Genetic analysis of cold tolerance during vegetative growth in tomato, Lycopersicon esculentum Mill.

The genetic basis of cold tolerance (CT) during vegetative growth in tomato was investigated by evaluating plants of a cold-tolerant primitive cultiva r (PI120256) and a cold-sensitive breeding line (UCT5) and their reciprocal F-1, F-2, F-3, BC1P1 and BC1P2 progeny under two temperature regimes of 15 /10 degreesC (cold stress) and 25/15 degreesC (control). Plants were evalua ted for shoot dry weight (DW) under cold stress and by a tolerance index (T I) measured as the ratio of DW under cold stress (DWs) to DW under control (DWc) conditions. Shoot DW was reduced in all genotypes in response to cold stress. However, PI120256 exhibited the highest CT (TI = 90.5%) and UCT5 t he lowest (TI = 38.9%). The TIs of the filial and backcross progeny were in termediate to the parents. Across generations, there was a positive correla tion (r = 0.76, p <0.01) between DWs and DWc indicating that growth under c old stress was influenced by plant vigor. However, the absence of a signifi cant correlation (r=0.47, p >0.05) between DWc and the TI and, in contrast, the presence of a significant correlation (r =0.92, p <0.01) between DWs a nd the TI suggest that plant vigor was not a determining factor in the expr ession of CT in PI120256 and its progeny. Generation means analyses of DWs and TI indicated that the variation among generations was genetically contr olled, with additive effects accounting for most of the variation. There we re no significant dominance effects, and epistatic effects were minor and i nvolved only additive x additive interactions. The results suggest that the inherent CT of PI120256 should be useful for improving CT of commercial cu ltivars of tomato.