Avirulance/virulence reaction of blast fungus on finger millet: A study on F₁ culture of a cross derived from host specific isolates of finger millet and foxtail millet

Host specificity of blast fungus (Magnaporthe grisea) was examined on four finger millet (viz., K7, GE5230, GPU26, PR202) and one local landrace of foxtail millet using F₁ progenies of a cross between two highly fertile and host specific pathogenic cultures isolated from a collection of field samples at central Himalayan region of Uttarakhand state in India. Parental isolate VII739 was virulent on finger millet and avirulent on foxtail millet cultivars, contrarily VII769 showed virulent reaction on foxtail millet and avirulent on finger millet cultivars. Data revealed that pathogenicity developed from the cross between finger millet isolates and foxtail millet isolate was conditioned by one (on K7 and PR202) and two (on GE5230) genes. The segregating ratio for 1:1:1:1 and 3:1:3:1 in combined analysis between K7 and PR202 and between PR202 and GE5230, respectively suggested that genes present in the cultivars were different and independent, contrarily 2:0:1:1 ratio between cultivars K7 and GE5230 demonstrated that one gene in GE5230 was identical to the one in K7. Avirulent genes for pathogen on K7, PR202 and GE5230 were designated respectively as AVR₁, AVR₂ and (AVR₁, AVR₃) and their corresponding resistance genes in cultivars as R₁, R₂ and (R₁, R₃). Avirulent reaction on GPU26 and foxtail millet cultivar explained that complex host species specificity of M. grisea existed in nature.