Abstract
Young seedlings of 5 Psidium species grown under water stress and non-stress conditions for about 2 months were frozen at -5°C. In non water-stressed seedlings, dieback was only about 30% of stem length in P. cattleianum var. lucidum and P. guineense and leaf damage was least in P. cattleianum var. lucidum. On the other hand, the stems of P. polycarpum and P. friedrichsthalianum were almost completely killed by freezing. The degrees of stem dieback of two P. guajava cultivars were intermediate. Water stress further decreased the freeze injury of two tolerant species and P. guajava cv. ′Fahrang′, whereas still more than 70% of stem length was killed in the stressed seedlings of two sensitive species.
In young guava (P. guajava) seedlings, the lower the leaf water potential, the greater the tolerance to freezing at-5°C. The treatment with water stress from Oct. and from Dec. effectively increased freeze tolerance, but the treatment from Aug. did not increase it. The season of water stress seems to influence cold hardiness. Water stress had little additional effect on the freeze tolerance of guava seedlings at -7°C.
Sugar and proline concentrations in the leaves were increased by water stress. The involvement of their levels in the increased cold hardiness due to water stress was briefly discussed. Specific differences in cold hardiness of Psidiums could not be explained in terms of differences in the level of either sugar or proline in the leaves among species.
