GENETIC STUDIES ON CYTOPLASMIC MALE STERILITY AND ANTHER INDEHISCENCE IN HYBRID RICE DEVELOPMENT
ABSTRACT
To evaluate the prospects of hybrid rice in Ghana, studies were undertaken, through participatory rural appraisal, to elicit farmer preferred traits and their readiness to adopt hybrids. The study also evaluated the performance of introduced hybrids, the genetics of anther indehiscence, stigma exertion and their possible application in hybrid rice breeding. A further study also identified potential maintainers and restorers from local germplasm for introduced Cytoplasmic Male Sterility lines using Simple Sequence Repeat markers and testcrosses. Although farmers were willing to adopt hybrid rice, their purchasing power was 5 times less than the anticipated price from seed companies. High yield, early maturity, grain quality, disease resistance, drought and submergence tolerance were farmers most preferred traits that breeders should be mindful of in developing local rice hybrids. Farmers‟ knowledge on hybrids was found to be very low. Extensive education will be necessary before large scale introduction of hybrids to farmers. Preliminary evaluation of introduced hybrids identified four promising hybrids (ARGH 1501, ARGH 1503, PAC 801 and SWARNA 2) with a mean yield advantage of 15-19.6% over the high yielding check variety „AgraRice‟. These four hybrids were selected for further testing and grain quality evaluation. With the exception of a few hybrids which were found to be susceptible to Bacterial Leaf Blight (BLB) and blast at some locations, the introduced hybrids generally had similar levels of tolerance to blast and BLB as checks. Aroma was not detected in any of the introduced hybrids. Molecular screening with SSR marker RM6100 grouped the available inbred lines into 30 potential restorers and 55 potential maintainers with 36% accuracy. One maintainer (WAS 127 -12-1-6-3-1) and 16 restorers were confirmed by testcrosses. Conversion of WAS 127 -12-1-6-3-1 into local CMS line was stopped because of sterility instability in the BC1F1 generation. More testcrosses are needed to identify a stable maintainer that can be converted to local CMS line. Compared to the local checks (AgraRice and Jasmine 85), WAS 127-12-1-2-3 showed high grain yield per plant when crossed onto CMS1 (IR69625A) and could be used as a restorer to develop locally adapted high yielding hybrids. Breeders should focus on other introduced aromatic materials for development of aromatic hybrids as none of the adapted aromatic varieties fully maintained or restored fertility of the CMS lines and thus will not be suitable as parents for local hybrid development. Anther indehiscence and stigma exertion is a form of functional male sterility exhibited by certain wide crosses. Reciprocal crosses suggest that cytoplasmic factors have no effect on the expression of anther indehiscence and stigma exertion. Temperature and relative humility could not modulate the fertility/sterility status of anther indehiscent plants. Two QTLs (qAI-6-1 and qAI-6-2) were identified on chromosome 6 for anther indehiscence. Two QTLs (qSE-6-1 and qSE-6-2) were also identified for stigma exertion on chromosome 6. The two QTLs for anther indehiscence co-locate with those of stigma exertion. Utilization of anther indehiscence and stigma exertion in hybrid rice breeding was hindered by trait fixation and propagation. QTLs identified from the study could assist in map based cloning of the underlining genes and future bioengineering of valuable male sterility.