Abstract
‘Hamlin’ sweet orange trees on ‘Carrizo’ citrange and ‘Swingle’ citrumelo rootstocks were treated weekly with Stimplex® crop biostimulant (5 mL/L) as either a soil drench or foliar spray. Half of the trees in each treatment were subjected to drought stress (irrigated at 50% of evapotranspiration) while the other half remained fully irrigated (100% ET). Results showed that Stimplex®-treated drought stressed trees on both rootstocks had significantly more total growth than untreated drought stressed trees, but did not achieve the same total growth as well irrigated trees. The maintenance of growth by applications of Stimplex® under drought stress conditions was found to be independent of carbon fixation as photosynthesis was depressed in all drought stress trees regardless of treatment. The Stimplex® effect may have been related to a small, but significant, improvement of plant water relations. However, the magnitude of this change doesn’t appear to fully explain the Stimplex® effect, suggesting that hormonal or other plant metabolite changes may be involved.
