Showing papers in "Annals of Applied Biology in 2016"

Weed species in tomato production and their role as alternate hosts of Tomato spotted wilt virus and its vector Frankliniella occidentalis

Abstract: Tomato spotted wilt virus (TSWV) is an important plant virus that infects a wide range of hosts including weeds making its management difficult. A survey was undertaken to establish the occurrence of weed species in tomato production systems in Kenya and their role as hosts of TSWV and its vectors. Selected weed species were further evaluated for their reaction to TSWV, transmission efficiency by Frankliniella occidentalis and ability to support thrips reproduction. Of the 43 weed species identified in the field, 29 species had been reported as hosts of TSWV, two were non-hosts and 11 had no record of their status. Among the more common species, Amaranthus hybridus, Solanum nigrum, Tagetes minuta and Datura stramonium were susceptible to the virus and supported high levels of thrips reproduction. The TSWV could not be transmitted to Galinsoga parviflora and Sonchus oleraceus by F. occidentalis despite them being highly susceptible in mechanical transmission tests. There was a significant correlation between feeding damage and number of larvae of F. occidentalis on different weeds. Occurrence of weeds that support thrips reproduction and are good hosts of TSWV is a clear indicator of their role in epidemiology and the importance of their management for disease control.

Quantitative trait loci mapping reveals pleiotropic effect for grain iron and zinc concentrations in wheat

Abstract: Malnutrition because of the deficiency of minerals such as iron (Fe) and zinc (Zn) afflicts over 2 billion people worldwide. Wheat is a major staple crop, providing 20% of dietary energy and protein consumption worldwide. Breeding wheat with elevated levels of grain Zn and Fe concentrations (GZn and GFe) represents a significant opportunity to increase the intake of these micronutrients for the resource poor people who depend on it as a major source of dietary energy. Synthetic hexaploid wheats (SHWs) have large genetic variation for GZn and GFe, which can be exploited for developing wheat varieties with higher concentrations of these minerals. The objective of this study was to localise genomic regions associated with GZn and GFe, thousand kernel weight (TKW) and test weight (TW) in a mapping population derived from the cross of Seri M82 and the SHW CWI76364. Major quantitative trait loci (QTL) on chromosome 4BS were detected for GZn and GFe; the QTL explained up to 19.6% of the total phenotypic variation for GZn and showed pleiotropic effects on GFe. This indicates that simultaneous improvement of GZn and GFe is feasible. Three and five QTL for TW and TKW were detected, respectively. One of the QTL for TKW was also located on chromosome 4BS. Positive correlations between plant height and GZn/GFe were observed. The 4BS QTL is of great interest for breeding biofortified wheat by means of marker-assisted selection.

Metabolic profile and antioxidant responses during drought stress recovery in sugarcane treated with humic acids and endophytic diazotrophic bacteria

Abstract: Water deficit is the major yield-limiting factor for sugarcane crop production that can be enhanced by inoculating with plant growth promoting bacteria (PGPB) combined with humic substances. The aim of this work was to examine changes to the metabolic profile and antioxidant enzyme activity of sugarcane treated with PGPB and humic acid (HA) after drought and then rehydration. The drought was imposed by withholding irrigation for 21 days thereby measuring enzyme activity, metabolic profile and photosynthetic rate 1 week after rehydratation. Growth of plants treated with HA, PGPB and with both treatments combined (PGPB + HA) was higher than control plants. The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities remained higher after rehydration only in plants treated with HA. Plants treated with HA and PGPB + HA exhibited increased transpiration, stomatal conductance and net photosynthesis than plants treated with PGPB. The PGPB-treated plants exhibited drought resistance that resembled ‘delayed stress onset’, which is a new term for preserving water in the plants tissues. Water preservation in plants treated with PGPB was corroborated by higher relative water content (RWC) than control plants at the end of the drought period. Plants treated with HA + PGPB exhibited the highest water potential after rehydration and high RWC. Osmotic adjustment in the other treatments (control, HA and PGPB) was indicated by a new pattern of metabolic response after rehydration, including generally enhanced carbohydrates and proteins and specific changes induced by HA-enhancing aromatic compounds, whereas PGPB exhibited enhanced fatty acids and other aliphatic H species. Humic acids assist with drought stress recovery by inducing antioxidant enzyme activity whereas PGPB induced preservation of leaf water potential and RWC by closing stomata efficiently, resulting in plant water preservation.

Cucurbit aphid-borne yellows virus (CABYV) modifies the alighting, settling and probing behaviour of its vector Aphis gossypii favouring its own spread.

Abstract: Plant pathogens are able to influence the behaviour and fitness of their vectors in such a way that changes in plant–pathogen–vector interactions can affect their transmission. Such influence can be direct or indirect, depending on whether it is mediated by the presence of the pathogen in the vector's body or by host changes as a consequence of pathogen infection. We report the effect that the persistently aphid-transmitted Cucurbit aphid-borne yellows virus (CABYV, Polerovirus) can induce on the alighting, settling and probing behaviour activities of its vector, the cotton aphid Aphis gossypii. Only minor direct changes on aphid feeding behaviour were observed when viruliferous aphids fed on non-infected plants. However, the feeding behaviour of non-viruliferous aphids was very different on CABYV-infected than on non-infected plants. Non-viruliferous aphids spent longer time feeding from the phloem in CABYV-infected plants compared to non-infected plants, suggesting that CABYV indirectly manipulates aphid feeding behaviour through its shared host plant in order to favour viral acquisition. Viruliferous aphids showed a clear preference for non-infected over CABYV-infected plants at short and long time, while such behaviour was not observed for non-viruliferous aphids. Overall, our results indicate that CABYV induces changes in its host plant that modifies aphid feeding behaviour in a way that virus acquisition from infected plants is enhanced. Once the aphids become viruliferous they prefer to settle on healthy plants, leading to optimise the transmission and spread of this phloem-limited virus.

Role of microRNAs in rice plant under salt stress

Abstract: Soil salinity is one of the most devastating factors threatening cultivable land. While low to moderate salt stress affects the plant growth rate and yields, the high-salt stress conditions are detrimental for plant growth. The problem of salinity is often compounded by mineral deficiencies and toxicities. Rice is essentially rated as salt-sensitive crop and its salt susceptibility is dependent on the growth stage. The genetic processes that are involved in coordinating the responses to salinity in rice are not very clearly understood, but can be somewhat explained by mechanisms that regulate ion homeostasis, osmolyte production, scavenging of toxic radicals, water conduction and root–shoot response coordination. This is achieved by modifying the gene expression. The microRNAs (miRs) represent an important class of endogenous small RNAs that have the potential to regulate gene expression at post-transcriptional levels. This review discusses the impact of salinity on rice crop and the current knowledge in the area of miRs with their role in the adaptive response to salt and other abiotic stresses, with a focus on rice.

Epidemiological study of Cucumber green mottle mosaic virus in greenhouses enables reduction of disease damage in cucurbit production

Abstract: Since 2007, the tobamovirus Cucumber green mottle mosaic virus (CGMMV) has become widespread in Israel, causing severe damage to trellised cucumber and melon in greenhouses and watermelon grown in open fields. To reduce disease damage below the economic threshold, this study focused on four objectives: (a) monitoring the patterns of virus distribution within commercial cucumber greenhouses; (b) studying the potential transmission of CGMMV by agrotechnical activities; (c) virus localization in plant tissues; and (d) searching for techniques that might be adapted for mitigating the disease in trellised cucurbit growth. The results of our surveys demonstrated the role of contaminated seeds and soil as primary inoculum sources, and secondary spread caused by agrotechnical activities. The patterns of secondary disease spread were demonstrated in a series of inoculation experiments involving contaminated knives, shears or hands on wet and dry plants, conducted under research-greenhouse conditions. In parallel experiments using CGMMV-specific antibody and secondary antibody conjugated to Alexa fluor 488, the viral coat protein was visualized in several plant tissues: phloem, xylem, trichomes and grasping tendrils. In addition, commercial-greenhouse experiments were aimed at reducing the number of inoculum sources by identifying and removing infected plants from the plots (early monitoring) prior to agrotechnical activities and/or by adding intermediate medium (IM), such as virus-free compost, to the planting pits at the planting stage. It is suggested that the use of IM combined with early monitoring, awareness of worker mobility (from contaminated structures to young planting areas) and proper sanitation (e.g. disinfection of agrotechnical tools) may reduce the yield losses caused by CGMMV below the economic threshold.

Early detection of bacterial diseases in apple plants by analysis of volatile organic compounds profiles and use of electronic nose

Abstract: DNA-based protocols are the standard methods for the diagnosis of infected plant material. Nevertheless, these methods are time-consuming and require trained personnel, with an efficacy depending on the sampling procedure. In comparison, recognition methods based on volatile compounds emissions are less precise, but allow a non-destructive mass screening of bulk samples, and may be implemented to steer molecular diagnosis. In this study, the analysis of volatile compounds is used for the discrimination of fire blight (Erwinia amylovora) and blossom blight (Pseudomonas syringae pv. syringae) on apple propagation material. Possible marker compounds were identified by gas chromatography–mass spectroscopy (GC-MS) and proton transfer reaction-time of flight-mass spectroscopy (PTR-ToF-MS). In addition, two commercial electronic noses were used for diagnosis. After a preliminary validation in vitro, a diagnostic protocol was successfully developed to scale up to real nursery conditions on cold stored, asymptomatic dormant plants.

Resistance to Tomato leaf curl New Delhi virus in Cucurbita spp.

Abstract: Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus (family Geminiviridae) first reported in India and its neighbouring countries. ToLCNDV severely affects zucchini crop (Cucurbita pepo) in the main production areas of Southern Spain since 2012. This emerging begomovirus is a serious threat to this and other cucurbit crops. Breeding resistant cultivars is the most promising method for disease control, but requires the identification of sources of resistance in the Cucurbita genus. In this work, we screened for ToLCNDV resistance a large collection of Cucurbita spp. accessions, including landraces and commercial cultivars of the main cultivated species, C. pepo, Cucurbita moschata and Cucurbita maxima and wild species. The screening was performed using mechanical and whitefly inoculation. The level of resistance was assessed by scoring symptom severity and by measuring the virus content with quantitative polymerase chain reaction in selected genotypes. Diversity in the response was observed within and among species. Severe symptoms and high viral amounts were found at 30 days after mechanical and whitefly inoculation in C. pepo, in all accessions belonging to the Zucchini morphotype and to other morphotypes of both subspecies, pepo and ovifera, and even in the wild relative Cucurbita fraterna. C. maxima was also highly susceptible. This species showed characteristic symptoms of leaf decay and intense yellowing, different from those of mosaic, curling and internode shortening found in C. pepo. The only species showing resistance was C. moschata. Four accessions were symptomless or had some plants with only mild symptoms after three independent rounds of mechanical inoculation with different inoculum sources. Two of them also remained symptomless after virus inoculation with viruliferous whiteflies. ToLCNDV was detected in these asymptomatic accessions at 15 and 30 days post inoculation, but viral amounts were much lower than those found in susceptible genotypes, suggesting a high level of resistance. The symptoms in the susceptible accessions of this species were also different, with a characteristic leaf mottling, evolving to a severe mosaic. The newly identified C. moschata resistant accessions are good candidates for breeding programmes to avoid the damage caused by ToLCNDV.

High productivity of wheat intercropped with maize is associated with plant architectural responses

Abstract: Mixed cultivation of crops often results in increased production per unit land area, but the underlying mechanisms are poorly understood. Plants in intercrops grow differently from plants in single crops; however, no study has shown the association between plant plastic responses and the yield advantage. Here, we assessed the productivity of wheat-maize intercropping as compared to sole wheat and sole maize, and the associated differences in wheat shoot and leaf traits. In two field experiments, intercrop wheat and maize were both grown in alternating strips consisting of six rows of wheat and two rows of maize. The traits of wheat plants in border rows of the strips were compared to the traits of plants in the inner rows as well as those in sole wheat. Leaf development, chlorophyll concentration and azimuth, as well as the final leaf and ear sizes, tiller dynamics of wheat and yield components of both crops were determined. The relative densities of wheat and maize in the intercrop were 0.33 and 0.67, respectively, but the corresponding relative yields compared to the respective monocultures were 0.46 for wheat and 0.77 for maize. Compared to wheat plants in the inner rows of the intercrop strips as well as in the monoculture, border-row wheat plants in the intercrop strips had (a) more tillers owing to increased tiller production and survival, and thus more ears, (b) larger top leaves on the main stem and tillers, (c) higher chlorophyll concentration in leaves, (d) greater number of kernels per ear and (e) smaller thousand-grain weight. Grain yield per metre row length of border-row wheat was 141% higher than the sole wheat, and was 176% higher than the inner-row wheat. The results demonstrate the importance of plasticity in architectural traits for yield advantage in multispecies cropping systems.

Effect of the trap crop Solanum sisymbriifolium and two biocontrol fungi on reproduction of the potato cyst nematode, Globodera pallida

Abstract: The potato cyst nematode, Globodera pallida, is one of the most important pests of potato worldwide. Owing to regulatory considerations and potential environmental impact, control options for this nematode are becoming increasingly limited. Solanum sisymbriifolium and biological control agents offer viable alternative options for controlling G. pallida. Therefore, experiments were conducted to determine the effect of the nematode trap crop S. sisymbriifolium, alone or in combination with the biocontrol agents Trichoderma harzianum or Plectosphaerella cucumerina, on population decline of G. pallida. Experiments were conducted for three different ‘cropping systems’: potato (Solanum tuberosum), S. sisymbriifolium, or soil only (fallow), each followed by a potato crop. Soil was amended with P. cucumerina, T. harzianum or left unamended, and then infested with nematodes at a rate of five eggs g−1 of soil. After 16 weeks in the greenhouse, plants were removed and the soil containing cysts was refrigerated at 4°C for 8 weeks, and then planted to potato. Cysts of G. pallida were counted after an additional 16-week period. The Pf/Pi of G. pallida was significantly reduced by 99% in potato following S. sisymbriifolium compared to both the potato-following-fallow and the potato-following-potato treatments. Amendment of soil with T. harzianum significantly reduced Pf/Pi of G. pallida by 42–47% in the potato-following-potato but not in either the potato-after-fallow nor in the potato-after-S. sisymbriifolium cycles which supports evidence that the plant species may play a role in the biocontrol activity of this fungus. Addition of the fungus P. cucumerina resulted in a 64% decrease in Pf/Pi in the potato-following-fallow in one experiment, and an 88% decrease in Pf/Pi in potato-following-potato but the decrease in Pf/Pi was not consistent over all experiments. However, both biocontrol fungi resulted in lower numbers of progeny cysts after an initial 16-week incubation with potato. To look at the effect of varied population density of the nematode on efficacy of S. sisymbriifolium to reduce G. pallida populations, potato, S. sisymbriifolium, or barley were planted into soil infested with G. pallida at rates of 5, 20 or 40 eggs g−1 soil applied as cysts (20, 80 or 160 cysts pot−1). After 16 weeks, numbers of cysts produced in each treatment were determined for each infestation rate. No new cysts were recovered from either S. sisymbriifolium or barley treatments, confirming that neither plant is a host for G. pallida. High numbers of cysts were recovered with potato. Soil from each treatment (containing original cysts and newly-formed cysts when present) were then planted with potato. After an additional 16 weeks, few cysts were found in the potato-after- S. sisymbriifolium treatments regardless of initial infestation rate. When potato followed barley, numbers of cysts were similar to those found after a single cycle of potato, indicating that the barley crop had no effect on the survival of initial inoculum. Overall, these results suggest that S. sisymbriifolium has potential to significantly reduce G. pallida populations, and also that the cropping system (i.e. the sequence of non-host and host plants) may play a significant role in the efficacy of fungal biological control agents.

Transmission of Grapevine virus A and Grapevine leafroll‐associated viruses 1 and 3 by Planococcus ficus and Planococcus citri fed on mixed‐infected plants

Abstract: The Grapevine virus A (GVA) and Grapevine leafroll-associated viruses 1 and 3 (GLRaV-1 and GLRaV-3) are associated with grapevine diseases that induce severe reductions in yield and berry quality. These three viruses are known to coexist in both grapevine and insect vectors, but their cotransmission has been poorly characterised so far. This study investigates the acquisition and transmission of GLRaV-1, GLRaV-3 and GVA by Planococcus ficus and Planococcus citri (Hemiptera: Pseudococcidae) following feeding on multiple-infected plants. The retention and load of the three viruses in the two insect species were analysed. After feeding onto GVA, GLRaV-1 and GLRaV-3 mixed-infected grapevines, nymphs of P. ficus and P. citri showed similar virus acquisition rates and retained low quantities of viruses until the third post-acquisition day. Despite the similar acquisition patterns, the two vectors differed in transmission efficiency: P. ficus showed a higher efficiency in transmitting GVA and GLRaV-3, whereas P. citri transmitted GLRaV-1 more efficiently. When focusing on the virus cotransmission, it appears that GVA could be transmitted to grapevine without GLRaV-1 and/or GLRaV-3 and that the transmission of both GLRaVs could take place in the absence of GVA. This comparative study involving different viruses and vector species improves the current knowledge of the semi-persistent transmission of these three viruses and contributes to the understanding of grapevine virus epidemiology.

Exploiting physical defence traits for crop protection: leaf trichomes of Rubus idaeus have deterrent effects on spider mites but not aphids

Abstract: Plants possess anti-herbivore defences that could be exploited for crop protection. The potential for deploying physical defence traits for more sustainable pest management (i.e. reduced pesticide application) has not been fully realised. Using a perennial crop (red raspberry, Rubus idaeus), we take the novel approach of quantifying within- and between-genotype variation in a resistance trait, leaf trichome density, to determine precisely the effect of trichomes on host plant preference and suitability for two shoot-feeding arthropods, the European large raspberry aphid (Amphorophora idaei) and two-spotted spider mite (Tetranychus urticae). Additionally, we tested whether this trait influenced searching behaviour of a generalist herbivore predator (lacewing larvae, Chrysoperla carnea). Although there was no consistent genotypic variation in R. idaeus suitability for T. urticae, our hypothesis that T. urticae would avoid high leaf trichome density was supported on certain genotypes. The deterrent effect was mainly on egg deposition rather than leaf selection by adults, with up to sixfold differences in leaf preference depending on the genotypes offered. By contrast, there was significant genotypic variation in R. idaeus suitability for A. idaei (10-fold variation in aphid abundance), but, contrary to our prediction, aphid preference and infestation levels were unrelated to leaf trichome density. Instead, A. idaei performed best on vigorous genotypes, indicating that plant tolerance traits contributed to R. idaeus suitability for aphids. Leaf trichomes had little effect on the behaviour of the beneficial control agent C. carnea larvae. We conclude that physical anti-herbivore defences, specifically leaf trichomes, could be deployed to deter particular arthropod pests. However, the mechanistic approach adopted here is necessary to avoid antagonistic effects on other pests or on natural enemies.

Transmission of ‘Candidatus Phytoplasma solani’ by Reptalus quinquecostatus (Hemiptera: Cixiidae)

Abstract: Transmission trials were carried out using Reptalus quinquecostatus (Cixiidae), a potential vector of ‘Candidatus Phytoplasma solani’ (‘Ca. P. solani’), to assess its ability to inoculate the phytoplasma to periwinkle (Catharanthus roseus), grapevine (Vitis vinifera), lavandin (Lavandula × intermedia) and tobacco (Nicotiana tabacum). Detection, genotyping and comparison of ‘Ca. P. solani’ strains carried by R. quinquecostatus showed that R. quinquecostatus carried a higher diversity of ‘Ca. P. solani’ than Hyalesthes obsoletus, major known vector of ‘Ca. P. solani’ strains. Molecular analyses also showed the presence of a new strain only in grapevines and R. quinquecostatus. ‘Ca. P. solani’ was successfully inoculated to periwinkles by R. quinquecostatus, but no transmission was achieved to the other tested plants. The ability to transmit ‘Ca. P. solani’ to plants and observations of adults feeding on grapevines in vineyards consolidate the hypothesis that R. quinquecostatus is a specific vector of ‘Ca. P. solani’ strains. Moreover, the discovery of a new genotype present in R. quinquecostatus and not in H. obsoletus, vector also present on grapes, suggests that R. quinquecostatus should have a direct role in ‘Ca. P. solani’ epidemiology. Overall, even if R. quinquecostatus has a minor or no role in ‘Ca. P. solani’ transmission from weeds to grapevines, it can have an indirect role in Bois Noir epidemiology. This planthopper can contribute to maintain an alternative ‘Ca. P. solani’ cycle in weeds even in the absence of H. obsoletus preferentially by maintaining pathogen reservoirs in wild compartments neighbouring susceptible crops.

Incidence, identification and pathogenicity of Cladobotryum mycophilum, causal agent of cobweb disease on Agaricus bisporus mushroom crops in Spain

Abstract: Between 2008 and 2011, outbreaks of cobweb were observed in commercial white button mushroom (Agaricus bisporus) crops in Castilla-La Mancha (Spain). In the last 3 years, the presence of the disease has notably increased resulting in serious economic losses. Based on morphological and genetic analyses, the casual agent of cobweb was identified as Cladobotryum mycophilum. A. bisporus mushroom crops were surveyed over a 2-year period to estimate the incidence of cobweb. The presence of the disease was detected in 32% of the mushroom crops observed, being of particular concern in autumn (44% of crops infected) and winter (37%). As regards the casing material, the percentage of crops affected by cobweb was 34% in crops using mineral casing and 29% in those cased with a peat-based casing, with no statistical relationship between the casing and the presence of cobweb. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in three peat-based casings (C1, C2 and C3). The effect of cobweb on mushroom productivity was evaluated by comparing mushroom production and the cobweb patches detected in the casing soil. The decrease in total yield of mushrooms attributed to cobweb reached 12.9% with C2, and the crop area colonised by cobweb reached a final percentage of 36% with C3.

Baseline sensitivity and efficacy of fluopyram against Botrytis cinerea from table grape in Italy

Abstract: Succinate dehydrogenase inhibitor (SDHI) fungicides constitute a relatively recent fungicide class registered for the treatment of grey mould on grapevine in Italy. The sensitivity profile to a novel compound fluopyram was established for a set of 203 Botrytis cinerea isolates collected from Sicilian vineyards within 2009–2012 prior its introduction into market. In addition, its performances were compared in in vitro and in vivo assays with other registered SDHI fungicide boscalid, to evaluate their frequency distributions EC50 values and cross-resistance patterns. Results of the article showed that EC50 values for fluopyram ranged from 0.05 to 1.98 µg mL−1. Although EC50 values of boscalid ranged from 0.01 to 89.52 µg mL−1, no cross-resistance relationship was observed between the two fungicides (r = 0.003; P = 0.964) within our B. cinerea population. On further confirming these data, boscalid failed in controlling grey mould infections when boscalid-resistant isolates were inoculated on grape berries whereas fluopyram exhibited a good efficacy against the same isolates. This study represents the first report on the baseline sensitivity to fluopyram within B. cinerea population from Sicilian table grape vineyards in Italy, and it clearly shows the lack of cross-resistance in vitro and in vivo between fluopyram and boscalid for the field pathogen isolates. These results provided useful information for managing of fungicide resistance suggesting that fluopyram could be a valid alternative to boscalid for the control of grey mould of table grape.

Triticum monococcum lines with distinct metabolic phenotypes and phloem-based partial resistance to the bird cherry-oat aphid Rhopalosiphum padi.

Abstract: Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry-oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.

Improving the performance of short-duration basmati rice in water-saving production systems by boron nutrition

Abstract: Over exploitation of groundwater and decreasing canal water resources are threating the productivity of conventional rice production systems in Asia which is the main rice bowl. Therefore, strategies are needed to produce more rice with less water in the shortest possible duration without compromising the yield to feed the increasing world population. Panicle sterility is one of the major obstacles in wide‐scale adoption of water‐saving rice production systems. Boron (B) deficiency, in water‐saving rice production systems, has been identified as a possible reason for panicle sterility. This 2‐year field study was aimed to investigate the potential of pre‐optimised boron application through various methods in improving the productivity of short‐duration basmati rice (Shaheen Basmati) in water‐saving production systems, as delivered through seed priming (0.1 mM boron), foliar spray (200 mM boron) or soil application (1 kg boron ha⁻¹), while hydropriming and no boron application were taken as control. Boron nutrition, by either way, improved the growth, water relations, morphology, yield‐related traits, panicle fertility, grain yield, grain quality and grain boron contents of short‐duration basmati rice; nonetheless, boron application as seed priming was superior and cost effective with maximum marginal rate of return. In conclusion, boron nutrition through seed priming is cost effective and may help improving the productivity, quality, and boron grain contents in short‐duration basmati rice under water‐saving production systems.

Diazotrophic bacilli isolated from the sunflower rhizosphere and the potential of Bacillus mycoides B38V as biofertiliser

Abstract: The nitrogen fixation by strains belonging to the Bacillus genus remains poorly explored. In this work, the diversity of endospore-forming bacilli isolated from the rhizosphere of sunflower was evaluated. A total of 101 strains were identified based on the V1-V2 variable regions of the 16S rRNA gene. Strains belonging to the genera Bacillus and Paenibacillus represented 41.6% and 58.4%, respectively, of total isolates. The production of indolic compounds was a common trait among the isolates, and approximately 75% of them exhibited positive nitrogenase activity; but only 9.2% displayed activities higher than 1 nmol C2H4 mg protein h−1. Within the genus Bacillus, the isolates related to the B. cereus group displayed the highest nitrogenase activity and were the second most frequent group of Bacillus sp. isolated. Plants inoculated with the isolate B38V showed the highest N content, and their shoot dry weights were significantly increased compared with positive control. Our results indicated that B38V, which belongs to the B. mycoides species, has the potential to promote sunflower growth. The data obtained in this study provide additional information concerning the diversity of Gram-positive diazotrophic within the genera Bacillus and Paenibacillus and their potential for the biofertilisation of sunflower crops.

Susceptibility and tolerance in hybrid and pure‐line rice varieties to herbivore attack: biomass partitioning and resource‐based compensation in response to damage

Abstract: Hybrid rice has been noted for its susceptibility to insects and diseases compared to pure-line (conventional) rice varieties. We investigated herbivory by Nilaparvata lugens, Sogatella furcifera and Scirpophaga incertulas on replicated three-line hybrid sets (parental and hybrid lines) in field and greenhouse experiments. In a field experiment, caterpillar densities and stemborer damage was similar among hybrid and parental lines. In field and greenhouse experiments, the cytoplasmic male sterile (CMS)-lines and maintainer lines had higher densities of planthoppers (including N. lugens and S. furcifera) than restorer or hybrid lines likely because of their wild abortive CMS-lineage. High nitrogen levels increased plant mortality due to N. lugens, but often reduced mortality from S. furcifera and S. incertulas: this was similar between hybrid and pure-line varieties. The hybrids were generally more tolerant of herbivory (lower biomass reductions per unit weight of insect) than the inbred parental lines. The addition of nitrogen to both the hybrid and pure-line varieties had contrasting effects on tolerance depending on the nature of the attacking insect: fertiliser increased tolerance to S. furcifera (lower losses of yield and shoot biomass per mg insect) and S. incertulas (lower yield, shoot and root biomass loss) but fertiliser reduced tolerance to N. lugens (higher loss of root biomass and no effects on yield and shoot biomass loss). Our results indicate that hybrid rice is not physiologically more susceptible to herbivores than are pure-line varieties even under high nitrogen conditions, but does have higher tolerance to insect damage.

Seed treatment with salicylic acid invokes defence mechanism of Helianthus annuus against Orobanche cumana

Abstract: The root holoparasitic angiosperm sunflower broomrape (Orobanche cumana) specifically affects sunflower (Helianthus annuus) growth and causes severe damage all over the world. This investigation was designed to examine the protective effects of salicylic acid (SA) treatment to the seeds of an O. cumana-susceptible cultivar of sunflower (TK0409). Sunflower seeds were pretreated with different concentrations (0, 0.5 and 1 mM) of SA and inoculated with O. cumana for 4 weeks. O. cumana infection resulted in reduction in plant biomass, endogenous SA level, and the expression of SA-related genes including pal, chs and NPR1. By contrast, O. cumana infection enhanced the production of reactive oxygen species, activities of antioxidant enzymes as well as contents of phenolics and lignin. Seed treatment with 1 mM SA increased sunflower biomass in terms of plant height, fresh weight and dry weight by 10%, 13% and 26%, respectively, via reducing the number and biomass of established O. cumana. The increase of hydrogen peroxide contents by 14% in the 1 mM SA treated sunflower plants appeared to be because of the inhibition of ascorbate peroxidase and catalase by exogenous SA. The enhanced expression of pathogenesis-related genes (PR3 and PR12, encoding chitinase and defensin, respectively) after 4 weeks of inoculation indicated that systemic acquired resistance was induced in the SA treated sunflower in which the level of endogenous SA was also elevated in a dose-dependent manner. The increased expression of a hypersensitive-responsive (HR) gene hsr indicated that the resistance of sunflowers might be associated with a hypersensitive reaction which was activated by exogenous SA treatment.

Biofumigant effect of new defatted seed meals against the southern root-knot nematode, Meloidogyne incognita

Abstract: In recent years, Brassica carinata defatted seed meals (DSMs) have been successfully applied as an amendment in the control of pests and soil pathogens in several countries with clear advantages for the environment and soil fertility. The effectiveness of this product is clearly linked to the release of bioactive compounds by the well-known glucosinolate (GL)–myrosinase (MYR) system. Until now, this commercial know-how has been limited to allyl-isothiocyanate, the breakdown product of hydrolysis catalysed by MYR of the GL sinigrin. Brassicaceae germplasm is an extremely wide-ranging family, considering that more than 3500 species have been classified in this family in nature, which contains around 200 different GLs. Therefore, there is a great potential for the availability of new still unexplored bioactive compounds. This study evaluated, in controlled glasshouse conditions, the effect of biofumigation on the nematode Meloidogyne incognita and that of biostimulation on tomato plants of 13 DSMs obtained from different Brassicaceae species at different levels of soil inoculation. Among the tested DSMs, the best results for all inoculations were achieved by Eruca sativa (rocket), Barbarea verna (land cress) and Brassica nigra (black mustard), whereas the other species gave either alternate results or results not different from untreated or sunflower DSM controls. All the DSMs, including sunflower, determined a clear positive effect on plant vigour. These first results open new perspectives for the application of biofumigation in plant protection and management.

Temperature-dependent development and demography of Zygogramma bicolorata (Coleoptera: Chrysomelidae) on Parthenium hysterophorus

Abstract: Development of Zygogramma bicolorata (Coleoptera: Chrysomelidae), was evaluated at 10°C, 15°C, 20°C, 25°C, 27°C, 30°C, 32°C, 35°C and 38°C with 65% RH and 10L:14D h on Parthenium hysterophorus. Development of immature was significantly (P < 0.05) prolonged to 63.65-days at 15 °C compared to 24.85-days at 35°C, while development was not recorded at 10°C and 38°C. For immature development, values of lower temperature threshold (Tmin) and thermal constant (K) were 4.31°C and 769.23 degree-day (DD), respectively, in linear model. Optimum temperature (Topt) for immature development was estimated to be 21.60°C with the help of cubic polynomial non-linear equation. Furthermore, other models were also evaluated to check the accuracy of estimated thresholds and biological values of integral coefficients. Consequently, non-linear model was accepted and recommended for description of thermal-based development of Z. bicolorata. Among the non-linear models Briere-2 model was found suitable for determination of developmental rate as Topt and Tmax with acceptable value of 27.19°C and 30.39°C, respectively. Demographic parameters were also studied at tested temperatures. Potential fecundity (Pf), intrinsic rate of increase (rm) and finite rate of increase (λ) were highest, however mean generation time (Tc) and doubling time (DT) were lowest at 27°C and 30°C, respectively. Kaplan-Meier (K-M) estimation showed an inversely proportional relationship between female survivorship and temperatures. Female biased sex ratio was evident at all constant temperatures tested. Thus, it can be concluded that development of immature of Z. bicolorata was decreased with increase of temperature and optimum development occurred at 27°C and 30°C. Moreover, life table parameters of Z. bicolorata can be used to develop the models of population dynamics and prediction.

Effects of nitrogen rates on grain yield and nitrogen agronomic efficiency of durum wheat genotypes under different environments

Abstract: Durum wheat is an important staple food crop in Tunisia and other Mediterranean countries and is grown in various climatic conditions. Production and yield are however severely limited not only by drought events but also by reduced levels of nitrogen fertilisation. A study was carried out at two locations in the sub-humid area of Tunisia: Mateur in 2009–10 and 2010–11 and Beja in 2011–12 and 2012–13 under rainfed conditions. Four durum wheat genotypes (landraces: Bidi, Azizi; improved: Om Rabia, Khiar) were evaluated for nitrogen agronomic efficiency and related agronomic traits under various nitrogen rates: 0, 50, 100, 150, 200 and 250 kg N ha−1, with three replications. There was a significant interaction effect (P ≤ 0.001) environments × genotypes × N treatments for grain yield (GY), biomass yield (BY), harvest index (HI), partial factor productivity of applied nitrogen (PFPN) and nitrogen agronomic use efficiencies (NAE). GY was the most affected trait by nitrogen applied showing an increase of 94% under high N treatment (250 kg N ha−1) compared to control plots without N treatments. A significant linear regression exists between GY (0 N) and GY for the different N rates (r = 0.70; P < 0.001). This effect was more pronounced for improved genotypes than landraces for all parameters excepting BY and NAEBY. BY showed +11% increase in landraces than improved genotypes. PFPN showed an average decrease of 65% under high-N fertilisation with 10% prevalence for improved genotypes. Landraces tend to promote vegetative growth while grain filling efficiency was higher for improved genotypes.

Bio‐efficacy of a chitosan based elicitor on Alternaria solani and Xanthomonas vesicatoria infections in tomato under tropical conditions

Abstract: With increasing problems of decreased efficacy, toxicity and environmental degradation due to the use of chemical fungicides, there is urgent need for developing alternative strategies for managing crop diseases. One approach currently being explored is the application of safe organic-based compounds to prime the defence systems of plants in order to prevent or limit infections by pathogens. Chitosan, a deacylated derivative of chitin, is one of the compounds known to promote plant defence and growth, but the mechanisms by which it is able to do so are still unclear. This study investigated the ability of a commercial chitosan extract (Armour-Zen®) to reduce disease incidence and induce the production of enzymes and expression of marker genes involved in plant defences for two important tomato pathogens, Alternaria solani and Xanthomonas vesicatoria. Foliar spray applications of the chitosan extract significantly reduced the incidences of both diseases in greenhouse and field grown tomato plants and also displayed a positive effect on growth and yields of tomato fruits. Chitosan-treated plants recorded elevated levels of defence enzymes and upregulation of the PIN II marker gene for defence signalling pathways when compared to the control. It was therefore proposed that chitosan would able to provide broad-range protection through induced systemic resistance mechanisms.

Behavioural response of winged aphids to visual contrasts in the field

Abstract: To test the behavioural response of winged aphid spring migrants to visual contrasts, we conducted a field trial in which water traps (painted in seven different shades of green and yellow) were set up on uncovered soil and on coloured boards (also painted in seven different colours including black, brown and various shades of green). In total, 56 trap–background combinations were tested. Out of the 4904 aphid individuals caught, 64.5% belonged to Aphis ssp. Using spectral measurements of both traps and backgrounds, as well as information on insect spectral sensitivity, an empirical colour choice model was built based on photoreceptor adaptation to the background, and colour opponency of the green and blue photoreceptor. Specifically, the visual input variable C* represents the difference between green–blue colour opponency values of the trap and the background. When C* > 0, the number of aphids linearly increased with C*. The model explained 64% of the behavioural response of the aphids. Applied to intercropping scenarios of sugar beet, the behavioural model showed a higher visual attractivity of a monocrop sugar beet than intercropped sugar beet. Implications for the use of mulches and for increasing plant diversity in cropping systems are discussed.

Genetic diversity and population structure of Sorghum mosaic virus infecting Saccharum spp. hybrids

Abstract: Sugarcane mosaic disease is widespread in many countries and has been identified to be caused by Sugarcane mosaic virus (SCMV), Sorghum mosaic virus (SrMV) and Sugarcane streak mosaic virus (SCSMV). Viral surveys of SCMV, SrMV and SCSMV were performed from 104 leaf samples of Saccharum spp. hybrid growing in China and two leaf samples in Myanmar. Sorghum mosaic virus was a major causal agent for sugarcane mosaic disease in China whereby 72.1% (75/104) of samples had SrMV infection alone, 6.7% (7/104) were mixed with SCMV and 17.3% (18/104) were mixed with SCSMV. Sugarcane streak mosaic virus infection alone occurred in 3.8% (4/104) of samples, but no single infections were observed for SCMV. Two viruses (SrMV and SCSMV) were detected in sugarcane mosaic samples in Myanmar. Phylogenetic analysis revealed that all of the SrMV isolates were clustered into three major lineages encompassing six phylogroups/genotypes based on the CP sequences (825 nucleotides) of 113 Chinese and 2 Burmese isolates from this study and 73 isolates reported worldwide. Six clearly distinct SrMV phylogroups (G1–G6) were formed and shared 74.3–94.1% nucleotide identity and 84.7–98.1% amino acid identity of CP sequences. SrMV-G5 was identified to be new distinct phylogroup that was restricted to the Fujian and Guangxi provinces. The unique SrMV-G6 phylogroup only occurred in Yunnan province. Insertion/deletion mutations, negative selection and frequent gene flow are factors driving the genetic evolution and population structure of SrMV in China.

Phenological growth stages of nashi tree (Pyrus pyrifolia): codification and description according to the BBCH scale

Abstract: The phenological growth stages of nashi tree were firstly described here using the BBCH scale. Based on this general scale, nashi phenology showed 8 of the 10 principal stages (0–9): bud, leaf and shoot development, inflorescence emergence, flowering, fruit development, fruit maturity and senescence. A schematic representation of the chronological progression of principal growth stages of nashi is also shown. The codification of the different growth stages is important for correct timing of general orchard management, particularly for disease and pest management. Besides, it will help farmers to efficiently schedule and manage nashi cultivation, as well as to improve knowledge dissemination among scientists around the World.