EFFECTS OF SALINITY ON SEED SET IN RICE

Salinity reduces fertility in rice (Oryza sativa L.), but little is known of the underlying cause(s), In order to determine the relative importance 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 after germination until the main tiller flowered. An increase in the salinity in the medium resulted in a decrease in the number of fertile florets and in the viability of pollen as determined both by pollen germination and by pollen staining with the tetrazolium salt 3-(4,5-dimethylithyazolyl)-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 plants grown in 50 mol m(-3) Na, Comparisons between crosses involving male and female parents grown at different salinities indicated that effects on the female plants dominated those on pollinator plants. Mineral analysis of leaves of different ages showed that there was a gradient of K concentration from leaf to leaf which was opposite to that of Na 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 the concentration of K in the pollen grains and stigmas of plants subjected to saline conditions, Correlations between the concentration of Na 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 larger than that in the younger leaves, and in particular very much larger than that in the lemmas and paleas.