Causes of sterility in tetraploid rice.

Abstract

1) The fertility of a tetraploid variety of rice was observed to be 70 per cent in pollen g'rains and 0-27 per cent in seed setting, showing lower fertility as compar.ed with the diploids where fertile pollen grains amout to 95 per cent and the percentage of, seed setting is 50-70 in number. 2) The tetraploid variety sets in many cases shrinked seeds which fail-to bring themselves to a successful development. 3) The tetraploid variety can be earlier in the ear han in that of the diploids when the short day treatment carried out. 4) Irs the tetraploid variety, uni-, bi-, tri- and quardri-valent chromosomes, are found in the rD:eiotic metaphase, the number of the quadrivalent chromo-somes being countd to be 10 in most ca, ses. Some irregularities aS to the behaviQr of chromosomes are fyequently observed . 5) As to the cause of sterility in the tetraploid variety, 'it may be pointed out the fact that, so far as these ' investigations go, 15-20 per cent of sterility is due to deformed garnete, 15 per ceint being du to env. ironmental disturbances ar;d 50 per cent ovyed to zygotic sterility. 6) The continuaus selection for three years for obtaining a teitraploid strain which hs high degree of fertility gives no effective results, and shows that the degree of fertility remarkably fluctuates year by year even in the individuals of the s'me strain.