Individual variation in lepto-leaf spot resistance and effects of phenotypic recurrent selection on its resistance in alfalfa (Medicago sativa L.)
1998
Takeda, Y. (Hokkaido. Konsen Agricultural Experiment Station, Nakashibetsu (Japan)) | Uchiyama, K. | Nakashima, K. | Yamaguchi, H.
Thirteen cultivars and breeding lines with moderate to relatively high resistance to Lepto-leaf spot (caused by Leptosphaerulina briosiana) were used for the estimation of individual variation in decease severity. Severities of Lepto-leaf spot were visually evaluated under natural infection in fall as 1 (least to 9 ( most severe). Maximum difference among the entries was 1.5 in mean scores of disease severity. "MSA-PL-L" was the lowest in the scores of severity, which was a check cultivar for Lepto-leaf spot resistance in U.S.A., and was followed by "Hisawakaba". Large individual variation in Lepto-leaf spot resistance was recognized within each entry. Standard deviation of severity was from 1.0 to 1.5 and the range of scores was from 6 to 8. Bidirectional mass selections by visual inspection of plants for Lepto-leaf spot resistance were conducted for two cycles using "Kitawakaba". The realized heritabilities of Lepto-leaf spot resistance, obtained by regression equation of the selection response on the cumulative selection differential, were 0.89 and 0.77 in the selection for resistance and susceptibility, respectively. The mean severity was 2.2 in the second generation selected for resistance and was significantly lower than that of "MSA-PL-L"
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