GENOTYPIC VARIATION IN THE EFFECT OF SALINITY ON FERTILITY IN RICE

The effect of salinity on the reproductive physiology of five rice gen otypes (IR54, IR26, IR2153-26-3-5-2, IR15324-117-3-2-2 and BR6), was i nvestigated by treatment from panicle initiation with sodium concentra tions of 20, 35 or 50 mol m(-3) in an 'artificial seawater'. In an exp eriment conducted in a glasshouse, plant height and dry weight were li ttle affected by the treatments. There was, however, genotypic variati on in the extent of the sodium accumulation, with IR15324-117-3-2-2 co ntaining the highest and IR2153-26-3-5-2 the lowest concentrations: so dium concentrations were higher in older than younger leaves. Salinity delayed flowering, reduced the number of productive tillers, the numb er of fertile florets per panicle, the weight per grain and the grain yield: effects on grain yield were very much more severe than on veget ative growth. Panicle length was also reduced as was the number of pri mary branches in a panicle: again there was genotypic; variation in th e response of these characters to salinity with the number of branches in IR2153-26-3-5-2 being particularly sensitive. The concentration of sodium increased in the pollen, stigmas, lemmas and paleas with each increment of external salinity. The highest concentrations of sodium i n pollen and stigmas was recorded in IR54 and IR15324-1 17-3-2-2. Poll en viability, whether tested with the tetrazolium salt thiazolyl blue (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyl monotetrazolium bromide or M TT), germination on stigmas, growth through the stylar tissue or F-1 s eed set, was reduced particularly in those genotypes accumulating most sodium. At all three salt levels, a genotype which accumulated more N a in its pollen produced less-viable pollen than those with less Na in their pollen. Since the amount of Na in the pollen was highly correla ted with the Na in the flag leaf, assessment of flag leaf Na should pr ove a useful indicator of the likely pollen viability. Stigmatic recep tivity was also reduced, when estimated either from germination of via ble pollen on stigmas of salt-grown plants, its growth through the sty lar tissue or F-1 seed set. The reduction of seed set in crosses sugge sted that the overall consequences of salinity are dominated by effect s on panicle development, stigmas and grain filling rather than on pol len. Analysis of the data suggests that genotypic variation exists in the extent to which salinity affects aspects of the plants reproductiv e physiology and development: this variation might be used in attempts to enhance the resistance of rice to salinity.