GENETICS OF RESISTANCE TO SPOT BLOTCH, Bipolaris sorokiniana, IN BREAD WHEAT

An experiment was conducted to determine the nature and number of genes for resistance to spot blotch (Bipolaris sorokiniana) in three genotypes of wheat (Triticum aestivum L.) Viz., PBW 343, PBW 373 and WH 581. Evaluation of all parents i.e., parent I (P-1), parent 2 (P-2), and the four generations viz., first filial generation (F-1), second filial generation F-2, backcross generation 1 (BC1) and backcross generation 2 (BC2) of these nine crosses was carried out under artificial epiphytotic conditions in the field. The F-1 hybrids between resistant and susceptible parents, namely, UP 2338, PBW 154 and Sonalika were resistant to spot blotch. Appearance of resistance in F1 indicated that resistance is dominant over susceptibility. The F-2 population derived from seven of these nine crosses segregated in a ratio of 15:1 (resistant: susceptible) for spot blotch reaction showing that resistance is conditioned by two dominant genes with duplicate gene interaction. On the other hand, 9:7 (resistant/susceptible) ratio in F-2 populations of two crosses (UP 2338 x WH 581 and Sonalika x WH 581) indicated complementary gene interaction. The backcross progenies with susceptible parents in each cross segregated into 3 resistant: 1 susceptible as expected further confirming the hypothesis.