Effects of Preharvest Weather Conditions on Firmness of 'McIntosh' Apples at Harvest Time
Apple fruit firmness is one of the main attributes indicating fruit quality at harvest. It is affected by numerous factors during the entire growing season. The effects of weather conditions during apple fruit development are often mentioned as a result of their impact on attributes linked to fruit firmness: fruit size, calcium concentration, water content, etc. In this study, the effects of weather conditions on 'McIntosh' apple firmness at harvest time were analyzed. Fruit were harvested at nine sites in Quebec and Ontario over 15 years (1996-2011). For each case, weather parameters were analyzed from full bloom until harvest, either in monthly sub-periods from May until September or in terms of days from full bloom (DFB) until harvest. Regression results highlighted the negative effect of lower air temperature conditions from 31 to 60 DFB, higher air temperature conditions and precipitations from 61 to 90 DFB, and higher temperature conditions from 91 DFB until harvest on 'McIntosh' apple firmness level at harvest. Precipitation from 61 to 90 DFB alone explained 39% of 'McIntosh' apple firmness variation at harvest time. The prediction of apple firmness at harvest time could be helpful for producers to adjust their marketing and storage strategies according to apple quality level.
Comparison of annual firmness levels at harvest in 'McIntosh' apples shows a slow decrease since the 1990s for Ontario and Quebec regions (Fig. 1). However, studies still have to be conducted on multiple comparisons between apple productions before and after the 1990s to detect the main factor explaining this decrease. Simple modifications in orchard management practices, apple tree loads per orchard, crop load, handling techniques, or fruit quality indices used to detect maturity levels might imply modifications of firmness levels at harvest (Harker et al., 1997). It has been suggested that the deterioration in textural properties of apples may be linked with development of more intensive growing systems within the orchard and greater standards for apple caliber, which lowers the overall firmness values at harvest. In England, this downward trend in apple firmness has been shown on 'Cox's Orange Pippin' apples, where between1966 and 1984, firmness after storage has declined by more than 10 Neutons (N)* despite improvement in controlled-atmosphere regimes over the years (Horscroft, 1989). The interpretation of such data remains problematic as a result of variations in methods for measuring firmness and fruit size, storage technologies, and length of storage period as the fruit industry becomes more sophisticated.
Fig. 1. 'McIntosh' apple firmness levels at harvest (N) as a function of years of harvest, for all sites and years of harvest included in this study, with a tendency curve plotted to the data. Note that ~62-72 N = ~14-16 lbs (Text version)
The full paper can be found In HortScience, April 2013.
* 1 lb = 4.5 N
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