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- Author or Editor: Sarah A. Weis x
Fruit from five regions worldwide were rated for scald development after four months in 0°C air plus one week at 20°C. Scald incidence was quantitatively related to preharvest temperature conditions and fruit maturity, as measured by starch index. Various low temperature cutoffs were used, and high temperatures over 30°C were also used in the equations. Where data were available light conditions and rainfall were included in the equations. Several models were developed and tested to determine if prediction equations could be of commercial value. The most successful equations explained over 50% of the variation in scald. While they could not predict exact percentages of fruit which would develop scald, equations could predict cases of very high and very low scald, thus identifying fruit requiring the greatest scald control measures and those needing minimal scald control action.
Fifty four trees in a block of `Sturdeespur' Delicious on M.106 rootstock were given soil applications of various combinations of boron and gypsum. Twenty 2.9 to 3.0 inch diameter fruit and 20 unsized randomly chosen fruit were separately weighed and analyzed for Ca, Mg, K, and B concentrations. The coefficient of variation among fruit weights was greater for unsized than sized samples. Analyses of variance showed similar treatment effects for the two sampling methods. However, by using both sized and unsized fruit, effects of treatment on fruit size, and effects of relationships between fruit size and fruit mineral concentration may be separated.
Preharvest environmental conditions apparently determine susceptibility of apples to postharvest scald development. Cool temperature, as hours below 10C, can greatly reduce susceptibility, but greater than 30C appears to enhance it. These effects appear to interact, because a high-temperature episode can cause loss of some low-temperature benefit. Shading of fruit increases their scald susceptibility and preharvest light conditions, along with preharvest rainfall, appear to be factors in scald susceptibility in New England. Fruit maturation reduces scald susceptibility. We are constructing models of contributions of these variables to scald susceptibility of fruit grown under different environmental conditions, and in this the relative importance of these variables is being evaluated.
Cool preharvest temperatures and increasing fruit maturity at harvest reduce poststorage superficial scald incidence. In the absence of cool preharvest temperatures, the role of fruit maturity in determining scald susceptibility becomes greater. Larger amounts of preharvest rainfall also contribute to reduction in scald incidence. Data from `Delicious' grown in a number of locations worldwide will be used to demonstrate this.
Fruit of equal size but varying Ca concentrations were harvested 4 times at weekly intervals for measurements of firmness, titratable acidity, soluble solids and starch, and of Ca, N, P, K, Mg, B, Fe, Mn, Zn, and A1 concentrations. In another experiment, fruit of 3 different sizes were measured generally as above. These measurements were compared with incidences of senescent breakdown, scald and rot after air storage at 0°C, and stepwise multiple linear regression was used to develop equations for predicting apple storage life. Among minerals and maturity indices, Ca, and starch concentrations, respectively, accounted for the most variations in senescent breakdown. Fruit diameter and fruit firmness also accounted for significant amounts of variation in breakdown after storage when fruit size varied. These results show that predictions of storage life based solely on mineral concentrations can be improved by incorporating maturity and size measurements at harvest when these factors are variable.
Forecasting equations for predicting poststorage senescent breakdown from prestorage fruit Ca concentrations were developed for ‘McIntosh’ and ‘Cox's Orange Pippin’ apples using classical linear regression and the Tobit model. A comparison of the 2 regression methods was also made using 2 hypothetical data sets. Where the dependent variable was limited and a significant portion of the data was at the limit, as with ‘McIntosh’ apples, the Tobit model provided a superior forecasting equation. However, in cases where the dependent variable was not limited or it was limited and a significant portion of the data was not at the limit, as with ‘Cox's Orange Pippin’ apples, classical linear regression and the Tobit model produced similar forecasting equations.
Equations were developed that could predict the incidence of senescent breakdown, bitter pit, and decay in ‘Cox's Orange Pippin’ apples and senescent breakdown and bitter pit in ‘Bramley's Seedling’ apples. The parameters used to predict the incidences of disorders included fruit Ca, P, and K concentrations; fruit weight; respiration rate; and fruit maturity. Each disorder and each cultivar had a unique prediction equation. Such equations must be established individually for a disorder, cultivar, and, probably, growing region. Given an appropriate data base, this method seems to have broad applicability as a predictive tool for these disorders. However, core flush and low temperature breakdown could not be predicted using the parameters measured in this study.
A 4-year study compared 4 methods of subsampling ‘McIntosh’ apples for mineral analyses intended for use in predicting postharvest senescent breakdown. Concentrations of Ca, Mg, K, P, and N were determined in outer cortex, whole fruit, and juice in 1979 and 1980, and in outer cortex and cortical plugs in 1981 and 1982. Multiple linear regression equations were developed for each sampling in 1979 and 1981 relating the natural logarithms (In) of Ca and P concentrations and Mg:Ca, K:Ca, and N:Ca ratios to In (breakdown percentage +1). Effectiveness of each equation as a predictor of breakdown during and following storage was tested using data collected the following year. Paired t tests comparing predicted breakdown, using 1979 equations and 1980 mineral analyses, to breakdown observed after storage in 1980-1981 showed that outer cortex- and whole fruit-based predictions were not significantly different from observed breakdown, but juice equations predicted significantly more breakdown than was observed. Correlation coefficients relating actual to predicted breakdown were positive and significant for all 3 methods. In 1981, separate equations were developed to predict fruit breakdown after air and after controlled atmosphere (CA) storage. Paired t tests showed the predicted incidence of breakdown following CA storage was not significantly different from actual breakdown incidences for either outer cortex or cortical plug equations. Breakdown incidence following air storage was less than predicted. In all instances, correlation between actual and predicted breakdown incidence was positive and significant. Outer cortex, whole fruit, and cortical plug analyses showed promise as breakdown predictors, but juice analyses were ineffective.
In a 4-year study of the relationships between Ca, K, P, Mg, and N concentrations in ‘McIntosh’ apples at harvest and the quality of fruit after storage, Ca was the most variable element among samples within seasons and was the element most consistently related to disorders, being negatively correlated with senescent breakdown, rot, and scald. No element was correlated significantly with fruit firmness at harvest or after storage. Susceptibility of orchard lots of fruit to breakdown could be predicted from mineral analyses of fruit 2 weeks before harvest. An arbitrary scoring system incorporating all 5 elements was correct 69% of the time in identifying lots with high or low potentials for breakdown, but the middle range of scores was not closely related to breakdown potential. A regression equation was developed relating only Ca concentration in fruit at harvest with occurrence of breakdown after storage. This equation represented samples either stored in 0°C air for 5 months or in 3° CA storage for 8 to 9 months, and also represented samples taken in 2 different years. This equation was a better predictor of breakdown during storage than was the mineral scoring system, and we propose that such an equation could be used to predict storage potential for ‘McIntosh’ apples.