The high-altitude form of L. hirsutum L.A. 1363 is a good source of low- temperature seed germination(Patterson et al. Aust. J. Plant Physiol. 5:609-617, 1978) and of the ability to develop under low night temperatures (Patterson & Payne, HortScience 1983, 18:340-341). The association between these two physiological traits was investigated. Successive generations of a 3rd backcross of L. hirsutum to L. esculentum were selected for the ability to grow under night/day temperatures of O deg. C (16 h)/20 deg. C (8 h) until they approached the performance of the L. hirsutum parent. The progeny of these plants were then compared to the L. hirsutum parent for speed of germination at 10 deg. C.
The ability of the cold-resistant selections to germinate as quickly at 10 deg. C as L. hirsutum appeared to have been lost; they required more than 30 days for 50% germination at 10 deg. C, as do most varieties of L. esculentum. An attempt was made to recover the ability for rapid germination at 10 deg. C, however. The first 5% to germinate at 10 deg. C of the cold-resistant selections were grown on, intercrossed, and their progeny compared again with L. hirsutum for germination at 10 deg. C. A proportion of these gave a separable population with rapid germination and the first 5% to germinate were selfed. The progeny of these plants varied in their speed of germination at 10 deg. C, with the progeny of one plant being indistinguishable in low temerature germination from L. hirsutum (15 days for 50% germination at 10 deg. C).
It appears therefore that the two physiological traits for cold resistance derived from L. hirsutum, (germination and development at low temperature) are, at least in part, separately inherited.