Comparison between phenotype variation and isozyme diversity within and between AA genome wild rice species

Comparison between phenotype variation and isozyme diversity within and

between AA genome wild rice species

M. Akimoto1, Y. Shimamoto1 and H. Morishima2

FacuLty of Agriculture, Hokkaido University, Sapporo 060-8589 Japan

National Institute of Genetics, Mishima 411-8540 Japan

Phylogenetic relationships among AA genome wild species related to cultivated rice have been studied by several researchers (reviewed by Morishima et a!. 1992), but their results were not always consistent. This is probably due to different tools as well as due to insufficient sample sizes used in respective studies. We examined variability of 22 quantitative characters and 29 isozyme loci for a total of 168 strains of five AA genome wild species; 57 strains of 0. rufipogon from Asia and Oceania, 49 strains of 0. glwnaepatula from Latin America, 19 strains of 0. meridionalis from Australia, 23 strains of 0. barthii from Africa and 20 strains of 0. longistaminata from Africa. Polymorphisms at phenotype and isozyme loci were examined by principal component analysis and scatter diagrams were generated using the first and second principal component scores.

A scatter diagram of 148 strains plotted by the first and second principal component scores based on the data of 22 characters was generated. The strains of 0. rufipogon and 0. g!wnaepatu!a were distributed in wider ranges than 0. meridionalis and 0. barthii, and seemed to be divided into continuously varying two and three groups, respectively; 0. rufipogon-I, H and 0. glumaepatula-I to ifi (Fig. la). The strains of 0. longistaminata

were not included in this character analysis, because they did not flower during our study period, and consequently sufficient data were not available. 0. rufipogon-I and 0. glumaepatu!a-I were plotted as overlapping each other. While, 0. rufipogon-II overlapped with 0. meridionalis and 0. barthii. Judging from character measurments, the former group tended to show much resource investment to vegetative growth rather than seed production, delayed reproduction and high pollen productivity, while the latter group showed the opposite trend. We could consider the former group as perennial-type wild rice and the latter as annual-type wild rice. Multiple variant T2 test proved no significant differences at 5% level between principal component scores of two perennial wild rice, 0. rufipogon-I and 0. g!umaepatula-I, as well as between three annual wild rice, 0. rufipogon-II, 0. meridionalis and 0. barthii (Table 1). 0. glumaepatula-H and -III differed significantly from other taxa, indicating that they developed unique phenotypes, respectively. Among 29 loci of 15 enzymes analyzed, 26 loci of 13 enzymes were polymorphic for the entire germplasm evaluated. A scatter diagram of 168 strains plotted by the first and second principal component scores revealed that the strains belonging to five species formed respective clusters and were separated from each other (Fig. Ib). Multiple variant T2 test proved significant differences between all pairs of five species at 5% level (Table 1), indicating that each species evolved with different isozyme genotypes. Intraspecies differentiation of 0. rufipogon into 0. rufipogon-I and II as classified in phenotype analysis was not clearly recognized (Fig. lb and Table 1). On the other hand, 0. glumaepatula-1I was plotted separately from 0. glumaepatula-I and III to some degree (Fig. ib), however, principal component scores did not differ significantly at 5% level between 0. glumaepatula-I, II and Ill (Table 1).

Phenotypes which are subjected to natural selection often evolve convergently unlike isozyme genotypes which are considered to be rather neutral. Plants, even with different

Table 1. Mean values and standard deviations (in parenthesis) of the first and second principal component scores at 22 quantiative characters and 29 isozyme loci

Research Notes

79

were not included in this character analysis, because they did not flower during our study period, and consequently sufficient data were not available. 0. rufipogon-I and 0. glumaepatu!a-I were plotted as overlapping each other. While, 0. rufipogon-II overlapped with 0. meridionalis and 0. barthii. Judging from character measurments, the former group tended to show much resource investment to vegetative growth rather than seed production, delayed reproduction and high pollen productivity, while the latter group showed the opposite trend. We could consider the former group as perennial-type wild rice and the latter as annual-type wild rice. Multiple variant T2 test proved no significant differences at 5% level between principal component scores of two perennial wild rice, 0. rufipogon-I and 0. g!umaepatula-I, as well as between three annual wild rice, 0. rufipogon-II, 0. meridionalis and 0. barthii (Table 1). 0. glumaepatula-H and -III differed significantly from other taxa, indicating that they developed unique phenotypes, respectively. Among 29 loci of 15 enzymes analyzed, 26 loci of 13 enzymes were polymorphic for the entire germplasm evaluated. A scatter diagram of 168 strains plotted by the first and second principal component scores revealed that the strains belonging to five species formed respective clusters and were separated from each other (Fig. Ib). Multiple variant T2 test proved significant differences between all pairs of five species at 5% level (Table 1), indicating that each species evolved with different isozyme genotypes. Intraspecies differentiation of 0. rufipogon into 0. rufipogon-I and II as classified in phenotype analysis was not clearly recognized (Fig. lb and Table 1). On the other hand, 0. glumaepatula-1I was plotted separately from 0. glumaepatula-I and III to some degree (Fig. ib), however, principal component scores did not differ significantly at 5% level between 0. glumaepatula-I, II and Ill (Table 1). Phenotypes which are subjected to natural selection often evolve convergently unlike isozyme genotypes which are considered to be rather neutral. Plants, even with different

Factor 2 T2 test�>

Taxa among which do not share the same characetr are significanty different after Hottelling�s multiple

variant T2 test with 0.05 significant level.

phylogenetic background, are likely to develop similar phenotypes when they are subjected to the same kind of natural selection. Perennial types of wild rice prefer stable and less disturbed environments where predictable density-dependent mortality is frequent. While, annual types tend to inhabit fragile and occasionally disturbed environments where unpredictable density-independent mortality is frequent. Isozyme analysis proved that the different species with similar phenotypes were genetically differentiated from each other, indicating that their phenotype similarity was most probably homoplacy caused by convergence under the same kind of natural selections.

Morishima, H., Y. Sano and H.I. Oka, 1992. Evolutionary studies in cultivated rice and its wild relatives. Oxford Survey in Evolutionary Biology 8: 135-184.