Physiological performance of papaya cultivars under abiotic stress conditions

The wider adaptability of papaya to tropical and subtropical environments has bestowed much significance to its cultivation in Indian subcontinent. However, the abiotic stresses particularly, higher ambient temperature (> 35 degrees C), photosynthetic photon flux density (> 1650 mu molm(-2)s(-1)) and water deficit (< 82 % leaf relative water content) experienced by the plants during summer months (March-May) influence many eco-physiological processes and chlorophyll fluorescence. Net CO2 assimilation (P-n) and stomatal conductance (g(s)) are the key physiological indices, that declined when the plants are exposed to abiotic stresses. Papaya, being a heavy yielder shows significant reduction in fruit and latex yield when there is a marginal reduction in P-n. In the present study, ecophysiological parameters viz., P-n, g(s), transpiration (E) and water use efficiency (P-n vertical bar E) were observed during summer months in selected papaya cultivars. Chlorophyll stability and fluorescence under dark- adapted conditions were also assessed. Excessive light intensity and high temperature or water deficit in the plant system sensitized the physiological processes to slow down, and the data on chlorophyll fluorescence revealed the influence of abiotic stress on photosynthetic processes. The papaya cv. Co7 had higher net CO2 assimilation (P-n = 15.7 mu mol m(-2) s(-1)) coupled with better physiological efficiency as evidenced by higher Fv/Fm (0.802). The stress tolerance was seen with higher Fm/Fo (4.05). The data on g(s), E and WUE were also found more associated to stress tolerance. The results of the present study might aid not only in identifying papaya cultivars those could tolerate summer months, but also in developing crop improvement and management systems.