The Phenotypic Fluctuation Factor for Male Sterility in A1 Male-Sterile Lines of Sorghum (Sorgum bicolor Moench)

The present study was conducted to clarify the factors shaping the extent of male sterility in A1 male-sterile lines of sorghum (Sorgum bicolor Moench). Eleven male-sterile lines (A-line) with A1 cytoplasm were grown both on a university farm during crop season and in growth chambers controlled under three different temperatures during the period from the 3rd to the 10th leaf stages in 1999. Based on the degree of seed and pollen fertility in artificial self-pollinated plant, A-lines were classified into 4 groups. Six cultivars of Group-1, ‘MS79,’ ‘CK60,’ ‘Martin,’ ‘Reliance,’ ‘Wheatland’ and ‘Tx624,’ showed stable male-sterility in all experimental conditions examined. ‘MS138’ of Group-2 showed variable sterility under minimum temperatures above 24℃, and ‘Tx3048’ of Group-3 showed variable sterility under maximum temperatures above 26.5℃ at flower initiation stage. Three cultivars of Group-4, ‘Redbine58,’ ‘Redlan’ and ‘Westland,’ showed variable sterility with restoration of pollen fertility in the field condition. In male-sterile sorghum lines like ‘MS138’ and ‘Tx3048,’ a physiological condition between early vacuolated pollen stage and engorged pollen stage is considered to be critical for conversion from sterile to fertile.