Abstract: The erossability of 30 hybridized and 6 selfcrossed combinations from the reciprocal crossing of 3 diploid rice ( Oryza sativa L. ) (2n = 2x = 24) and 3 autotetraploid rice (2n = 4x = 48) was investigated. The lower seed-sets (10.01%~21.78 % ) of the autotetraploidy combinations may be attributed to the presence of more abnormal pollen in the anthers. The seed-sets of the heteroploidy cross combinations were even lower (0.20% ~ 1.64%), but there was obvious different seed-settings between the two mating methods. If the autotetraploid rice was used as the female parents and the diploids as the male parents, higher seed-sets (0.42%- 1.64%) were found in the hybridized combination. However, the seed-sets in the combinations were lower (0.20% ~ 0.85% ) if the diploid rice was used as the female parents and the autotetraploids used as the male parents. The seed-sets of the autoheteroploidy combinations could be outstandingly improved by repeating the pollination twice. Besides, the results from the embryological examination of APⅣ (4) x APⅣ (2) cross showed that the total rate of fertilizations, including single fertilizations of an egg with a sperm (25. 0% ), two polar nuclei with a sperm (3.3%), and double fertilization of an egg and two polar nuclei with two sperms (5.9%), was lower(34.2% ). The survival rate of the autotriploid plants obtained by the conventional cross method was very low ( 0. 07% ), but that obtained by ovary culture method was higher (0.78%). Which surpassed 11.14 times than that of the former.

Key words: Heteroploid rice, Frequency of fertilization, Ovary culture, Triploid plant