title: 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.
authors.affiliation: The International Maize and Wheat Improvement Center (CIMMYT), International Apdo. Postal 6-641, 06600 Mexico, D.F. Mexico.
authors.forename: Samuel
authors.initials: S
authors.lastname: Trachsel
authors.affiliation: Shanghai Academy of Agricultural Sciences (SAAS), Postal 201106, Shanghai, China.
authors.forename: Dapeng
authors.initials: D
authors.lastname: Sun
authors.affiliation: The International Maize and Wheat Improvement Center (CIMMYT), International Apdo. Postal 6-641, 06600 Mexico, D.F. Mexico.
authors.forename: Felix M
authors.initials: FM
authors.lastname: SanVicente
authors.affiliation: Shanghai Academy of Agricultural Sciences (SAAS), Postal 201106, Shanghai, China.
authors.forename: Hongjian
authors.initials: H
authors.lastname: Zheng
authors.affiliation: The International Maize and Wheat Improvement Center (CIMMYT), International Apdo. Postal 6-641, 06600 Mexico, D.F. Mexico.
authors.forename: Gary N
authors.initials: GN
authors.lastname: Atlin
authors.affiliation: The International Maize and Wheat Improvement Center (CIMMYT), International Apdo. Postal 6-641, 06600 Mexico, D.F. Mexico.
authors.forename: Edgar Antonio
authors.initials: EA
authors.lastname: Suarez
authors.affiliation: CIMMYT, ICRISAT Campus, Patancheru, Hyderabad, 502 324, India.
authors.forename: Raman
authors.initials: R
authors.lastname: Babu
authors.affiliation: The International Maize and Wheat Improvement Center (CIMMYT), International Apdo. Postal 6-641, 06600 Mexico, D.F. Mexico.
authors.forename: Xuecai
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000222:Adaptation, Physiological; D003433:Crosses, Genetic; D055864:Droughts; D040641:Quantitative Trait Loci; D014329:Tropical Climate; D003313:Zea mays / Q000235:genetics / Q000502:physiology*