Genetic analysis of bud necrosis disease caused by groundnut bud necrosis virus (GBNV) in tomato (Solanum lycopersicumL.)

In the present study for the first-time genetics and nature of gene action for resistance to bud necrosis disease in tomato was deciphered based on mechanical sap inoculation under the environment-controlled glasshouse conditions with the pure culture of GBNV. To accomplish this study, two resistant (IIHR-2901 and IIHR-2953) and one susceptible parent (PKM-1) were used to generate F-1, F-2, BC(1)P(1)and BC(1)P(2)populations. Castle wright estimation suggested that the trait is governed by the single gene blocks in both the crosses. Chi-square estimation also indicated that the resistance to bud necrosis disease in the cross PKM-1 x IIHR-2901 is controlled by one or two recessive genes while in the cross PKM-1 x IIHR-2953, it was found to be governed by one or two dominant genes based on the segregation pattern observed in F(2)generation. However, the results remain inconclusive, as the segregation in backcrosses was not behaving as expected for both the crosses. This showed that the classical Mendelian genetics and additive-dominance model were inadequate to explain the genetical mechanism of resistance to bud necrosis disease of tomato. It may be either due to the presence of modifiers in the background or may be due to the presence of epistatic interactions. Later, in this study presence of epistatic interaction was confirmed by the significance of scaling test in both the crosses. Estimates of six parameters [m, d, h, i, j and l] through generation mean analysis, suggested the preponderance of non-allelic interactions mostly of additive x dominance [j] type with negative signs in both the crosses and additive x additive [i] interaction with positive sign in the cross between PKM-1 x IIHR-2953. Complementary type of epistasis has been observed for both the crosses as both the componentsviz.,dominance [h] and dominance x dominance [l] were in similar direction. Hence, all the above results indicated that the improvement for resistance to bud necrosis disease could be possible through recombination breeding, hybridization followed by selection at later generations with more emphasis on selection between families and lines.