S03 - Session O2 - Screening morpho-physiological and yield traits for improving grafted tomato transplant performance under abiotic stresses

Authors: Daniel Leskovar *, Desire Djidonou, Samikshya Bhattarai, Chungkeun Lee , Josh Harvey, Kevin Crosby

Increasing global population, climate change, and land use necessitates improved crop production using sustainable methods. However, improving tomato ( Solanum lycopersicum ) production in extreme environments is challenging. Our research team has conducted field, high tunnel and growth chamber tomato studies aimed at 1) screening and selecting thermotolerant scions and rootstocks genotypes based on yield performance, 2) identifying yield stability of scion/rootstock grafted combinations across protected vs. open field environments, and 3) understanding physiological-biochemical trait responses to abiotic stresses. We identified superior thermotolerant responses in 'Truster' and two TAMU rootstocks grafted onto 'Shourouq' scions, and > 10 high yielding cultivars out of 43 tomato scions evaluated. Stability studies comparing commercial and TAMU varietal responses to grafting and environment showed significant GxE interactions for yield components, with over 70% of trait variation deriving from environmental effects. 'HM1823' scions grafted onto 'Multifort' and 'Estamino' rootstocks were the most stable and highest yielding grafting combinations. We identified chlorophyll fluorescence and leaf electrolyte leakage as traits most correlated with total yield in field conditions and heat stress resistance in controlled conditions. In controlled environment grafting experiments, we demonstrated that 'Maxifort' rootstocks improved and reduced contents of various heat stress-responsive enzymes, under optimal and high heat conditions compared to ungrafted controls but did not influence leaf enzyme content. Lastly, we explored the potential of rootstocks of tomato wild relatives ( S. pennellii , S. peruvianum ) to improve scion drought resistance. Wild type grafted scions exhibited improved water potential, leaf relative water content and water use efficiency, net photosynthetic rate, and malondialdehyde content, but lower proline content, compared to 'Multifort' grafted and self-grafted controls. Taken together, our program has identified tomato varieties well-suited to grafting and cultivation in extreme environments as well as physiological traits associated with improved stress resistance, that warrant additional attention in future experimental and breeding endeavors.