Showing papers in "Annals of Applied Biology in 2013"

Nitrogen losses from the soil/plant system: a review

Abstract: Losses of nitrogen from the soil/plant system not only reduce soil fertility and plant yield but can also create adverse impacts on the environment. Ammonia emissions into the atmosphere contribute to acid rain and represent an indirect source of nitrous oxide greenhouse gas emissions. Nitrate leaching losses into rivers and lakes can cause eutrophication resulting in excessive growth of aquatic weeds and algae, which can reduce fish populations and the recreational value of the water. Nitrate contamination of drinking water supplies can cause health risks. Legislation that is designed to limit nitrate leaching losses from land has become a constraint on agricultural land use in many countries. Nitrous oxide emissions into the atmosphere contribute to the depletion of the ozone layer and also make a significant contribution to climate change. This review describes the nitrogen cycle in temperate soil/plant systems, the processes involved in each of the individual nitrogen loss pathways, the factors affecting the amounts of losses and the methods that are available to reduce these losses. The review has shown that careful management of temperate soil/plant systems using best management practices and newly developed technologies can increase the sustainability of agriculture and reduce its impact on the environment.

Do plants need nitrate? The mechanisms by which nitrogen form affects plants

Abstract: The literature on nitrogen (N) form effects on plants at different stages of their development has been critically reviewed, assessing the possible mechanisms of these effects. In particular, nitrate (NO3−) was compared with the other forms of N utilised by plants. It is concluded that the form of N available to plants can affect their time and rate of seed germination, leaf expansion and function, dry matter partitioning between shoot and root, and root architecture. The magnitude of these effects is dependent on environmental factors outside the supply of N. The mechanism of these effects is variable. Assessment of the importance of root or shoot NO3− assimilation under different environmental conditions is an important area for further study.

Spatial and temporal variation in the control failure likelihood of the tomato leaf miner, Tuta absoluta

Abstract: Insecticide resistance is frequently associated with field control failure, but such an assessment of its likelihood seldom occurs. This phenomenon is a potential cause of the control failure of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae); therefore we surveyed insecticide resistance as the control failure likelihood for a duration of 7 years in 20 field populations of this species. The insecticide label rate was used as the discriminating concentration, and the minimum efficacy threshold required for insecticides in Brazil (i.e. 80% efficacy) was the targeted efficacy. The spatial and temporal variations of the control failure likelihood were also assessed, as was the potential influence of land topography for the area-wide pattern observed. Most populations of T. absoluta were susceptible to abamectin, chlorfenapyr and spinosad and not to bifenthrin, triflumuron and teflubenzuron. The indoxacarb susceptibility varied in space and time. Spatial dependence was observed for abamectin and indoxacarb. The control failure likelihood of T. absoluta was higher for bifenthrin, triflumuron and teflubenzuron. A flat topography and the wind direction may favour the spread of the control failure likelihood and should be considered in designing pest management programs for T. absoluta.

Genetic diversity in morphological characters and phenolic acids content resulting from an interspecific cross between eggplant, Solanum melongena, and its wild ancestor (S. incanum)

Abstract: This work was partially financed by the Ministerio de Ciencia y Tecnologia (AGL2009-07257 and RF-2008-00008-00-00).

Burkholderia sp. SCMS54 reduces cadmium toxicity and promotes growth in tomato

Abstract: Cadmium (Cd) can enter soil through the use of fertilisers, calcareous, pesticides and industrial and/or domestic effluents. Cd can leach into groundwater and be taken up by plants, potentially leading to reductions in plant growth and yield. In soil, plant roots interact with heavy metal (HM)-tolerant microorganisms that may promote plant growth. Soil microorganisms may also be able to solubilise or mobilise soil metals, thereby acting as bioremediators. A better understanding of the interaction among plants, metals, microorganisms and soil will lead to improved plant tolerance. Two multi-tolerant bacteria from the Burkholderia genus were isolated from Cd-contaminated and Cd-uncontaminated soil of a coffee plantation. In addition to its high tolerance to Cd, the strain SCMS54 produces indole-acetic acid (IAA), solubilises inorganic phosphate and produces siderophores, demonstrating its potential to contribute to beneficial plant–microorganism interactions. When interacting with tomato plants exposed to Cd, the bacterium led to decreases in plant peroxide and chlorosis levels, promoted relative plant growth and decreased the root absorption of Cd, resulting in increased plant tolerance to this highly toxic HM. The results indicated that the inoculation of tomato plants with Burkholderia sp. SCMS54 promotes better growth in plants cultivated in the presence of Cd. This phenomenon appears to be attributed to a mechanism that decreases Cd concentrations in the roots via a beneficial interaction between the bacteria and the plant roots.

A historical overview of the appearance and spread of Musa pests and pathogens on the African continent: highlighting the importance of clean Musa planting materials and quarantine measures

Abstract: The genus Musa is not native to Africa. It evolved in tropical Asia, from southwest India eastward to the island of New Guinea. There is a growing circumstantial evidence which suggests that the East African Highland banana and the tropical lowland plantain were cultivated on the African continent since before 1 AD. It is also probable that ABB cooking and AB and AAB dessert cultivars were brought to the continent from India by Arabian traders from 600 AD, and that these were disseminated throughout East Africa. During the colonial era, the main centres of distribution for banana cultivars were botanical gardens, such as Zomba in Malawi, Entebbe in Uganda and Amani in Tanzania. It appears that the very early introductions of Highland banana and plantain arrived in Africa as a relatively clean material without the conspicuous pests and diseases that affect them in Asia. In contrast, several devastating problems now impact the crop in Africa, including nematodes, the borer weevil and diseases, most notably banana bunchy top, banana streak, Sigatoka leaf spots, Xanthomonas wilt and Fusarium wilt. We (a) provide chronological overviews of the first reports/observations of different Musa pests and pathogens/diseases in Africa, (b) highlight specific examples of when a pest or pathogen/disease was introduced via planting materials and (c) give recent examples of how the pests and pathogens spread to new regions via planting materials. In total, these production constraints threaten banana and plantain production throughout the continent and impact those who can ill afford lost production, the small-holder producer. Our intent in this review is to highlight the significance of these problems and the great importance that infested planting materials have played in their development.

Rhizosphere microbes facilitate redox homeostasis in Cicer arietinum against biotic stress

Abstract: The aim of this study was to evaluate the potentiality of three compatible rhizosphere microbes, viz. fluorescent Pseudomonas aeruginosa (PHU094), Trichoderma harzianum (THU0816) and Mesorhizobium sp. (RL091), in community to mobilise antioxidant mechanisms in chickpea under the challenge of Sclerotium rolfsii. The microbes were applied as seed treatment in different combinations in two sets and the pathogen was inoculated in one of the sets after 3weeks of sowing. A comparative study was conducted on the effect of the microbial combinations on host antioxidant mechanisms between the two sets. In pathogen challenged plants host defence responses included higher accumulation of hydrogen peroxide (H2O2) at petiolar and interveinal regions of leaf and high activities of catalase (CAT), glutathione reductase (GR) and guaiacol peroxidase (GPx) compared to unchallenged plants. The antioxidant enzyme activities increased 1.8−3.3 and 1.9−3.1 folds at 48 and 72h, respectively, in the triple microbe treated challenged plants compared to unchallenged ones. Although, ascorbate peroxidase (APX) activity was significantly low, ascorbic acid (AA) and chitinase accumulation was high in the pathogen challenged plants. Antioxidant flavonols associated with host defence namely myricetin, quercetin and kaempferol also accumulated in high amounts in pathogen challenged plants. Among the microbial treatments, the triple microbe combination induced the highest response in all parameters as compared to dual or single application of the same microbes. The triple microbe consortium modulated the chickpea antioxidant mechanisms more efficiently and modulation of oxidative stress was directly correlated with lower plant mortality, thus demonstrating the synergistic behaviour of the microbes in protecting chickpea from the pathogen.

A new clade of Dickeya spp. plays a major role in potato blackleg outbreaks in North Finland

Abstract: Until recently Dickeya was regarded as a pathogen not established in Finland. As a result the blackleg symptom observed on potato was often associated with Pectobacterium atrosepticum. The occurrence of Dickeya spp. on potato in Finland was first reported in 2004. Since then the prevalence of Dickeya has been monitored through surveys and routine test of seed lots produced in the country. The results of monitoring of Dickeya spp. in seed lots produced in Finland between the years 2004 and 2008 indicated a steady increase in the incidence of Dickeya spp. The highest incidence was observed in samples from the 2006 growing season where about 37% were positive for Dickeya spp. The summer in 2006 was one of the warmest summers recorded in 100 years in Finland. The majority of infected lots were imported varieties. Since recently heavy blackleg outbreaks have occurred in production fields in the High Grade (HG) zone. A detailed study of these incidents of blackleg outbreaks in North Finland during the years 2008 and 2010 indicated that Dickeya spp. was the major component in the observed blackleg complex. It was detected and isolated from almost all symptomatic plants investigated. Repetitive sequences PCR (REP-PCR) and Pulsed Field Gel Electrophoresis (PFGE) analysis of strains isolated in Finland showed identical pattern with those isolated recently in other European countries with a proposed name ‘Dickeya solani’. Moreover, the dnaX gene sequence of the representative strains isolated in Finland indicated 100% similarity to the dnaX sequences of ‘D. solani’. The study presents the first report of a detailed analysis of bacteria involved in potato blackleg complex from natural field outbreaks in North Finland HG zone and characterisation of the ‘D. solani’ strains playing the major role in the disease complex.

Relative incidence, spatial distribution and genetic diversity of cucurbit viruses in eastern Spain

Abstract: Viral diseases that could cause important economic losses often affect cucurbits, but only limited information on the incidence and spatial distribution of specific viruses is currently available. During the 2005 and 2006 growing seasons, systematic surveys were carried out in open field melon (Cucumis melo), squash and pumpkin (Cucurbita pepo), watermelon (Citrullus lanatus) and cucumber (Cucumis sativus) crops of the Spanish Community of Valencia (eastern Spain), where several counties have a long standing tradition of cucurbit cultivation and production. Surveyed fields were chosen with no previous information as to their sanitation status, and samples were taken from plants that showed virus-like symptoms. Samples were analysed using molecular hybridisation to detect Beet pseudo-yellows virus (BPYV), Cucurbit aphid-borne yellows virus (CABYV), Cucumber mosaic virus (CMV), Cucumber vein yellowing virus (CVYV), Cucurbit yellow stunting disorder virus (CYSDV), Melon necrotic spot virus (MNSV), Papaya ring spot virus (PRSV), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV). We collected 1767 samples from 122 independent field plots; out of these, approximately 94% of the samples were infected by at least one of these viruses. Percentages for the more frequently detected viruses were 35.8%, 27.0%, 16.5% and 7.2% for CABYV, WMV, PRSV and ZYMV, respectively, and significant deviations were found on the frequency distributions based on either the area or the host sampled. The number of multiple infections was high (average 36%), particularly for squash (more than 57%), with the most frequent combination being WMV + PRSV (12%) followed by WMV + CABYV (10%). Sequencing of WMV complementary DNA suggested that ‘emerging’ isolates have replaced the ‘classic’ ones, as described in southern regions of France, leading us to believe that cucurbit cultivation could be severely affected by these new, emerging isolates.

Trichoderma species on Agaricus bisporus farms in Serbia and their biocontrol

Abstract: Twenty Trichoderma isolates were collected on 13 Serbian Agaricus bisporus farms and one in Bosnia and Herzegovina during 2006–2010. Twelve isolates were classified into five species by standard mycological studies and ITS1/ITS4 sequence analyses, namely Trichoderma atroviride, Trichoderma koningii, Trichoderma virens, Trichoderma aggressivum f. europaeum and Trichoderma harzianum. Eight isolates were not identified to the species level but were shown to be related to T. harzianum. The isolates of T. harzianum exhibited the highest virulence to the harvested A. bisporus pilei and T. virens and T. aggressivum f. europaeum the lowest. Antifungal activity of two biofungicides based on Bacillus subtilis and tea tree oil and the fungicide prochloraz manganese were tested in vitro to all Trichoderma isolates. Prochloraz manganese and B. subtilis were highly toxic to all tested Trichoderma isolates, their ED50 values were below 0.3 and 1.3 mg L−1, respectively. Tea tree oil did not exhibit a significant antifungal activity (ED50 = 11.9–370.8 mg L−1). The effectiveness of biofungicides was evaluated against T. harzianum in a mushroom growing room, and they were applied alone or in combination with the fungicide at a respective proportion of 20:80%. Prochloraz manganese showed higher effectiveness than both tested biofungicides or their respective mixtures. The biofungicide based on B. subtilis demonstrated greater effectiveness in preventing disease symptoms than tea tree oil. B. subtilis combined with the fungicide revealed less antagonism in effectiveness against pathogen than tea tree oil.

Cytology of infection, development and expression of resistance to Plasmodiophora brassicae in canola

Abstract: The timing and expression of resistance to four isolates of Plasmodiophora brassicae, collected from research sites where pathotypes 2, 3, 5 and 6 (Williams' system) had been dominant when characterised in 2006, were assessed in four new commercial cultivars of canola (Brassica napus) with resistance to clubroot. Each of the resistant cultivars was highly resistant to all four of the isolates, and there was no difference in their response to infection. Root hair infection occurred at high levels, but pathogen development occurred more slowly than in a susceptible cultivar (control). Secondary infection and development in cortical cells was severely inhibited in each of the resistant cultivars; only a few bi-nucleated plasmodia were observed at 12 days after inoculation (DAI), and plasmodia were rarely observed at 18 and 24 DAI. In contrast, development in the susceptible cultivar had progressed to resting spores by 24 DAI. A dense ring of accumulated reactive oxygen species (ROS) was observed in the endodermis, pericycle and vascular cambium of non-inoculated controls and inoculated plants of the resistant cultivars. However, the ROS ring disappeared rapidly in infected plants of the susceptible cultivar. Plasmodia invaded the stele of susceptible roots by preferentially colonising the xylem parenchyma cells. Expansion and enlargement of lignified xylem cells was observed by 35 DAI. The absence of any specific points of ROS accumulation or lignification of epidermal or cortical cells in the resistant cultivars indicates that a hypersensitive response is not the main mechanism of resistance in these lines. The uniform response of these resistant cultivars to the four isolates of P. brassicae indicates that the resistance in each cultivar may be conditioned by a gene(s) from a single source that confers broad resistance, because most sources of resistance to P. brassicae are pathotype specific.

Physiological and morphological traits associated with adaptation of lucerne (Medicago sativa) to severely drought‐stressed and to irrigated environments

Abstract: Adaptation to severe drought and to irrigated cropping can both contribute to increased water use efficiency of lucerne, but knowledge on the relevant adaptive traits is limited. Five cultivars featuring contrasting adaptive responses for 3-year forage yield across 10 agricultural environments of the western Mediterranean basin were currently studied, to identify physiological and morphological traits associated with specific and wide-adaptation responses. The landraces Mamuntanas, Demnat 203 and Erfoud 1, and the varieties SARDI 10 and Prosementi, were grown in replicated metal containers (55 cm long × 12 cm wide × 75 cm deep; 21 plants per container) under irrigation (weekly restoring soil field capacity) and under moderate and severe drought stress (implying decreased irrigation for 30 days followed by withheld irrigation for 33 and 58 days, respectively). Cultivar post-stress survival reflected the known cultivar adaptation to drought-prone agricultural environments. Demnat 203, specifically adapted to irrigated, frequently mown environments, displayed higher amounts of starch, soluble proteins and total nitrogen in the crown and the root under irrigation. This was due to outstanding organ size and, for starch, higher concentrations. Mamuntanas, specifically adapted to drought-prone environments, exhibited high water-soluble carbohydrate concentration in storage organs under severe stress, along with a water-conservation strategy implying less water used in initial drought-stress phases due to limited early root development that resulted in more water available under severe stress. Drought-tolerant germplasm also displayed lower wilting under early stress, more plants with green tissues under severe stress, and more stems per plant in stress or favourable conditions. Multivariate patterns of cultivar variation for physiological and morphological traits were strictly associated with cultivar variation for adaptation pattern. Our results highlighted the difficulty to combine some traits of environment-specific adaptive value into a unique widely adapted variety, supporting the selection of varieties specifically adapted to irrigated or severely drought-prone environments.

Fruit pit hardening: Physical measurement during olive fruit growth

Abstract: In drupe-type fruits, pit hardening, resulting from sclerification of the fruit endocarp, is widely used as a phenological marker for both physiological studies and orchard management. In spite of the importance of pit hardening for understanding fruit development processes and for agricultural practices, however, its quantification has remained obscure and precision has been lost with time and lax usage. In this study, we used a mechanical device to measure the physical pressure required to break the olive pit in order to define the timing of pit hardening more precisely and to permit closer observation of its relationship to fruit and endocarp growth and development. Over 4 years we found that pit-hardening pressure increased following a sigmoid pattern, at first gradually but then with a large and rapid increment of change in a relatively short period of time. The rapid acceleration of hardening began at the time when pit longitudinal and transverse diameters attained their maximum size. That timing is consistent with the anatomical differentiation of the sclerified endocarp cells which can no longer expand nor divide. The results improve our knowledge of pit hardening and provide a more precise context for evaluating the metabolic costs, physiological interactions and genetic controls of stone fruit endocarp development. On a practical level, the association of the intensification of pit-breaking pressure with the cessation of pit expansion indicates that pit diameters can be useful morphological markers to identify the onset of this period.

Plant-parasitic nematodes as invasive species: characteristics,uncertainty and biosecurity implications

Abstract: Few species of plant-parasitic nematodes (PPN) are currently recognised as invasive but this is largely because of insufficient investigation and recognition. We compared the characteristics of PPN with those of invasive species generally, using the propagule pressure, abiotic and biotic factors (PAB) framework. Most PPN had many of the characteristics of invasive species and hence have the potential to become invasive. The most common characteristics included: adaptations for human mediated dispersal; multiple entry pathways; microscopic size; large number of propagules; high fecundity; many or cosmopolitan hosts; short lifecycle; ability to survive harsh or unfavourable conditions; ability to vary sex ratios; and ability to overcome host plant resistance. Information is lacking for many characteristics of many species and their impacts remain unquantified, which leaves some important unanswered questions and challenges for assessing PPN as invasive species. However many economically important PPN species have not been recognised as invasive, even when most of the known characteristics and data suggests they should be.

Pseudomonas syringae pv. actinidiae detection in kiwifruit plant tissue and bleeding sap

Abstract: The rapid spreading of the disease during last few years highlighted the need of a quick, sensitive and reliable method for Pseudomonas syringae pv. actinidiae (Psa) detection, to find possible inoculum sources and limit the pathogen spreading. A PCR method, using new primers designed on the gene encoding a putative outer membrane protein P1, was developed to detect Psa in symptomatic and asymptomatic tissue; a nested-PCR was also applied. Bleeding sap samples, collected in early spring from orchards with symptomatic and asymptomatic trees, were used both for PCR assays and for pathogen isolation and identification. The PCR and nested PCR methods were able to detect Psa presence at very low concentration from plant and pollen extracts; RFLP analyses with BclI on PCR and nested PCR amplicons confirmed the assay specificity, while the digestion with BfmI and AluI allowed to discriminate Psa strains isolated before 2008 from those isolated after 2008. Furthermore, the PCR and nested PCR on crude bleeding sap samples detected the presence of the pathogen in 3 and 5 of the 15 assayed samples, respectively. Direct isolation from the same samples and bacterial identification confirmed the results of molecular analysis.

Characterisation of Pectobacterium wasabiae and Pectobacterium carotovorum subsp. carotovorum isolates from diseased potato plants in Finland

Abstract: To identify bacteria causing soft rot and blackleg in potato in Finland, pectinolytic enterobacteria were isolated from diseased potato stems and tubers. In addition to isolates identified as Pectobacterium atrosepticum and Dickeya sp., many of the isolated strains were identified as Pectobacterium carotovorum subsp. carotovorum. Phylogenetic analysis and biochemical tests indicated that one of the isolates from potato stems resembled Pectobacterium wasabiae. Furthermore, two blackleg-causing P. carotovorum strains recently isolated in Europe clustered with P. wasabiae, suggesting that at least some of these isolates were originally misidentified. All the other Finnish P. carotovorum isolates resembled the subsp. carotovorum type strain in biochemical tests but could be clustered into two distinct groups in the phylogenetic analysis. One of the groups mainly contained strains isolated from diseased tubers, whereas the other mainly included isolates from potato stems. In contrast to the tuber isolates, the stem isolates lacked genes in Type III secretion genes, were not able to elicit a hypersensitive response in tobacco leaves and produced only small amounts of autoinducers in the stationary phase in vitro. P. wasabiae isolate was able to cause similar amount of blackleg-like symptoms as P. atrosepticum in a field experiment with vacuum-infiltrated tubers, whereas both P. atrosepticum and P. carotovorum isolates reduced emergence and delayed growth more than P. wasabiae. Our findings confirm the presence of P. wasabiae in Finland and show that the Finnish P. carotovorum subsp. carotovorum isolates can be divided into two groups with specific characteristics and possibly also different ecologies

Susceptibility of tall fescue to Rhizoctonia zeae infection as affected by endophyte symbiosis

Abstract: Endophytic fungi belonging to the genus Neotyphodium often form symbiotic associations with grasses. The host plants usually benefit from the association with an endophyte. Presence of the symbiont may increase host resistance to infection by some pathogens. However, the exact mechanism of the lower susceptibility of endophyte-infected plants to diseases is still unclear. Growth chamber trials were conducted to determine whether (a) tall fescue plants infected with the endophyte Neotyphodium coenophialum (E+) are more resistant to sheath and leaf spot disease caused by Rhizoctonia zeae than endophyte-free (E−) plants, and (b) R. zeae growth inhibition is associated with endophyte presence. Tall fescue genotypes, each symbiotic with a genetically different native endophyte strain, were inoculated with isolates of R. zeae. The tillers infection by R. zeae, density of endophyte hyphae and content of total phenolic compounds in tillers were studied. Antifungal activity of the N. coenophialum towards R. zeae, Rhizoctonia solani, Bipolaris sorokiniana and Curvularia lunata was also investigated in dual-culture assays. For Tf3, Tf4, TfA2 and TfA9 tall fescue genotypes, the E+ plants had reduced R. zeae infection. In the Tf9 and Tf8085 genotypes, R. zeae infection was similar for both E+ and E− plants. The strongest effect was observed for the Tf4 endophyte. A strongly positive correlation (r = 0.94) occurred between endophyte hyphal density and disease index across all tall fescue genotypes. Dual-culture assays showed no inhibitory interaction between the seven endophyte strains and the R. zeae isolates; however, some endophytes inhibited R. solani, B. sorokiniana and C. lunata. Endophyte presence increased the production of phenolic compounds by the host grasses. The level of phenolics also differed significantly depending on the time of analysis after inoculation of plants by R. zeae. The results indicate that N. coenophialum can suppress disease severity caused by R. zeae infection. The mechanism of higher resistance of E+ plants is likely not based on direct inhibition such as antibiosis or competition. Thus, the induction of specific mechanisms in the host plant, for example, production of phenolic compounds, seems to be the main way of providing resistance to the grass by the endophyte.

Microscopic and biochemical aspects of sorghum resistance to anthracnose mediated by silicon

Abstract: The use of silicon (Si) in agriculture has attracted a great deal of interest from researchers because of the numerous benefits of this element to plants, especially when they are submitted to abiotic and/or biotic types of stress. The host's increased resistance to diseases, promoted by Si, is mainly associated with the deposition of this element in the tissues and the potentiation of defence mechanisms. However, the mechanisms involved in Si-mediated host resistance need to be further investigated. Thus, this study aimed to microscopically and biochemically elucidate the resistance of sorghum to anthracnose. In the leaves of plants supplied with Si, in addition to a greater deposition of Si at the infection sites, the acervuli were smaller in number compared to the leaves of plants not supplied with Si. Additionally, the activities of the defence enzymes peroxidases and polyphenoloxidases and the concentration of anthocyanins were higher in the leaves of plants supplied with Si. It can be concluded that Si, in addition to participate in the physical barrier that slows or prevents Colletotrichum sublineolum penetration in sorghum leaves, also plays a role in the biochemical aspect of sorghum resistance to anthracnose.

Molecular polymorphism and linkage analysis in sweet passion fruit, an outcrossing species

Abstract: One of the current challenges of tropical fruit crop improvement is to incorporate molecular marker-based approaches into conventional breeding programmes. This study was designed to build an integrated genetic map of the sweet passion fruit (Passiflora alata), a diploid (2n = 18) outcrossing species which is greatly appreciated for in natura consumption, and reported to inspire cosmetic and pharmaceutical companies to create plant-derived compounds. With this in mind, a full-sib family of 180 individuals was genotyped using different molecular marker types, such as amplified fragment length polymorphisms (AFLP), microsatellite-AFLP (M-AFLP), simple sequence repeats (SSR), resistance gene analogues (RGA) and target region amplification polymorphism (TRAP). On average, the rate of polymorphism between the parental genotypes was 20.3%. We also searched for single nucleotide polymorphisms (SNPs) in some AFLP bands and in seven gene fragments, and found one SNP every 87 bp. All SNPs were biallelic and occurred most frequently in putative gene fragments (81.5%) rather than in AFLP bands (60.0%) analyzed. Excellent gel profiles were obtained allowing the recognition of all types of segregation expected for a progeny of an outcrossing species. Multipoint linkage analysis was performed using OneMap software, with logarithm of the odds (LOD) score ≥ 5.6 and recombination fraction <0.5. The resulting integrated map consists of 549 markers, 2.0% of which fit a segregation ratio of 1:1:1:1, 1.3% a ratio of 1:2:1, 27.3% a ratio of 3:1 and 69.4% a ratio of 1:1. The map spanned a total of 2073.0 cM, with an average distance between adjacent markers of 3.8 cM. This is the first linkage study on sweet passion fruit and should prove useful for quantitative trait loci mapping.

Characterization and pathogenicity of Fusarium proliferatum causing stem rot of Hylocereus polyrhizus in Malaysia

Abstract: During a series of sampling in 2008 and 2009, stem rot disease was detected in Hylocereus polyrhizus plantations in Malaysia, with symptom appeared as circular, brown sunken lesion with orange sporodochia and white mycelium formation on the lesion surface. Eighty-three isolates of Fusarium were isolated from 20 plantations and were morphologically identified as F. proliferatum based on the variability of colony appearance, pigmentation, growth rate, length of chains, production of bluish sclerotia, concentric ring aerial mycelium and sporodochia. Three species-specific primers, namely ITS1/proITS-R, PRO1/2 and Fp3-F/4-R successfully produced PCR products and confirmed that the isolates from stem rot of H. polyrhizus were F. proliferatum isolates. From BLAST search of translation elongation factor 1-alpha (TEF1-α) sequences, the isolates showed 99–100% similarity with F. proliferatum deposited in GenBank which further confirmed that the isolates were F. proliferatum. The results from amplification of MAT-allele specific primers indicated that 14.5% of F. proliferatum isolates carried MAT-1 allele and 85.5% carried MAT-2. Crossing results showed that all 83 F. proliferatum isolates were male fertile showing positive crosses with the tester strains of MATD-1 and MATD-2. Perithecia oozing ascospore were produced. Forty isolates as representative were evaluated for pathogenicity test, produced rot symptoms similar to those observed in the fields which confirmed the isolates as the causal agent of stem rot of H. polyrhizus. To our knowledge, this is the first report of stem rot of H. polyrhizus caused by F. proliferatum in Malaysia.

Flavescence dorée phytoplasma deregulates stomatal control of photosynthesis in Vitis vinifera.

Abstract: Flavescence doree (FD) is among the major grapevine diseases causing high management costs; curative methods against FD are unavailable. In FD-infected plants, decrease in photosynthesis is usually recorded, but deregulation in stomatal control of leaf gas exchange during FD infection and recovery is unknown. We measured the seasonal time course of gas exchange rates in two cultivars (‘Barbera’ and ‘Nebbiolo’) during the term of 1 year when grapevines experienced a water stress and another with no drought, with difference in gas exchange rates in response to FD infection and recovery as assessed by symptom observation and phytoplasma detection through PCR analysis. Chlorophyll fluorescence was also evaluated at the time of maximum symptom severity in ‘Barbera’, the cultivar showing the most severe stress response to FD infection, causing the highest damage in vineyards of north-western Italy. In FD-infected plants, net photosynthesis and transpiration gradually decreased during the season, more during the no drought year than during drought. During recovery, healthy (PCR negative) plants infected 2 years before, but not those infected an year before, regained the gas exchange performances to the level as measured before infection. The relationships between stomatal conductance and the residual leaf intercellular CO2 concentration (ci) discriminated healthy versus FD-infected and recovered plants; at the same ci, FD-infected leaves had higher non-photochemical quenching than healthy ones. We conclude that metabolic, not stomatal, leaf gas exchange limitation in FD-infected and recovered grapevines is the basis of plant response to FD disease. In addition, we also suggest that such response is dependent upon water stress, by showing that water stress superimposes on FD infection in terms of stomatal and metabolic non-stomatal limitations to carbon assimilation.

Phenological growth stages of Camellia japonica

Abstract: Camellia japonica is the most important ornamental species within the genus Camellia, with over 32 000 cultivars. On the basis of data from 72 cultivars maintained in a live camellia germplasm bank in Pontevedra (NW Spain), the phenological growth stages of C. japonica are described using the Biologische Bundesantalt and Chemische scale. The main stages of development for buds, leaves, shoots, harvestable vegetative plant parts, flowers and fruits are given. Eight main stages were defined, with a total of 42 secondary stages. This scale provides growers and researchers with uniform criteria on the selection and description of phenological stages for best management and study of C. japonica.

Genetic diversity of legume yellow mosaic begomoviruses in Indonesia and Vietnam

Abstract: High incidences of yellow mosaic symptoms were observed in soybean and yard-long bean crops in Indonesia in 2009 and in mungbean crops in Vietnam in 2011. All five soybean and 20 yard-long bean samples from Java, Indonesia, and 15 mungbean samples from Vietnam with symptoms tested positive for begomovirus infection by polymerase chain reaction (PCR) with primer pair PAL1v1978B/PAR1c715H. On the basis of collection location and the nucleotide sequence comparisons of the 1.5 kb begomoviral DNA-A components amplified, a subset of samples comprising two soybean and six yard-long bean isolates from Indonesia and five mungbean isolates from Vietnam were taken forward for more detailed examination. Sequence comparison and phylogenetic analysis of the full-length sequences of all Indonesian and Vietnam isolates alongside other legume-infecting begomoviruses revealed that all the isolates from Indonesia were Mungbean yellow mosaic India virus (MYMIV) strain-A, and all from Vietnam were Mungbean yellow mosaic virus (MYMV) strain-B. To the best of our knowledge, this is the first identification of MYMIV and MYMV associated with yellow mosaic of legumes in Indonesia and Vietnam, respectively. The epidemiological implications and potential consequences of the emergence of legume-infecting begomoviruses on legume production in these areas of Southeast Asia are discussed.

Transmissibility of Broad bean wilt virus 1 by aphids: influence of virus accumulation in plants, virus genotype and aphid species

Abstract: Broad bean wilt virus 1 (BBWV-1) is transmitted by several aphid species in a non-persistent manner. Transmission efficiency by vectors is a key factor for understanding virus epidemiology and applying disease control measures based on limiting virus spread. We evaluated the transmission rates of two genetically divergent BBWV-1 isolates (PV-132 from USA and Ben from Spain) infecting broad bean (Vicia faba L.) by isofemale lines of nine aphid species from eight different genera collected in Spain. Our analyses showed that: (a) the virus concentration in the source plant was a key factor in BBWV-1 transmissibility; (b) The Spanish isolate Ben was transmitted more efficiently than the American isolate PV-132 by most aphid species, but this was only due to the higher accumulation of Ben in plants, as both isolates had similar transmissibility after adjusting virus concentration and (c) The transmission rate varied greatly between the different aphid species.

Volatile compounds from leaves of the African spider plant (Gynandropsis gynandra) with bioactivity against spider mite (Tetranychus urticae)

Abstract: Previous studies have demonstrated that Gynandropsis gynandra emits acetonitrile as a foliar volatile from intact plants and isolated leaves, and that this compound is an effective spider mite repellent. This study has used gas chromatography–mass spectrometry to investigate volatile compounds emitted from homogenised G. gynandra leaves to evaluate their tissue acetonitrile content and to look for other compounds that might be exploited for the management of spider mites. Acetonitrile was absent from the homogenised tissues of five lines of G. gynandra, studied over two seasons. Thirteen volatile compounds were emitted by G. gynandra at significantly higher levels than mite-susceptible pot roses, including isothiocyanates, aldehydes, esters, alcohols and terpenes. Six representative compounds were selected to assess bioactivity. Spider mite populations were completely inactive after a 2 h exposure to butyl isothiocyanate, 2,4-heptadienal or β-cyclocitral, when evaporated from 0.5 µL of pure compound in a 100 mL air space. The same level of inactivity was achieved after exposure to 5.0 μL of (Z)-2-pentenol or a 25 μL volume of 50% v/v Z-3-hexenal or 5% w/v methyl isothiocyanate. Dissipation of β-cyclocitral following 24 h exposure to its concentration of 5 μL in a 100 mL air space resulted in a 6% recovery of the spider mites but at higher concentrations no recovery was observed. These identified compounds may have potential as extracted products for management of spider mites in roses, and a high constitutive content of them in roses may be of value in targeted plant breeding for enhanced insect resistance. The range of isothiocyanates found in G. gynandra accounts for the bitter taste of the leaves when used as a traditional vegetable in Eastern Africa and provides a target for manipulation to improve palatability.

Antifungal activity of aluminium-containing salts against the development of carrot cavity spot and potato dry rot

Abstract: As an alternative to the use of synthetic chemical fungicides to control plant disease, aluminium-containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus-like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that various aluminium-containing salts provided strong inhibition of all the tested pathogens (Alternaria solani, Botrytis cinerea, F. sambucinum, P. sulcatum and Rhizopus stolonifer) with minimal inhibitory concentration of 1–10 mM. Aluminium chloride and aluminium sulphate were generally the most effective, inhibiting mycelial growth of pathogens by as much as 47% and 100%, respectively, at a salt concentration of 1 mM. Applied at 5 mM, aluminium sulphate also provided 28% and 100% inhibition of dry rot and cavity spot, respectively. Aluminium chloride (5 mM) reduced dry rot by 25% whereas aluminium lactate (5 mM) decreased cavity spot lesions by 86%. These results indicate that various aluminium-containing salts may provide an alternative to the use of synthetic fungicides to control these pathogens.

Biological control of the wheat root rot caused by Fusarium graminearum using some PGPR strains in Saudi Arabia

Abstract: The aim of this study was to evaluate the efficacy of selected bacterial strains against the wheat soil-borne pathogen Fusarium graminearum under greenhouse conditions. The most potent isolates were 3 isolates out of 18 isolates, which have numbers 3, 9 and 10 with in vitro inhibition index 42.5%, 41.3% and 46.3% respectively. Isolates 3 and 10 were selected for the following experiments. Isolates 3 and 10 were identified as Bacillus subtilis MAA03 and Pseudomonas fluorescens MAA10, respectively according to International Identification Keys and, confirmed by using Biolog system and 16S rDNA where the strains exhibited more than 99.5% sequence identity. Their close taxonomic relationship was further documented by phenotypic similarities. The using of B. subtilis and P. fluorescens separately or in mixture as biocontrol agent against F. graminearum on wheat significantly increased the final germination percent, the mean daily germination and germination index of wheat cultivar, while the mean germination time was significantly decreased relative to infested control. The final infection percent, the mean daily infection and infection index were decreased significantly, while the mean infection time was significantly increased relative to infested control. The use of P. fluorescens as biocontrol agent was the most efficient than B. subtilis or in mixture and the best treatment was seed coating. The application of B. subtilis and P. fluorescens separately or in combination significantly affected the growth parameters of wheat cultivar Tabuki, the root length was significantly increased in seed coating and seed soaking treatments, while non-significantly decreased in case of soil drench treatment relative to infested control. Shoot length was significantly decreased in case of seed coating treatment relative to infested control. The shoot fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The root fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The number of leaves was significantly increased in all treatments relative to infested control.

Effect of short‐duration high temperatures on weed seed germination

Abstract: Thermal soil disinfestation techniques are effective reducers of weed seedbank and weed emergence. Two experiments (Expt 1 and Expt 2) were conducted to test the effect of brief exposure to varying temperatures on the seed germination of Amaranthus retroflexus, Echinochloa crus-galli, Galinsoga quadriradiata, Portulaca oleracea, Setaria viridis and Solanum nigrum. To this end, species seeds were moistened with loamy-sand soil and placed into test tubes. The tubes were heated rapidly and then cooled by dipping them into a hot water bath until target temperatures were achieved. Expt 1 temperatures ranged between 55°C and 85°C at 5°C intervals and Expt 2 ranged between 48°C and 86°C at 2°C intervals. Thereafter, the tubes were dipped into a cooling (1°C) water bath. Exposure to target temperatures ranged between 2 s and 5 s. Soil temperatures were monitored using embedded thermocouples. A log-logistic dose–response model described the effect of heating on seed germinability; temperatures required for 99% reductions were calculated. On the basis of the predictive model equation used, weed species' germination sensitivity to high temperature exposure can be ranked as follows: E. crus-galli (79.6°C), S. viridis (75.8°C), S. nigrum (74.6°C), P. oleracea (72.2°C), A. retroflexus (70.9°C) and G. quadriradiata (68.1°C). The interval between no effects to complete seed devitalisation occurred at temperatures varying from 6.5°C to 15.7°C. Seed size and weight varied directly with heat tolerance. Study results not only inform the timing and optimal adjustment for effective thermal soil treatment, but also demonstrate a relatively simple and generalizable methodology for use in other studies.

Effects of oxidative stress caused by NaCl or Na2SO4 excess on lipoic acid and tocopherols in Genovese and Fine basil (Ocimum basilicum)

Abstract: With this investigation, we aimed to study more deeply the antioxidative response to moderate doses of NaCl or Na 2 SO 4 in two cultivars of basil differentially sensitive to salinity. Tolerance to salinity was previously evaluated by the extent of growth inhibition whereas the antioxidant response was assessed studying the changes in the activities of superoxide dismutase (SOD) and catalase as well as in the amounts of tocopherols and lipoic acid. To make possible the comparison of the responses of basil cv. Genovese and cv. Fine to different salts, the experiment was carried out with equimolar concentrations of Na + . The results showed that changes caused by salinity were dependent on cultivar and exposure time. In particular, cv. Genovese was more sensitive to Na 2 SO 4 excess than cv. Fine whereas both of them had higher SOD activity under NaCl salinity. Generally, Fine basil withstood salinity better than Genovese, being endowed with higher constitutive levels of reduced lipoic acid [dihydrolipoic acid (DHLA)] as well as of α- and γ-tocopherols. Moreover, cv. Fine showed the ability to utilise DHLA and to synthesise tocopherols during stressful conditions. Thus, more than one mechanism was involved in basil in the detoxification of reactive oxygen species during salt stress. In fact, when lipoic acid did not participate in the regeneration of reduced ascorbate and glutathione form, high amounts of tocopherols were present, likely protecting cell membranes from oxidative damage and making basil tolerant to moderate salinity.