Physiological mechanisms responsible for tolerance to, and recuperation from, drought conditions in four different rubber clones

Abstract

Rubber tree cultivation distributed over a wide geographic area. Plant cultivation in these areas, however, generally imposes some type of abiotic stress such as drought. In order to identify the mechanisms responsible for rubber tree tolerance to, and recuperation from, drought conditions, we investigated some physiological characteristics associated with photosynthesis in five-month old plants of four different clones (RRIM 600, IAC 40, PR 255, and GT 1) exposed to progressive soil water deficits and the subsequent reestablishment of irrigation. The plants were submitted to 32 d of imposed drought (32 DIS) followed by soil rehydration for 15 d (15 DSR), totaling 47 d of experimental procedures. Gas exchange, chlorophyll fluorescence, relative water content, water potential (Ψw), cell viability, and photosynthetic pigments, proline, and hydrogen peroxide concentrations were evaluated. Decreasing Ψw resulted in diminishing photosynthetic and transpiration rates, as well as stomatal conductance in the clones. With the exception of the seedlings of clone PR 255, limitations of intracellular CO2 concentrations under water deficit conditions were related to reductions in stomatal conductance. Photochemical processes as well as concentrations of hydrogen peroxide and proline were altered by water deficits in all of the clones, although all of the physiological processes recovered after 15 DSR in all of the clones. Clone PR 255 was the most susceptible to drought, showing photosynthetic electron transport inefficiency and the lowest cell viability. The clones GT 1, IAC 40, and RRIM 600 were found to be superior to clone PR 255 in terms of their growth and oxidative metabolism under water stress conditions, suggesting their greater adequacy for rubber tree cultivation in nontraditional areas experiencing hot, strongly sunny periods with low humidity during the rainy season or winter, and/or irregular rainfall.