Predicting Stages of Sweet Corn (Zea mays L.) Development1

Abstract

The characteristics, limitations, and accuracy of 3 thermal (heat) unit systems were examined. One was a modified polynomial regression system and 2 were base temperature : cutoff temperature systems. All gave about the same minimum coefficient of variation if the proper parameters were used. Distinct differences were noted for the temperature-rate relationships found in 3 periods: planting to the 4th leaf, 4th leaf to silk, and silk to harvest. No consistent advantage was found for maximums alone, minimums alone, or both maximums and minimums as independent variables over the use of the mean daily temperature. Planting dates used alone or in conjunction with thermal units were effective sometimes in reducing error of the predictive system. It is hypothesized that they reflect differences in climatic factors that show a trend during the growing season. The estimation of the 4th leaf stage failed to increase the accuracy of the prediction of silking or harvest dates enough to make the effort practical. The establishment of the 80% silking stage by field observation increased the accuracy of harvest date prediction. The use of the Barger base temperature : cutoff temperature system with appropriate parameters is recommended.

Developmental Responses of Lilium longiflorum Bulblets to Constant or Alternating Temperatures in Vitro1

“…In order to have some basis for comparison of treatments, we chose the number of days in culture at each temperature to equalize the product of incubation temperature x time (days). We found no literature and have no data to support the assumption of a linear relationship between L. longiflorum bulblet development and the product of temperature x time as is assumed by the use of heat units (2). However, we felt that comparisons based on equal heat units were preferable to using equal times at different temperatures.…”

“…Because we chose time in culture at each temperature to equalize heat units, our experiments test the heat-unit model of a linear relationship between development and the product of temperature and time (2). None of the data fit this model.…”

Foliar Emergence from Bulblets of Lilium longiflorum Thunb. as Related to in Vitro Generation Temperatures1

“…Treating fieldgrown bulbs similarly resulted in an increase in extractable growth-promoting substances and overcame shoot dormancy (17). The short duration of these hot-water treatments as well as the observed changes in growth substances do not fit the linear growth-rate by time or physiological maturity phenomena implied by a consideration of heat units (1). Apparently high temperatures influence the physiological system controlling leaf or shoot emergence in the Easter lily.…”

Overcoming Dormancy in Lilium longiflorum Bulblets Produced in Tissue Culture1

“…Tissue isolation and sterile culture techniques have been described previously (18). Time in in vitro culture was based on equal heat units (HU) which were calculated by multiplying the number of days that the culture was maintained by the incubation temperatures, 25° or 30°C (2). Therefore, cultures were incubated at 25° for 112 days (2800 HU) or at 30° for 93 days (2790 HU).…”