Phylogenetic Differentiation of Cultivated Rice. XV

Abstract

Hybrid inviability may be, as pointed out by Stebbins (1950) with many examples at hand, "the most widespread of the barriers which separate plant species ". The cases so far known are, however, interspecific. Its occurrence within a species has not been known, and the genes responsible for this phenomenon have not been analysed, so far as the writer is aware.

Chromosomal Location of HWA1 and HWA2, Complementary Hybrid Weakness Genes in Rice

“…Many postzygotic reproductive barrier forms have been reported in rice (Oryza sativa), such as hybrid weakness (e.g., Oka 1957), hybrid pollen sterility (e.g., Long et al 2008), and hybrid sterility causing female gamete abortion (e.g., Chen et al 2008). Among them, hybrid weakness is definable as weak growth occurring in F 1 hybrids derived from crosses between two normal strains.…”

“…In rice, two hybrid weakness phenomena from different intraspecific cross combinations have been reported: one by Oka (1957) and the other by Amemiya and Akemine (1963). The hybrid weakness reported by Oka (1957) resulted from use of a set of complementary dominant genes: L 1 and L 2 .…”

“…The hybrid weakness reported by Oka (1957) resulted from use of a set of complementary dominant genes: L 1 and L 2 . They were renamed L-1-a and L-1-b by Kinoshita (1984); then Hwa-1 and Hwa-2 by Sato et al (1987).…”

“…According to Oka (1957), hybrids carrying both Hwa1-1 and Hwa2-1 showed the following symptoms: germination and growth in the seedling stage were quite normal until the seedlings had developed three to four leaves, at which time growth stopped and the leaves yellowed. The phenotype differs considerably from that of hybrids carrying both Hwc1-1 and Hwc2-1, of which the symptoms are characterized by root growth inhibition appearing just 5 days after germination (Ichitani et al 2001;Saito et al 2007).…”

“…The distribution of Hwa1-1 and Hwa2-1 genes was limited to some Indian cultivars (Oka 1957). Based on results of three-way cross combinations, Oka (1957) reported that P.T.B.10 (accession 414) and P.T.B.7 (accession 419) carry Hwa1-1 and Hwa2-1, respectively, whereas Pei-ku (accession 108), Padi ase banda (accession 647), and Kissin (accession 521) carry neither Hwa1-1 nor Hwa2-1.…”