Rice Varieties.

12 p

The Semidwarfs - A New Era in Rice Production.

52 p

Genomic Diversity and Introgression in O. sativa Reveal the Impact of Domestication and Breeding on the Rice Genome

The domestication of Asian rice (Oryza sativa) was a complex process punctuated by episodes of introgressive hybridization among and between subpopulations. Deep genetic divergence between the two main varietal groups (Indica and Japonica) suggests domestication from at least two distinct wild populations. However, genetic uniformity surrounding key domestication genes across divergent subpopulations suggests cultural exchange of genetic material among ancient farmers.In this study, we utilize a novel 1,536 SNP panel genotyped across 395 diverse accessions of O. sativa to study genome-wide patterns of polymorphism, to characterize population structure, and to infer the introgression history of domesticated Asian rice. Our population structure analyses support the existence of five major subpopulations (indica, aus, tropical japonica, temperate japonica and GroupV) consistent with previous analyses. Our introgression analysis shows that most accessions exhibit some degree of admixture, with many individuals within a population sharing the same introgressed segment due to artificial selection. Admixture mapping and association analysis of amylose content and grain length illustrate the potential for dissecting the genetic basis of complex traits in domesticated plant populations.Genes in these regions control a myriad of traits including plant stature, blast resistance, and amylose content. These analyses highlight the power of population genomics in agricultural systems to identify functionally important regions of the genome and to decipher the role of human-directed breeding in refashioning the genomes of a domesticated species

Identification of rice cultivars resistant to Lissorhoptrus oryzophilus (Coleoptera: Curculionidae), and their use in an integrated management program

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States and is a particularly severe pest in Louisiana The current management program for this insect in Louisiana relies heavily on insecticides, most notably the seed treatment fipronil (Icon). Diversification of the management program by incorporation of alternative strategies is needed to improve the effectiveness and long-term stability of the program. In the three experiments reported here, three components of a diversified management program for the rice water weevil in Louisiana - host plant resistance, treatment of seeds with Icon, and the cultural practice of delayed flooding - were investigated. Comparison of the densities of weevil larvae on the roots of several commercial cultivars indicated that the long-grain cultivar \u27Jefferson\u27 was more resistant to infestation by the rice water weevil than the other cultivars. The medium-grain cultivars \u27Bengal\u27, \u27Earl\u27 and \u27Mars\u27 and the long-grain variety \u27Cocodrie\u27 were the most susceptible to infestation. Comparison of yield data from untreated plots and plots treated with Icon indicated that the long-grain cultivars Cocodrie, Lemont, and Jefferson were more tolerant of weevil injury than the other cultivars. A 2-wk delay in flooding was associated with yield benefits in plots not treated with Icon. Treatment of seeds with Icon controlled weevils in all three screening experiments. The implications of these results for the development of an integrated management program for the rice water weevil are discussed. © 2001 Entomological Society of America

Efeito de diferentes herbicidas na nodulação e na atividade da nitrogenase no amendoim Effect of herbicides on nodulation and nitrogenase activity in peanuts

Em ensaio de herbicidas na cultura do amendoim (Arachis hypogaea L.), realizado em Ribeirão Preto, SP, em 1984/85, sem o uso de inoculante, não foram encontrados nódulos nos diferentes tratamentos. Como é comum sua presença em amendoim nessa região, suspeitou-se que os herbicidas utilizados pudessem ter efeito inibitório na nodulação. Avaliou-se, então, o efeito de alachlor, linuron, oxadiazon, pendimetalin e trifluralin aplicados na dose recomendada, na nodulação e na atividade da nitrogenase, durante dois anos consecutivos, usando-se sementes inoculadas e não inoculadas. Foram feitas amostragens aos 28, 42, 63, 84 e 105 dias após a semeadura, observando-se nodulação abundante, em todos os tratamentos, e reduções ocasionais na nodulação e na fixação do nitrogênio, porém não consistentes nas diversas amostragens. A atividade da população nativa de Rhizobium em geral permaneceu num nível maior do que nos tratamentos com inoculação. Embora alguns herbicidas tenham afetado a nodulação e a fixação do nitrogênio, não houve influência na produção de grãos.<br>No nodules were found in a peanut herbicide trial held at Ribeirão Preto, State of São Paulo, Brazil, during the growing season 1984/85. Since spontaneous nodulation is commom in this region, a hypotheses was raised that herbicides could have an inhibitory effect on nodulation. To test the effect of herbicides on nodulation and nitrogenase activity an experiment was carried out on two consecutive years, using a factorial design with two factors: a) five herbicides (alachior, linuron, oxadiazon, pendimethalin and trifluralin) applied in usual dosages and a control without herbicide and b) with and without Bradyrhizobium inoculation. Samples were collected at 28, 42, 63, 84 and 105 days after planting. The results showed that nodulation was abundant in all treatments. Nitrogenase activity in the non inoculated treatments persisted for a longer period than in the inoculated ones. Although some herbicides reduced nodulation and nitrogen fixation, peanut grain production was not affected