Field Screening and Molecular Characterization of Urdbean Genotypes for Yellow Mosaic Disease

Urdbean [Vigna mungo (L.) Hepper], an Indian native pulse crop, is grown throughout India and Southeast Asian countries. In India, urdbean is also referred to as black gram or urad dal and about 70% of its global production is produced there. Due to its wide adaptability and climate resilience, it is grown in all the cropping seasons in India. Despite being the largest producer and consumer of urd beans, India has been unable to keep up with the demand of the world’s population, which is expanding quickly. In India, it is cultivated on an approximately 3.19 million hectares, producing about 1.95 million tonnes with an average yield of 596 kg per hectare (Raju, 2019). Pulses in general and urdbeans in particular have very poor global production when compared to cereals, which compromises the nutritional security. The productivity of urdbean oscillates upon various biotic and abiotic stresses. The occurrence of several environmental stresses, the production and productivity of urdbean is in declining trend in majority of urdbean growing areas (Patel et al., 2020; Sah et al., 2021). The yield losses (5-100%) in urdbean reported due to various biotic stresses which are responsible for the fluctuation in the average yield depending upon disease severity, susceptibility of cultivars and population of whitefly (Nene, 1972; Sahni et al., 2016; Equbal et al., 2016; Prema and Rangaswamy 2018). The biotic stresses like yellow mosaic, powdery mildew, cercospora leaf spot and web blight are major limiting factors for high yield (Kumari et al., 2020). Among these, Yellow mosaic disease (YMD), caused by mungbean yellow mosaic virus (MYMV), is a most destructive viral disease of urdbean not only in India, but also in Pakistan, Bangladesh, Sri Lanka and contiguous areas of South East Asia (Bashir et al., 2006). In India, this virus cause more severe yellow mosaic disease in urdbean than mungbean (Williams et al., 1968). In addition to dramatically reducing yield, the MYMV infection also negatively affects grain size and quality (Singh and Shrivastva, 1985; Sahni et al., 2016). The primary factors affecting yield decline are the decrease in seed weight and the number of pods/plant seeds/pod (Nene, 1973; Sahni et al., 2016; Kumari et al., 2020). Even though India has a sizable region dedicated to urdbean farming, MYMV infections are causing low productivity levels (Sahni et al., 2016). The chemical management of the vector is not financially viable since controlling whiteflies necessitates frequent sprays of insecticide. Sprayings that are repeated put the environment and human health in peril (Nariani, 1960). Instead, if virus resistant cultivars are available, using them is the greatest strategy to reduce the frequency of YMD in regions where the infection represents a significant productivity bottleneck. The use of resistant crop types is considered the reasonable, powerful and ideal approach of reducing viral infections.

The breeding for resistance is one of the important strategies for developing disease resistant variety (Gupta et al., 2020). However, conventional breeding requires a long time, which can be accelerated using molecular markers. Past few decades, DNA markers are extensively used for resistance breeding. Random amplified polymorphic DNA is one of the simplest and fastest DNA marker technologies which is widely used in characterization of genotypes and tagging of genes associated with specific character. In present investigation as attempt was made to characterize the MYMY resistant and susceptible urdbean genotypes using RAPD markers.

In this study, 100 urdbean genotypes were assessed for their resistance and susceptibility against MYMV under natural field conditions during four consecutive seasons (two summer seasons and two Kharif seasons) during 2017-2018). Based on the disease reaction and occurrence of YMD, urdbean genotypes were grouped in different reaction group (Table 1). Out of the 100 genotypes examined, only one (NDU 12-1) was found to be consistently MYMV disease-free in both the summer and Kharif seasons, twenty-seven were determined to be highly resistant and four genotypes consistently displayed resistance throughout a two-year period (Table 1). Five genotypes showed moderately resistance reaction (Table 1). Forty-seven genotypes were observed to be susceptible (Table 1). Sixteen genotypes were found to be highly susceptible to MYMV in both seasons over two years, with severe yellow discoloration of leaves covering 50-75 per cent of the foliage, plants stunting and pod size reduction. Forty-seven genotypes were found to be moderately susceptible, susceptible and highly susceptible to MYMV in one of the seasons (Table 1).



The current investigation demonstrated that certain genotypes responded differently to MYMV during the summer and Kharif seasons. The variation in temperature and relative humidity, which may have a direct impact on the vector population and its migration, may be the cause of the variation in illness incidence and disease reaction. Earlier reports have noted a similar impact of climate on vector populations (Singh and Gurha, 1994). Several researchers have already recorded similar types of varietal ratings (Pathak and Jhamaria, 2004; Kumari et al., 2020). Identification of resistance genotypes was encouraged in a prior work by Kumari et al., (2020) and comparable to our discovery, NDU12-1 was also revealed to be the disease-free against MYMV in field conditions (Kumari et al., 2020).

Analysis was done on the seed yield and disease incidence of urdbean genotypes that displayed disease-free, HR, R and MR reactions to MYMV in both the season for two years. The range of seed production for urdbean genotypes exhibiting different levels of resistance (disease-free, HR, R and MR) against MYMV varied from 6.43 g to 0.07 g per plant. With a disease incidence of 3.17 per cent, VBN (BG) 7 had the highest seed yield (6.43 g/plant), followed by IPU 2-43 (5.40 g/plant), KUG 586 (5.24 g/plant) and KUG 503 (5.84 g/plant). It also demonstrated a high level of resistance, with a rating scale of “2” indicating yellow specks with a constrained spread covering 0.1-5 per cent of leaf area. Kopergaon barely yielded 0.07 g of seeds per plant, despite having a “3” rating for disease resistance and a 96.16 per cent disease incidence rate. Similar to this, ACM 05-007 only yielded 1.16 g of seeds per plant while displaying high resistance (rating scale: 2) and a disease incidence rate of 10.5%. While UG-218 had a 4.36 g seed output per plant, was rated as having a moderate level of resistance and had a disease incidence of 98.00 per cent. Stable genotypes for seed yield per plant in blackgram were also reported previously (Natarajan, 2001; Kumari et al., 2020). Previous report suggests that resistance against YMD is rare and scarce (Gill et al., 1983). Based on these results, it can be said that only four genotypes namely, VBN (BG) 7, IPU 2-43, KUG 586 and KUG 503 were found to have superior seed yield and MYMV resistance out of a total of 100 genotypes tested.

In the current study, 24 selected urdbean genotypes that displayed disease-free, highly resistant, resistant, moderately resistant and susceptible reactions during field screening were examined for RAPD markers linked to MYMV resistance. Twelve randomly chosen decamer primers were used to measure the variation between 24 urdbean genotypes (Fig 1). It’s interesting to note that all 12 primers examined in this study displayed polymorphism. The range of polymorphism observed in this study varied from 22.22 to 88.88% (Table 2). The degree of polymorphism observed in this study on urdbean is comparable to reports from earlier investigations (Arulbalachandran et al., 2009; Binyamin et al., 2011). The highest amount of polymorphism (88.88%) was produced by primer OPB-07, whereas the lowest level (22.22%) was seen with primer OPD-07. High values of Jaccord’s similarity coefficient, which ranged from 0.727 to 0.965, showed that all of the genotypes under consideration shared a close genetic similarity (Table 3). On the basis of RAPD data, a dendrogram was created and it revealed two significant clusters (I and II) (Fig 2). Cluster I was further divided in to two sub-cluster (IA and IB) (Fig 2).









Based on our field research, all of the MYMV resistant genotypes were grouped together in cluster I, whereas all of the susceptible genotypes were grouped together in cluster II. Additionally, cluster I was split into the subclusters IA and IB. VBN(BG)7, Naveen (Local resistance check), LRB332, KUG503, PU09-35, IPU10-23, UH08-05 and Uttara (Highly resistance) were the ten genotypes that made up Cluster IA.

The remaining 11 genotypes which made up Cluster IB, of which two (IGKU02-1 and KU1106) were discovered to be moderately resistant in one season, while the remaining nine were discovered to be resistant or extremely resistant in that same season. TAU-1, TAU-4 and LBG623 (Local Susceptible Check), which were extremely susceptible, are included in Cluster II. According to the study’s findings, there is a high degree of genetic similarity among the genotypes of urdbean.

In present investigation, a total of 100 urdbean genotypes were evaluated against MYMV resistance. Out of 100 urdbean genotypes studied, one genotype (NDU 12-1) consistently showed a disease-free reaction, while thirty one genotypes were found to be resistant to MYMV. These thirty two urdbean genotypes identified as resistant for MYMV may be exploited in further breeding programme aimed at the development of MYMV resistant varieties of urdbean. On the basis of RAPD data, a dendrogram was created and it revealed two significant clusters. Based on our field research, all of the MYMV resistant genotypes were grouped together in cluster I, whereas all of the susceptible genotypes were grouped together in cluster II. Additionally, cluster I was split into the subclusters IA and IB. According to the study’s findings, there is a high degree of genetic similarity among the genotypes of urdbean. The outcome of present study may be exploited in future MYMV resistance breeding programmes in urdbean.