Two genes conferring resistance to Pythium stalk rot in maize inbred line Qi319.

Stalk rots are destructive diseases in maize around the world, and are most often caused by the pathogen Pythium, Fusarium and other fungi. The most efficient management for controlling stalk rots is to breed resistant cultivars. Pythium stalk rot can cause serious yield loss on maize, and to find the resistance genes from the existing germplasm is the basis to develop Pythium-resistance hybrid lines. In this study, we investigated the genetic resistance to Pythium stalk rot in inbred line Qi319 using F2 and F2:3 population, and found that the resistance to Pythium inflatum in Qi319 was conferred by two independently inherited dominant genes, RpiQI319-1 and RpiQI319-2. Linkage analysis uncovered that the RpiQI319-1 co-segregated with markers bnlg1203, and bnlg2057 on chromosome 1, and that the RpiQI319-2 locus co-segregated with markers umc2069 and bnlg1716 on chromosome 10. The RpiQI319-1 locus was further mapped into a ~500-kb interval flanked by markers SSRZ33 and SSRZ47. These results will facilitate marker-assisted selection of Pythium stalk rot-resistant cultivars in maize breeding. To our knowledge, this is the first report on the resistance to P. inflatum in the inbred line Qi319, and is also the first description of two independently inherited dominant genes conferring the resistance of Pythium stalk rot in maize.

Resistance of Faba Bean and Pea Germplasm to Callosobruchus chinensis (Coleoptera: Bruchidae) and Its Relationship With Quality Components.

In total, 339 faba bean (Vicia faba L.) and 100 pea (Pisum sativum L.) accessions were screened for their ability to resist Callosobruchus chinensis L. in free choice laboratory tests. Four, 15, and 43 faba bean varieties were highly resistant, resistant, and moderately resistant to C. chinensis, respectively. Three immune, three highly resistant, and six resistant accessions were discovered among the pea germplasm. The faba bean and pea varieties presented a hundred-kernel weight reduction varied from 0.18 to 35.36% for faba bean varieties and 0 to 56.53% for pea varieties. Varieties with brown and black seed color had significantly fewer wormholes and higher C. chinensis resistance than varieties with light-color seeds. Resistance to C. chinensis showed a significant, positive correlation with catechin, total polyphenol, and γ-aminobutyric acid contents, but a significant, negative correlation with oligosaccharide content. Correlation coefficients (r) between infestation rate of faba bean and total phenol, catechin, and oligosaccharide contents were -0.9723, -0.8071, and 0.7631, respectively. The values of r for pea resistance and total phenol, catechin, and oligosaccharide content were -0.8846, -0.7666, and 0.8308, respectively. The results suggest that quality components in faba bean and pea have a great role in resistance against C. chinensis.

Quantitative trait loci mapping of resistance to Laodelphax striatellus (Homoptera: Delphacidae) in rice using recombinant inbred lines.

Laodelphax striatellus Fallén (Homoptera: Delphacidae), is a serious pest in rice, Oryza sativa L., production. A mapping population consisting of 81 recombinant inbred lines (RILs), derived from a cross between japonica' Kinmaze' and indica' DV85' rice, was used to detect quantitative trait loci (QTLs) for the resistance to L. striatellus. Seedbox screening test (SST), antixenosis test, and antibiosis test were used to evaluate the resistance response of the two parents and 81 RILs to L. striatellus at the seedling stage, and composite interval mapping was used for QTL analysis. When the resistance was measured by SST method, two QTLs conferring resistance to L. striatellus were mapped on chromosome 11, namely, Qsbph11a and Qsbph11b, with log of odds scores 2.51 and 4.38, respectively. The two QTLs explained 16.62 and 27.78% of the phenotypic variance in this population, respectively. In total, three QTLs controlling antixenosis against L. striatellus were detected on chromosomes 3, 4, and 11, respectively, accounting for 37.5% of the total phenotypic variance. Two QTLs expressing antibiosis to L. striatellus were mapped on chromosomes 3 and 11, respectively, explaining 25.9% of the total phenotypic variance. The identified QTL located between markers XNpb202 and C1172 on chromosome 11 was detected repeatedly by three different screening methods; therefore, it may be important to confer the resistance to L. striatellus. Once confirmed in other mapping populations, these QTLs should be useful in breeding for resistance to L. striatellus by marker-assisted selection of different resistance genes in rice varieties.

Rapid development of microsatellite markers for Callosobruchus chinensis using Illumina paired-end sequencing.

BACKGROUND: The adzuki bean weevil, Callosobruchus chinensis L., is one of the most destructive pests of stored legume seeds such as mungbean, cowpea, and adzuki bean, which usually cause considerable loss in the quantity and quality of stored seeds during transportation and storage. However, a lack of genetic information of this pest results in a series of genetic questions remain largely unknown, including population genetic structure, kinship, biotype abundance, and so on. Co-dominant microsatellite markers offer a great resolving power to determine these events. Here, we report rapid microsatellite isolation from C. chinensis via high-throughput sequencing. PRINCIPAL FINDINGS: In this study, 94,560,852 quality-filtered and trimmed reads were obtained for the assembly of genome using Illumina paired-end sequencing technology. In total, the genome with total length of 497,124,785 bp, comprising 403,113 high quality contigs was generated with de novo assembly. More than 6800 SSR loci were detected and a suit of 6303 primer pair sequences were designed and 500 of them were randomly selected for validation. Of these, 196 pair of primers, i.e. 39.2%, produced reproducible amplicons that were polymorphic among 8 C. chinensis genotypes collected from different geographical regions. Twenty out of 196 polymorphic SSR markers were used to analyze the genetic diversity of 18 C. chinensis populations. The results showed the twenty SSR loci were highly polymorphic among these populations. CONCLUSIONS: This study presents a first report of genome sequencing and de novo assembly for C. chinensis and demonstrates the feasibility of generating a large scale of sequence information and SSR loci isolation by Illumina paired-end sequencing. Our results provide a valuable resource for C. chinensis research. These novel markers are valuable for future genetic mapping, trait association, genetic structure and kinship among C. chinensis.