Rootstock-mediated physiological and fruit set responses in pepper under heat stress

An increase in high temperature causes major losses in pepper yields, especially in greenhouses when extending the cropping season to late spring or summer in mild climate areas. Grafting has been identified as a possible tool to cope with this abiotic stress. The objective of this study was to analyze the heat stress impact on a sweet pepper variety grafted onto rootstocks with diverse heat stress tolerances to evaluate high-temperature effects on the leaf metabolism, pollen traits and fruit set. To do so, under two greenhouses conditions (28/22 degrees C and 38/ 22 degrees C for control and heat stress, respectively), we compared the variety grafted onto two rootstocks (VA/A57 and VA/A55, tolerant and nontolerant, respectively), and used varieties ungrafted (VA) and self-grafted (VA/VA) as controls. VA/A57 obtained the lowest electrolyte leakage, non-disturbed chlorophyll and carotenoids con-centration values, increased ascorbic acid and phenols concentrations, and no hydrogen peroxide accumulation. These findings indicate better predisposition to overcome heat stress than other plant combinations. Such physiological responses in leaves conferred by the tolerant rootstock coincided with the highest proline con-centration in anthers, and better pollen germination and fruit set compared to the other graft combinations. We conclude that grafting peppers onto a heat stress-tolerant rootstock, such as A57, could overcome negative high-temperature effects better than an ungrafted variety. Moreover, the better physiological performance noted in vegetative parts conferred by a heat stress-tolerant rootstock would also lead to better performance in the reproductive development phase. All this indicates that using tolerant rootstocks in pepper could be an inter-esting method to alleviate heat stress effects on this crop.