Selection Effectiveness for the Resistance to Net Blotch in Barley

Selection effectiveness for the resistance to net blotch was estimated by using two sets of F2 and F3 populations derived from the crosses between resistant and susceptible parents. In every F2 and F3 population, disease ratings showed a continuous distribution. As many F3 lines with intermediate resistance had a smaller variance and homozygous genotype, the resistance might be controlled by a few genes. The heritabilities of the disease rating were estimated　by correlation coefficients and regression coefficients between each F2 plant and the descended F3 lines. Another estimate for heritability was calculated by the selection differential in the F2 plants and genetic gain in the F3 lines. Despite the different level of resistance in the resistant parents of the two crosses, the three kinds of heritabilities estimated were similar and ranged from 0.6 to 0.8. Because of the fewer number of genes controlling the disease resistance and the higher heritabilities, selection in a early generation may be effective for net blotch resistance in barlcy.

抵抗性と罹病性の両親間の交雑に由来する2組のF2集団とその後代のF3系統を用いて、大麦網斑病における抵抗性の選抜効果を推定した。F3系統の平均値と分散から、病斑指数の分散が小さく、すでに固定した系統が多数存在したので、抵抗性は少数の遺伝子に支配されているとみられた。F2個体とF3系統間の親子相関、親子回帰およびF2の選抜差とF3系統の遺伝獲得量から遺伝率を推定したところ、2組の交雑組合せで抵抗性親の病斑指数は異なっていたにもかかわらず、3種類の遺伝率の推定値はいずれも0.6～0.8の値を示した。遺伝率が高く、しかも関与する遺伝子数であるため、雑種集団で連続変異を示す場合の大麦網斑病抵抗性の選抜はF2からでも効果的とみられた。