Abstract
NERICA rices are interspecific inbred progeny derived from crosses between Oryza sativa × O. glaberrima. In this study, we evaluated 70 BC2 interspecific lines, developed by crossing a tropical japonica variety (WAB 56-104) as the recurrent parent to an O. glaberrima variety (CG 14) as the donor parent, followed by the use of anther culture to derive doubled haploids (DH) (26 lines) or eight generations of inbreeding to fix the lines (44 lines). Seven of these BC2 derived inbred lines have been released as NERICA 1-NERICA 7. This study examined the relative contribution of each parent and the extent of genetic differences among these 70 sister lines using 130 well-distributed microsatellite markers which cover 1725 cM of the rice genome. The average proportion of O. sativa recurrent parent genome was 87.4% (1,508 cM), while the observed average proportion of O. glaberrima donor genome was 6.3% (108 cM). Non-parental alleles were detected in 83% of the lines and contributed an average of 38 cM per line (~2.2% of genomic DNA). Lines that had undergone eight generations of inbreeding in the field contained significantly more non-parental alleles (av. 2.7%) compared to the DH lines (av. 1.3%) that were developed from BC2 anthers. Using both cluster and principal component analyses, two major groups were detected in these materials. The NERICA varieties (NERICA 1 to 7) clustered in one group while the remaining 63 lines clustered in another group, suggesting that the second group may offer significant opportunities for further selection and variety development.
Highlights
Rice is the staple food of nearly one-half of the world's population, and contributes over 20% of the total caloric intake of humans (Bhattacharjee et al, 2002)
O. sativa alleles were detected at all 130 marker loci in one or more individuals but only 57 markers (43.8%) showed introgressions from O. glaberrima
When the data from the 130 markers were used to estimate the proportion of each parental genome in the 70 individuals, O. glaberrima DNA represented from 0.9 to 12.1% of the genome (Table 1; Figure 2) while O. sativa represented between 79.0 to 94.4%
Summary
Rice is the staple food of nearly one-half of the world's population, and contributes over 20% of the total caloric intake of humans (Bhattacharjee et al, 2002). The genus Oryza consists of 22 wild and 2 cultivated species - Asian rice (O. sativa) and African rice (O. glaberrima). Long before Asian rice was introduced to Africa, local farmers in West Africa had domesticated O. glaberrima. O. glaberrima germplasm harbors a reservoir of genes that have allowed the species to survive and prosper in West Africa for more than 3500 years (Bidaux, 1978; Carpenter, 1978). These genes confer valuable traits, including (i) rapid and profuse vegetative growth coupled with droopy lower leaves (Jennings et al, 1979; Koffi, 1980) that contribute
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