32. Isozyme markers for plant height and spikelet fertility in rice

The F\2\ progeny of a Japonica-Indica cross, ES70-6/SS404, was studied for quantitative traits, spikelet fertility and isozyme segregation. Both the parents are African traditional varieties of O. sativa from Tanzania and Senegal, respectively.

A total of 321 F\2\ plants were surveyed at seven isozyme loci. Plant groups having different alleles at each isozyme locus were compared with one another for plant height and spikelet fertility by the analysis of variance, which was conducted after square root transformation of the data. A significant difference between the plant groups may be considered as showing linkage of the given isozyme locus with at least one gene-locus concerned in the studied trait, called quantitative trait locus or QTL (Tanksley et al. 1982).

Three isozyme markers, Est-1, Pgi-2 and Acp-1, had effects of plant height (Table 1). Spikelet fertility was associated with Est-1 and Pgi-2. Pgi-2 and Acp-1 are independent. Est-1 is also independent of Pgi-2 (unpubl. data). Therefore, there can be at least two QTL's for plant height and spikelet fertility.

Thus, Est-1 and Pgi-2 are markers for these two characters. This suggests that plant height and spikelet fertility are, in part, controlled by linked genes or by pleiotropic effects of the same genes. Relationships of plant height with pollen and/or spikelet fertility were reported by Oka (1978). Our result supports this observation and provides an explanation of the genetic basis. As the Indica and Japonica varieties differ in morph-physiological, enzymatic and other traits, these traits are expected to be interrelated in hybrids.

Analysis of quantitative traits by marker loci was successfully made in tomato (Tanksley et al. 1982; Weller et al. 1988) and in maize (Edwards et al. 1987). In rice, such studies may provide a new insight on varietal differentiation.

In our data, it is worth noting that in Acp-1, Pgi-2 and Sdh-1, homozygotes for the allele from the Japonica parent were much fewer than those for the allele from the Indica parent.

Table 1. Test for difference in plant height and spikelet fertility between genotypes for each enzyme locus, in the F\2\ of ES70-6 (Japonica) X SS404 (Indica)

Edwards, M.D., C.W. Stuber and J.F. Wendel, 1987. Molecular-marker facilitated investigations of quantitative trait loci in maize, 1. Numbers, genomic distribution and types of gene action. Genetics 116: 113-125.

Oka, H.I., 1978. Phylogenetic differentiation of cultivated rice, 21. The sporophytic pollen sterility: Its genetic basis and intervarietal relationships as shown by F\2\ sterility. Jpn. J. Genet. 53: 397-410.

Tanksley, S.D., H. Medina-Filho and C.M. Rick, 1982. Use of naturally occurring enzyme variation to detect and map genes controlling quantitative traits in an interspecific backcross of tomato. Heredity 49: 11-25.

Weller, J.I., M. Soller and T. Brody, 1988. Linkage analysis of quantitative traits in an interspecific cross of tomato (Lycopersicum esculentum X L. pimpinellifollium) by means of genetic markers. Genetics 118: 329-339.