Due to increasing practices of direct seeding in rice under rainfed and irrigated conditions, tolerance to hypoxic or anaerobic condition is becoming an important trait. Considerable genetic diversity is present in our native rice landraces and varieties which is unexploited. Identifying and characterization of contrasting genotypes with acquired tolerance would reveal new donors with improved water logging tolerance for breeding programs which might be suitable for direct seeding systems. Apparently, there is lack of standard screening procedure for anaerobic germination trait in the rice landraces and varieties of Tamil Nadu. The present study designed new methods (Protray and beaker method) to screen for anaerobic germination by assessing simple seed and seedling characters such as germination per cent, greater shoot length by means of coleoptiles elongation and higher vigor index to find the donors for anaerobic stress tolerance. Genotypes differing in their tolerance to anaerobic germination were grouped as: (Highly Tolerant: Anaikomban, Ottadaiyan, Muthuvellai, Rajamannar, CR1009; Moderately tolerant: Improved White Ponni: Highly Susceptible: CO 43 and FR13A). Genotypes showing contrasting behavior to anaerobic stress tolerance were selected to study the physiological basis of anaerobic stress tolerance. The results showed that the tolerant genotypes recorded higher germination per cent, greater shoot length by means of coleoptile elongation and recorded higher vigor index. Further, the tolerant genotypes in this study depicted higher amylase activity, higher Alcohol Dehydrogenase(ADH) activity and lower peroxidase activity highlighting the role of these key enzymes to promote germination and survival under low oxygen conditions.

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