Wild mungbean resistance to the nematode Meloidogyne enterolobii involves the induction of phenylpropanoid metabolism and lignification.

Root-knot nematodes (Meloidogyne spp.) are plant parasites causing annual economic losses amounting to several billion US dollars worldwide. One of the most aggressive species is M. enterolobii, a growing threat to agriculture due to its broad host range and ability to overcome many known resistance genes. Mungbean, a nutritionally and economically valuable crop, is particularly vulnerable to nematodes and pathogens. However, research focusing on mungbean resistance to M. enterolobii is scarce, and the corresponding defense mechanisms are poorly understood. Here, we screened mungbean accessions and identified an accession strongly resistant to M. enterolobii. Transcriptome analysis revealed 2730 differentially expressed genes (DEGs) in this resistant accession (CPI106939) compared to 1777 in the susceptible accession (Crystal) 7 days after nematode inoculation. The gene ontology (GO) upregulated in CPI106939 with functions related to plant-pathogen interactions, plant hormone signaling, oxidative stress, and plant immunity. Plant defense-related genes (WRKY, PAL, MAPK, POD and PR) were also significantly induced in CPI106939. Metabolome analysis showed that four secondary metabolites related to phenylpropanoid metabolism and lignification were significantly enriched in CPI106939. The induced immune response and secondary metabolites may underpin the enhanced resistance to M. enterolobii, providing insight into the resistance mechanisms in accession CPI106939 as well as candidate genes controlling the interaction between mungbean and its nematode parasite. Our study therefore provides foundations for the breeding of new varieties with intrinsic M. enterolobii resistance.

Bruchid beetle ovipositioning mediated defense responses in black gram pods.

BACKGROUND: Black gram [Vigna mungo (L)] seeds are a rich source of digestible protein and dietary fibre, both for human and animal consumption. However, the quality and quantity of the Vigna seeds are severely affected by bruchid beetles during storage. Therefore, analyses of the expression of the bruchid induced transcript dynamics in black gram pods would be helpful to understand the underlying defense mechanism against bruchid oviposition. RESULTS: We used the RNAseq approach to survey the changes in transcript profile in the developing seeds of a moderately resistant cultivar IC-8219 against bruchid oviposition using a susceptible cultivar T-9 as a control. A total of 96,084,600 and 99,532,488 clean reads were generated from eight (4 each) samples of IC-8219 and T-9 cultivar, respectively. Based on the BLASTX search against the NR database, 32,584 CDSs were generated of which 31,817 CDSs were significantly similar to Vigna radiata, a close relative of Vigna mungo. The IC-8219 cultivar had 630 significantly differentially expressed genes (DEGs) of which 304 and 326 genes up and down-regulated, respectively. However, in the T-9 cultivar, only 168 DEGs were identified of which 142 and 26 genes up and down-regulated, respectively. The expression analyses of 10 DEGs by qPCR confirmed the accuracy of the RNA-Seq data. Gene Ontology and KEGG pathway analyses helped us to better understand the role of these DEGs in oviposition mediated defense response of black gram. In both the cultivars, the most significant transcriptomic changes in response to the oviposition were related to the induction of defense response genes, transcription factors, secondary metabolites, enzyme inhibitors, and signal transduction pathways. It appears that the bruchid ovipositioning mediated defense response in black gram is induced by SA signaling pathways and defense genes such as defensin, genes for secondary metabolites, and enzyme inhibitors could be potential candidates for resistance to bruchids. CONCLUSION: We generated a transcript profile of immature black gram pods upon bruchid ovipositioning by de novo assembly and studied the underlying defense mechanism of a moderately resistant cultivar.

Disparate genetic variants associated with distinct components of cowpea resistance to the seed beetle Callosobruchus maculatus.

KEY MESSAGE: Polygenic genome-wide association mapping identified two regions of the cowpea genome associated with different components of resistance to its major post-harvest pest, the seed beetle Callosobruchus maculatus. Cowpea (Vigna unguiculata) is an important grain and fodder crop in arid and semi-arid regions of Africa, Asia, and South America, where the cowpea seed beetle, Callosobruchus maculatus, is a serious post-harvest pest. Development of cultivars resistant to C. maculatus population growth in storage could increase grain yield and quality and reduce reliance on insecticides. Here, we use a MAGIC (multi-parent, advanced-generation intercross) population of cowpea consisting of 305 recombinant inbred lines (RILs) to identify genetic variants associated with resistance to seed beetles. Because inferences regarding the genetic basis of resistance may depend on the source of the pest or the assay protocol, we used two divergent geographic populations of C. maculatus and two complementary assays to measure several aspects of resistance. Using polygenic genome-wide association mapping models, we found that the cowpea RILs harbor substantial additive-genetic variation for most resistance measures. Variation in several components of resistance, including larval development time and survival, was largely explained by one or several linked loci on chromosome 5. A second region on chromosome 8 explained increased seed resistance via the induction of early-exiting larvae. Neither of these regions contained genes previously associated with resistance to insects that infest grain legumes. We found some evidence of gene-gene interactions affecting resistance, but epistasis did not contribute substantially to resistance variation in this mapping population. The combination of mostly high heritabilities and a relatively consistent and simple genetic architecture increases the feasibility of breeding for enhanced resistance to C. maculatus.

Host-mediated RNAi for simultaneous silencing of different functional groups of genes in Meloidogyne incognita using fusion cassettes in Nicotiana tabacum.

KEY MESSAGE: This study establishes possibility of combinatorial silencing of more than one functional gene for their efficacy against root-knot nematode, M. incognita. Root-knot nematodes (RKN) of the genus Meloidogyne are the key important plant parasitic nematodes (PPNs) in agricultural and horticultural crops worldwide. Among RKNs, M. incognita is the most notorious that demand exploration of novel strategies for their management. Due to its sustainable and target-specific nature, RNA interference (RNAi) has gained unprecedented importance to combat RKNs. However, based on the available genomic information and interaction studies, it can be presumed that RKNs are dynamic and not dependent on single genes for accomplishing a particular function. Therefore, it becomes extremely important to consider silencing of more than one gene to establish any synergistic or additive effect on nematode parasitism. In this direction, we have combined three effectors specific to subventral gland cells of M. incognita, Mi-msp1, Mi-msp16, Mi-msp20 as fusion cassettes-1 and two FMRFamide-like peptides, Mi-flp14, Mi-flp18, and Mi-msp20 as fusion cassettes-2 to establish their possible utility for M. incognita management. In vitro RNAi assay in tomato and adzuki bean using these two fusion gene negatively altered nematode behavior in terms of reduced attraction, invasion, development, and reproduction. Subsequently, Nicotiana tabacum plants were transformed with these two fusion gene hairpin RNA-expressing vectors (hpRNA), and characterized via PCR, qRT-PCR, and Southern blot hybridization. Production of siRNAs specific to Mi-flp18 and Mi-msp1 was also confirmed by Northern hybridization. Further, transgenic events expressing single copy insertions of hpRNA constructs of fusion 1 and fusion-2 conferred up to 85% reduction in M. incognita multiplication. Besides, expression quantification revealed a significant reduction in mRNA abundance of target genes (up to 1.8-fold) in M. incognita females extracted from transgenic plants, and provided additional evidence for successful gene silencing.

Role of MgO nanoparticles in the suppression of Meloidogyne incognita, infecting cowpea and improvement in plant growth and physiology.

Root-knot disease, caused by Meloidogyne spp., alters histology as well as physiology of the roots thus influencing metabolism of vegetative and reproductive parts leading to huge losses in crop productivity. The experimental plant, Vigna unguiculata L. (cowpea of Fabaceae family) var. Gomti is an economically important pulse crop plant. An experiment was conducted to evaluate the effects of different concentrations (0, 25, 50 or 100 ppm) and various modes of applications (root dip, soil drench or foliar spray) of MgO nanoparticles on cowpea infected with M. incognita. The MgO nanoparticles were synthesized chemically and characterized by transmission and scanning electron microscopy (TEM, SEM), UV-Vis spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The scanning electron microscopy images of second stage juveniles of M. incognita treated with MgO nanoparticles (50 and 100 ppm) exhibited indentations, roughness and distortions in the cuticular surface, in comparison to the control untreated juveniles. MgO nanoparticles, in varying concentrations (50, 100 and 200 ppm), were dispensed into the plants by root dip, soil drench and foliar spray methods and their efficacy was assessed in terms of morphological characteristics, yield parameters and biochemical attributes of M. incognita infected plants. In planta trials revealed that 100 ppm dose of MgO nanoparticles, as root dip application, demonstrated reduced nematode fecundity, decreased number and smaller size of galls; enhanced plant growth, increased chlorophyll, carotenoid, seed protein, and root and shoot nitrogen contents. From these findings it could be inferred that MgO nanoparticles played twin roles, first as a nematicidal agent and the other as growth promotion inducer.

Demography-Dispersal Trait Correlations Modify the Eco-Evolutionary Dynamics of Range Expansion.

Spreading populations are subject to evolutionary processes acting on dispersal and reproduction that can increase invasion speed and variability. It is typically assumed that dispersal and demography traits evolve independently, but abundant evidence points to correlations between them that may be positive or negative and genetic, maternal, or environmental. We sought to understand how demography-dispersal correlations modify the eco-evolutionary dynamics of range expansion. We first explored this question with the beetle Callosobruchus maculatus, a laboratory model in which evolutionary acceleration of invasion has been demonstrated. We then built a simulation model to explore the role of trait correlations in this system and more generally. We found that positive correlations amplify the positive influence of evolution on speed and variability while negative correlations (such as we found empirically) constrain that influence. Strong negative genetic correlations can even cause evolution to decelerate invasion. Genetic and nongenetic (maternal and environmental) correlations had similar effects on some measures of invasion but different effects on others. Model results enabled us to retrospectively explain invasion dynamics and trait evolution in C. maculatus and may similarly aid the interpretation of other field and laboratory studies. Nonindependence of demography and dispersal is an important consideration for understanding and predicting outcomes of range expansion.

A second VrPGIP1 allele is associated with bruchid resistance (Callosobruchus spp.) in wild mungbean (Vigna radiata var. sublobata) accession ACC41.

Two bruchid species, azuki bean weevil (Callosobruchus chinensis L.) and cowpea weevil (Callosobruchus maculatus F.), are the most important insect pests of mungbean [Vigna radiata (L.) Wilczek] after harvest. Improving bruchid resistance is a major goal for mungbean breeders. Bruchid resistance in mungbean is controlled by a single major locus, Br. The tightly linked VrPGIP1 and VrPGIP2, which encode polygalacturonase-inhibiting proteins (PGIPs), are the candidate genes at the Br locus associated with bruchid resistance. One VrPGIP1 resistance allele and two VrPGIP2 resistance alleles have been identified. In this study, we fine-mapped the bruchid-resistance genes in wild mungbean (V. radiata var. sublobata) accession ACC41 using the F2 population (574 individuals) derived from the 'Kamphaeng Saen 2' (susceptible) × ACC41 (resistant) cross. A QTL analysis indicated that the resistance to the azuki bean weevil and cowpea weevil in ACC41 is controlled by a major QTL (qBr5.1) and a minor QTL (qBr5.2), which are only 0.3 cM apart. qBr5.1 and qBr5.2 accounted for about 82% and 2% of the resistance variation in the F2 population, respectively. qBr5.1 was mapped to a 237.35-kb region on mungbean chromosome 5 containing eight annotated genes, including VrPGIP1 and VrPGIP2. An examination of the ACC41 VrPGIP1 and VrPGIP2 sequences revealed a new allele for VrPGIP1 (i.e., VrPGIP1-2). Compared with the wild-type sequence, VrPGIP1-2 has five SNPs, of which four cause amino acid changes (residues 125, 129, 188, and 336). A protein sequence analysis indicated that residues 125 and 129 in VrPGIP1-2 are in a ß-sheet B1 region, whereas residues 188 and 336 are in a C10-helix region and at the end of the C-terminal region, respectively. Because the ß-sheet B1 region is important for interactions with polygalacturonase (PG), residues 125 and 129 in VrPGIP1-2 likely contribute to bruchid resistance by inhibiting PG. Our results imply that VrPGIP1-2 is associated with the bruchid resistance of wild mungbean accession ACC41. This new resistance allele may be useful for breeding mungbean varieties exhibiting durable bruchid resistance.

Characterization of Male-Produced Aggregation Pheromone of the Bean Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae).

Aggregation of the bean flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), has been observed on cowpea, Vigna unguiculata (L.) Walp. To understand the mechanism underpinning this behavior, we studied the responses of M. sjostedti to headspace volatiles from conspecifics in a four-arm olfactometer. Both male and female M. sjostedti were attracted to male, but not to female odor. Gas chromatography/mass spectrometry (GC/MS) analyses revealed the presence of two distinct compounds in male M. sjostedti headspace, namely (R)-lavandulyl 3-methylbutanoate (major compound) and (R)-lavandulol (minor compound); by contrast, both compounds were only present in trace amounts in female headspace collections. A behavioral assay using synthetic compounds showed that male M. sjostedti was attracted to both (R)-lavandulyl 3-methylbutanoate and (R)-lavandulol, while females responded only to (R)-lavandulyl 3-methylbutanoate. This is the first report of a male-produced aggregation pheromone in the genus Megalurothrips. The bean flower thrips is the primary pest of cowpea, which is widely grown in sub-Saharan Africa. The attraction of male and female M. sjostedti to these compounds offers an opportunity to develop ecologically sustainable management methods for M. sjostedti in Africa.

Isopentyl Butanoate: Aggregation Pheromone of the Brown Spiny Bug, Clavigralla tomentosicollis (Hemiptera: Coreidae), and Kairomone for the Egg Parasitoid Gryon sp. (Hymenoptera: Scelionidae).

The brown spiny bug, Clavigralla tomentosicollis Stål (Hemiptera: Coreidae) is a key pest of leguminous crops in many countries in Africa, causing significant yield losses especially in cowpea, pigeon pea and common beans. Although C. tomentosicollis uses olfaction to aggregate, little is known about the identity of the aggregation pheromone. This study aimed to identify the aggregation pheromone of C. tomentosicollis and to test its potential role in the behavior of its egg parasitoid, Gryon sp. In Y-tube olfactometer bioassays, only male volatiles strongly attracted both sexes of C. tomentosicollis. Coupled gas chromatography/electroantennographic detection (GC/EAD) and GC/mass spectrometry were used to identify antennally-active compounds from male volatiles. Antennae of both sexes detected identical components including a male-specific component, identified as isopentyl butanoate, which was also detected by antenna of the egg parasitoid. In olfactometer bioassays, both sexes of C. tomentosicollis and the egg parasitoid responded to isopentyl butanoate. These results suggest that isopentyl butanoate serves as an aggregation pheromone for both sexes of C. tomentosicollis and a useful kairomone to attract the parasitoid in the management of C. tomentosicollis.

Copy if dissatisfied, innovate if not: contrasting egg-laying decision making in an insect.

The use of conspecific cues as social information in decision making is widespread among animals; but, because this social information is indirect, it is error-prone. During resource acquisition, conspecific cues also indicate the presence of competitors; therefore, decision makers are expected to utilize direct information from resources and modify their responses to social information accordingly. Here, we show that, in a non-social insect, unattractive egg-laying resources alter the behavioural response to conspecific cues from avoidance to preference, leading to resource sharing. Females of the adzuki bean beetle Callosobruchus chinensis avoid laying eggs onto beans that already have conspecific eggs. However, when we provided females with bean-sized clean glass beads with and without conspecific eggs, the females preferred to add their eggs onto the beads with eggs. The glass beads, once coated with water extracts of adzuki beans, enabled the females to behave as if they were provided with the beans: the females preferred bean-odoured glass beads to clean glass beads and they avoided the substrates with eggs. When females are provided with unattractive egg-laying substrates only, joining behaviour (i.e. copying) might be advantageous, as it takes advantage of information about positive attributes of the substrate that the focal animal might have missed. Our results suggest that given only unsatisfactory options, the benefits of copying outweigh the costs of resource competition. Our study highlights the importance of integrating multiple information sources in animal decision making.

Population dynamics of Aphis gossypii Glover and in sole and intercropping systems of cotton and cowpea.

Population dynamics of aphids have been studied in sole and intercropping systems. These studies have required the use of more precise analytical tools in order to better understand patterns in quantitative data. Mathematical models are among the most important tools to explain the dynamics of insect populations. This study investigated the population dynamics of aphids Aphis gossypii and Aphis craccivora over time, using mathematical models composed of a set of differential equations as a helpful analytical tool to understand the population dynamics of aphids in arrangements of cotton and cowpea. The treatments were sole cotton, sole cowpea, and three arrangements of cotton intercropped with cowpea (t1, t2 and t3). The plants were infested with two aphid species and were evaluated at 7, 14, 28, 35, 42, and 49 days after the infestations. Mathematical models were used to fit the population dynamics of two aphid species. There were good fits for aphid dynamics by mathematical model over time. The highest population peak of both species A. gossypii and A. craccivora was found in the sole crops, and the lowest population peak was found in crop system t2. These results are important for integrated management programs of aphids in cotton and cowpea.

The behavior of Aphis gossypii and Aphis craccivora (Hemiptera: Aphididae) and of their predator Cycloneda sanguinea (Coleoptera: Coccinellidae) in cotton-cowpea intercropping systems.

The intercropping is an important cultural practice commonly used in pest management. It is based on the principle that increased plant diversity in the agro-ecosystem can lead to reductions of pest populations in the crop. The current study aimed to assess the impact the colored fiber cotton-cowpea intercropped systems on Aphis gossypii and Aphis craccivora and on their predator Cycloneda sanguinea and the losses and the dispersion behavior of these aphids and their predator in these cropping systems. The experiment had a randomized block experimental design with two bioassays and four treatments. The number of apterous and alate aphids (A. gossypii) per cotton plant was 1.46 and 1.73 or 1.97 and 2.19 times highest in the solid cotton system than that found in the cotton-cowpea intercropped systems (S1) and (S2), respectively. On the other hand, the cotton-cowpea intercropped systems (S1 and S2) reduced, respectively, in 43% and 31% the number of apterousA. gossypiiper cotton plant compared to the control. Implementing cotton-cowpea intercropped system in the S1 scheme reduced A. gossypii infestation, favored the multiplication of C. sanguinea, and allowed obtaining heavier open bolls.

Identification of single nucleotide polymorphism markers associated with resistance to bruchids (Callosobruchus spp.) in wild mungbean (Vigna radiata var. sublobata) and cultivated V. radiata through genotyping by sequencing and quantitative trait locus analysis.

BACKGROUND: Bruchid beetles are an important storage pest of grain legumes. Callosobruchus sp. infect mungbean (Vigna radiata) at low levels in the field, multiply during grain storage and can destroy seed stocks in a few months. Resistance against bruchid beetles has been found in wild mungbean V. radiata var. sublobata TC1966 and in cultivated mungbean line V2802. RESULTS: Bruchid resistance data were obtained from recombinant inbred line populations TC1966 (V. radiata var. sublobata) × NM92 (F12) and V2802 (V. radiata) × NM94 (F7). More than 6,000 single nucleotide polymorphic markers were generated through genotyping by sequencing (GBS) for each of these populations and were used to map bruchid resistance genes. One highly significant quantitative trait locus (QTL) associated with bruchid resistance was mapped to chromosome 5 on genetic maps of both populations, suggesting that TC1966 and V2802 contain the same resistance locus. Co-segregation of all markers associated with resistance indicated the presence of only one major resistance QTL on chromosome 5, while QTL analysis based on physical map positions of the markers suggested the presence of multiple QTLs on different chromosomes. The diagnostic capacity of the identified molecular markers located in the QTL to correctly predict resistance was up to 100 %. CONCLUSIONS: Molecular markers tightly linked to bruchid resistance loci of two different mungbean resistance sources were developed and validated. These markers are highly useful for developing resistant lines.

The damage caused by Callosobruchus maculatus on cowpea grains is dependent on the plant genotype.

BACKGROUND: Beans from cowpea cultivars fertilized with mineral N or inoculated with various rhizobium strains may contain different nitrogen concentrations and nitrogen metabolite composition, which affects the beans' defense mechanisms against pests. In this study, the population growth of Callosobruchus maculatus reared on beans from four cowpea cultivars fertilized with different nitrogen sources was evaluated. The factors tested were beans from four cowpea cultivars and seven different nitrogen sources: mineral N fertilization, inoculation with five strains of symbiotic diazotrophic bacteria, and soil nitrogen (absolute control). RESULTS: BRS Tapaihum and BRS Acauã cultivars had lower cumulative emergence and instantaneous rate of population growth of the insects compared with other cultivars, indicating antixenosis resistance against C. maculatus. Inoculation of BRS Acauã cultivar with the diazotrophic bacteria strain BR 3299 resulted in higher mortality of C. maculatus. For BRS Tapaihum cultivar, inoculation with diazotrophic bacteria strains BR3267, BR 3262 and BR 3299, and nitrogen fertilization resulted in higher mortality among C. maculatus. CONCLUSION: BRS Tapaihum and BRS Acauã cultivars showed the lowest cumulative insect emergence and instantaneous rates of population growth, and the highest insect mortality, mainly when the grains were obtained from plants inoculated with rhizobial strains. © 2016 Society of Chemical Industry.

Off-season survival and life history of beet armyworm, Spodoptera exigua (Hubner) on various host plants.

The beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), has become a significant pest of chickpea in recent years. The polyphagous nature allows it to survive on various hosts during the off-season, creating a great menace to the crop in the following season. To assess the incidence and document the alternate hosts of S. exigua, a rapid roving survey was conducted in 11 chickpea-growing areas of Prakasam district, Andhra Pradesh, India. Additionally, the life history traits of S. exigua were studied on major alternate host plants under laboratory conditions (27 ± 1 °C and 70 ± 2% RH) to understand the survival, life expectancy and potential contribution to future populations. The results show that, among the different crops surveyed, the maximum larval incidence was noticed in maize (1.93 larvae/plant), cowpea (1.73 larvae/plant), and sunflower (1.68 larvae/plant) during the off-season. Life history studies of S. exigua showed that highest larval survival percentage was observed on chickpea (83.6%), while the lowest was on maize (44.5%). The mean developmental time for larvae was longest on maize (27.1 days) and shortest on chickpea (14.9 days). Larvae did not develop beyond the third instar when fed with chilli. The growth index statistics showed chickpea (9.2) was the most suitable host plant, whereas maize (0.9) was the least suitable host. The age-stage-specific survival rate (Sxj) varied across developmental stages, and the survival curves overlapped, indicating different growth rates among individuals. The life expectancy (exj) at age zero was highest on groundnut (37.06 days). The intrinsic rate of increase (r) of S. exigua was lowest on maize (0.10 ± 0.0013) and highest on chickpea (0.22 ± 0.0010). Similarly, the net reproductive rate (R0) was highest on chickpea (846.39 ± 18.22) and lowest on maize (59.50 ± 2.06). The population doubled every 3.08 ± 0.011 days on chickpea compared to 7.22 ± 0.80 days on maize. The study conclusively indicates that chickpea and sunflower, primarily cultivated during the rabi season in India, are the most preferred hosts for S. exigua. In contrast, maize and cotton, mainly grown during the kharif season, are less preferred and merely support the pest's survival. Consequently, S. exigua switches hosts between different crops growing seasons, so effective management of S. exigua during the kharif season can help prevent pest outbreaks during the rabi season.

Delineation of Genotype-by-Environment interactions for identification and validation of resistant genotypes in mungbean to root-knot nematode (Meloidogyne incognita) using GGE biplot.

Susceptibility to root-knot nematodes (Meloidogyne spp.) is one of the major factors limiting mungbean production in South and South-East Asia. Host-pest-environment interaction in mungbean and root-knot nematode (M. incognita) was investigated in multi-location field evaluation using 38 promising mungbean genotypes extracted from initial evaluation of 250 genotypes under sick plots considering second stage freshly hatched juvenile as inoculants. The extent of environmental and genotype-by-environment interactions (GGE) was assessed to comprehend the dynamism of resistance and identification of durable resistant mungbean genotypes. Among environmental factors, nematode activity was highly influenced by rainfall and minimum temperature. The GGE biplot and multiple comparison tests detected a higher proportion of genotype × environment (GE) interaction followed by genotype and environment on number of nematode galls, gall index and reproduction factor. The first two principal components (PCs) explained 64.33% and 66.99% of the total variation of the environment-centered gall scoring and reproduction factor data, respectively. The high GE variation indicated the presence of non-cross over interactions which justify the necessities of multi-location testing. Detection of non-redundant testing locations would expedite optimum resource utilization in future. The GGE biplot analysis identified genotypes such as PM-10-12, IPM-410-3 and NVL-641 as the outperforming and desirable genotypes with durable resistance against M. incognita which can be exploited in mungbean breeding programmes globally. On the contrary, the highest gall scoring and reproduction factor were recorded in genotype IPM-9901-8. Computation of confidence interval (CI) at 95% level through bootstrapping increased precision of GGE biplot towards genotype recommendation. Furthermore, total phenol content, ascorbic acid, phenlylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activities were also higher in identified resistant genotypes and this information would be useful for devising mungbean breeding strategies in future for resistance against root-knot nematodes.

A Novel Root-Knot Nematode Resistance QTL on Chromosome Vu01 in Cowpea.

The root-knot nematode (RKN) species Meloidogyne incognita and M. javanica cause substantial root system damage and suppress yield of susceptible cowpea cultivars. The narrow-based genetic resistance conferred by the Rk gene, present in some commercial cultivars, is not effective against Rk-virulent populations found in several cowpea production areas. The dynamics of virulence within RKN populations require a broadening of the genetic base of resistance in elite cowpea cultivars. As part of this goal, F1 and F2 populations from the cross CB46-Null (susceptible) x FN-2-9-04 (resistant) were phenotyped for M. javanica induced root-galling (RG) and egg-mass production (EM) in controlled growth chamber and greenhouse infection assays. In addition, F[Formula: see text] families of the same cross were phenotyped for RG on field sites infested with Rk-avirulent M. incognita and M. javanica The response of F1 to RG and EM indicated that resistance to RKN in FN-2-9-04 is partially dominant, as supported by the degree of dominance in the F2 and F[Formula: see text] populations. Two QTL associated with both RG and EM resistance were detected on chromosomes Vu01 and Vu04. The QTL on Vu01 was most effective against aggressive M. javanica, whereas both QTL were effective against avirulent M. incognita Allelism tests with CB46 x FN-2-9-04 progeny indicated that these parents share the same RKN resistance locus on Vu04, but the strong, broad-based resistance in FN-2-9-04 is conferred by the additive effect of the novel resistance QTL on Vu01. This novel resistance in FN-2-9-04 is an important resource for broadening RKN resistance in elite cowpea cultivars.

Meloidogyne incognita (Nematoda: Meloidogynidae) sterol-binding protein Mi-SBP-1 as a target for its management.

Meloidogyne incognita is a polyphagous plant-parasitic nematode that causes considerable yield loss in agricultural and horticultural crops. The management options available for M. incognita are extremely limited. Here we identified and characterised a M. incognita homolog of Caenorhabditis elegans sterol-binding protein (Mi-SBP-1), a transcriptional regulator of several lipogenesis pathway genes, and used RNA interference-mediated gene silencing to establish its utility as a target for the management of M. incognita. Mi-sbp-1 is predicted to be a helix-loop-helix domain containing DNA binding transcription factor, and is present in the M. incognita genome in three copies. The RNA-Seq analysis of Mi-sbp-1 silenced second stage juveniles confirmed the key role of this gene in lipogenesis regulation in M. incognita. In vitro and host-induced gene silencing of Mi-sbp-1 in M. incognita second stage juveniles resulted in loss of nematodes' ability to utilise the stored fat reserves, slower nematode development, and reduced parasitism on adzuki bean and tobacco plants. The multiplication factor for the Mi-sbp-1 silenced nematodes on adzuki bean plants was reduced by 51% compared with the control nematodes in which Mi-sbp-1 was not silenced. Transgenic expression of the double-stranded RNA construct of the Mi-sbp-1 gene in tobacco plants caused 40-45% reduction in M. incognita multiplication, 30-43.8% reduction in the number of egg masses, and 33-54% reduction in the number of eggs per egg mass compared with the wild type control plants. Our results confirm that Mi-sbp-1 is a key regulator of lipogenesis in M. incognita and suggest that it can be used as an effective target for its management. The findings of this study can be extended to develop methods to manage other economically important parasitic nematodes.

Development of an SNP-based high-density linkage map and QTL analysis for bruchid (Callosobruchus maculatus F.) resistance in black gram (Vigna mungo (L.) Hepper).

Black gram (Vigna mungo var. mungo) is an important pulse crop in Asia. The cowpea weevil (Callosobruchus maculatus) is a stored-seed insect pest (seed weevil/bruchid) that causes serious postharvest losses in pulse crops, including black gram. In this study, we constructed a high-density linkage map for black gram and identified quantitative trait loci (QTLs) for C. maculatus resistance. A recombinant inbred line (RIL) population of 150 lines from a cross between BC48 [cultivated black gram (var. mungo); bruchid-susceptible] and TC2210 [wild black gram (var. silvestris); bruchid-resistant] were used to construct a linkage map of 3,675 SNP markers from specific-locus amplified fragment sequencing. The map comprised 11 linkage groups spanning 1,588.7 cM with an average distance between adjacent markers of 0.57 cM. Seeds of the RIL population grown in 2016 and 2017 were evaluated for C. maculatus resistance through two traits; the percentage of damaged seeds (PDS) and infestation severity progress (AUDPS). Inclusive composite interval mapping identified three QTLs each for PDS and AUDPS. Two QTLs, qVmunBr6.1 and qVmunBr6.2, mapped about 10 cM apart on linkage group 6 were common between PDS and AUDPS. Comparative genome analysis revealed that qVmunBr6.1 and qVmunBr6.2 are new loci for C. maculatus resistance in Vigna species and that genes encoding a lectin receptor kinase and chitinase are candidates for qVmunBr6.2. The high-density linkage map constructed and QTLs for bruchid resistance identified in this study will be useful for molecular breeding of black gram.

Construction of a high density linkage map and genome dissection of bruchid resistance in zombi pea (Vigna vexillata (L.) A. Rich).

Zombi pea (Vigna vexillata) is a legume crop that is resistant to several biotic and abiotic stresses. Callosobruchus maculatus and Callosobruchus chinensis are serious stored-insect pests of legume crops. We constructed a high-density linkage map and performed quantitative trait loci (QTLs) mapping for resistance to these insect species in zombi pea. An F2 population of 198 individuals from a cross between 'TVNu 240' (resistant) and 'TVNu 1623' (susceptible) varieties was used to construct a linkage map of 6,529 single nucleotide polymorphism markers generated from sequencing amplified fragments of specific loci. The map comprised 11 linkage groups, spanning 1,740.9 cM, with an average of 593.5 markers per linkage group and an average distance of 0.27 cM between markers. High levels of micro-synteny between V. vexillata and cowpea (Vigna unguiculata), mungbean (Vigna radiata), azuki bean (Vigna angularis) and common bean (Phaseolus vulgaris) were found. One major and three minor QTLs for C. chinensis resistance and one major and one minor QTLs for C. maculatus resistance were identified. The major QTLs for resistance to C. chinensis and C. maculatus appeared to be the same locus. The linkage map developed in this study will facilitate the identification of useful genes/QTLs in zombi pea.