LAUSR

Abstract One of major problems of sub-tropical papaya (Carica papaya L.) cultivation is its susceptibility to low temperature. Here, we report the effect of five low temperature regimes on five C. papaya genotypes and one distant relative cold tolerant species Vasconcellea cundinamarcensis, under complete controlled conditions of National Phytotron Facility. The level of low temperature stress perceived by the seedling plants (8-week-old) was quantified by the quantum efficiency of photosystem II (PSII) by measuring the chlorophyll fluorescence (Fv/Fm). The cold tolerant V. cundinamarcensis reflected the most stable Fv/Fm values irrespective of temperature regimes as compared to the other C. papaya genotypes. Induction of cold treatment increased the membrane lipid peroxidation leading to higher malondialdehyde (MDA) content, which could have reduced the membrane stability index (MSI) of the papaya genotypes, which was most pronounced in the genotype Red Lady with 35.71% reduction at 20/10 °C day/night temperature regimes as compared to control. The results suggested a genotype-specific increase in leaf proline content, while the total chlorophyll content and relative water content (RWC) decreased under low temperature regimes as compared to the control. Our results showed that chlorophyll fluorescence, membrane lipid peroxidation and MSI can be used to determine the extent of damage and screening the potential genotypes for cold stress in cultivated species C. papaya.