THE PREDICTION OF BITTER PIT

There is an obvious advantage to the fruit grower in being able to predict at harvest time the extent to which a consignment of apples is likely to develop bitter pit while in store.
Since bitter pit is related, at least in part, to nutrition it is reasonable to consider leaf or fruit analyses as possible predictors.

Leaf analysis data (nitrogen, phosphorus, potassium, calcium and magnesium in July and August) and fruit analysis data (nitrogen, phosphorus, potassium, calcium and magnesium at harvest) were available, together with postharvest bitter pit assessments, from a number of orchards in south-east England for each of three years.
The fruit was stored in 2–3 per cent oxygen and 1 per cent carbon dioxide at 4°C until early March.
Unfortunately for this investigation, bitter pit levels were low, with a high proportion of zeros and one year’s data had to be discarded on this count.

Correlation coefficients between bitter pit and each leaf or fruit nutrient were calculated for each year.
The ratio (K+Mg)/Ca was also considered as a possible predictor.
In so doing it was noted that potassium levels were aproximately double the magnesium levels and it was questioned whether the inclusion of magnesium was likely to have much numerical effect on the ratio.
Accordingly consideration was given to the simpler ratio K/Ca.
Finally the ratio K/(Mg+Ca) was similarly considered.

Results for one year (and they were similar for both years) are given in Table 64.1.

Table 64.1 CORRELATION COEFIENTS BETWEEN BITTER PIT AND VARIOUS NUTRIENTS

	July leaf	August leaf	Fruit
N	-0.36	-0.27	-0.08
P	0.01	0.21	0.27
K	-0.21	0.22	0.23
Ca	0.13	-0.18	-0.49
Mg	-0.40	-0.10	0.11
(K+Mg)/Ca	-0.26	-0.07	0.56
K/Ca	-0.22	-0.06	0.56
K/(Mg+Ca)			0.50

Symposium on Mineral Nutrition and Fruit Quality of Temperate Zone Fruit Trees

D.A. HOLLAND

https://doi.org/10.17660/ActaHortic.1980.92.66