Identification of several small main-effect QTLs and a large number of epistatic QTLs for drought tolerance related traits in groundnut (Arachishypogaea L.)

Cultivated groundnut or peanut (Arachis hypogaea L.), an allotetraploid (2n = 4x = 40), is a self pollinated and widely grown crop in the semi-arid regions of the world. Improvement of drought tolerance is an important area of research for groundnut breeding programmes. Therefore, for the identification of candidate QTLs for drought tolerance, a comprehensive and refined genetic map containing 191 SSR loci based on a single mapping population (TAG 24 × ICGV 86031), segregating for drought and surrogate traits was developed. Genotyping data and phenotyping data collected for more than ten drought related traits in 2–3 seasons were analyzed in detail for identification of main effect QTLs (M-QTLs) and epistatic QTLs (E-QTLs) using QTL Cartographer, QTLNetwork and Genotype Matrix Mapping (GMM) programmes. A total of 105 M-QTLs with 3.48–33.36% phenotypic variation explained (PVE) were identified using QTL Cartographer, while only 65 M-QTLs with 1.3–15.01% PVE were identified using QTLNetwork. A total of 53 M-QTLs were such which were identified using both programmes. On the other hand, GMM identified 186 (8.54–44.72% PVE) and 63 (7.11–21.13% PVE), three and two loci interactions, whereas only 8 E-QTL interactions with 1.7–8.34% PVE were identified through QTLNetwork. Interestingly a number of co-localized QTLs controlling 2–9 traits were also identified. The identification of few major, many minor M-QTLs and QTL × QTL interactions during the present study confirmed the complex and quantitative nature of drought tolerance in groundnut. This study suggests deployment of modern approaches like marker-assisted recurrent selection or genomic selection instead of marker-assisted backcrossing approach for breeding for drought tolerance in groundnut

Cropping systems strategy for effective management of Fusarium wilt in safflower

In many parts of India intensive cultivation of safflower on Vertisols appears to have aggravated the problem of Fusarium wilt in safflower due to the soil borne fungus, Fusarium oxysporum Schlecht f. sp. carthami Klisiwiez and Houstan (FOC). In a long-term field experiment at Patancheru, India, we evaluated four diverse dryland cropping systems that each included safflower for their effectiveness in controlling Fusarium wilt in safflower. Sorghum (rainy season crop) and safflower (post-rainy season crop) were grown every alternate year as a two-year rotation with: (1) sorghum intercropped with pigeonpea (S/PP − S + SF); (2) cowpea intercropped with pigeonpea (C/PP − S + SF); (3) sorghum followed by chickpea (S + CP − S + SF); (4) sorghum followed by safflower (S + SF − S + SF). Continuous sorghum and safflower (S + SF − S + SF) had higher Fusarium wilt incidence of fully wilted safflower plants (31%) and a larger build-up of Fusarium propagules (1728 cfu g−1 of soil) than other cropping systems. The inclusion of a legume such as chickpea in the rotation (S + CP − S + SF) reduced wilt incidence (7% fully wilted plants) and the level of inoculum in the soil to about 800 cfu g−1. There was a significant increase in safflower seed yield and biomass yield (883 and 1733 kg ha−1, respectively) in the S + CP − S + SF rotation compared with the S + SF − S + SF rotation (605 and 1323 kg ha−1, respectively). Nitrogen application at rates of 0 to 120 kg N ha−1 had no effect on wilt incidence in safflower, but increased seed and biomass yield significantly. Intercrop rotations (S/PP − S + SF and C/PP − S + SF) were less effective to manage the Fusarium wilt. The Area Under Disease Progress Curve (AUDPC) was almost 10 times higher in the S + SF − S + SF rotation (2842) compared with the S + CP − S + SF rotation (297). Wilt progress throughout the season in all four systems was linear, with significant differences in intercepts and rates of disease progress among cropping systems; the rate of disease progress was significantly greater in the S + SF − S + SF rotation compared with the other three systems, which were similar. There was also a strong linear relationship between wilt incidence and the number of Fusarium propagules in the soil; regressions had the same slope but different intercepts in each system. There was no relationship between wilt incidence and seed yield; nitrogen had the largest effect on yields. A break from safflower cultivation for one year in the post-rainy season by growing chickpea as a sequential crop after sorghum, or as an intercrop with pigeonpea and sorghum, combined with higher rates of nitrogen application to safflower appears to be an effective strategy for reducing Fusarium populations and sustaining safflower yield