Chilling injury in husk tomato leaves as defined by scanning calorimetry

Chilling injury is a common disorder to both tropical and some temperate sp ecies. Husk tomato plants (Physalis ixocarpa L.) were used to study chillin g injury and define temperature ranges at which such injury occurs. Greenho use-grown 'Cerro Gordo' husk tomato plants were used. Samples were taken fr om the first true leaf of 1-month-old plants. Preliminary tests using elect ric conductivity (EC) were carried out to narrow a temperature range. Resul ts indicated that 1 h exposure between 6 and 3 degrees C was enough for lea f tissue to increase ion leakage. Afterwards a differential scanning calori metric assay was done in a range from 15 to 0 degrees C and a scanning rate of 7 degrees C h(-1). To include the effects of period and temperature exp osure, 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 de grees C. Activity recovered (%) was estimated by comparison to activity at 25 degrees C. A highly significant interaction between exposure and tempera ture was found, confirming EC results. On average, exposures above Ih and t emperatures below 6 degrees C caused the lowest recovery in activity as def ined 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 anal ysis of scanning data was done. First by a fourth order polynomial regressi on to fit such data, followed by a second derivative to estimate inflection points associated with slope changes. Such inflections are regarded as cha nges in tissue metabolic activity, and our results clearly narrow such poin t ca. 5 degrees C. Therefore, we can conclude that conditions leading to th e lowest recovery in metabolic activity include exposures to temperatures a t or below 5 degrees C for 1 h or more. (C) 2000 Elsevier Science B.V. All rights reserved.