Observations on the infection and rotting of apples var. Bramley's Seedliong by Diaporthe perniciosa

Abstract

SUMMARY In N. Ireland Diaporthe perniciosa March is a common inhabitant of the dead wood of Bramley's Seedling apple trees, and its pycnospores, extruded throughout the growing season, are responsible for fruit infections which result in stalk‐end rots during storage. Pycnidia were produced in culture only after exposure to light, near‐UV radiation being particularly favourable. The carbon source in the medium influenced pycnidia production: high yields were obtained where mannitol was used. Only a‐spores germinated under the conditions tested, giving optimum germination at 25 d̀C. in a water film. No germination occurred at less than 98% R.H. Germ tubes and hyphae developed appressoria after germination on artificial surfaces but on apple skin most spores produced only a protuberance from which penetration hyphae developed directly. The cuticle and epidermal cells of apples of all ages were penetrated within a few days of inoculation. Intact surfaces and lenticels were penetrated equally. Susceptibility to further rotting increased with age of the fruit. Apples loaded with spores early in the season rotted later than similar apples loaded just before picking. Polygalacturonase was detected in sap expressed from rotted apples of various ages, the level of activity being correlated with the susceptibility of the fruit.

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

“…and D . perniciosa, which also initiate latent infections during the growing season (Edney, 1956; Ayob & Swinburne, 1970), N . galligena cannot penetrate intact apple fruit cuticle.…”

“…The development of rots in store is affected by the date of infection, depth of entry wound or lenticel and the number of spores applied. Infections immediately before harvest generally cause the earliest rots by G. perennans and D. perniciosa (Edney, 1958; Ayob & Swinburne, 1970) and early picking has been recommended to reduce rotting by Gloeosporium spp. (Rasmussen, 1958).…”

“…The ability of the fungus to penetrate and colonize intact skin, lenticels or wounds was compared using apple segments embedded in paraffin wax in aluminium cups (Ayob & Swinburne, 1970). One segment, from each of twenty apples, was inoculated Infection of apples by Nectria galligena 255 by placing a droplet (0.05 ml containing c. 5000 conidia) on needle punctures 0.3, 0.8, 1-2 or 2.5 mm deep, on the unblemished cuticle between lenticels or directly on to lenticels.…”

“…(Edney, 1956) and Diaporthe perniciosa March. (Ayob & Swinburne, 1970). Immature Bramley's Seedling apples appear to resist progressive rotting by N .…”