Postharvest Diseases, Disorders, and Mineral Content of Organically Grown Apples

Also as part of my M.Sc. thesis (DeEll, 1991), a study was designed to investigate postharvest diseases and disorders, as well as mineral concentrations, of organically and conventionally grown 'McIntosh' and 'Cortland' apples stored at 3^oC in ambient air or in standard CA for 4 and 8 months. The same 14 orchards located in Nova Scotia, as noted above in the previous article, were also used for these evaluations in 1989 and 1990.

More conventionally grown apples were marketable after storage, compared to the organically grown apples (73 versus 59.5%, respectively). This was largely due to higher incidence of apple scab, russetting, and storage rots in the organic apples. The incidence of scab (Venturia inaequalis) was 30 and 10.5% in organically grown 'McIntosh' and 'Cortland', respectively, compared to <1% in conventionally grown apples. The higher incidence of russet (formation of cork resulting from dead epidermal cells) in organic apples (16.5%, versus 5.9% in conventional) was likely caused by the surfactants used as fungicides by the organic apple producers, since surfactants are known to increase russetting. Storage rots were mainly blue mold (Penicillium expansum), gray mold (Botrytis cinerea) and bull's eye rot (Gloeosporium perennans). Organically grown apples either contained more pathogens at harvest or were more susceptible to infection during storage than the conventionally grown apples, as organic apples developed more storage rots (16%, versus 9.8% in conventional). This was likely due to the conventional orchards having a more effective fungicide program.

Organically grown 'McIntosh' stored in ambient air for 8 months had the highest incidence of senescent breakdown (7.2%), while conventionally grown 'McIntosh' stored in CA for 8 months had the highest incidence of internal browning (5.6%). Conventionally grown 'McIntosh' stored in air had a higher incidence of scald than organically grown 'McIntosh' (19 versus 3.3%, respectively). After 4 months of storage in air, organically grown 'McIntosh' had a higher incidence of splitting (4%, versus 1.6% in conventional). Production method did not influence core browning.

Organically grown apples had higher phosphorus (P) and potassium (K) concentrations and lower nitrogen (N) concentrations than conventionally grown apples (Table 1). Production method did not influence calcium (Ca) or magnesium (Mg) concentrations, and there were no significant differences in apple yield per tree or apple weight loss during storage. Many storage disorders that develop in apples are associated with low calcium and phosphorus concentrations, as well as with high nitrogen concentrations. Therefore, the lower nitrogen and higher phosphorus concentrations in organically grown apples could possibly be advantageous in reducing the incidence of storage disorders. However, a direct relationship between mineral concentrations and storage disorders could not be concluded from this study.

For more information and details, please see the following scientific article: DeEll, J.R., and R.K. Prange. 1993. Postharvest physiological disorders, diseases, and mineral concentrations of organically and conventionally grown McIntosh and Cortland apples. Can. J. Plant Sci. 73:223-230.

¹ *, NS = significant at P<0.05 or not significant.