Abstract：In southern China，tomato is susceptible to abnormal high temperature in late spring cultivation and early autumn cultivation．Tomato heat resistance can be improved by grafting cultivation with heat-resistant rootstock．In order to screen the germplasm resources of tomato rootstock with strong heat resistance，this study conducted heat stress treatment on 20 tomato rootstock seeds and seedlings，and evaluated the heat resistance of these rootstock germplasm according to the heat damage phenotype and physiological indexes of seedling growth．The results showed that heat damage had restrained the seed germination of tomato rootstock．Along with the temperature rising，germination rate was significantly reduced．The germination rate of rootstock seeds mostly dropped to below 50% at 34 ℃，below 23% at 37 ℃，and to 0 at 40 ℃．‘G3’，‘N3’ and‘ Q2’ showed strong high temperature resistance（HR）under subhigh temperature（34 ℃/28 ℃）and high temperature（37 ℃/28 ℃）stress，while ‘A1’，‘Q3’，‘Q4’，‘Q5’ and ‘Y4’ showed moderate high temperature resistance（MR）or high temperature resistance（R）．The seedling heat damage index was extremely positively correlated with plant height and MDA content in leaves，and significantly or extreme significantly negatively correlated with SPAD value，stem diameter，fresh weight and dry weight of the whole plant，and free proline contents of leaves．According to the above 7 growth physiological indexes，the heat resistance of these tested germplasm was comprehensively evaluated by subordinate function value method．And the heat resistance of ‘G3’，‘N3’ and ‘Q2’ was ranked from 1-3，Which was consistent with the heat damage indexes of seedlings under sub-high temperature stress．In summary，‘G3’，‘N3’ and ‘Q2’ were strong heat tolerant germplasm resources，and could be used as backbone material for selective breeding of heat-resistant tomato rootstocks．
