In this study, powdery mildew susceptible parent TBU-43-1 and resistant parent PU-609-43 were crossed. Parents, F1, F2, B1 and B2 of cross TBU-43-1 × PU-609-43 were screened for powdery mildew disease incidence and PDI was worked out. On the basis of PDI, plants were classified into two classes i.e., susceptible and resistant. The F1 showed susceptible reaction to powdery mildew. The segregating F2 population displayed the segregation in 3:1 ratio for susceptible and resistant reaction to powdery mildew disease. The segregation of F2 generation for powdery mildew disease reaction was confirmed in backcross generation. Also the Chi-square test indicated that the 3:1 ratio was perfectly fit for the susceptible and resistant reaction for powdery mildew disease. Thus, the current investigation revealed that a monogenic recessive gene controls powdery mildew resistance.

Blackgram, inheritance, resistance, powdery mildew, monogenic, recessive gene.

Black gram, scientifically known as Vigna mungo (L.) Hepper, is a one of the important short-duration crop which belongs to family Fabaceae. It is important legume crop which is widely grown around the world, especially in Asia (Sharma et al., 2019; Khan et al., 2020). It is also known as urdbean, urd, mash and black lentil. India is primary centre of origin of blackgram. It is mainly grown in Asian nations such as Pakistan, Myanmar, and various regions of southern Asia (Basamma, 2011). World's largest producer as well as consumer of blackgram is India. It is cultivated on over 3.56 lakh hectares in Maharashtra, where it produces 2.27 lakh tons and has a productivity of 638 kg ha-1 (Ministry of Agriculture, Govt. of India, 2022). Blackgram is nutritious crop which is rich in protein (20-26%) with high lysine content. But since last few years, there is decrease in yield due to biotic and abiotic stresses. Among the biotic stresses, powdery mildew is an important disease on blackgram with an estimated yield loss of 20-40% (Singh, 1980). To tackle powdery mildew in blackgram, breeding for resistance has been acknowledged as a sustainable and effective strategy (Manivannan et al., 2021). To minimize the further epidemic losses, it is important to identify and utilize the resistant sources or cultivars for development of disease resistant varieties. Significant knowledge about the genetic mechanism behind the resistance may be obtained by examining the genetic basis of resistance to powdery mildew in black gram. By using marker-assisted selection or other breeding approaches, this knowledge may helps in the identification of superior parental lines for breeding programs and serve as a guide for the development of resistant cultivars. In regard to this, the current investigation uses six generations of a cross to investigate the inheritance of powdery mildew resistance in blackgram.

The current study was carried out at Botany farm, PGI, Mahatma Phule Krishi Vidyapeeth, Rahuri during Kharif, 2021. It includes six generations of cross i.e., parents, F1, F2, B1 and B2. The experimental material consist of two genotypes viz., TBU-43-1 (susceptible parent) and PU-609-43 (resistant parent) obtained from Oilseed Research Station, Jalgaon (Plate 1). F1’s were made during Rabi, 2020. During Kharif, 2020, F2 population was raised from these F1 and new F1’s were developed for final evaluation trial. B1 and B2 were made during Rabi, 2021. For screening powdery mildew disease use of spreader row technique was done. In this experiment, susceptible powdery mildew variety TBU-43-1 was sown as a border row on 24 June, 2021. Susceptible variety was sown after every four test entries to ensure high disease pressure at the time of normal sowing i.e., on 8 July, 2021. Furthermore, infection spreads at vulnerable times, which are 20 and 40 days after sowing, increasing the pressure for spreading the disease. To establish the crop, recommended agronomic techniques were followed. To sustain the conidial spore population in the field during the cropping season, fungicides were not used.

When 100% disease was detected on infector rows (TBU-43-1), percent disease intensity (PDI) observations were recorded. The incidence of powdery mildew disease was noted on selected leaves of each plant in the parent, F1, F2, B1, and B2 generations. The leaves were graded using a progressive scale ranging from 0 to 5 (Table 1). The PDI was calculated using the formula given by Wheeler (1969). The data was analyzed using the Chi-square test to confirm the goodness of fit (Fisher, 1930).

Table 1: Rating scale for powdery mildew reaction.

The result of present study revealed the resistance of powdery mildew in blackgram for cross TBU-43-1 × PU-609-43. In parent PU-609-43, the PDI ranged from 2.22 to 8.89 with mean of 6.67. Hence was classified as resistant to powdery mildew disease. The PDI value in parent TBU-43-1 ranged from 26.67 to 48.89 with a mean value of 38.32 and classified as moderately susceptible for powdery mildew.

PDI values in the F1 of cross (TBU-43-1 × PU-609-43) was ranged from 24.44-48.89 with mean value of 33.73. The susceptible reaction in F1 generation of cross (S × R) was indicating that is recessive gene controls the resistance (Table  2).

Out of total 275 F2 population of cross (TBU-43-1 × PU-609-43), 196 plants were found to be susceptible with PDI value between 25.1- 50 hence grouped as moderately susceptible. Apart from this, 79 plants were found to be resistant. From these 79 plants, 13 plants showed PDI values between 0.1-10 which were grouped as resistant. Remaining 66 plants showed PDI values between 10.1 – 25 which were grouped as moderately resistant. Thus according to disease rating scale F2 population of cross (TBU-43-1 × PU-609-43) was grouped into two main classes viz., resistant and susceptible (Table 3). The ratio of resistant : susceptible was good fit into monogenic ratio i.e., 1 resistant : 3 susceptible with χ2 value of 2.03 which was non-significant for observed and expected frequency with ‘ρ’ value 0.15 (Table 4).

Plate 1. Parents reaction to powdery mildew.

Table 2: The reaction of parents and their F1 of cross TBU-43-1 × PU-609-43 against powdery mildew disease in black gram.

Table 3: Segregation of powdery mildew resistance in F2, B1 and B2 generations of cross (TBU-43-1 × PU-609-43) in black gram.

Table 4 : Inheritance of powdery mildew disease resistance in blackgram.

  R: Resistant, S: Susceptible, χ2: Chi-square value, P: Probability, ns.: Non-significant

The segregation of F2 generation for powdery mildew disease reaction was confirmed in backcross generation. In B1 generation, all 29 plants were found to be susceptible. In contrast, from 28 plants examined in B2, 17 were categorized as susceptible, and 11 as resistant (Table 3). From these 11 plants, 3 were resistant and 8 were moderately resistant. The observed ratio of susceptible to resistant plants was 1:1, which again did not deviate significantly from the expected ratio. The segregation of resistant and susceptible plants good fit into ratio of 1 resistant : 1 susceptible. The calculated χ2 value of 1.28 was lower than the χ2 table value of 3.84, indicating a non-significant difference with 0.26 probability value (Table 4).

Similar outcomes were stated by Kaushal and Singh (1989), Nisar and Ghafoor (2009); Kanwade et al. (2019); Punithavathy et al. (2023). According to Kute et al. (2003), duplicate recessive genes control resistance. Nonetheless, Chaitieng et al. (2002); Khajudparn et al. (2007); Srivastava et al. (2013); Pulate (2016) ; Kohakade (2021) revealed the contradicting results. They reported that one dominant gene controlled the resistance to powdery mildew. Reddy (2009); Basamma (2011), however, showed that resistance was controlled by two dominant genes. Additive gene action was reported by Sorajjapinun et al. (2005); Waraluk et al. (2009) to influence mungbean resistance to powdery mildew.

To summerize, the current research conclude that the segregation of resistance to powdery mildew disease of a blackgram cross TBU-43-1 × PU-609-43 follows the monogenic ratio. These results may be helpful in the development of breeding techniques to increase disease resistance as well as to understand the resistant of blackgram to the powdery mildew disease. The result above suggests that expression of blackgram's resistance to powdery mildew disease is controlled by a single recessive gene. Recombination breeding or immediate selection would be preffered to increase resistance in blackgram for powdery mildew.

For the development of a powdery mildew resistant variety in blackgram, the resistant plants recognized for powdery mildew in F2 should be used. The causal organism is an obligate parasite and infected plants can serve as a means of artificial inoculation. However, environmental variables may mitigate the severity of the disease which makes conventional breeding quite challenging. In order to develop blackgram resistant to the powdery mildew disease, it is therefore more beneficial to identify QTLs and use marker assisted selection.

Ankita P. Kamble, Nandakumar S. Kute and Gorakshanath C. Shinde (2024). Genetic Study for Inheritance of Powdery Mildew Disease Resistance in Blackgram [Vigna mungo (L.) Hepper]. Biological Forum – An International Journal, 16(5): 146-149.