Physio-Biochemical Heat Stress Responses of Grafted Tomato Plants

Abstract

This research investigated the effects of heat stress on tomato plants grafted onto commercial ‘Maxifort’ and wild relative Solanum pennellii and Solanum peruvianum rootstocks. Heat-tolerant ‘Celebrity’ and heat-sensitive ‘Arkansas Traveler’ cultivars were used as scions, and non-grafted or self-grafted plants were used as controls. After grafting, seedlings were subjected to temperatures set at 38/30°C (16 h day/ 8 h night) for heat treatment and 26/19°C for the control treatment for 21 days in growth chambers. Heated and control plants were established in high tunnel and open field during spring (March - June) and summer (June - September) for each treatment, respectively. In addition, thermotolerance traits of ‘Maxifort’-grafted seedlings were examined by exposing them after 7 days of post-heat stress recovery period (25/18°C) following 14 days of heat stress (38/30°C). S. pennellii and S. peruvianum rootstocks demonstrated adverse effects on shoot growth regardless of the heat stress conditions, possibly due to low graft compatibility with commercial scion cultivars. After field transplanting in clay loam soil, the wild type seedlings had reduced plant growth and fruit yield compared to non-grafted and ‘Maxifort’-grafted plants. Comparing rootstocks, S. pennellii-grafted plants showed the highest susceptibility to heat stress as evident for several physio-biochemical parameters including gas exchange rate, chlorophyll fluorescence and antioxidant enzymes as well as fruit yield. On the other hand, S. peruvianum-grafted plants not only demonstrated less heat sensitivity in fruit yield in the high tunnel environment but also showed significant heat stress-tolerant responses in the growth chamber, such as higher amino acid content, enzymatic and non-enzymatic antioxidant capacity and photosynthetic traits compared to other rootstock treatment groups. ‘Maxifort’-grafted plants also showed morpho-physiological iii improvements than non-grafted and self-grafted plants, including shoot and root growth, protein content and root antioxidant enzyme activities, but most of these benefits were reduced after the recovery period. The experiments also showed no beneficial effects of rootstocks on alleviating the heat sensitivity in ‘Arkansas Traveler’ compared to ‘Celebrity’ cultivars. In conclusion, considering all environments, rootstocks and scions, S. peruvianum was the most effective rootstock to enhance the thermotolerance of scion tomato plants, while S. pennellii was the most susceptible.