Managed environments in the form of well watered and water stressed trials were performed to study the genetic basis of grain yield and stay green in sorghum with the objective of validating previously detected QTL. As variations in phenology and plant height may influence QTL detection for the target traits, QTL for flowering time and plant height were introduced as cofactors in QTL analyses for yield and stay green. All but one of the flowering time QTL were detected near yield and stay green QTL. Similar co-localization was observed for two plant height QTL. QTL analysis for yield, using flowering time/plant height cofactors, led to yield QTL on chromosomes 2, 3, 6, 8 and 10. For stay green, QTL on chromosomes 3, 4, 8 and 10 were not related to differences in flowering time/plant height. The physical positions for markers in QTL regions projected on the sorghum genome suggest that the previously detected plant height QTL, Sb-HT9-1, and Dw2, in addition to the maturity gene, Ma5, had a major confounding impact on the expression of yield and stay green QTL. Co-localization between an apparently novel stay green QTL and a yield QTL on chromosome 3 suggests there is potential for indirect selection based on stay green to improve drought tolerance in sorghum. Our QTL study was carried out with a moderately sized population and spanned a limited geographic range, but still the results strongly emphasize the necessity of corrections for phenology in QTL mapping for drought tolerance traits in sorghum.

In the northern region of the state of Minas Gerais, lack of rainfall limits crop production in the field, which is possible only with irrigation. Agricultural and physiological practices have been intensively searched to overcome drought effects and consequently increase production. In this context, the objective of this study was to characterize morphophysiological and morphoanatomical changes and evaluate the attributes of grain yield under field conditions in two hybrids contrasting for drought tolerance. The experiment was carried out for 2 years (2010 and 2011) and the water deficit was imposed by stopping irrigation for 22 days at the pre-flowering stage. At the end of the stress treatment, leaf and root anatomy and morphophysiological characteristics (leaf water potential, chlorophyll content, percentage of dry leaves, leaf area, stomatal conductance, chlorophyll fluorescence, and anthesis-silking interval) were evaluated. For a better interpretation of tolerance of the hybrids in the evaluated characteristics, an index was used stress index. Hybrid DKB 390 (tolerant) surpassed hybrid BRS 1030 (sensitive) in grain yield. Furthermore, it presented lower percentage of dry leaves, higher flowering synchronization, higher stomatal conductance, and higher Fv/Fm relationship. In the root, DKB 390 showed higher amount of aerenchyma in the cortex, an increase of exodermis width, and numerous metaxylem with smaller diameter. In the leaf, it presented higher number of stomata and smaller distance between the vascular bundles in the leaf blade. The study concluded that significant morphophysiological and morphoanatomical changes, which are related to drought tolerance, occurred in DKB 390, leading to a higher yield in the field.

Drought is a major limitation of maize cultivation in Brazil. Agronomic and physiological practices have been considered to overcome this stress and consequently, increase grain production. The present study investigated the role of abscisic acid (ABA) application in some physiological parameters, in two hybrids with contrasting drought resistance (DKB 390 and BRS 1030 resistant and sensitive, respectively). Contrasting resistance to drought in these genotypes was determined in previous studies. Water deficit was imposed for 10 days at flowering stage, in association with the application of 100 lM abscisic acid on plant canopy. Evaluations of gas exchange, chlorophyll fluorescence, relative water content (RWC), and endogenous ABA content were performed during stress period and also at water recovery (recovery irrigation). A significant functional relationship was observed between RWC and the parameters of gas exchange and fluorescence. During water recovery, no differences were observed among the treatments. DKB 390 presented higher photosynthesis rate (P n) and electron transport rate (ETR) under water stress, while BRS 1030 presented higher intercellular CO 2 concentration (C i) and lower photochemical quenching (qP), non-photochemical quenching (NPQ), and lower F v /F m ratio. DBK 390 was more responsive to ABA application than BRS 1030, presenting higher endogenous ABA content in the first day of stress. DBK 390 with ABA application reduced the effect of water stress through maintenance of water status, an increase of photosynthetic parameters, and a decrease of decline in the functions of photosystem II during stress. Keywords Zea mays L. Á Water stress Á Water status Á Gas exchanges Á Quenching Communicated by J.-H. Liu.

-The maize genebank (GBmaize) preserves nearly 4,000 accessions for conservation and use. The use is however restricted because the accessions do not perform as well as the elite genotypes. This problem can be reduced by prebreeding, i.e., by extending the information on germplasm and introgressing useful alleles. Since irregular rainfall distribution and drought induce maize yield losses, drought tolerance is a main breeding target. In this study, the GBmaize accessions were evaluated for drought tolerance. Environmental factors, genotypes and the respective interactions influence the phenotypic expression. There was however no interaction genotype -irrigation level, so no accessions with different performance under the two water regimes could be identified. The performance of the following accessions was promising for a number

The development of aluminum (Al)-tolerant cultivars is a complementary strategy to overcome the constraints caused by Al toxicity on acid soils and can contribute positively to the food supply for the growing global population. A major Al tolerance quantitative trait locus in maize is controlled by a citrate transporter encoded by ZmMATE1. Our goal was to evaluate the impact of the superior allele of ZmMATE1 on the yield performance of maize lines and hybrids cultivated on acid soils. Near-isogenic lines carrying the superior allele of ZmMATE1, and the recurrent Al-sensitive parent were crossed with elite lines, generating near-isogenic hybrids contrasting for these alleles. All maize genotypes carrying this superior allele were more Al tolerant in nutrient solution than their isogenic counterparts having the ZmMATE1 allele derived from the Al-sensitive parent. These genotypes were cultivated in control and Al stress soils for 2 yr. Aluminum toxicity caused a significant yield reduction of 18.7% for lines and 14.7% for hybrids over the 2 yr. The yield performance of maize genotypes declined in the second year compared with the first year, probably due to water deficiency after the grain-filling stage. The superior allele of ZmMATE1 in maize hybrids conferred yield gains from 21 to 48% compared with the hybrids harboring the alternative allele in the Al stress soil in the first and second years, respectively. As this superior allele is rare in maize and is likely absent in several elite germplasms, molecular breeding based on ZmMATE1 can improve maize yield stability on acid soils.