The pathogenicity and host specificity of Penicillium spp. on pome and citrus fruit

Abstract

Penicillium includes some of the most concerning postharvest pathogens of pome and citrus fruit. The pathogenicity and aggressiveness of selected Penicillium spp. previously isolated from South African and European Union fruit export chains were investigated on pome and citrus fruit. New insight and findings were documented in this study. Penicillium digitatum, the most aggressive pathogen on citrus, was also identified the most aggressive on „Beurre Bosc‟, „Beurre Hardy‟ and „Sempre Rosemarie‟ pears. It was also the third most aggressive species on „Granny Smith‟ and „Cripps Pink‟ apples. To our knowledge this is the first report where P. digitatum has been described as an aggressive pathogen on certain pome fruit cultivars. The most concerning species in terms of decay on the evaluated apple cultivars („Royal Gala‟, „Granny Smith‟, „Golden Delicious‟, „Topred‟ and „Cripps Pink‟) and two pear cultivars („Packham‟s Triumph‟ and „Forelle‟) were P. expansum and P. crustosum respectively. New reports concerning spoilage caused by these species were noted on citrus. Penicillium expansum decay and tissue-response lesions were noted on „Nules Clementine‟, „Owari Satsuma‟, „Delta Valencia‟, „Midknight Valencia‟ and „Eureka‟ seeded. Penicillium crustosum caused decay and tissue-response lesions on „Nules Clementine‟, „Nova‟, „Owari Satsuma‟, „Delta Valencia‟, „Cambria Navel‟, „Eureka‟ seeded and „Star Ruby‟. In contrast to more aggressive infections and large surface lesions, some tissue-response lesions sporulated despite their small size, thus allowing the species to complete their life cycle. The second most aggressive species affecting citrus was P. italicum. Pathogenicity of P. solitum was also confirmed on some apple and pear cultivars, although a broader cultivar range and higher level of aggression was observed on pears. Penicillium brevicompactum was only found to be pathogenic on pears. New information regarding host-Penicillium interactions, the potential of cross-infection and the impact each species may have on fruit moving through the market chain was added. Future studies should examine the link between host susceptibility as influenced by maturity and the pathogenic potential of non-host pathogens. Further research is needed to elaborate on the pathogenicity of P. digitatum on pome fruit. Information on market-end losses, the causal agents involved, and inoculum levels and sources may prove beneficial in solving industry problems at the retail-end.