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Mexico City, Mexico

Pinto R.S.,University of Adelaide | Reynolds M.P.,CIMMYT
Theoretical and Applied Genetics | Year: 2015

Key message: QTL related to cooler canopy temperatures are associated with optimal root distribution whereby roots proliferate at depth under drought or near to surface under hot, irrigated conditions.Abstract: Previous research using a bread wheat RIL population of the Seri/Babax cross showed that common QTL were associated with cooler canopies under both drought and heat-stressed conditions. A subset of RIL was grown under water-limited and hot-irrigated field environments to test how cooler canopies are related to root development. Eight sisters and the two parents were used in the study with genotypes grouped as COOL or HOT according to their respective QTL for canopy temperature and previous phenotypic data. Root mass production and residual available soil moisture were measured around anthesis at four depth profiles (from 0 to 120 cm depth). When considering different root profiles, there was a clear interaction of QTL with environment. Under water stress, the COOL genotypes showed a deeper root system allowing the extraction of 35 % more water from the 30–90 cm soil profile. The strategy under heat was to concentrate more roots at the surface, in the 0–60 cm soil layer where water was more available from surface irrigation. Since COOL genotypes showed better agronomic performance, it can be concluded that their QTL are associated with more optimal root distribution in accordance with water availability under the respective stresses. The study demonstrates the importance of root development under both water-limited and hot-irrigated environments, and shows a common genetic basis for adaptation to both stresses that appears to be associated with sensitivity of roots to proliferate where water is available in the soil profile. © 2015, The Author(s).

Pask A.J.D.,CIMMYT | Reynolds M.P.,CIMMYT
Crop Science | Year: 2013

The global wheat (Triticum aestivum L.) growing area under irrigation has risen to approximately 20%. However, future availability and quality of irrigation water is likely to decline due to competition from the needs of the expanding population combined with the effects of climatic change. Recent genetic improvements of the yield of irrigated spring wheat lines reported by CIMMYT have been associated with significantly higher biomass, suggesting that either crops are becoming more water use efficient or are extracting more water from their environment. Water uptake characteristics of eight CIMMYT spring bread wheat cultivars-released during the period between 1950 and 2009-were measured in three contrasting irrigation regimes in northwestern Mexico during 2009/2010 and 2010/2011 and compared with crop growth. Increases in yield and biomass of genotypes were associated with additional water uptake in all environments whilst the water use efficiency for yield and biomass production was unchanged across cultivars but increased as a main effect of reduced water supply. Modern cultivars showed increased ability to extract moisture from deeper soil profiles (60-120 cm) especially during grain filling, associated with higher stomatal conductance in the fully irrigated environment and lower canopy temperatures in all environments. Expression of C isotope discrimination was progressively lower with increasing water stress. Results indicated increased water uptake by roots especially from deeper soil profiles allowing greater water harvest. © © Crop Science Society of America All rights reserved.

The green area displayed by a crop is a good indicator of its photosynthetic capacity, while chlorophyll retention or 'stay-green' is regarded as a key indicator of stress adaptation. Remote-sensing methods were tested to estimate these parameters in diverse wheat genotypes under different growing conditions. Two wheat populations (a diverse set of 294 advanced lines and a recombinant inbred line population of 169 sister lines derived from the cross between Seri and Babax) were grown in Mexico under three environments: drought, heat, and heat combined with drought. In the two populations studied here, a moderate heritable expression of stay-green was found-when the normalized difference vegetation index (NDVI) at physiological maturity was estimated using the regression of NDVI over time from the mid-stages of grain-filling to physiological maturity-and for the rate of senescence during the same period. Under heat and heat combined with drought environments, stay-green calculated as NDVI at physiological maturity and the rate of senescence, showed positive and negative correlations with yield, respectively. Moreover, stay-green calculated as an estimation of NDVI at physiological maturity and the rate of senescence regressed on degree days give an independent measurement of stay-green without the confounding effect of phenology. On average, in both populations under heat and heat combined with drought environments CTgf and stay-green variables accounted for around 30% of yield variability in multiple regression analysis. It is concluded that stay-green traits may provide cumulative effects, together with other traits, to improve adaptation under stress further. © 2012 The Author.

Lopes M.S.,CIMMYT | Reynolds M.P.,CIMMYT
Crop Science | Year: 2011

It has been shown previously that under drought, synthetic hexaploid derived wheat (Triticum aestivum L.) lines outperformed recurrent parents in part due to increased root mass at depth and better water extraction capacity. A group of four elite synthetic derived (SYN-DER) lines and parents was grown under full irrigation and drought conditions to dissect some of the physiological features conferring tolerance to drought. Synthetic derived wheat lines showed on average a 26% yield increase as compared to the parental hexaploid wheats under terminal drought. Different strategies for drought tolerance were observed, including earliness to flowering, greater root mass at depth, greater water extraction capacity, and increased water use efficiency (WUE) at anthesis. Some degree of independence was identified between these traits when comparing SYN-DER lines suggesting that these traits are regulated by different genes. The elite SYN-DER line 'Vorobey' was an important source of improved root mass at depth under drought. We conclude that the use of wild species of wheat has the potential to improve a range of stress-adaptive traits and may permit modern bread wheat to become adapted to a wider range of environments including climate change scenarios. © Crop Science Society of America.

Thierfelder C.,CIMMYT | Mwila M.,Zambia Agriculture Research Institute ZARI | Rusinamhodzi L.,CIMMYT
Soil and Tillage Research | Year: 2012

Sustainable and resilient cropping systems are required in southern Africa to arrest declining soil fertility and offset the future negative effects of climate change. Conservation agriculture (CA) has been proposed as a potential system for improving soil quality and providing stable yields through minimum soil disturbance, surface crop residue retention (mulching) and crop rotations or associations. However, concerns have been raised about the lack of evidence of the benefits of CA for small-scale farmers in southern Africa. This research was carried out in two communities and one on-station site in Zambia to provide more scientific evidence about the effects of CA on soil quality, infiltration, soil moisture and crop performance. Results from Kayowozi showed that maize yields in a direct seeded CA treatment, using cowpea seeded with a dibble stick in full rotation, increased by up to 78% after four cropping seasons in comparison to a conventional control using a ridge and furrow system. At Malende, maize yields for animal traction rip-line seeded and direct seeded plots were, on average, 75% and 91% higher than a conventionally tilled control plot after six cropping seasons. Detailed studies undertaken at the Monze Farmer Training Centre revealed that CA treatments, especially that using cotton in rotation, increased water infiltration and soil moisture. In some years, infiltration was five times higher on CA fields than on those using conventional tillage. Carbon increases were only found at the on-station long-term trial, where, over time, CA plots outperformed conventional practice leading to an overall increase of 12% carbon in the first 30. cm, compared with decreases of 15% in the conventional control. Comparative analyses between the on-farm and on-station trials point to a lack of adequate mulching, which might be the reason for lower carbon at the on-farm sites. We conclude that the effects of CA can build up on different soil types in most systems, but that scaling up and out requires the whole community to be targeted, rather than relying on individual farmers to overcome constraints related to the set-up in rural communities. © 2012 Elsevier B.V.

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