A Genetic Resource for Rice Improvement：introgression Library of Agronomic Traits for All AA Genome Species in Genus Oryza

Background: Rice improvement depends on the availability of genetic variation, and AA genome Oryza species are the natural reservoir of favorable genes which are useful for rice breeding. Developing the introgression library using multiple AA genome species was rarely reported.Results: In this study, to systematically evaluate and utilize potentially valuable QTLs/genes or allelic variations, based on the evaluation and selection of agronomic traits, 6372 introgression lines (ILs) were raised by crossing 330 accessions of 7 AA genome species as the donor parents, with three elite cultivars of O. sativa, Dianjingyou 1, Yundao 1 and RD23 as the recurrent parents, respectively. Further, twenty-six, twenty-six and nineteen loci were detected in the multiple donors using 1,401 ILs in the Dianjingyou 1 background for grain length, grain width, and the ratio of grain length to grain width, respectively. Interestingly, ten loci had opposite effect on grain length in the different donors, so did grain width. Moreover, one locus for grain width, qGW3.1, was validated using the segregation population derived from the donor of O. glumaepatula. Conclusions: This introgression library provided the powerful resource for future rice improvement and genetic dissection of allelic variations. Selections of favorable alleles that are present in wild relatives proceed the driving force of the rice domestication.

Maize Introgression Library Provides Evidence for the Involvement of liguleless1 in Resistance to Northern Leaf Blight

Plant disease resistance is largely governed by complex genetic architecture. In maize, few disease resistance loci have been characterized. Near-isogenic lines are a powerful genetic tool to dissect quantitative trait loci. We analyzed an introgression library of maize (Zea mays) near-isogenic lines, termed a nested near-isogenic line library for resistance to northern leaf blight caused by the fungal pathogen Setosphaeria turcica. The population was comprised of 412 BC5F4 near-isogenic lines that originated from 18 diverse donor parents and a common recurrent parent, B73. Single nucleotide polymorphisms identified through genotyping by sequencing were used to define introgressions and for association analysis. Near-isogenic lines that conferred resistance and susceptibility to northern leaf blight were comprised of introgressions that overlapped known northern leaf blight quantitative trait loci. Genome-wide association analysis and stepwise regression further resolved five quantitative trait loci regions, and implicated several candidate genes, including Liguleless1, a key determinant of leaf architecture in cereals. Two independently-derived mutant alleles of liguleless1 inoculated with S. turcica showed enhanced susceptibility to northern leaf blight. In the maize nested association mapping population, leaf angle was positively correlated with resistance to northern leaf blight in five recombinant inbred line populations, and negatively correlated with northern leaf blight in four recombinant inbred line populations. This study demonstrates the power of an introgression library combined with high density marker coverage to resolve quantitative trait loci. Furthermore, the role of liguleless1 in leaf architecture and in resistance to northern leaf blight has important applications in crop improvement.