Identification of QTL for Early Vigor and Stay-Green Conferring Tolerance to Drought in Two Connected Advanced Backcross Populations in Tropical Maize (Zea mays L.)

Abstract

We aimed to identify quantitative trait loci (QTL) for secondary traits related to grain yield (GY) in two BC1F2:3 backcross populations (LPSpop and DTPpop) under well-watered (4 environments; WW) and drought stressed (6; DS) conditions to facilitate breeding efforts towards drought tolerant maize. GY reached 5.6 and 5.8 t/ha under WW in the LPSpop and the DTPpop, respectively. Under DS, grain yield was reduced by 65% (LPSpop) to 59% (DTPpop) relative to WW. GY was strongly associated with the normalized vegetative index (NDVI; r ranging from 0.61 to 0.96) across environmental conditions and with an early flowering under drought stressed conditions (r ranging from -0.18 to -0.25) indicative of the importance of early vigor and drought escape for GY. Out of the 105 detected QTL, 53 were overdominant indicative of strong heterosis. For 14 out of 18 detected vigor QTL, as well as for eight flowering time QTL the trait increasing allele was derived from CML491. Collocations of early vigor QTL with QTL for stay green (bin 2.02, WW, LPSpop; 2.07, DS, DTPpop), the number of ears per plant (bins 2.02, 2.05, WW, LPSpop; 5.02, DS, LPSpop) and GY (bin 2.07, WW, DTPpop; 5.04, WW, LPSpop), reinforce the importance of the observed correlations. LOD scores for early vigor QTL in these bins ranged from 2.2 to 11.25 explaining 4.6 (additivity: +0.28) to 19.9% (additivity: +0.49) of the observed phenotypic variance. A strong flowering QTL was detected in bin 2.06 across populations and environmental conditions explaining 26–31.3% of the observed phenotypic variation (LOD: 13–17; additivity: 0.1–0.6d). Improving drought tolerance while at the same time maintaining yield potential could be achieved by combining alleles conferring early vigor from the recurrent parent with alleles advancing flowering from the donor. Additionally bin 8.06 (DTPpop) harbored a QTL for GY under WW (additivity: 0.27 t/ha) and DS (additivity: 0.58 t/ha). R2 ranged from 0 (DTPpop, WW) to 26.54% (LPSpop, DS) for NDVI, 18.6 (LPSpop, WW) to 42.45% (LPSpop, DS) for anthesis and from 0 (DTPpop, DS) to 24.83% (LPSpop, WW) for GY. Lines out-yielding the best check by 32.5% (DTPpop, WW) to 60% (DTPpop, DS) for all population-by-irrigation treatment combination (except LPSpop, WW) identified are immediately available for the use by breeders.

Identification of Tropical Maize Germplasm with Tolerance to Drought, Nitrogen Deficiency, and Combined Heat and Drought Stresses

“…We evaluated testcrosses rather than lines to account for hybrid vigor or heterosis, which is responsible for a substantial portion of observed tolerance to abiotic stress (Araus et al, 2010;Trachsel et al, 2016). We evaluated testcrosses rather than lines to account for hybrid vigor or heterosis, which is responsible for a substantial portion of observed tolerance to abiotic stress (Araus et al, 2010;Trachsel et al, 2016).…”

Stay-Green and Associated Vegetative Indices to Breed Maize Adapted to Heat and Combined Heat-Drought Stresses

“…Heat stress, however, was consistent throughout the season in both years, as reflected by both the mean daily maximum temperature (37.3 and 37.6 • C for 2014 and 2015, respectively) and the frequency of days with temperatures above the optimum (0.88 and 0.93 for 2014 and 2015, respectively). Compared to experiments carried out by CIMMYT using germplasm of similar genetic background under non-stressed conditions [14,34,35], grain yield was 53% and 82% lower for the experiments carried out in 2014 and 2015, respectively. These large yield reductions as a result of heat and combined heat and drought stress reflect the synergy of both stress factors when they occur together, as reported earlier [8].…”

“…Averaged across experiments, AUC SG was lower in 2015 relative to 2014 as a result of larger stress experienced during 2015, whereas the correlation of AUC SG with grain yield was similar in both years (r g = 0.56 and 0.50 for 2014 and 2015, respectively). Stability across years, correlations with grain yield, and high heritability (h 2 = 0.48-0.93), in addition to importance of stay-green shown in the past [34,35], make AUC SG a useful secondary trait for use in breeding programs in which target environments are characterized by frequent droughts after flowering and are exposed to heat stress. Although all trials in this study were exposed to stress around flowering and grain filling, it is expected that AUC SG is also a useful secondary trait under non-stressed conditions [14,19].…”

Combining Ability and Heterosis of Maize Genotypes under Water Stress during Seed Germination and Seedling Emergence

“…Similar results were found by Guimarães et al (2014), in which PCA was efficient to separate maize hybrids submitted to water stress during the vegetative stage. However, higher specific leaf area under drought conditions may result in further loss of water and, consequently, low foliar efficiency (Trachsel et al, 2016). However, higher specific leaf area under drought conditions may result in further loss of water and, consequently, low foliar efficiency (Trachsel et al, 2016).…”

“…Initial seedling vigor is directly related to the rapid accumulation of dry matter in shoots (Rebolledo et al, 2015). However, higher specific leaf area under drought conditions may result in further loss of water and, consequently, low foliar efficiency (Trachsel et al, 2016). Thus, some characteristics of plants that result in water conservation can be beneficial in drought conditions, such as deep and well-developed root systems (Lopes et al, 2011).…”