Male and female gamete abortions, and reduced affinity between the uniting gametes as the causes for sterility in an indica/japonica hybrid in rice

Abstract

Hybrid sterility frequently occurs in crosses between indica and japonica subspecies of Asian cultivated rice. In this study, we investigated the cytological processes involved in formation and development of male and female gametes as well as their interactions in fertilization, using an indica/japonica hybrid in comparison with an indica/indica hybrid. It was found that more than 50% of the microspores generated in the indica/ japonica hybrid could not develop into functional pollen. The abortion rate of microspores in the indica/japonica hybrid was much higher than that in the indica/indica hybrid. Abortive embryo sacs made up roughly 70% of the embryo sacs examined in the indica/japonica hybrid, which was also much higher than that detected in the indica/indica hybrid. Moreover, the amount of pollen adherence on stigmas of the indica variety upon handpollination with pollen from the japonica variety was much lower than the indica/indica pollination, and the number of pollen adhered on the stigmas by natural selfpollination was much greater in the indica/indica hybrid than in the indica/japonica hybrid. The indica/japonica hybrid also encountered difficulties in pollen tube growth after pollination, and the fertilization rate of the indica/ japonica hybrid was much lower than that of the indica/ indica hybrid. These results clearly illustrate the complexity of the mechanisms underlying inter-subspecific hybrid sterility in rice involving both pre-and post-zygotic reproductive isolation mechanisms.

Morphological, Cytological and Embryological Characterization of F1 A. cepa × A. roylei Hybrids

“…The degeneration of the entire embryo sac preceded by atypical megasporocyte was described in the indica/japonica hybrid. Although no irregularities were observed during the division of the megasporocyte, most of them occurred after meiosis, when some abnormal megaspores failed to form typical mononucleate embryo sacs (Liu et al, 2004;Zeng et al, 2009). On the other hand, investigation of female meiosis in A. roylei (Sharma and Gohil, 2011) resulted in identification of additional chromosomes and multivalents in embryo sac mother cells that, as the authors suggest, may adversely affect the reproductive capacity and lead to production of genetically imbalanced gametes.…”

Interspecific incompatibility in wide hybridization of plants and ways to overcome

“…indica × O. sativa subsp. japonica мейоз до образования тетрад протекает нормально, но после этой стадии происходят многочисленные нарушения в разви-тии микроспор и пыльников (Liu et al, 2004).…”

Identification of neutral genes at pollen sterility loci Sd and Se of cultivated rice (Oryza sativa) with wild rice (O. rufipogon) origin

“…There are different theories about the hybrid sterility in rice, such as male gamete abortions Liu et al, 2004), female gamete abortions (Yokoo, 1984;Liu et al, 2004) and reduced dehiscence of anthers . Among them, pollen and embryo sac sterility are the two most important factors which cause hybrid sterility and both of them have contributed almost equally to spikelet fertility (Song et al, 2005).…”