Genetics and genomics of stomatal traits for improvement of abiotic stress tolerance in cereals

In traditional breeding programmes for improving abiotic stress tolerance of cereals , direct selection for grain yield is slow and costly, requiring many years and sites of field trials. Grain yield largely depends on the flag leaf characteristics and functions and is correlated to the ability of the plant to regulate its water content and to synthesize, store and relocate carbohydrates from leaves to grains. Despite the recognition of the importance of the flag leaf in cereals , little is known about genetic control of its cellular structure and development under stress. The leaf stomata cells regulate water loss by transpiration and photosynthetic CO2 uptake in plants. In order to maintain a high photosynthetic rate for higher yield under drought and salinity conditions, it is critical to explore the mechanisms of control of stomata. A major crucial challenge in breeding for abiotic stress tolerance is the knowledge about the physiological and genetic mechanisms that regulate stomatal morphology and development connected to grain yield. Quantitative trait loci (QTL) mapping has been used to identify the genes that are subject to natural variation of stomatal traits in wheat, barley and rice. Over the last decade, several studies have demonstrated the importance of stomatal density and size and their positive association with physiological processes in grain yield. Further, considerable genetic variation exists for stomatal and epidermal cell traits that could be exploited for marker-assisted breeding and used for creation of new effective traits in cereals.