Rootstock-mediated variation in tomato vegetative growth under drought, salinity and soil impedance stresses.

There is increasing interest in using novel rootstocks to confer resistance to abiotic stresses in horticultural species, and to understand the physiological mechanism(s) conferring these responses. The same scion (Solanum lycopersicum 'Boludo F-1', 'Monsanto') was grafted onto 144 different rootstocks: six accessions from S. lycopersicum ('Cerasiforme') and S. pimpinellifolium, selected for drought tolerance (sourced from AVRDC); nine introgression lines from S. lycopersicum x S. pennellii and x S. habrochaites, selected for high root/shoot ratio, salinity and drought tolerances (sourced from TGRC); and a population of 129 recombinant inbred lines (RILs) derived from a salt sensitive genotype of S. lycopersicum var. cerasiforme and a salt tolerant line from S. pimpinellifolium L. (sourced from IVIA). Plants were grown in greenhouses in hydroponics (salinity stress) or soil (soil drying or high soil mechanical impedance) for 2-5 weeks (during the vegetative stage), and shoot fresh weight (SFW) was recorded at the end of each experiment. Although rootstock effects on SFW were related for the soil drying and impedance assays, no relation was found between SFW under salinity and SFW under the other stresses. Indeed, the best rootstocks for drought stress were different to those that were the best for salinity and high soil impedance. For each abiotic stress, some graft combinations had higher SFW (up to 90% more) than the self-grafted commercial cultivar 'Boludo F-1'. The search for genetic factors contributing to this variation will be the objective of a future study.