The infection of apples, cv. Bramley's Seedling, by Nectria galligena Bres

Abstract

S U M M A R YI n laboratory experiments germinating conidia penetrated lenticels and wounds but not the intact surfaces of apples. Date of harvest had no significant effect on the numbers of apples infected with Nectria galligena but the earliest picks rotted first in barn store. Inoculations of unpicked apples resulted in small arrested lesions which only developed into progressive rots after a considerable period in store. Rots developed most quickly from inoculations made between mid-August and mid-September. The size of rot increased with spore number and many inoculations with 10-100 conidia remained as arrested lesions.Arrested lesions developed 10-1 5 days after unripe apples were inoculated and consisted of a zone of fungal colonization surrounded by suberized, necrotic cells in which compounds toxic to both N . galligena and Penicillium expansum were detected. No antifungal compounds were found in progressive rots of mature apples or in healthy apples of any age. Antifungal activity, measured by inhibition of P. expansum, was greatest 15-20 days from inoculation of unripe apples with N . galligena but decreased after a total of 35 days incubation at 20 "C. Much less antifungal activity was produced in ripe or dessert apples.

Induction of Nectria galligena Mutants Resistant to Benzoic Acid and Study of Their Aggressiveness Towards Immature Apples

“…It has been shown (Swinburne, 1971) that N. gaZZigena can cause cell death well in advance of the hyphal tip, so that the diameter of the necrotic zone visible at the surface of the fruit does not necessarily reflect precisely the volume of tissues colonized by the fungus. However, the comparison between the two strains remains valid.…”

The effect of store conditions on the rotting of apples, cv. Bramley's Seedling, by Nectria galligena

“…Artificial inoculations have shown that during the initial stages of infection of apples N.galligena colonizes only a small area of tissue (Swinburne, 1971) within and around which benzoic acid accumulates, which eventually inhibits further fungal growth (Brown & Swinburne,197 I). Presumably natural infections follow a similar pattern, and such infections will remain latent until changes in sugar concentrations or pH within the apple reduce the toxicity of benzoic acid to a point at which the fungus begins to grow and degrade the benzoic acid (Brown & Swinburne, 1 9 7 3~) .…”

“…Efiect of store conditions on the rotting of apples 47 & Swinburne, 1971), and although no causal relationship has been established a likely explanation of the effect of CO, on rotting is that either synthesis of this compound is reduced or degradation accelerated in concentrations greater than 8 yo. Available evidence suggests that CO, inhibits synthesis as the concentration of benzoic acid accumulated in apples treated with proteolytic enzymes is depressed by CO, (Swinburne, 1973).…”

“…Bramley's Seedling, for all experiments were obtained from Jackson's Orchard, Horticultural Centre, Loughgall. Inoculations of harvested apples were made by a cork borer method, using a cork borer of 6 mm diameter (Swinburne, 1971), with an isolate of N.galligena, F7B/67, previously described (Brown & Swinburne, 1973~).…”

Lower Temperatures More Effective than Atmosphere Modification in Controlling Botrytis and Nectria Rots in Stored Apples

“…Conidia of N. galligena are believed to enter apple fruits through lenticels only (Swinburne 1971). Recent work also suggested that conidia may infect fruit via stomata based on the observations that young fruitlets, on which lenticels may not have formed, were most susceptible to N. galligena (Xu and Robinson 2010).…”