A LIGHT-INTENSITY SENSITIVE CHLOROPHYLL MUTANT IN SORGHUM

A light-intensity sensitive chlorophyll mutant, gs(3), was discovered in a local sorghum [Sorghum bicolor (L.) Moench] population at Hays, K ansas, and analyzed genetically after crosses with normal green inbred s. The mutation causes the loss of chlorophyll of varying degrees and formation of lengthwise while stripes on leaves, leaf sheaths, glumes, and white kernels at soft dough stage. In field tests, the mutant beh aved like a simply inherited recessive trait, producing a ratio of 3 n ormal green:1 chlorophyll deficiency in the F-2 generation and a ratio of 1 normal green:1 chlorophyll deficiency in the backcross populatio ns. The selfed progeny from the mutant were virtually all mutant type, and the F-2 green plants segregated into 2 segregating:1 true breedin g F-3 families, confirming the F-2 data and showing that the mutant is under the control of a single recessive allele. However, the chloroph yll mutant often failed to show under low light intensity (585 mu mol/ m(2)/s) when grown in a growth chamber or in a greenhouse during the w inter months, and no definitive segregation ratio could be determined even if both green and striped trait did appear, suggesting that the m utant allele is light intensity regulated. Instability or occurrence o f variegated phenotypes, specific chlorophyll deficient patterns, coul d not breed true, and the rare reversion to normal green plants sugges ted that the expression of chlorophyll deficient trait may be regulate d by a transposable genetic system.