Electrolyte Leakage Induced by Chilling in Passiflora Species Tolerant to Different Climates

Abstract

A method was devised to measure chilling sensitivity in a series of species and hybrids of Passiflora having a range of climatic requirements. Leaves from plants which had been grown under 25°C day/18°C night were chilled at 0°C in the dark. At the same time, leakage of electrolyte from thin strips of these leaves was measured at 0°C using conductivity. Two main stages of leakage were found: a relatively slow rate (stage 1) which was followed by a high rate (stage 2), during which most of the electrolyte was lost from the tissue. Potassium was the principal cation lost from the tissue, and its leakage was proportional to that of total electrolyte during the time course of leakage. Stage 2 occurred at about the same time as obvious lesions appeared on whole leaves, and apparently signified lethal chilling injury. When different species were compared, those which had originated from the tropical lowlands (P. maliformis L. and P. edulis Sims forma flavicarpa Degener) were killed in less than 10 days, but those tolerant of cooler climates (P. caerulea L. and P. edulis Sims) survived much longer. From the behaviour of a number of species and hybrids, the rate of leakage during stage 1 was related to the time taken to reach stage 2. Resistance to chilling in the species and hybrids examined was not an all-or-nothing property, but showed a gradual increase in the series: P. edulis forma flavicarpa < P. maliformis < P. cincinnata Masters < P. edulis < P. caerulea, with some hybrids occupying intermediate positions.