Physiology and performance of anaerobic germination tolerant rice varieties under direct seeded cultivation

Good seed germination is prerequisite for direct seeded rice cultivation to withstand anaerobic conditions. In transplanted rice cultivation, major constrains are labour cost and huge water requirements. To overcome these problems, development of rice varieties with anaerobic germination tolerance is mandatory. Hence, the study evaluated 99 rice landraces and 8 varieties of Tamil Nadu for anaerobic germination tolerance. Z score analysis revealed, 14 rice genotypes for good germination percentage and classified eight as moderately tolerant genotypes. These 22 rice germplams were grown under direct seeded condition inside the flooding tank which imitated the field conditions. Results showed that, Karuppukavuni and Kalanamak had good germination percentage along with higher α-amylase content (9.81 mg maltose/min) and longer coleoptiles under waterlogged condition. Contrasting genotypes viz., Karuppukavuni, Kalanamak (highly tolerant); TKM13 and Anna R4 (moderately tolerant) were further dissected for suitability under direct seeded rice cultivation. More synthesis of seed GA in tolerant genotypes (Karuppukavuni-90.57 ng/g and Kalanamak-88.13 ng/g) after 7 days of anoxic stress coupled with higher photosynthetic rate (23.55 μmol CO₂ m⁻² s⁻¹), stomatal conductance (0.34 mol H₂O m⁻² s⁻¹) and chlorophyll fluorescence (0.758) recorded on 45 days after sowing were the traits conferring anaerobic germination tolerance. Finally, two traditional rice landraces namely Karuppukavuni and Kalanamak were identified as donors to be used in crop improvement programmes aimed in developing direct seeded rice varieties.