Degrees of sexuality in sexual plants of guineagrass by the simplified embryo sac analysis.

Abstract

Degrees of sexuality in lowly and highly sexual plants of guineagratss which were isolated by progeny tests in the previous paper of the authors, were investigated by using the simplified embryo sac analysis, and compared with degrees of sexuality by frequency of off-type plants in progenies. In embryo sac analysis, ovules were classified into sexual or apomictic reproduction to detect the type of embryo sacs. Sexual embryo sac was 8-nucleate, and aposporous one was 4-nucleate. As ovules examined kept their original forms intact in pistils, reproductive behavior in polyembryonic ovules was easily identifled by determining the dominant embryo sac in multiple ones. Highly sexual diploid plants were revealed to be completely sexual based upon the embryo sac type. All ovules had single sexual embryo sacs excluding several sterile ones. Highly sexual tetraploid plant, N68/96-8, was also identified to be completely sexual, and its offsprings after open-pollination were segregated in degrees of sexuality. Five out of 10 offsprings were completely sexual, one was obligate apomictic, and the other four were facultative apomictic. Two lowly sexual plants, N68/84-1 and 73/61-9, and their offsprings after self-and open-pollination, were shown to have low frequencies of sexual embryo sacs except N68/84-1 which had rather higher rate of sexual embryo sacs. No plants with high degrees of sexuality were segregated in their offsprings. Both degrees of sexuaiity by embryo sac analysis and progeny test, agreed well excluding degrees in a few facultative apomicts. This analysis was appeared to provide more accurate estimation of degree of sexuallty. Complete sexuality observed in this study was recognized to be useful for producing controlled hybrid plants in sexual X apomictic cross in the first procedure of hybridization breeding in this apomictic grass.