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 3 to the 10 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°C, and ‘Tx3048’ of Group-3 showed variable sterility under maximum temperatures above 26.5°C 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.