Phenotypic and physiological evaluation for drought and salinity stress responses in rice.

Drought and salinity stresses seriously affect rice plant growth and yield. The growing need to improve rice cultivars for drought and salt tolerance requires the development of reproducible screening methods that simulate field conditions, and which provide quantitative data for statistical testing and selection of genotypes with differential responses. In addition, the study of molecular responses to drought and salt stress requires controlled conditions for growth and treatments that are reportable and comparable between different laboratories. Drought, also known as soil water deficit, can result from insufficient moisture for a plant to grow adequately and complete its life cycle. Salinity due to excess sodium chloride affects rice at seedling and flowering stages, reducing root and leaf growth. Both these abiotic stresses can lead to major physiological and biochemical changes such as reduced photosynthesis and reprogramming of gene expression. The methods presented in this chapter can be applied for (a) examination of stress responses in rice vegetative and reproductive tissues to identify and characterize molecular and physiological responses; (b) testing of candidate genes by overexpression or knockout studies evaluated for altered stress response phenotypes; and (c) screening of different genotypes such as accessions or segregating populations for their quantitative responses to abiotic stress parameters.