Differential heterosis in a natural population of Asian wild rice (Oryza rufipogon Griff.) due to reproductive strategy and edge effect

Abstract

Asian common wild rice (Oryza rufipogon) is a polycarpic perennial plant with a mixed inbreeder/outbreeder strategy. Seeds and clones are both reproductive components of the population. However, when collected in the flowering stage, the two differ substantially as to whether they have experienced natural selection directly or not. This study is aimed at evaluating mechanisms for the survival of a population by comparing genetic structure among subpopulations that are classified in terms of: (1) reproductive systems (clones or seeds); and also (2) location (fringe or inside). First, the genotypes determined at seven SSR (Simple Sequence Repeat) loci showed that parameters of observed heterozygosity (H O ) and outcrossing rate (t) were clearly higher in clones (H O ¼ 0.609, t ¼ 82.4%) than in seeds (H O ¼ 0.346, t ¼ 35.5%), although the two had approximately the same values for the number of alleles (A) and expected heterozygosity (H E ) (A ¼ 4.43 in both clones and seeds, H E ¼ 0.709, 0.692 in clones and seeds, respectively). This result indicates that the individuals showing 'heterosis', with high numbers of heterozygous loci and outcrossing rates, are more likely to survive in the natural habitat. Secondly, parameters of observed heterozygosity and outcrossing rates were lower for seeds from the fringe area (H O ¼ 0.238, t ¼ 24.6%) compared to seeds from the inside area (H O ¼ 0.443, t ¼ 60.7%), although values were similar in clones of both the fringe and inside areas. This result suggests that the 'edge effect' might be due mainly to the restriction of wind strength in fringe area of the forested swamp.

Population structural analysis of an <i>in-situ</i> conservation site for wild rice in Laos

“…A previous study of genetic variation based on qualitative and quantitative genetic characteristics suggested the highest level of genetic differentiation was between seeds at the fringe and seeds in deep water (Kuroda et al, 2005a). Our data inferred by genetic distances calculated by multiple SSR markers suggested that there is weak differentiation between annuals and deep water perennial (Fig.…”

“…The present study demonstrated despite the perennial sub-populations in the center of the swamp having relatively higher genetic variation than outlying annual and perennial sub-populations, LV27 is a single population composed of annual and perennial subpopulations, which share genetic material with little restriction of gene flow. In a previous study undertaken in 1998, 19 plants (nine and ten nodes from a fringe site and inside area, respectively) and 19 seeds (nine and ten nodes from a fringe site and deep water area, respectively) and seven SSR loci were analyzed (Ho and He) (Kuroda et al, 2005a). In the present study, 14 polymorphic SSR markers were examined in 46 annuals and 73 within pond perennials.…”

“…1, Table 1). In a previous study, Kuroda et al (2005a) found 16% of annual individuals were in fringe areas of LV27 in March, 1998. We could detect annuals only in areas disturbed by water-buffalo.…”

“…The wild rice in the in-situ conversation area located on the Vientiane plain of Laos designated LV27 (N 18.14.00, E 102.41.26) (Yamanaka et al, 2003;Kuroda, et al, 2005a), is a complex population consisting of annual and perennial types (Kuroda et al, 2005b). Annuals are defined as those germinating directly from seeds by any stimulation or disturbance at peripheral areas of swamps.…”

Was Asian Rice (Oryza sativa) Domesticated More Than Once?

“…[47,83,84]). Annual and perennial wild rice in various parts of Asia can be found in the same area [33] and sometimes at the same site as part of a contiguous population ( [33]; first author's personal observations in Cambodia, India and Myanmar). The type of gradation in wild rice populations that can be found at some sites is illustrated (Fig.…”