Showing papers by "Rana Munns published in 2011"

Major genes for Na+ exclusion, Nax1 and Nax2 (wheat HKT1;4 and HKT1;5), decrease Na+ accumulation in bread wheat leaves under saline and waterlogged conditions

Abstract: Two major genes for Na(+) exclusion in durum wheat, Nax1 and Nax2, that were previously identified as the Na(+) transporters TmHKT1;4-A2 and TmHKT1;5-A, were transferred into bread wheat in order to increase its capacity to restrict the accumulation of Na(+) in leaves. The genes were crossed from tetraploid durum wheat (Triticum turgidum ssp. durum) into hexaploid bread wheat (Triticum aestivum) by interspecific crossing and marker-assisted selection for hexaploid plants containing one or both genes. Nax1 decreased the leaf blade Na(+) concentration by 50%, Nax2 decreased it by 30%, and both genes together decreased it by 60%. The signature phenotype of Nax1, the retention of Na(+) in leaf sheaths resulting in a high Na(+) sheath:blade ratio, was found in the Nax1 lines. This conferred an extra advantage under a combination of waterlogged and saline conditions. The effect of Nax2 on lowering the Na(+) concentration in bread wheat was surprising as this gene is very similar to the TaHKT1;5-D Na(+) transporter already present in bread wheat, putatively at the Kna1 locus. The results indicate that both Nax genes have the potential to improve the salt tolerance of bread wheat.

Plant Adaptations to Salt and Water Stress: Differences and Commonalities

Abstract: Drought and salinity are the most significant abiotic stresses to limit the production of the world's staple food crops. Knowledge about physiological traits, and new molecular tools to identify key genes or to provide molecular markers, has the potential to increase yield over the present limits. The employment of molecular knowledge needs appropriate experimental design and accurate phenotyping. Testing the value of physiological traits and key candidate genes is crucial for progress towards crop improvement on dry and saline land. This chapter reviews specific traits for drought and salinity tolerance, and experimental methods that could distinguish drought and salinity adaptations. The use of new phenomics techniques combined with rapidly advancing molecular tools provides a powerful impetus to identify key traits and genes for stress tolerance, and new methods to introduce these genes into important food crops.

A screening method to identify genetic variation in root growth response to a salinity gradient

Abstract: Salinity as well as drought are increasing problems in agriculture. Durum wheat (Triticum turgidum L. ssp. durum Desf.) is relatively salt sensitive compared with bread wheat (Triticum aestivum L.), and yields poorly on saline soil. Field studies indicate that roots of durum wheat do not proliferate as extensively as bread wheat in saline soil. In order to look for genetic diversity in root growth within durum wheat, a screening method was developed to identify genetic variation in rates of root growth in a saline solution gradient similar to that found in many saline fields. Seedlings were grown in rolls of germination paper in plastic tubes 37 cm tall, with a gradient of salt concentration increasing towards the bottom of the tubes which contained from 50-200 mM NaCl with complete nutrients. Seedlings were grown in the light to the two leaf stage, and transpiration and evaporation were minimized so that the salinity gradient was maintained. An NaCl concentration of 150 mM at the bottom was found suitable to identify genetic variation. This corresponds to a level of salinity in the field that reduces shoot growth by 50% or more. The screen inhibited seminal axile root length more than branch root length in three out of four genotypes, highlighting changes in root system architecture caused by a saline gradient that is genotype dependent. This method can be extended to other species to identify variation in root elongation in response to gradients in salt, nutrients, or toxic elements.

Hordeum marinum-wheat amphiploids maintain higher leaf K+:Na+ and suffer less leaf injury than wheat parents in saline conditions

Abstract: Wheat is only moderately tolerant of salinity and is sensitive to waterlogging. Salt and waterlogging tolerance in wheat might be improved by wide hybridization with more stress tolerant wild relatives in the Triticeae. Wide hybridization between the waterlogging-tolerant halophyte Hordeum marinum and nine wheat cultivars (Triticum spp.) produced amphiploids containing all chromosomes from H. marinum and the wheat parent. The amphiploids had lower Na+, higher K+, and a much higher K+:Na+ ratio in leaves than the respective wheat parent, and several also had less leaf injury, when grown in saline conditions. Growth responses of two amphiploids (one with a bread wheat cv. Westonia and one with a durum wheat cv. Tamaroi) were studied in a range of salinity and waterlogging treatments over 25 d. Growth of the H90-Tamaroi amphiploid was greater than Tamaroi at 100–300 mM NaCl, whereas the H90-Westonia amphiploid was not different from Westonia, although both amphiploids had higher leaf K+:Na+ ratios. Under a combination of waterlogging and salinity, both amphiploids were superior to the wheat parents. This study demonstrates the potential of genes from H. marinum to improve the salt and waterlogging tolerance of wheat.