Molecular marker-assisted genotyping of mungbean yellow mosaic India virus resistant germplasms of mungbean and urdbean

Expression profiling and characterization of key RGA involved in lentil Fusarium wilt Race 5 resistance

Fusarium wilt is a major threat to lentil production in India and worldwide. The presence of evolving virulent races has imposed the necessity of reliable management practices including breeding for resistance using unexplored germplasms. The magnitude of resistance by the plant is determined by rapid recognition of the pathogen and induction of defence genes. Resistance gene analogues have been key factors involved in the recognition and induction of defence response. In the present study, the expression of key RGA previously cloned was determined in three resistant accessions (L65, L83 and L90) and a susceptible accession (L27). The expression was assessed via qPCR at 24, 48 and 72 hpi against virulent race5 (CG-5). All the RGAs differentially transcribed in resistant and susceptible accession showed temporal variation. RGA Lc2, Lc8, Ln1 and Lo6 produced cDNA signals during early infection (24 hpi) predicting its involvement in recognition. LoRGA6 showed significant upregulation in L65 and L83 while downregulating in L27 and the full length of LoRGA6 loci was isolated by 5' and 3' RACE PCR. In-silico characterization revealed LoRGA6 loci code for 912 amino acids long polypeptide with a TIR motif at the N terminal and eight LRR motifs at the C terminal. The tertiary structure revealed a concave pocket-like structure at the LRR domain potentially involved in pathogen effectors interaction. The loci have ADP binding domain and ATPase activity. This has further paved the path for functional analysis of the loci by VIGS to understand the molecular mechanism of resistance.

Major viral diseases in grain legumes: designing disease resistant legumes from plant breeding and OMICS integration

Grain legumes play a crucial role in human nutrition and as a staple crop for low-income farmers in developing and underdeveloped nations, contributing to overall food security and agroecosystem services. Viral diseases are major biotic stresses that severely challenge global grain legume production. In this review, we discuss how exploring naturally resistant grain legume genotypes within germplasm, landraces, and crop wild relatives could be used as promising, economically viable, and eco-environmentally friendly solution to reduce yield losses. Studies based on Mendelian and classical genetics have enhanced our understanding of key genetic determinants that govern resistance to various viral diseases in grain legumes. Recent advances in molecular marker technology and genomic resources have enabled us to identify genomic regions controlling viral disease resistance in various grain legumes using techniques such as QTL mapping, genome-wide association studies, whole-genome resequencing, pangenome and 'omics' approaches. These comprehensive genomic resources have expedited the adoption of genomics-assisted breeding for developing virus-resistant grain legumes. Concurrently, progress in functional genomics, especially transcriptomics, has helped unravel underlying candidate gene(s) and their roles in viral disease resistance in legumes. This review also examines the progress in genetic engineering-based strategies, including RNA interference, and the potential of synthetic biology techniques, such as synthetic promoters and synthetic transcription factors, for creating viral-resistant grain legumes. It also elaborates on the prospects and limitations of cutting-edge breeding technologies and emerging biotechnological tools (e.g., genomic selection, rapid generation advances, and CRISPR/Cas9-based genome editing tool) in developing virus-disease-resistant grain legumes to ensure global food security.

Gamma-rays and EMS induced resistance to mungbean yellow mosaic India virus in mungbean [Vigna radiata (L.) R. Wilczek] and its validation using linked molecular markers

PURPOSE

Mungbean yellow mosaic India virus (MYMIV) is a serious constraint in the mungbean which is a potential source of easily digestible high-quality proteins, fibers, minerals, and vitamins in Asian countries. Developing resistant cultivars is the most cost-effective, eco-friendly, and sustainable approach to protect mungbean from MYMIV damage. Mutation breeding provides a quick and cost-effective way of developing resistance as lack of genetic variability is the biggest bottleneck for other traditional breeding tools.

MATERIALS AND METHODS

Outstanding but MYMIV-sensitive varieties of mungbean, viz., MH 2-15 and MH 318 were mutagenized through various individual and combined doses of gamma-rays and Ethyl methanesulfonate (EMS) and evaluated in M₂ and M₃ generations for the appearance of resistance reactions. This was subsequently validated through marker-assisted genotyping using previously reported Yellow Mosaic Disease (YMD) linked markers.

RESULTS

The phenotyping in M₃ generation yielded 64 MYMIV resistant mutants whereas, marker-assisted genotyping identified the 22 mutants with true resistance. Markers YR4, CYR1, and CEDG180 were found associated with MYMIV resistance whereas, DMB-SSR158 did not show any amplification. Among identified resistant mutants, ten lines exhibited at par and two revealed a little higher seed yield over controls.

CONCLUSIONS

The mutagenesis created significant variability in MYMIV resistance as well as seed yield per plant. YR4, CYR1, and CEDG180 are found to be linked with the MYMIV loci in the mungbean and could be utilized for MYMIV resistance breeding. Mutant M-37 from MH 2-15 and M-104 from MH 318 exhibited more seed yield along with MYMIV resistance which upon further validation can be released as a variety. The induced mutagenesis integrated with powerful emerging molecular and next-generation sequencing (NGS) tools would be highly helpful in breeding mungbean for durable resistance against threatening MYMIV.

Influence of virus-host interactions on plant response to abiotic stress

Environmental factors play a significant role in controlling growth, development and defense responses of plants. Changes in the abiotic environment not only significantly alter the physiological and molecular pathways in plants, but also result in attracting the insect pests that carry a payload of viruses. Invasion of plants by viruses triggers the RNA silencing based defense mechanism in plants. In counter defense the viruses have gained the ability to suppress the host RNA silencing activities. A new paradigm has emerged, with the recognition that plant viruses also have the intrinsic capacity to modulate host plant response to environmental cues, in an attempt to favour their own survival. Thus, plant-virus interactions provide an excellent system to understand the signals in crosstalk between biotic (virus) and abiotic stresses. In this review, we have summarized the basal plant defense responses to pathogen invasion while emphasizing on the role of RNA silencing as a front line of defense response to virus infection. The emerging knowledge indicates overlap between RNA silencing with the innate immune responses during antiviral defense. The suppressors of RNA silencing serve as Avr proteins, which can be recognized by the host R proteins. The defense signals also function in concert with the phytohormones to influence plant responses to abiotic stresses. The current evidence on the role of virus induced host tolerance to abiotic stresses is also discussed.

Functional Markers for Precision Plant Breeding

Advances in molecular biology including genomics, high-throughput sequencing, and genome editing enable increasingly faster and more precise cultivar development. Identifying genes and functional markers (FMs) that are highly associated with plant phenotypic variation is a grand challenge. Functional genomics approaches such as transcriptomics, targeting induced local lesions in genomes (TILLING), homologous recombinant (HR), association mapping, and allele mining are all strategies to identify FMs for breeding goals, such as agronomic traits and biotic and abiotic stress resistance. The advantage of FMs over other markers used in plant breeding is the close genomic association of an FM with a phenotype. Thereby, FMs may facilitate the direct selection of genes associated with phenotypic traits, which serves to increase selection efficiencies to develop varieties. Herein, we review the latest methods in FM development and how FMs are being used in precision breeding for agronomic and quality traits as well as in breeding for biotic and abiotic stress resistance using marker assisted selection (MAS) methods. In summary, this article describes the use of FMs in breeding for development of elite crop cultivars to enhance global food security goals.

V. R, Tripathi K, Kumar RR, Aski M, Singh A, Roy A, Priti, Kumari N, Dasgupta U, Kumar A, Praveen S, Nair RM. Yellow Mosaic Disease (YMD) of Mungbean (Vigna radiata (L.) Wilczek): Current Status and Management Opportunities

Globally, yellow mosaic disease (YMD) remains a major constraint of mungbean production, and management of this deadly disease is still the biggest challenge. Thus, finding ways to manage YMD including development of varieties possessing resistance against mungbean yellow mosaic virus (MYMV) and mungbean yellow mosaic India virus (MYMIV) is a research priority for mungbean crop. Characterization of YMD resistance using various advanced molecular and biochemical approaches during plant-virus interactions has unfolded a comprehensive network of pathogen survival, disease severity, and the response of plants to pathogen attack, including mechanisms of YMD resistance in mungbean. The biggest challenge in YMD management is the effective utilization of an array of information gained so far, in an integrated manner for the development of genotypes having durable resistance against yellow mosaic virus (YMV) infection. In this backdrop, this review summarizes the role of various begomoviruses, its genomic components, and vector whiteflies, including cryptic species in the YMD expression. Also, information about the genetics of YMD in both mungbean and blackgram crops is comprehensively presented, as both the species are crossable, and same viral strains are also found affecting these crops. Also, implications of various management strategies including the use of resistance sources, the primary source of inoculums and vector management, wide-hybridization, mutation breeding, marker-assisted selection (MAS), and pathogen-derived resistance (PDR) are thoroughly discussed. Finally, the prospects of employing various powerful emerging tools like translational genomics, and gene editing using CRISPR/Cas9 are also highlighted to complete the YMD management perspective in mungbean.

Association mapping for mungbean yellow mosaic India virus resistance in mungbean (Vigna radiata L. Wilczek)

The present study aimed to detect the marker-trait association of a selected diverse panel of 127 mungbean genotypes against mungbean yellow mosaic India virus (MYMIV). Virus-specific primers pairs viz., AC-abut/AV-abut and BC-abut/BV-abut confirmed the involvement of MYMIV in yellow mosaic disease development and the same was validated through restriction digestion analysis. 256 genome-wide microsatellite markers were screened on a test panel in which 93 polymorphic markers were used in association studies. Population structure analysis led to formation of six distinct subpopulations. 1097 alleles were detected among 127 test genotypes whereas number of alleles ranged 2-22 and PIC values ranged 0.27-0.92%, indicating ample amount of variation at genome level. 15 microsatellite markers were detected as associated with MYMIV resistance, among them three microsatellites explained 11-14% phenotypic variation. The specific regions close to CEDG293, DMB-SSR008 and DMB-SSR059 associated with MYMIV resistance were detected, located on linkage group 2, 4 and 9 and may prove useful in marker-assisted mungbean improvement programme for enhancing MYMIV resistance.

Biotic and Abiotic Constraints in Mungbean Production-Progress in Genetic Improvement

Mungbean [Vigna radiata (L.) R. Wilczek var. radiata] is an important food and cash legume crop in Asia. Development of short duration varieties has paved the way for the expansion of mungbean into other regions such as Sub-Saharan Africa and South America. Mungbean productivity is constrained by biotic and abiotic factors. Bruchids, whitefly, thrips, stem fly, aphids, and pod borers are the major insect-pests. The major diseases of mungbean are yellow mosaic, anthracnose, powdery mildew, Cercospora leaf spot, halo blight, bacterial leaf spot, and tan spot. Key abiotic stresses affecting mungbean production are drought, waterlogging, salinity, and heat stress. Mungbean breeding has been critical in developing varieties with resistance to biotic and abiotic factors, but there are many constraints still to address that include the precise and accurate identification of resistance source(s) for some of the traits and the traits conferred by multi genes. Latest technologies in phenotyping, genomics, proteomics, and metabolomics could be of great help to understand insect/pathogen-plant, plant-environment interactions and the key components responsible for resistance to biotic and abiotic stresses. This review discusses current biotic and abiotic constraints in mungbean production and the challenges in genetic improvement.

Tropical food legumes: virus diseases of economic importance and their control

Diverse array of food legume crops (Fabaceae: Papilionoideae) have been adopted worldwide for their protein-rich seed. Choice of legumes and their importance vary in different parts of the world. The economically important legumes are severely affected by a range of virus diseases causing significant economic losses due to reduction in grain production, poor quality seed, and costs incurred in phytosanitation and disease control. The majority of the viruses infecting legumes are vectored by insects, and several of them are also seed transmitted, thus assuming importance in the quarantine and in the epidemiology. This review is focused on the economically important viruses of soybean, groundnut, common bean, cowpea, pigeonpea, mungbean, urdbean, chickpea, pea, faba bean, and lentil and begomovirus diseases of three minor tropical food legumes (hyacinth bean, horse gram, and lima bean). Aspects included are geographic distribution, impact on crop growth and yields, virus characteristics, diagnosis of causal viruses, disease epidemiology, and options for control. Effectiveness of selection and planting with virus-free seed, phytosanitation, manipulation of crop cultural and agronomic practices, control of virus vectors and host plant resistance, and potential of transgenic resistance for legume virus disease control are discussed.

Assessment of genetic diversity and population structure of mung bean (Vigna radiata) germplasm using EST-based and genomic SSR markers

Mung bean is an important legume crop in tropical and subtropical countries of Asia and has high nutritional and economic value. However the genetic diversity of mung bean is poorly characterized. In this study, our goal was to develop and use microsatellite simple sequence repeat (SSR) markers for germplasm evaluation. In total, 500 novel expression sequence tag EST-based SSRs (eSSRs) and genomic SSRs (gSSRs) were developed from mung bean transcriptome and genome sequences. Of these, only 58 were useful for diversity evaluation in a panel of 157 cultivated and wild mung bean accessions from different collection sites in East Asia. A total of 2.66 alleles were detected on average per locus which shows that polymorphism is generally low for the species. The average polymorphic information content (PIC) of gSSRs was higher than eSSRs and most of the polymorphic gSSRs were composed of di- and tri-nucleotide repeats (52.4% and 38.1% of all loci, respectively). The genotypes were differentiated into nine subgroups by cluster analysis, and the wild mung bean accessions separated well from the cultivated accessions. Analysis of molecular variance indicated that 22% of variance was observed among populations and 78% was due to differences within populations. Clustering, population structure analyses showed that non-Chinese cultivated and wild mung bean accessions were separated from Chinese accessions, but no geographical distinctions existed between genotypes collected in China. Interestingly, the average PIC value of cultivated mung bean (0.36) was higher than that of wild mung bean (0.25) showing that further collecting and wide crosses are necessary for mung bean improvement.

Genomics and molecular breeding in lesser explored pulse crops: current trends and future opportunities

Pulses are multipurpose crops for providing income, employment and food security in the underprivileged regions, notably the FAO-defined low-income food-deficit countries. Owing to their intrinsic ability to endure environmental adversities and the least input/management requirements, these crops remain central to subsistence farming. Given their pivotal role in rain-fed agriculture, substantial research has been invested to boost the productivity of these pulse crops. To this end, genomic tools and technologies have appeared as the compelling supplement to the conventional breeding. However, the progress in minor pulse crops including dry beans (Vigna spp.), lupins, lablab, lathyrus and vetches has remained unsatisfactory, hence these crops are often labeled as low profile or lesser researched. Nevertheless, recent scientific and technological breakthroughs particularly the next generation sequencing (NGS) are radically transforming the scenario of genomics and molecular breeding in these minor crops. NGS techniques have allowed de novo assembly of whole genomes in these orphan crops. Moreover, the availability of a reference genome sequence would promote re-sequencing of diverse genotypes to unlock allelic diversity at a genome-wide scale. In parallel, NGS has offered high-resolution genetic maps or more precisely, a robust genetic framework to implement whole-genome strategies for crop improvement. As has already been demonstrated in lupin, sequencing-based genotyping of the representative sample provided access to a number of functionally-relevant markers that could be deployed straight away in crop breeding programs. This article attempts to outline the recent progress made in genomics of these lesser explored pulse crops, and examines the prospects of genomics assisted integrated breeding to enhance and stabilize crop yields.

Detection of quantitative trait loci for mungbean yellow mosaic India virus (MYMIV) resistance in mungbean (Vigna radiata (L.) Wilczek) in India and Pakistan

Yellow mosaic disease (YMD) is one of the major diseases affecting mungbean (Vigna radiata (L.) Wilczek). In this study, we report the mapping of the quantitative trait locus (QTL) for mungbean yellow mosaic India virus (MYMIV) resistance in mungbean. An F8 recombinant inbred line (RIL) mapping population was generated in Thailand from a cross between NM10-12-1 (MYMIV resistance) and KPS2 (MYMIV susceptible). One hundred and twenty-two RILs and their parents were evaluated for MYMIV resistance in infested fields in India and Pakistan. A genetic linkage map was developed for the RIL population using simple sequence repeat (SSR) markers. Composite interval mapping identified five QTLs for MYMIV resistance: three QTLs for India (qYMIV1, qYMIV2 and qYMIV3) and two QTLs for Pakistan (qYMIV4 and qYMIV5). qYMIV1, qYMIV2, qYMIV3, qYMIV4 and qYMIV5 explained 9.33%, 10.61%, 12.55%, 21.93% and 6.24% of variation in disease responses, respectively. qYMIV1 and qYMIV4 appeared to be the same locus and were common to a major QTL for MYMIV resistance in India identified previously using a different resistant mungbean.

Genetic diversity of mungbean (Vigna radiata L.) in iron and zinc content as impacted by farmers' varietal selection in Northern India

From the last few years a debate has been continuing over the issue of malnutrition and hunger in the developing countries. The present article investigates the importance of participatory varietal selection in the development of a suitable cultivar of mungbean along with the nutritional content and the agronomic traits of the cultivars selected by farmers in participatory varietal selection. A combination of the conventional survey strategy, participatory varietal selection, molecular markers, and chemical analysis were used to carry out the study, and results revealed that the farmers have the capacity to utilize available genetic resources to manage disease, and they can identify the disease at early stages of plant development. The genetic diversity was studied using 23 inter-simple sequence repeat marker, which shows that the extent of genetic diversity ranges from 65% to 87%, while chemical analysis of selected mungbean cultivars shows a moderate amount of iron (3.9 mg/100 g) and zinc (2.5 mg/100 g).