Soybean (Glycine max) pollen germination characteristics, flower and pollen morphology in response to enhanced ultraviolet-B radiation.

BACKGROUND AND AIMS Ultraviolet-B (UV-B) radiation effect on reproductive parts of the plants has received little attention. We studied the influence of UV-B radiation on flower and pollen morphology, pollen production and in vitro pollen germination and tube growth of six genotypes of soybean (Glycine max). METHODS Soybean genotypes were investigated by growing them under four levels of biologically effective UV-B radiation of 0 (control), 5, 10 and 15 kJ m(-2) d(-1) in sunlit controlled-environment chambers. KEY RESULTS Reductions in lengths of flower, standard petal, and staminal column along with reduced pollen production, germination and tube growth were observed in all genotypes with increasing UV-B radiation. Combined response index (CRI), the sum of percentage relative responses in flower size, pollen production, pollen germination and tube growth due to UV-B radiation varied with UV-B dosage: -67 to -152 with 5 kJ m(-2) d(-1), -90 to -212 with 10 kJ m(-2) d(-1), and -118 to -248 with 15 kJ m(-2) d(-1) of UV-B compared to controls. Genotypes were classified based on the UV-B sensitivity index (USI) calculated as CRI per unit UV-B, where D 90-9216, DG 5630RR and D 88-5320 were classified as tolerant (USI > -7.43), and DP 4933RR, Stalwart III and PI 471938 were sensitive (USI < -7.43) in their response to UV-B radiation. Pollen grains produced in plants grown at 15 kJ m(-2) d(-1) UV-B radiation were shrivelled and lacked apertures compared to control and other UV-B treatments in both sensitive and tolerant genotypes, and the differences were more conspicuous in the sensitive genotype (PI 471938) than in the tolerant genotype (D 90-9216). The number of columellae heads of the exine was reduced with increasing UV-B radiation. CONCLUSIONS Soybean genotypes varied in their reproductive response to UV-B radiation. The identified UV-B tolerant genotypes could be used in future breeding programmes.