Factors affecting the incidence of neck rot (Botrytis allii Munn) in Pukekohe longkeeper onions

Abstract

Neck rot caused by the fungus Botrytis allii (Munn), is a disease which develops in stored onion crops and is generally considered the major problem affecting storage onions throughout the world.

Growers in New Zealand have become increasingly concerned at heavy losses suffered in recent years. In normal seasons Botrytis rot ranging from 15 to 20 percent is not uncommon after the first two months of storage, while in unfavourable seasons 20sto 50 percent loss may occur in the same period. The last two seasons have been the worst on record with heavy losses occurring in all major growing districts. In 1964 some export lines were rejected by importing countries while in 1965 wholesale prices rose more than tenfold between harvest and late storage, largely through losses caused by Botrytis. Potential markets exist for an increase in New Zealand onion production, but there is an urgent need to improve keeping quality by reduciIl8 the incidence of Botrytis allii.

For many years the main variety grown for storage or export has been Pukekohe Longkeeper. Major commercial interest has centered around why B. allii incidence has increased over recent years. Wilson (1964) suggested that any one or more of the following factors may be involved; changes in cultural practices, an increase in the level of disease inoculum, or changes in the genetical characteristics of the variety through selection.

The present study concerned: (a) methods of predicting storage ability by quantitative tests at harvest on firmness, specific gravity, dry matter and cell size. (b) the effects of fertilizer and irrigation on disease incidence and the reliability of prediction methods.