Identification and confirmation of greenbug resistance loci in an advanced mapping population of sorghum

SUMMARYGreenbug infestations to sorghum can cause severe and above economic threshold damage in the Great Plains of the United States. The current study was conducted to identify quantitative trait loci (QTLs) and potential candidate genes residing within the QTL region responsible for greenbug resistance in an advanced mapping population. Inter-crossed populations are useful in detecting QTLs tightly linked to genetic markers with high resolution. In the current study, QTLs responsible for greenbug resistance in sorghum were mapped using an inter-cross population derived from two parents, BTx623 (greenbug-susceptible line) and PI 607900 (greenbug-resistant line). Molecular markers for 115 loci were used to construct a linkage map which eventually facilitated tagging portions of the sorghum genome regions responsible for greenbug resistance. The molecular genetic map covered all the chromosomes of sorghum with a total genome length of 963·0 cM. The advanced mapping population revealed and confirmed the location of greenbug resistance loci, which explained a high phenotypic variation from 72·9 to 80·9% of greenbug resistance. The loci for greenbug resistance were mapped to the region flanked by markers Starssbnm 93 and Starssbnm 102 on chromosome 9 with an increased allelic effect from the resistant parent. The locations of these loci were compared with a previous study on QTL analysis using an F2 mapping population. The results from the present study were in agreement with the findings in the F2 QTL analysis and identified QTLs had a better confidence interval. The markers/QTLs identified from the current study can be effectively utilized in marker-assisted selection and map-based cloning experiments.

Dissection of the genetic architecture for soybean seed weight across multiple environments

Seed weight (SW), measured as mass per seed, significantly affects soybean (Glycine max (L.) Merr.) yield and the quality of soybean-derived food. The objective of the present study was to identify quantitative trait loci (QTLs) and epistatic QTLs associated with SW in soybean across 129 recombinant inbred lines (RILs) derived from a cross between Dongnong 46 (100-seed weight, 20.26 g) and ‘L-100 (4.84 g). Phenotypic data were collected from this population after it was grown in nine environments. A molecular genetic map including 213 simple sequence repeat (SSR) markers was constructed, which distributed in 18 of 20 chromosomes (linkage groups). This map encompassed ~3623.39 cM, with an average distance of 17.01 cM between markers. Nine QTLs associated with SW were identified. These QTLs explained 1.07–18.43% of the observed phenotypic variation in the nine different environments, and the phenotypic variation explained by most QTLs was 5–10%. Among these nine QTLs, qSW-3 (Satt192) and qSW-5 (Satt568) explained 2.33–9.96% and 7.26–15.11% of the observed phenotypic variation across eight tested environments, respectively. QTLs qSW-8 (Satt514) and qSW-9 (Satt163) were both identified in six environments and explained 8.99–16.40% and 3.68–18.43% of the observed phenotypic variation, respectively. Nine QTLs had additive and/or additive × environment interaction effects, and the environment-independent QTLs often had higher additive effects. Moreover, nine epistatic pairwise QTLs were identified in different environments. Understanding the existence of additive and epistatic effects of SW QTLs could guide the choice of which reasonable SW QTL to manipulate and could predict the outcomes of assembling a large number of SW QTLs with marker-assisted selection of soybean varieties with desirable SW.