Association Analysis of Three Diverse Rice (Oryza sativa L.) Germplasm Collections for Loci Regulating Grain Quality Traits.

Rice ( L.) end-use cooking quality is vital for producers and billions of consumers worldwide. Grain quality is a complex trait with interacting genetic and environmental factors. Deciphering the complex genetic architecture associated with grain quality provides essential information for improved breeding strategies to enhance desirable traits that are stable across variable climatic and environmental conditions. In this study, genome-wide association (GWA) analysis of three rice diversity panels, the USDA rice core subset (1364 accessions), the minicore (MC) (173 accessions after removing non-), and the high density rice array-MC (HDMC) (383 accessions), with simple sequence repeats, single nucleotide polymorphic markers, or both, revealed large- and small-effect loci associated with known genes and previously uncharacterized genomic regions. Clustering of the significant regions in the GWA results suggests that multiple grain quality traits are inherited together. The 11 novel candidate loci for grain quality traits and the seven candidates for grain chalk identified are involved in the starch biosynthesis pathway. This study highlights the intricate pleiotropic relationships that exist in complex genotype-phenotypic associations and gives a greater insight into effective breeding strategies for grain quality improvement.

Rice Pi-ta gene Confers Resistance to the Major Pathotypes of the Rice Blast Fungus in the United States.

ABSTRACT The Pi-ta gene in rice prevents the infection by Magnaporthe grisea strains containing the AVR-Pita avirulence gene. The presence of Pi-ta in rice cultivars was correlated completely with resistance to two major pathotypes, IB-49 and IC-17, common in the U.S. blast pathogen population. The inheritance of resistance to IC-17 was investigated further using a marker for the resistant Pi-ta allele in an F(2) population of 1,345 progeny from a cross of cv. Katy with experimental line RU9101001 possessing and lacking, respectively, the Pi-ta resistance gene. Resistance to IC-17 was conferred by a single dominant gene and Pi-ta was not detected in susceptible individuals. A second F(2) population of 377 individuals from a reciprocal cross between Katy and RU9101001 was used to verify the conclusion that resistance to IC-17 was conferred by a single dominant gene. In this cross, individuals resistant to IC-17 also were resistant to IB-49. The presence of Pi-ta and resistance to IB-49 also was correlated with additional crosses between 'Kaybonnet' and 'M-204', which also possess and lack Pi-ta, respectively. A pair of primers that specifically amplified a susceptible pi-ta allele was developed to verify the absence of Pi-ta. We suggest that Pi-ta is responsible for resistance to IB-49 and IC-17 and that both races contain AVR-Pita genes.

Development and mapping of 2240 new SSR markers for rice (Oryza sativa L.).

A total of 2414 new di-, tri- and tetra-nucleotide non-redundant SSR primer pairs, representing 2240 unique marker loci, have been developed and experimentally validated for rice (Oryza sativa L.). Duplicate primer pairs are reported for 7% (174) of the loci. The majority (92%) of primer pairs were developed in regions flanking perfect repeats > or = 24 bp in length. Using electronic PCR (e-PCR) to align primer pairs against 3284 publicly sequenced rice BAC and PAC clones (representing about 83% of the total rice genome), 65% of the SSR markers hit a BAC or PAC clone containing at least one genetically mapped marker and could be mapped by proxy. Additional information based on genetic mapping and "nearest marker" information provided the basis for locating a total of 1825 (81%) of the newly designed markers along rice chromosomes. Fifty-six SSR markers (2.8%) hit BAC clones on two or more different chromosomes and appeared to be multiple copy. The largest proportion of SSRs in this data set correspond to poly(GA) motifs (36%), followed by poly(AT) (15%) and poly(CCG) (8%) motifs. AT-rich microsatellites had the longest average repeat tracts, while GC-rich motifs were the shortest. In combination with the pool of 500 previously mapped SSR markers, this release makes available a total of 2740 experimentally confirmed SSR markers for rice, or approximately one SSR every 157 kb.