Differential fertility restoration of restorer genes to WA-cytoplasmic male sterility system in rice (Oryza sativa L.)

Abstract

The present investigation reports the influence of residual genetic background in restoration ability of the restorers. In a systematic set of crosses involving five WA-cms and ten restorer lines evaluated for combining ability P1292 recorded significantly poor while PRR72 significantly superior general combining ability for spikelet fertility. The cross combinations involving WA-cms line PMS2A and these two restorers constituted the basic experimental material for genetic analysis of fertility restoration. The F1 plants of these crosses were backcrossed to the cms line to develop testcross (BC1F1) progenies. The F1 ' F2 and BC1F1 plants were transplanted in the field using single seedling per hill at the Indian Agricultural Research Institute, New Delhi to study the inheritance of fertility restoration. Allelic test was conducted for fertility restorer genes present in two restorer lines. The F1 plants from the cross between PRR72 and P1292 were testcrossed to the cms PMS2A to develop three way testcross (TWCF1) progeny for allelic relationship studies. Pollen and spikelet fertility of the plants were assessed in each case and plants were classified as fully fertile (FF), semi fertile (SF), semi sterile (SS) or completely sterile (CS). For estimation of pollen fertility, anthers of three randomly taken spikelets representing lower, middle and top portion of the panicle were smeared in 1% 12-KI solution and examined under a light microscope. The pollen grains were classified as sterile or fertile based on their staining behaviour and shape [1]. Based on pollen fertility analysis, plants were classified as FF (>60%), SF(31-60%), SS(1-30%) or CS «1%). Similarly, with respect to spikelet fertility, all the plants were classified as FF (>70%), SF (41-70%), SS(1-40%) or CS(less than 1 %). Chi-square analysis was employed to test the goodness of fit of the genetic hypothesis. Presence or absence of SS and CS plants in TWCF1 was used to indicate the absence or presence of identical restorer genes in the restorer lines [2].