Host specificity, pathogenicity and virulence of various Penicillium species on deciduous fruit crops

The South African deciduous fruit industry is a major player in the international export markets and is constantly under pressure to ensure blemish free top quality fruit. More complex and extended supply chains are exposing fruit to postharvest pathogens for longer periods of time while the product is in transit and being distributed. Complex fruit trade networks result in a bigger variety of fruit from various countries being retained together potentially exposing the surfaces to an increasing range of pathogens. Numerous Penicillium spp. have been associated with spoilage on different fruit types and if not regularly removed, contribute to heavy inoculum loads in distribution centers. This study investigates pathogenicity and virulence of selected Penicillium spp. isolated from South African and European Union fruit export chains (pear and citrus). Penicillium expansum was the most- and P. crustosum the second most virulent on all the apple (cvs. Royal Gala, Granny Smith, Golden Delicious, Top Red and Cripps Pink) and two of the pear cultivars (Packham’s Triumph, Forelle) tested. Penicillium digitatum was the most virulent on Beurre Bosc, Beurre Hardy and Sempre (Rosemarie) pears and third most virulent on Granny Smith and Cripps Pink. To our knowledge this is the first report where P. digitatum has been described as highly virulent on certain pome fruit cultivars. These cultivars are also the most commonly associated with decay on the export markets resulting in considerable end-market losses. This study provides new information on host specificity and the importance of pathogenic Penicillium spp. isolated from the fruit supply chain environment.