Chilling injury in husk tomato leaves as defined by scanning calorimetry

Abstract

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 R 2 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.