Abstract
A barley mutant resistant to barley yellow mosaic virus (BYMV) was selected from a total of 150 early mutants induced from a variety Chikurin lbaraki I with physical and chemical mutagens. The original variety is a six-rowed covered form with winter habit. The mutant, coded as Ea 52, was originally screened as an early mutant from M3 after acute irradiation of growing plants at vegetative stage with 250R of gamma-rays. When grown in a field severely infested with BYMV, all early mutants except Ea 52 showed mpre or less leaf yellowing characteristic to BYMV disease and proved to be highly susceptible, while Ea 52 exhibited no such external symptoms. The mutant Ea 52 was crossed as male parent to a susceptible mutant Ea 17 that has a similar degree of earliness. Segregation of resistance and susceptibility to disease in F2 was clear-cut from the absence or presence of leaf yellowing and stunting. The number of resistant and susceptible plants was 44 and 126 respectively, giving a good fit to the Mendelian ratio of I : 3 that is expected from a single gene inheritance. The resistant character was completely recessive to the susceptible. No sign of association of the disease resistance with heading time was observed. Although diseased plants more or less reco-vered their growth as temperature rose ih April, almost all of them produced lower number of tillers, smaller plant weight and lower culm length at maturity.
