PHYSIOLOGICAL AND MICROCLIMATOLOGICAL CHANGES INDUCED ON TOMATO BY A FLOATING COVER

Abstract

The use of floating covers such as Agribon on tomato (Lycopersicon esculentum Mill.) plants has prevented the growth inhibition observed in this species when planted during the autumn-winter season, in the subtropical lowlands of the State of Morelos, México. In this study, the physiological responses for a cultivar from the State of Guerrero planted in Morelos were evaluated in the same season and submitted to three coverage periods with Agribon (0, 30 and 60 days after transplanting). Also some microclimatic factors were evaluated under those treatments. The results revealed a severe growth inhibition (89 to 97 % in biomass accumulation, and 75 to 88 % in leaf area) recorded in the uncovered plants as compared to the covered ones, which was accompanied by a doubling of leaf blade thickness, and by a 95 % decrease in photosynthetic rate and a loss of 70 to 83 % in transpiration rate. On the other hand, the protection conferred by Agribon increased the fruit yield by 4 to 7 times as compared to unprotected plants. These effects are attributed to the cover´s capacity to retain water vapor, thus increasing the relative humidity and reducing the vapor pressure deficit under the cover. The limiting levels of those environmental factors are estimated in 30 % and 25 mbar, respectively, for tomato plants. The coverage for 60 days promoted a higher biomass accumulation in vegetative structures, whereas the best fruit yield was obtained with the 30-day treatment.