Contribution of Ancestral Lines in the Development of New Cultivars of Rice
Crop genetic uniformity is today a principal concern of plant breeders, and was the major cause of the southern leaf blight, Helminthosporium maydis Race T , epidemic on corn (Zea mays L.) in 1970. Genetic diversity can be measured, to a degree, by coefficient of parentage (r) measurements based on pedigree analysis. The objectives of this study were to construct four pedigree schematics to represent the rice (Oryza sativa L.) cultivars released in the USA, determine the relative genetic contribution of ancestral lines, and examine the genetic trends, by location, that result from using specific germplasms in cultivar development of rice. An examination of the pedigrees of 140 rice accessions demonstrated that all of the parental germplasm can be traced to 22 plant introductions in the southern Rice Belt (Arkansas, Louisiana, Mississippi, Missouri, and Texas) and 23 plant introductions in the western Rice Belt (California). The genetic base of the southern breeding programs can be traced to 13 parental accessions in Arkansas, 12 in Texas, and 16 in Louisiana. Furthermore, 10 of the 12 and 13 parental accessions in the Texas and Arkansas breeding programs, respectively, are identical and 8 of the 13 and 16 accessions in the Arkansas and Louisiana breeding programs, respectively, are identical. An examination of r showed that among the long-grain cultivars ‘Lebonnet’ and ‘Lemont’ have more than 72% of their genes in common and almost 90% of the genes are common in the medium grain cultivars, ‘Calrose’ and ‘Caloro.’ Furthermore, the r value between locations for long grain cultivars showed that ~24 and ~19% of the genes are common in the Arkansas and Texas and the Arkansas and Louisiana cultivars, respectively. These data show how closely related the current rice cultivars are that have been released in the USA.
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