A Morpho-physiological Analysis of Diverse Drought Resistant and Sensitive Rice Genotypes to Identify Distinguishing Anatomical Root Phenes

A set of 37 genotypes selected from a survey of over 200 diverse germplasms, for their diverse drought tolerance mechanisms, were analyzed in this study for root physiological traits that are indicative of different drought resistance mechanisms. The genotypes include controls such as the drought sensitive IR64 and Nipponbare, along with the drought resistant Nagina 22 (N22) and Bengal landraces to identify distinguishing phenotypic features of resistant accessions. Anatomical traits studied include total areas of the cross-sections of the stele, cortex, aerenchyma, cortical-cell, and xylem tissue; the number of aerenchyma, xylem vessels, cortical cell file number and size that together describe a number of root phenes, or individual traits that can be analyzed genetically. To make paired comparisons in size using cross-section area the ratio of xylem to stele, stele to cortex, cortex to cross-section, stele to cross-section, cortical cell area to cortex, and aerenchyma to cortical cell area were calculated. Architectural traits were evaluated for root diameter, number of crown roots, lateral root densities, root length and root angles. To study the expression of genes with known function in root traits, the intrinsic gene expression levels of ten candidate genes under optimal growth conditions were estimated by qRT-PCR, which was then used in correlation studies with the data on phenotypic variation. These correlations between gene expression and root phenotype across diverse rice genotypes provide a novel insight to the role of these genes in determining root phenes and their potential function in drought resistance.