Search Results
You are looking at 1 - 2 of 2 items for :
- Author or Editor: Peter A. Jolliffe x
- Journal of the American Society for Horticultural Science x
Abstract
Currently, median seed survival period (P50) is a seed storage index estimated from a probit model Y = a + bX, where Y = probit transformed viability proportions and X = in effect seed lifetimes; therefore, P50 = (5 − a)/−b, where 5 is the probit of 50% germination. Since use of the probit model is based on the assumption of normally distributed seed “lifetimes,” our purpose was to eliminate this restriction by means of a new substitute model. Pearl millet [Pennisetum americanum (L.) Schum.] seeds were stored under constant conditions at 21°C and seed moisture contents of 18% or 14%. The seeds stored at 14% moisture content exhibited a statistically normal distribution of lifetimes, while those stored at 18% moisture content underwent rapid viability loss concomitant with a statistically non-normal, positively skewed distribution. Several empirical models other than the probit were used to describe deterioration of both populations; however, we propose a nonlinear four-parameter Weibull distribution for seed lifetimes. A useful property of the function is flexibility in modeling data, which may be normally distributed or positively skewed. Parameter initialization is facilitated by plotting the data on paper with transformed scales. Weibull parameters were used to generate seed mortality rate curves, P50, and a new storage index, M/MV, where M is mode and MV is modal value. Inaccuracy in estimating initial seed mortality (Y intercept) is a negative feature we found associated with most of the empirical models investigated, including the Weibull. Evidence is presented to show the extreme dynamics of the system in the vicinity of the Y intercept, particularly in the case of seeds with 18% moisture content, which had deteriorated after 4 months of storage at 21°C and 90% RH.
Abstract
Sunscald was induced by exposing fruit of tomato (Lycopersicon esculentum mill.) to intense solar radiation; similar injury was caused by radiation from incandescent lamps. Injurious radiation treatments caused fruit temperature to exceed 40°C and altered fruit respiration rates. High air temperatures enhanced injury, but exposure to 0 to 100% O2 concentrations during radiation treatments had little influence on fruit response. Infrared wavelengths (>0.7 µm) were effective in inducing injury. Tissue water may serve as an important absorber of radiant energy. Overheating of the fruit appeared to be the main cause of injury, and storage at different temperatures, photoperiods, or O2 levels did not reverse injury induced by previous irradiation.