PHYSIOLOGY OF PROLONGED WATERLOGGING STRESS IN SEEDLINGS FROM WILD Carica papaya L. PLANTS COLLECTED AT YUCATAN, MEXICO

Background: Papaya (C. papaya L.) is one of the most economically significant fruit crops in Mexico, as it is the leading global exporter. Although Yucatán is not among the country's top producing states, it holds great importance as the center of origin and distribution for this crop. This explains the current presence of wild papaya populations in unperturbed remote sites within the Yucatan State, which can serve as a genetic source for genetic improvement of current cultivated varieties, as they exhibit a higher level of tolerance to stress factors such as waterlogging caused by climate change. Therefore, it is essential to characterize the physiological response of these wild genotypes to abiotic stress factors. Objective: To characterize the physiological response to prolonged waterlogging stress of wild C. papaya genotypes. Methodology: A system was designed to induce waterlogging in three-months-old C. papaya plants. Plantlets were subjected to waterlogging (100% of roots submerged) for seven days. During the waterlogging stress, the following variables were measured every 24 hours: PSII efficiency (Fv/Fm), photosynthesis, transpiration, stomatal conductance, leaf loss, and petiole binding angle. Data collected from each parameter were analyzed using student t test analysis. Results: Seedlings from wild papaya populations exhibited a rapid response to waterlogging stress of some photosynthetic parameters, and with prolonged exposure, the plants eventually lose several leaves but papaya wild seedlings survive after 7 days of waterlogging (pw). Transpiration and stomatal conductance variables dropped after 24 hours pw and remained low throughout the experiment. Leaf loss began to be noticeable at around 72 hours pw. Additionally, leaf inclination angle exhibited variations starting from 24 hours pw, probably related to epinasty caused by ethylene accumulation. However, Fv/Fm remained high even after 7 d of being waterlogged.  Implications: The results suggest that waterlogging stress has an impact on the physiology of wild papaya plants, however, this rapid response of closing stomata and maintaining photosynthesis could be a mechanism to tolerate this stress. The fact that wild papaya plants were able to maintain high values of Fv/Fm even after 7d of waterlogging, might be associated to waterlogging tolerance, as there are reports that in commercial papaya cultivars, this parameter rapidly decline during the first 24h to values much lower than those found here for wild papaya plants. Conclusions: It is necessary to perform further comparative studies between wild papaya genotypes vs commercial papaya cultivars and assess the performance of wild papaya plantlets during recovery periods once the stress is released.