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Heterosis and Isozyme Divergence in Indica Rice

Dep. of Botany and Plant Pathology, Purdue Univ., West Lafayette, IN 47907
CIRAD, IRAT, Nogent-Sur-Marne, France
Int. Rice Res. Inst. (IRRI), Los Baños, Laguna, Philippines

^* Corresponding author.

Earlier studies conducted in China indicated an association of heterosis in rice (Oryza sativa L.) crosses with certain esterase and peroxidase isozyme patterns. To search for methods that predict yield heterosis in hybrid rice breeding program at IRRI, we studied isozyme variation of 18 rice cultivars (seven maintainers and 11 restorers of ‘WA’ cytosterility system) and 75 F₁, hybrids derived from these parents to determine the relationship between yield heterosis in the F₁s and isozyme diversity among their parents. Isozyme variation among parental lines was found for six genes, viz., Est-9, Est-2, Amp-3, Sdh-1, Pgi-2, and Pgd-1. Midparent heterosis for yield ranged from –44.6 to 156.7%. Our studies did not show any association between magnitude of heterosis in F₁s and isozyme variation among parents. The reason our results differed from those reported in China may be because most of the parental lines used in our studies were elite rice cultivars bred at IRRI from complex crosses involving parents of various geographic origin that allowed extensive recombination among genes. Consequently, linkage disequilibrium between isozyme markers and gene blocks involved in heterosis for yield might have disappeared.

Key Words: Oryza sativa L. • Isozyme variation • Prediction of heterosis • Hybrid rice • Rice Breeding methods

Received for publication November 10, 1986.

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