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, Kansas, and analyzed genetically after crosses with normal green inbreds. 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 behaved like a simply inherited recessive trait, producing a ratio of 3 normal green:1 chlorophyll deficiency in the F-2 generation and a ratio of 1 normal green:1 chlorophyll deficiency in the backcross populations. The selfed progeny from the mutant were virtually all mutant type, and the F-2 green plants segregated into 2 segregating:1 true breeding F-3 families, confirming the F-2 data and showing that the mutant is under the control of a single recessive allele. However, the chlorophyll 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 winter months, and no definitive segregation ratio could be determined even if both green and striped trait did appear, suggesting that the mutant allele is light intensity regulated. Instability or occurrence of variegated phenotypes, specific chlorophyll deficient patterns, could not breed true, and the rare reversion to normal green plants suggested that the expression of chlorophyll deficient trait may be regulated by a transposable genetic system.