Effects of Safflower Sterility Genes on the Inflorescence and Pollen Grains

Abstract

Three interacting, unlinked, nuclear genes are reported to control the inheritance of male-female sterility in safflower (Carthamus tinctorius L.). In a cross between US-10 cultivar (genotype S(1)S(1)s(2)s(2)s(3)s(3)) and a geographically distant Indian line 57-147 (genotype s(1)s(1)S(2)S(2)S(3)S(3)), F-2 plants segregated 57 fertile:7 sterile. Sterile genotypes set no seed under natural conditions. This study reports the effects of sterility genes on the inflorescence and pollen grains. Floret elongation was limited in sterile plants at bloom. Lengths of florets in the sterile individuals showed a 17% and a 40% reduction one day before and on the day of anthesis, respectively. This resulted in a conspicuous pinched appearance of the capitula. Lack of seed development in sterile plants hindered the expansion of capitula and prevented the dried florets from lying against the imbricate bracts as in normal fertile plants. The percentage pollen stainability was 96.1 in US-10, 87.5 in 57-147, 91.3 in the F-1, 90.5 in fertile F-2, and 1.4 in sterile F-2 plants. However, none of the stainable pollen grains of the sterile F-2 plants was viable. The mean pollen diameter was 53.2 in US-10, 56.3 in 57-147, 53.9 in the F-1, 58.1 in fertile F-2, and 35.8 mu m in sterile F-2 plants. Sterile plants exhibited a greater variation in pollen diameter than the fertile plants. Light and scanning electron microscopy observations revealed the absence of normally sculptured and tricolpate pollen from the sterile plants. The results suggest that the sterility genes have their effects primarily on reproductive organs, but do not hinder vegetative development and growth of sterile plants before they bloom.