Articles
MINERAL CONTENT OF ANJOU PEAR FRUIT AFFECTED WITH GREEN BLOTCH
It is usually accompanied by superficial cork (indentations of 1–2 mm in diameter) which usually occurs at the calyx end.
Small corky specks (1 mm in diameter) may sometimes occur under the indentations.
Although the above symptoms do not generally interfere with the dessert quality of the fruit, it sometimes causes heavy fruit rejection in many orchards of the Pacific Northwest due to its unattractiveness.
This disorder may occur six weeks prior to harvest.
There is no published research which fully describes the symptoms, causes or control of green blotch (alfalfa greening). Therefore, in 1976 and 1977, both normal and affected fruit from the same orchards were collected at commercial maturity and stored at 0 °C for mineral analyses.
The fruit were weighed, and rated (1–10) for amount of green stain and superficial cork.
The fruit peel and flesh were analysed for nitrogen by the Kjeldahl method, and phosphorus, potassium, calcium, magnesium, manganese, boron, copper, iron, zinc and aluminium by emission spectrograph.
In 1976, fruit from orchards affected with green blotch (green stain plus superficial cork) had higher levels of nitrogen, phosphorus and potassium in the peel and flesh but lower levels of calcium than normal fruit from the same orchard.
In 1977, the incidence of green stain was significantly correlated with high levels of nitrogen in the peel and flesh whereas the incidence of superficial cork was significantly correlated with low levels of calcium in the peel and flesh.
There are indications that the above imbalances may be related to certain cultural practices and environmental factors such as vigorous rootstocks, high rates of nitrogen fertilizer, pear psylla control, abundant soil moisture, and cool cloudy weather during the latter part of the growing season.
Further research is needed to verify these trends and to provide control measures to reduce the incidence of this disorder.