of inoculated plants due to treatment, their weight increased from 7.83 to 10.50 g. In the field experiment, tomato plants sprayed six times with cinnamon were better developed than the control plants. The most significant effect was observed for Hamlet variety - the mean number of leaves was higher by 27.3% and the mean number of branches by 19.7% compared to the untreated control plants. Thus it was proved that cinnamon powder has potential to inhibit B. cinerea growth and also has a stimulating effect for tomato plants.
21 citations
TL;DR: The findings suggest that the haplotype H is likely to be endemic in northern Europe and that the genetic diversity within the Lso species is higher than previously assumed.
Abstract: A previously unknown haplotype of the plant pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) was found in cultivated carrots and parsnips in eastern Finland. That same haplotype was found in western Finland, over 300 km away, in the family Polygonaceae, the species Fallopia convolvulus (wild buckwheat) and Persicaria lapathifolia (pale persicaria) growing as weeds within carrot and parsnip fields. The infected plants, both apiaceous and polygonaceous, showed symptoms of foliar discolouration. This is the first report of Lso bacteria in plants of the family Polygonaceae. The finding that the polygonaceous plants infected with a previously unknown haplotype of Lso were growing among the apiaceous plants infected with Lso haplotype C suggests that these two haplotypes might be transmitted by different vectors. Phylogenetic analyses showed that the new haplotype, called haplotype H, is distinct from the previously characterized haplotypes and appears to have diverged early from their common ancestor. Multi-locus sequence analysis revealed four different sequence types (strains) within the haplotype H. These findings suggest that the haplotype H is likely to be endemic in northern Europe and that the genetic diversity within the Lso species is higher than previously assumed.
20 citations
TL;DR: It is demonstrated that severity of charcoal root-rot disease in N fertilized soybean can be reduced by AMF inoculation, suggesting that N fertilization could increase the risk of diseases in soybean but mycorrhiza could contribute to soybean charcoal root rot control even if the crop is under N fertilizers.
Abstract: The capacity of arbuscular mycorrhizal fungi (AMF) to alleviate the negative effects incited by root pathogens in a range of plant hosts has been established. On the other hand, accumulated evidence also shows that fertilization practices can negatively impact AMF. Nevertheless, the interaction between AMF, pathogens and fertilizers, especially nitrogen (N) fertilizers, has not been previously reported. In this work, the effect of nitrogen on both the severity of the pathogen Macrophomina phaseolina (charcoal root rot) and the protection by the arbuscular mycorrhiza fungi (AMF) Rhizophagus intraradices was investigated in greenhouse experiments using soybean (Glycine max) as a host. The treatments were two levels of N (0 and 92 kg of urea ha−1), inoculation and non-inoculation with the AMF, and infection and non-infection with the pathogen. Soybean was harvested at R4 phenological stage (completed pod formation). Plant biomass, numbers of pods and leaves, plant height, root length, greenness index, mycorrhizal colonization and disease severity were measured. Pathogen infection reduced soybean biomass and negatively affected the greenness index, but co-inoculation with AMF improved these parameters. Nitrogen fertilization reduced AMF colonization but not arbuscules percentage. N fertilization increased disease severity but mycorrhizal symbiosis was able to reduce it. These results demonstrate that severity of charcoal root-rot disease in N fertilized soybean can be reduced by AMF inoculation. The implication of these results is that N fertilization could increase the risk of diseases in soybean but mycorrhiza could contribute to soybean charcoal root rot control even if the crop is under N fertilization.
TL;DR: The present study reveals that the primer sets can be used for molecular identification and will facilitate a largescale survey of the distribution of species and monitoring the epidemics.
Abstract: Macrophomina is a widely distributed genus of phytopathogenic fungi with a wide range of plant hosts. The present study aimed to design specific primers for the rapid identification/detection of three Macrophomina species (M. phaseolina, M. pseudophaseolina, and M. euphorbiicola). The reference sequences of four nuclear genes actin (ACT), β-tubulin (βT), calmodulin (CAL) and translation elongation factor 1-alpha (TEF1-α) of each Macrophomina species were submitted for the generation of specific primers using automated software packages. The better specific primers set generated for detection of each species were selected and synthesized. Polymerase chain reaction (PCR)-based assays were conducted to verify the specificity with isolates of the three species of Macrophomina and 42 species of other genera. Three primer sets to amplify of regions CAL (MpCalF/MpCalR, MsCalF/MsCalR and MeCalF/MeCalR) and three primer sets to amplify of regions TEF-1α (MpTefF/MpTefR, MsTefF/MsTefR and MeTefF/MeTefR) were designed for M. phaseolina, M. pseudophaseolina, and M. euphorbiicola, respectively. The specific primers MpCalF/MpCalR from region CAL amplified only the isolates of M. phaseolina. However, the MsCalF/MsCalR and MeCalF/MeCalR amplified non-target isolates. The specific primers MpTefF/MpTefR, MsTefF/MsTefR, MeTefF/MeTefR from region TEF-1α, exhibited high specificity in amplifying only the target isolates. No fragment was detected from other fungal species tested, confirming high specificity of these primers. This is the first report to develop specific primers for the identification of M. phaseolina, M. pseudophaseolina, and M. euphorbiicola. The present study reveals that the primer sets can be used for molecular identification and will facilitate a largescale survey of the distribution of species and monitoring the epidemics.
TL;DR: Application of a bio-formulation containing a plant growth-promoting rhizobacteria mixture as a seed treatment as well as by soil drenching was found to be effective in controlling sunflower root-rot disease and significantly decreased the disease severity rating by 44–55% of the non-treated control in 2 years.
Abstract: Biological farming using a mixture of bio-agents that are compatible with each other and adapted to the plant rhizosphere is a strategic approach to manage crop disease. This study is a unique approach to manage the root-rot disease complex caused by Macrophomina phaseolina, Rhizoctonia solani, and Fusarium solani in sunflower plants grown in calcareous soil using a mixture of rhizobacteria strains, namely Azotobacter chroococcum ZCR, Azospirillum brasilense SBR, and Klebsiella pneumoniae KPR. These strains were screened in vitro for N2 fixation and phosphate solubilization, as well as the production of indoleacetic acid, siderophore, and hydrogen cyanide. Interestingly, the rhizobacteria strains exhibited promising biofertilizer and biocontrol properties. Furthermore, they significantly inhibited the growth of root-rot pathogens in a dual culture assay. Notably, the rhizospheric bacteria exhibited successful colonization of the rhizoplane of sunflower plants and persisted at high levels for up to 60 days (8 × 104–12 × 104 cfu g−1 fresh root). In field experiments under naturally infested soil conditions, application of a bio-formulation containing a plant growth-promoting rhizobacteria mixture (HALEX bio-formulation) as a seed treatment as well as by soil drenching was found to be effective in controlling sunflower root-rot disease and significantly decreased the disease severity rating by 44–55% of the non-treated control in 2 years. In addition, treating with rhizobacteria significantly improved plant growth, yield, and oil content and decreased weight loss due to pathogen-induced stress. Consequently, it is suggested that farmers use this rhizobacteria mixture as a promising eco-friendly approach for effective management of root-rot disease complex in sunflowers in semi-arid regions.
TL;DR: Results suggest that Bx-FAR-1 suppresses the plant immune response in the N. benthamiana intracellular site and may contribute to the pathogenicity of B. xylophilus in the early infection stages.
Abstract: Bursaphelenchus xylophilus is an economically important pathogen that has caused serious damage to pine forests. Fatty acid and retinol-binding proteins (FARs) are nematode-specific proteins. One FAR gene, Bx-FAR-1, was identified from the transcriptome of B. xylophilus as a putative effector. It was upregulated in both highly and weakly virulent isolates in early infection stages. Transient expression assays showed that Bx-FAR-1 inhibited BAX- and INF1-induced cell death in Nicotiana benthamiana when secreted into the intracellular site. Bx-FAR-1 was expressed in the glandular tissues, intestines, and seminal vesicles of nematodes by in situ hybridization. Silencing Bx-FAR-1 via in vitro RNA interference attenuated the reproductive ability and pathogenicity of B. xylophilus as well as increased the expression of the pathogenesis-related gene 6 and JA biosynthesis gene LOX-5 (lipoxygenase-5) in pine trees. These results suggest that Bx-FAR-1 suppresses the plant immune response in the N. benthamiana intracellular site and may contribute to the pathogenicity of B. xylophilus in the early infection stages.
TL;DR: In this paper, the interaction between Foc race 1 and Radopholus similis, a burrowing nematode that parasitizes banana plants, was analyzed using one moderately susceptible cultivar and seven resistant cultivars of banana.
Abstract: Fusarium oxysporum f. sp. cubense (Foc) causes Panama disease or Fusarium wilt of bananas. The association between soil-inhabiting fungi and nematodes can increase the severity of symptoms and suppress the resistance of plants to diseases. In this study, the interaction between Foc race 1 and Radopholus similis, a burrowing nematode that parasitizes banana plants, was analyzed using one moderately susceptible cultivar and seven resistant cultivars of banana. Two Foc isolates that differed in virulence were tested. The analyses of symptoms and stained fungal structures in the roots demonstrated that R. similis interacting with Foc in different inoculation sequences caused changes in symptom severity and the resistance pattern to Foc isolate 0801 (race 1) in cultivars ‘Terra Maranhao’, ‘BRS Pacovan Ken’, ‘BRS Vitoria’, and ‘BRS Platina’. The data generated in this study have relevant implications for banana breeding programs in the classification of cultivars for durable resistance to Fusarium wilt and for understanding pathogen interactions during occurrence of the disease.
TL;DR: Assessment of the effect of temperature on the reaction of six melon accessions selected previously for their resistant response to M. phaseolina suggests that these genotypes are not suitable for hot-climate growing areas.
Abstract: Macrophomina phaseolina is the causal agent of charcoal rot disease of melons causing significant losses worldwide. Use of resistant cultivars is a desirable method for controlling this disease, but there is no information about the influence of temperature on the resistant behavior found in melon accessions. The purpose of the present study was to assess the effect of temperature on the reaction of six melon accessions selected previously for their resistant response to M. phaseolina. Accessions were inoculated with M. phaseolina isolate CMM-1531 and grown under accurately controlled environmental conditions at different temperature regimes (25, 28, 31, and 34 °C) in a replicated experiment. The increase in temperature increased the severity of symptoms in most genotypes, but this effect was less pronounced in the highly susceptible control, the cultivar ‘Piel de sapo’, and in the most resistant accession, the wild African agrestis Ag-15591Ghana, that remained resistant even at 34 °C. The use of several screening temperatures allowed a better characterization of accessions that behaved similarly as highly resistant at 25 °C (Con-Pat81Ko, Dud-QMPAfg, Can-NYIsr and Ag-C38Nig), but in which resistance breaking was observed with temperature rises. Temperatures of 28 °C and 31 °C were sufficient to make Dud-QMPAfg, Ag-C38Nig and Can-NYIsr moderately resistant, whereas Con-Pat81Ko remained highly resistant. All these genotypes were susceptible at 34 °C, which suggest that are not suitable for hot-climate growing areas. The most promising accession was Ag-15591Ghana, whose resistance was confirmed in two greenhouse experiments under stressful temperatures (>34 °C). The behavior of these sources should be confirmed in naturally infested fields, but the controlled screening methods presented here are essential to characterize new resistance sources and to conduct genetic studies when a high number of plants must be managed under controlled environmental conditions.
TL;DR: It is highlighted that Tunisian durum wheat landraces may harbour variable and stable sources of resistance to Z. tritici at seedling and adult plant stages, which would represent a good basis for further investigation and deployment in breeding programs to enhance STB resistance.
Abstract: Tunisia is one of the main producers of durum wheat, the most consumed cereal in Tunisia and represents a trademark of several local dishes such as couscous and bulgur. Nonetheless and despite its leading stand in the local consumption and commercial share, a scarcity in Tunisian durum wheat production has long been a major problem obstructing the fulfilment of the increasing local demand. Septoria tritici blotch (STB) caused by Zymoseptoria tritici (Z. tritici) is one of the most common and detrimental foliar disease on durum wheat in Tunisia causing considerable yield losses. To-date and despite the damaging effects of STB on durum wheat, limited sources of resistance to Z. tritici have been identified. In this present study, we assessed necrosis and pycnidia development of a collection of 304 Tunisian durum wheat landraces representative of 11 landrace populations and artificially inoculated with Z. tritici at the seedling stage under controlled conditions and at the adult plant stage under field conditions. Based on necrosis and pycnidia scores, a hierarchical classification analysis clustered the durum wheat landraces into three phenotypic classes of response to Z. tritici, namely resistant, intermediate and susceptible genotypes. While resistant plants represented the most frequent class at the seedling stage, susceptible phenotypes were more frequent at the adult plant stage. Nevertheless, a heat map correlation study showed that resistant landraces with low-percentages of necrosis and pycnidia at seedling and adult plant stages represented the dominant group within the tested collection. Moreover, the assessed frequencies per landrace populations of the resistant, the intermediate and the susceptible accessions to Z. tritici infection at the adult plant stage for pycnidia development has shown that the landrace populations Badri, Jneh Khotifa (JK), Mekki and Taganrog were the highest resistant accessions, in contrast to the landrace populations Biskri, Mahmoudi, Azizi and Biada where susceptible genotypes were predominant. Mahmoudi and Azizi represented the most variable landrace populations encompassing the three phenotypic classes. Our results highlight that Tunisian durum wheat landraces may harbour variable and stable sources of resistance to Z. tritici at seedling and adult plant stages, which would represent a good basis for further investigation and deployment in breeding programs to enhance STB resistance.
TL;DR: Bean plants inoculated with Trichoderma-soil isolates showed a higher percentage of germination, hypocotyl diameter, length of the root system, and dry weight of aerial parts and root system than plants inoculate withtrichoderMA-seed isolates.
Abstract: The common bean is a legume crop distributed worldwide. Dry bean production has gone through increasing difficulties due to relatively low yields in the last few years. Rhizoctonia solani is one of the root and hypocotyl pathogens that causes most of the economic losses in this crop. One promising strategy to control plant diseases is the use of biological control agents, able to reduce the negative effects of pathogens and to promote positive responses in the plant. Trichoderma spp. is a fungal genus ubiquitous in soil that can grow in soil or in any of the above ground parts of plants. The aims of this work were to study the effect of Trichoderma on bean plant growth, in the presence of the phytopathogen R. solani, according to the Trichoderma isolation source (seed or soil). Fifty-five Trichoderma isolates collected from bean seeds and from bean field soils were analyzed. Among them, those isolated from soil samples showed a higher plant growth promotion activity than those strains isolated from seeds, in the presence of R. solani. Furthermore, bean plants inoculated with Trichoderma-soil isolates showed a higher percentage of germination, hypocotyl diameter, length of the root system, and dry weight of aerial parts and root system than plants inoculated with Trichoderma-seed isolates.
TL;DR: Results suggest that bio-inoculants of Mesorhizobium sp.
Abstract: Antagonistic Plant growth promoting rhizobacteria can contribute to disease management by induction of host defenses and biological control of pathogens. The present study was thus planned to develop a bio-inoculant with the ability to promote plant growth and reduce disease incidence due to Fusarium oxysporum sp. ciceris in chickpea. Isolates of Mesorhizobium sp. (6) and endophytic bacteria (5) were screened as potential antagonists exhibiting 50–93.7% growth inhibition of Fusarium wilt (in vitro). Selected Mesorhizobium sp. and endophytic bacteria were assessed for their compatibility to develop dual combinations with no mutual inhibition. Dual inoculants significantly enhanced in vitro plant growth promoting traits viz., Indole Acetic Acid, siderophores, phosphate solubilization and 1-aminocyclopropane-1-carboxylate-deaminase enzyme activity. Dual mesorhizobia and endophytic bio-inoculants (able to grow with recommended fungicide captan @ 3 g/kg seed) were further assessed in wilt-sick field conditions for growth, symbiosis, soil health, yield and bio-control parameters in two chickpea varieties (PBG-7 and PBG-1). Seed priming with dual inoculants significantly enhanced growth, symbiosis, soil quality parameters and antioxidant enzymes viz., catalase, peroxidase and total phenols over control. Dual bio-inoculant LGR2 + LCNE8 improved the grain yield by 6.5% over captan as the control. These results suggest that bio-inoculants of Mesorhizobium sp. and endophytic bacteria under a competitive environment can be explored as bio-fertilizers/bio-protectants for improving productivity and suppression of Fusarium wilt in chickpea.
TL;DR: Pathogenicity trials showed that the four species tested were pathogenic to blueberry plants and revealed that N. parvum, was the most aggressive species, and most likely the main causal agent of blueberry stem blight and dieback in Portugal.
Abstract: Blueberry (Vaccinium corymbosum) cultivation in Portugal has been growing considerably in the last decade, making it a highly profitable fruit crop. Species of Botryosphaeriaceae are relevant pathogens of blueberry causing stem blight and dieback. In this study a survey was carried out in blueberry orchards in the centre region of Portugal in order to assess which species of Botryosphaeriaceae are associated with stem blight and dieback symptoms. Their presence as endophytes was also evaluated in asymptomatic plants. Four species were identified, Botryosphaeria dothidea, Neofusicoccum parvum, N. australe and N. eucalyptorum. Of these, B. dothidea and N. parvum were the most commonly found. Pathogenicity trials showed that the four species tested were pathogenic to blueberry plants and revealed that N. parvum, was the most aggressive species, and most likely the main causal agent of blueberry stem blight and dieback in Portugal. Neofusicoccum eucalyptorum, a common Eucalyptus pathogen, is reported for the first time as a pathogen of blueberry. This represents a significant host jump whose potential future effects on blueberry plantations are not fully understood.
TL;DR: Both the combined use and individual application of B. amyloliquefaciens and T. asperellum via foliar spray or growth medium application or both have the potential to control bacterial spot on tomato.
Abstract: To date, few studies have focused on the combined use of two biocontrol agents to manage bacterial spot on tomato. Thus, the goal of this study was to evaluate the effects of the combined and individual use of Bacillus amyloliquefaciens and Trichoderma asperellum on the nutrient contents of tomato plants and bacterial spot on tomato caused by Xanthomonas perforans. Tomato plants were treated with the foliar spray and growth medium application of B. amyloliquefaciens or T. asperellum or both. Plants treated with sterile water served as the uninoculated control, and a copper standard consisting of cupric hydroxide plus an ethylene bisdithiocarbamate (EBDC) fungicide was also included. The application methods used for B. amyloliquefaciens and T. asperellum significantly influenced the P, K, and Mg contents in tomato plants. All biocontrol treatments significantly reduced the final disease severity of bacterial spot on tomato by 25.6–56.0% and the area under the disease progress curve (AUDPC) by 33.9–57.2% compared with the untreated control. The application of either B. amyloliquefaciens or T. asperellum via growth medium produced statistically equivalent results in reducing the final disease severity compared with the standard, but the other biocontrol treatments were significantly better than the standard. Similarly, the application of either B. amyloliquefaciens or T. asperellum via growth medium produced statistically equivalent results in lowering the AUDPC compared with the standard. However, the other biocontrol treatments significantly reduced the AUDPC by 39.7–44.8% compared with the standard. In summary, both the combined use and individual application of B. amyloliquefaciens and T. asperellum via foliar spray or growth medium application or both have the potential to control bacterial spot on tomato.
TL;DR: Identification based on biological, molecular, and molecular methods revealed that the soy pathogenic bacteria is Kosakonia cowanii species, and it is believed that the presence of such pathogens in the environment pose a serious threat for the crops and is also a warning, that in the near future the authors may be faced a new type of bacterial pathogens.
Abstract: Soybean (Glycine max Willd.) is one of the most economically important crops in the world, and it’s importance continuously increasing. Routine screening of Polish soybean fields has revealed an outburst of a new disease of soybean plants, with symptoms resembling those described for the bacterial blight, caused by Pseudomonas syringae pv. glycinae, and bacterial pustule caused by Xanthomonas axonopodis pv. glycines. The symptoms were observed in the field, on the leaves of investigated plants. The goal of this paper was the identification and characterization of the causal agent of that disease. Our studies have excluded virus and fungi and pointed the bacteria as the disease causal agent. Identification based on biological (Biolog Gen III), and molecular methods (16S rDNA, and gyrB sequencing, PCR species-specific testing) revealed that the soy pathogenic bacteria is Kosakonia cowanii species. We believe that the presence of such pathogens in the environment pose a serious threat for the crops and is also a warning, that in the near future we may be faced a new type of bacterial pathogens: both epi- and endophytic, abundant in the natural environment, with huge metabolic potential, and ability of quick colonization of new ecological niches and hosts, e.g. opportunistic pathogens of plants or humans. What’s important is that the plant-pathogenic and plant-epiphytic “environmental” strains of such species can be distinguished from each other only post factum, in the pathogenicity tests. They are indistinguishable or very hard to distinguish morphologically, biochemically or molecularly.
TL;DR: Eight bacterial isolates originating from the apple phyllosphere or soil environment that were previously selected using the pear fruitlet test showed the ability of the tested bacteria to protect flowers at medium to high levels, depending on the experiment, and in some cases this protection was even higher than that of the copper product used for comparison.
Abstract: This study included eight bacterial isolates originating from the apple phyllosphere or soil environment that were previously selected using the pear fruitlet test (Mikicinski 2017). Identification of these isolates based on phenotypic assays and DNA analysis showed that five of them belonged to species for which an antagonistic activity against Erwinia amylovora and the protective capacity of apple and pear against fire blight were not previously demonstrated. These were L16 identified as Pseudomonas vancouverensis, 3 M as Pseudomonas chlororaphis subsp. aureofaciens, 35 M – Pseudomonas congelans, 43 M – Enterobacter ludwigii, and 59 M – Pseudomonas protegens. Investigation of the biotic relationships between the tested strains and E. amylovora showed that 3 M, 35 M and 59 M inhibited the growth of the pathogen on five out of six media used (NAS, KB, LB, R2A, NAG), but 43 M did not do so on any of these media. Strain L16 did not inhibit the growth of the pathogen on LB or R2A medium. In contrast, all strains grown on medium 925 stimulated the growth of the pathogen, which showed no growth without co-cultivation with these strains. The experiments on apple trees and detached apple branches showed the ability of the tested bacteria to protect flowers at medium to high levels, depending on the experiment (55–93%). In some cases, this protection was even higher than that of the copper product used for comparison. In studies assessing the bacterial ability to protect shoots of M.26, the highest efficacy was observed for strains 35 M (96%) and 43 M (93%) but on ‘Gala Must’ all tested strains showed 100% of efficacy.
TL;DR: The model can be useful for investigating the effect of strategic disease management tools such as the use of resistant varieties or to investigate the behaviour of the pathosystem under scenarios of climate change.
Abstract: A process-based simulation model for the grapevine-downy mildew pathosystem was developed in order to quantitatively synthesize the literature available and to provide a tool to guide strategic decisions for disease management. The model includes: i) the main processes involved in the disease dual epidemics on leaves and clusters, from inoculum mobilisation to disease multiplication on foliage, and to infection of clusters; and ii) host dynamics, i.e. crop development, growth, and physiological and disease-induced senescence. A numerical evaluation was performed to investigate the response of the model to changes of the main epidemiological parameters, i.e. the basic infection rate corrected for the removals (RcOPT), the duration of latency period (LP), the duration of infectious period (IP), and the rate of primary infections (P). Increasing values of RcOPT and IP, and decreasing values of LP resulted in a faster increase of the epidemic on both foliage and clusters, while decreasing values of P delayed epidemics. The simulated dynamics of epidemics on foliage and clusters conformed to patterns of dual epidemics observed for downy mildew. The model can be useful for investigating the effect of strategic disease management tools such as the use of resistant varieties or to investigate the behaviour of the pathosystem under scenarios of climate change.
TL;DR: A survey of fungal leaf spots on macadamia trees in 20 commercial orchards in Queensland revealed two distinctive types of symptoms that were identical to the respective field disease symptoms.
Abstract: Extensive leaf spot was observed on all leaves of young macadamia trees planted in new orchards in Queensland, Australia. The loss in photosynthetic ability of these trees may contribute to their demise and poor establishment compared to trees without symptoms. A survey of fungal leaf spots on macadamia trees in 20 commercial orchards in Queensland revealed two distinctive types of symptoms. Leaves showing circular dark brown spots with yellow halos (Type 1) and irregular dark brown spots (Type 2) were collected. Fungal isolates associated with the infected leaves were identified by morphological characteristics and DNA sequencing as Neopestalotiopsis clavispora for Type 1 spots and Colletotrichum siamense for Type 2 spots. Koch’s postulates were fulfilled for N. clavispora and C. siamense. Pathogenicity assays showed that both fungi caused severe leaf spots, which are identical to the respective field disease symptoms. In order to clearly characterise them, the two leaf spots were named as Pestalotiopsis leaf spot (Type 1 spots) and Colletotrichum leaf spot (Type 2 spots). This is the first report of N. clavispora and C. siamense causing leaf spots in macadamia in Australia.
TL;DR: The identification and pathogenicity of Colletotrichum species related to mango anthracnose in Taiwan are reported, and all five species showed pathogenic on fruit, and C. siamense isolates C-526 and C-848 caused significantly larger lesions on leaves than other isolates.
Abstract: Mango is widely grown in Taiwan and anthracnose is one of the most important diseases of this crop. The aim of this study was to investigate Colletotrichum species associated with mango and the pathogenicity of these fungal species. From 2006 to 2017, mango tissue from 33 mango orchards were collected. Eighty-seven isolates associated with mango were analyzed preliminarily by comparing partial glyceraldehyde-3-phosphate dehydrogenase sequences. Four species belonging to C. gloeosporioides complex were preliminarily identified, namely C. asianum (68 isolates), C. fructicola (four isolates), C. siamense (eight isolates) and C. tropicale (two isolates). The other five isolates were identified as belonging to the C. acutatum complex. Ten isolates, belonging to different Colletotrichum species according to glyceraldehyde-3-phosphate dehydrogenase sequences prediction, were used for further morphology and multi-gene phylogenetic analysis. Five species were identified, namely C. asianum, C. fructicola, C. siamense, C. tropicale and C. scovillei. All five species showed pathogenicity on fruit, and C. asianum isolates C-1076 and C-1646 as well as C. siamense isolate C-526 caused larger lesions than the other isolates. On mango leaves, C. asianum, C. fructicola, C. siamense and C. scovillei isolates were pathogenic, while C. tropicale isolates, C-141 and C-303, failed to cause significant foliar lesions. In addition, C. siamense isolates C-526 and C-848 caused significantly larger lesions on leaves than other isolates. This study reports the identification and pathogenicity of Colletotrichum species related to mango anthracnose in Taiwan.
TL;DR: All species identified in this survey were able to induce disease in cassava roots and seedlings, and the most frequently isolated species were L. brasiliense, L. parva associated with cassava diseases worldwide.
Abstract: Cassava is a starch-rich, high-calorie tuberous root used as human and animal food, as well as an input material in various industries. Black root rot (BRR) and stem cutting dry rot (SCDR) are cassava diseases that compromise product quality and can greatly reduce crop yields. Consequently, the aim of this study was to identify Botryosphaeriaceae species associated with both diseases in areas of the northeast of Brazil and in areas of the Minas Gerais State in the southeast of the country and infer a correlation between them. Fungal species were identified by morphology combined with phylogenetic analyses of partial sequences of translation elongation factor 1 alpha (tef1-α), internal transcribed spacer (ITS) and RNA polymerase subunit II (rpb2). Five species were identified as being associated with both BRR and SCDR (Lasiodiplodia euphorbicola, L. hormozganensis, L. parva, L. theobromae, and Neoscytalidium dimidiatum), while five others were associated only with SCDR (L. brasiliense, L. caatinguensis, L. iraniensis, L. laeliocattleyae, and L. pseudotheobromae). All species identified in this survey were able to induce disease in cassava roots and seedlings. In decreasing order, the most frequently isolated species were L. theobromae, N. dimidiatum, and L. euphorbicola. This is the first report of L. brasiliense, L. caatinguensis, L. hormozganensis, L. iraniensis, L. laeliocattleyae, and L. parva associated with cassava diseases worldwide.
TL;DR: Drought cannot be considered as a predisposing factor required for Phytophthora root disease development in cork oaks; although the adverse effects of both factors likely have synergistic consequences in the decline and death of affected oaks.
Abstract: Drought has been assumed as a predisposing factor in the decline caused by Phytophthora cinnamomi on Mediterranean Quercus forests, enhancing cork oak susceptibility to the root infection. However, P. cinnamomi outbreaks appear associated to waterlogged soils, with infections being particularly successful when soil moisture content fluctuates from flooding to water deficiency. We obtained cork oak seedlings potentially predisposed to Phytophthora disease by exposing them to a short (3 weeks) or a long (6 weeks) drought. These seedlings subjected to drought, together with well-watered seedlings, were exposed to two different soil concentrations of P. cinnamomi inoculum (chlamydospores) and submitted to high soil humidity for 4 weeks. Values of root necrosis were significantly higher in inoculated oak seedlings compared to non-inoculated control seedlings, but no significant differences were observed depending on previous drought treatments. Consequently, drought cannot be considered as a predisposing factor required for Phytophthora root disease development in cork oaks; although the adverse effects of both factors (drought and Phytophthora root infections) likely have synergistic consequences in the decline and death of affected oaks.
TL;DR: Overall, fluopyram has significant nematicidal activity against B. xylophilus and shows potential to be a new trunk-injection agent.
Abstract: Fluopyram, an excellent nematicide, has better water solubility than abamectin; this feature is important for its systemic transport in trees as a trunk-injection agent. To identify the potential of fluopyram as a trunk-injection agent against Bursaphelenchus xylophilus, its toxicity to different developmental stages and effects on the egg hatching and reproduction of B. xylophilus were studied. Fluopyram exhibited significant nematicidal activity similar to that of abamectin, with LC50 values of 0.945, 1.69 and 3.23 mg L− 1 for second-stage juveniles (J2), third-stage juveniles (J3) and fourth-stage juveniles/adults (J4/adults), respectively. The hatching rate at a fluopyram concentration of 3 mg L− 1 was 20.78%, significantly lower than that in the control group (90.48%) at 24 h. In addition, the reproduction of B. xylophilus at a concentration of 2.21 mg L− 1 decreased significantly, similar to the effect of abamectin at 1.42 mg L− 1. In a hydroponic experiment, fluopyram treatment decreased the number of B. xylophilus at a concentration of 64 mg L− 1. Fluopyram exhibited a greater inhibitory effect than abamectin. Overall, fluopyram has significant nematicidal activity against B. xylophilus and shows potential to be a new trunk-injection agent.
TL;DR: Transmission efficiency of GLRaV-3 and GVA is tested from nine field-collected source vine samples of Vitis vinifera cv Chardonnay by first instars of Planococcus ficus to suggest that GVA may have a higher likelihood of establishing new infections in concert with GLRaVs than in single infections.
Abstract: Grapevine leafroll-associated virus 3 (GLRaV-3) is the most prevalent and destructive virus species that contributes to grapevine leafroll disease, an economically damaging disease that affects vineyards globally. Grapevine virus A (GVA) is a virus species in the rugose wood complex and is associated with several vineyard diseases. Both virus species are transmitted by several mealybug species. Transmission efficiency is a major facet of pathogen spread and may be influenced by virus species interactions in the vector or host. We tested transmission efficiency of GLRaV-3 and GVA from nine field-collected source vine samples of Vitis vinifera cv Chardonnay by first instars of Planococcus ficus. Transmission of GLRaV-3 was 22% greater than transmission of GVA. Establishment of new mixed GLRaV-3/GVA infections did not differ significantly from single GLRaV-3 infections following inoculation by P. ficus. These results suggest that GVA may have a higher likelihood of establishing new infections in concert with GLRaV-3 than in single infections.