Evaluation of different drought stress periods on Hevea brasiliensis grown in ultisols of south eastern Nigereia at nursery stage
As global demand for natural rubber increases, a major challenge for cultivation of rubber plants is their inability to withstand unfavorable environmental conditions in the context of global climate change. Drought remains one of the most biologically demanding and ecologically limiting factors among all environmental constraints. Drought stress can occur at any stage of the growing process, and cause complete loss of crops or serious damage to yield. Field experiments were conducted on the evaluation of different drought stress periods on natural rubber (Hevea brasiliensis) at the Research Farm of National Root Crops Research Institute, (NRCRI) Umudike, South Eastern Nigeria during the 2012 and 2013 cropping season to screen 10 genotypes of rubber seedlings collected from Rubber Research Institute of Nigeria for tolerant to drought conditions, to select tolerant genotypes for development of new clones of natural rubber and to study the relationships between drought tolerant genotypes. The experiments were laid out in a Randomized Complete Block Design (RCBD) in the field using three replications. Thirty rubber seedlings per plot were transplanted from pre-nursery to the main nursery at the spacing of 100 x 30 cm on a well prepared bed. Results obtained in the field over the two years indicated that variations existed in the level of drought tolerance among the genotypes. For agronomic traits, all the traits showed significant differences (P<0.05) among the genotypes. Nig 804, RRIM 600 and GT1 recorded the fastest growth after exposure to 40 days of drought stress while Nig 800, PB5/51 and RRIM 628 recorded the least plant growth across the drought stress periods especially after 40 days of subjection to drought stress and the same trend was also observed in the number of leaves and plant girth recorded among the genotypes in both years. GT1, RRIM 600, PR107 and Nig 804 showed more tolerance to drought conditions from 0 to 40days than the other genotypes and PB5/51, RRIM 628 and Nig 800 were found to be more susceptible to drought when compared with the other genotypes in the field. Life saving irrigation may become an essential farm practice for the survival of these genotypes in the nursery as well as in the field during the dry seasons or periods of drought.
Key words: Hevea genotypes and drought stress periods