271 Unidirectional Wind Load Influences Growth, Morphology, and Physiology of Papaya

Abstract

Trade winds are a widespread horticultural consideration throughout the tropics. Growth and productivity of most horticultural crops are not optimal on sites that are exposed to these chronic, unidirectional winds. We conducted four container studies on an exposed site, using clear plastic or screening material to provide three levels of wind exposure: 0%, 36%, or 100%. Two studies were conducted with direct-seeding, such that seedling emergence and early growth were determined for 7 weeks. Two studies were conducted using 8-week-old nursery plants that had been grown in a protected nursery. These plants were transplanted to the experimental site and grown for 6 weeks. Cultivars were `Known You 1', `Sunrise', and `Tainung 2'. Full exposure to wind reduced height up to 32%, increased root: canopy ratio up to 36% and exhibited no influence or slightly reduced stem cross-sectional area when compared with full protection from wind. Net carbon dioxide assimilation (Pn) was measured on intervals of about 2 h throughout several 24-h periods. Although the daily pattern depended on cultivar and date, the general trend was for Pn to be unaffected by wind from early to mid-morning, and for Pn of the unprotected plants to decline below that of the protected plants throughout the rest of the day. The Pn of plants receiving intermediate protection was highly variable among the cultivars and dates in relation to the protected and unprotected plants. Moreover, dark respiration of the unprotected plants was greater than the protected plants throughout the entire nocturnal period. The primary influence of wind on growth of young papaya seedlings was a shift in biomass allocation in favor of the stem base and roots.