EFFECTS OF SALINITY ON SEED SET IN RICE

Salinity reduces fertility in rice (Oryza sativa L.), but little is kn own of the underlying cause(s), In order to determine the relative imp ortance of pollen viability and stigmatic receptivity for seed setting , plants of the rice cultivar IR36 were treated with 'artificial' sea water (0, 10, 25 or 50 mol m(-3) with respect to NaCl) from 1 month af ter germination until the main tiller flowered. An increase in the sal inity in the medium resulted in a decrease in the number of fertile fl orets and in the viability of pollen as determined both by pollen germ ination and by pollen staining with the tetrazolium salt 3-(4,5-dimeth ylithyazolyl)-2,5-diphenyl monotetrazolium bromide. In order to assess the effects of salt on stigmas, seed production was measured for salt -grown and non-salt-grown female plants pollinated with viable pollen (from plants grown in the absence of salt), The percentage of seed set was reduced by 38% when the female plants were grown in 10 mol m(-3) Na and by 72% at 25 mol m(-3) Na: no seed setting was recorded for pla nts grown in 50 mol m(-3) Na, Comparisons between crosses involving ma le and female parents grown at different salinities indicated that eff ects on the female plants dominated those on pollinator plants. Minera l analysis of leaves of different ages showed that there was a gradien t of K concentration from leaf to leaf which was opposite to that of N a and Cl at all levels of applied salinity: K was maximal in the flag leaf, where Na and Cl were minimal, Analysis also revealed that there was an increase in the concentrations of Na and Cl and a decrease in t he concentration of K in the pollen grains and stigmas of plants subje cted to saline conditions, Correlations between the concentration of N a End Cl in pollen and pollen staining and pollen germination in vitro suggest that Na and Cl per se were responsible for the poor viability , The change in ionic concentrations in pollen and stigmas was much la rger than that in the younger leaves, and in particular very much larg er than that in the lemmas and paleas.