ENVIRONMENTAL FACTORS CAUSING PHYSIOLOGICAL DISORDERS IN PAPAYA PLANTS

Abstract

Brazil is the world largest grower and exporter of papayas. The climate of the regions where the fruit is cultivated makes it possible to produce, harvest and provide the market with papayas on a year-round basis. The light and environmental conditions, together with modern planting techniques that utilize low levels of agricultural chemicals furnish the market a high quality fruit. Knowledge of how papaya responds to environmental factors provides a scientific basis to develop management strategies to optimize fruit yield and quality. A better understanding of genotypic responses to specific environmental factors will contribute to efficient agricultural zoning and papaya breeding programs. Main physiological disorders affecting papaya are pulp gelification and skin freckles. Magnesium and calcium deficiencies in the pulp of the gelled tissue may be related to the disruption of proton pump functioning. Identifying the mechanisms of the disorder is an active research area in Brazil. Skin freckles (SF) in papaya is a visual disorder that reduces the commercial value. In Brazil, SF incidence was observed in the common cultivars and has been observed in almost all countries with commercial papaya production. Since SF was not associated with low calcium tissue levels in January, we proposed a re-assessment of the concept that the low tissue calcium contents in the January sampling may reduce cell wall stability and membrane integrity facilitating latex leaking. It is proposed that the high calcium contents associated with high temperature and large diurnal temperature fluctuations in September contributed to greater cell wall rigidity facilitating increased turgor pressure resulting in the rupture of the latex vessels and latex leaking. Environmental factors profoundly affect the physiological disorders in papaya and an understanding of their interaction with physiological processes is extremely important for economically sustainable production in the nursery or field plantation. With improved, science-based management, growers will increase papaya fruit productivity and quality.