Chilling injury in husk tomato leaves as defined by scanning calorimetry

Chilling injury is a common disorder to both tropical and some temperate species. Husk tomato plants (Physalis ixocarpa L.) were used to study chilling injury and define temperature ranges at which such injury occurs. Greenhouse-grown ‘Cerro Gordo’ husk tomato plants were used. Samples were taken from the first true leaf of 1-month-old plants. Preliminary tests using electric conductivity (EC) were carried out to narrow a temperature range. Results indicated that 1 h exposure between 6 and 3°C was enough for leaf tissue to increase ion leakage. Afterwards a differential scanning calorimetric assay was done in a range from 15 to 0°C and a scanning rate of 7°C h−1. To include the effects of period and temperature exposure, a factorial experiment was carried out with exposures from 0 to 3 h at half an hour intervals, and isotherms were done at 0, 3, 6, 9, and 12°C. Activity recovered (%) was estimated by comparison to activity at 25°C. A highly significant interaction between exposure and temperature was found, confirming EC results. On average, exposures above 1 h and temperatures below 6°C caused the lowest recovery in activity as defined by the algorithm Actrec (%)=(97−16t+2.5T)/(1−0.01t+0.02T) with an R2 of 0.95. Since a clear temperature breaking point was not observed, an analysis of scanning data was done. First by a fourth order polynomial regression to fit such data, followed by a second derivative to estimate inflection points associated with slope changes. Such inflections are regarded as changes in tissue metabolic activity, and our results clearly narrow such point ca. 5°C. Therefore, we can conclude that conditions leading to the lowest recovery in metabolic activity include exposures to temperatures at or below 5°C for 1 h or more.