Cold Temperature Tolerance of Wild Tomato Species

Abstract

Accessions of several wild tomato species [ Lycopersicon hirsutum H. and B. (LA 1363 and LA 1777), L. chilense Dun. (LA 1969 and LA 1971), and Solanum lycopersicoides Dun. (LA 1964)] were examined for cold tolerance and compared to the fast germination of L. esculentum Mill. PI 341988 and to the normal germination of ‘UC82B’. The wild accessions were collected above 3000 m and presumed to be cold-tolerant because of natural habitat. A number of characteristics, including germination, emergence, chlorophyll fluorescence, electrolyte leakage, and plastochron index were used to evaluate chilling resistance. PI 341988 germinated faster than the other genotypes at temperatures above 10°C, but germination of this accession virtually ceased below 10°. The high-altitude accessions continued to germinate, albeit at a reduced rate, below 10°. Growth rates at 12°/6° (day/night) were compared to growth at 24°/18° and were found to be greater in the high-altitude accessions than ‘UC82B’ The reduction in chlorophyll fluorescence when leaf disks were exposed to 1° was less in the high-altitude accessions than in ‘UC82B’, indicating less effect of this temperature on photosynthesis in the wild species. Electrolyte leakage was greater in ‘UC82B’ and LA1777 ( L. hirsutum ) than high-altitude accessions of L. chilense and S. lycopersicoides , but evidence is presented that this method is not reliable in screening for cold tolerance. Crosses were made between ‘UC82B’ and the wild species, and segregating populations were screened using the methods mentioned above. In each population, there were plants that showed cold resistance similar to the wild parent, suggesting the possibility of developing cold-tolerant cultivars.