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In higher plants, proline is a candidate biochemical solute, being well known as a stress indicator, especially of water deficit stress. (Yoshiba et al., 1997). The proline biosynthesis pathway in plant s has been well established via glutamate intermediate, using P5CS (∆1 pyrroline- 5 -carboxylate synthetase) to P5C (∆1 -pyrroline-5-carboxylate), subsequently oxidized to the final product proline by P5CR (∆1-pyrroline- 5-carboxylate reductase). Also, proline degradation has been discovered through ProDH (proline dehydrogenase) from proline to P5C (∆1-pyrroline-5- carboxylate) and then P5CDH (∆1-pyrroline-5- carboxylatedehydrogenase) (Verslues and Sharma, 2010). The function of proline in plant defence responses to water deficit stress has been reported, including signal transduction, osmoregulation and antioxidant systems (Dalauney and Verma, 1993).Plant growth and productivity is adversely affected by abiotic stresses induced changes in proline content and polyphenol oxidase enzyme activity. Field experiments were conducted at the National Research Centre for banana, Thiruchirapalli, during the growing season of 2011-2013 to compare the changes in proline content and PPO enzyme activity in twelve main crop and ratoon crop ofbanana cultivars and hybrids in 5th and 7th MAP (Month after Planting) under two levels of irrigation. The lowest reduction in the bunch yield of tolerant banana cultivars and hybrids viz., Karpuravalli, Karpuravalli x PisangJajee, Saba, and Sannachenkathali with the highest increase in proline and PPO enzyme activity was observed in 5th and 7th MAP stage due to 50 per cent depletion in available soil moisture (ASM) of the stress.Not Availabl