Pathogenic Penicillium spp. on Apple and Pear

Abstract

Numerous Penicillium spp. have been associated with postharvest fruit spoilage. This study investigates pathogenicity and aggressiveness of selected Penicillium spp. previously isolated from South African and European Union fruit export chains. Penicillium expansum was the most-and P.crustosum the second most aggressive on all apple cultivars (Royal Gala, Granny Smith, Golden Delicious, Topred and Cripps Pink) and two pear cultivars (Packham"s Triumph and Forelle) tested.Penicillium digitatum was the most aggressive on Beurre Bosc, Beurre Hardy and Sempre (Rosemarie) pear cultivars and the third most aggressive on Granny Smith and Cripps Pink apple cultivars. To our knowledge this is the first report where P. digitatum has been described as aggressive 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. Penicillium brevicompactum was detected pathogenic on pears, but was not further evaluated in the study.Penicillium solitum was observed more pathogenic (broader cultivar range and higher disease incidence) and aggressive (larger lesions) on pear cultivars than on apple cultivars. This study provides new information on host specificity and the importance of pathogenic Penicillium spp.isolated from various environments in the shipping and marketing channels. INTRODUCTIONThe South African pome fruit industry is economically important in terms of global trade. The industry produces over 1.1 million tons of fruit of which 46.6% are exported as fresh produce, earning close to $431.6 million in net export realization in 2012 (9). Postharvest losses have been reported as high as 50% in developing countries (5,21,26). Significant losses have been attributed to decay caused by Penicillium spp. (12,14,16,20,22,32).A report by Sanderson and Spotts (22) indicates that numerous Penicillium spp. naturally inhabit pome fruit environments (packinghouses and storage facilities) and are prominent on fruit bins. Of these species, P. expansum Link ex Gray, P. crustosum Thom, and P. solitum Westling have been described as the most important on apples (Malus domestica L. Borkh.) and pears (Pyrus communis L.) in causing decay (14,22,32). Other pathogenic species reported include P. aurantiogriseum Dierckx., P. brevicompactum Dierckx., P.commune Thom, P. griseofulvum Dierckx., P. verrucosum, Dierckx. and P. carneum Frisvad (2,12,16,18,23). However, these species have less often been associated with decay of pome fruit.Several other Penicillium spp. isolated from pome fruit environments (2,22) are best known as pathogens on other fruit crops. These include P. digitatum (Pers.:Fr.) Sacc. on citrus (8) and P. glabrum (Wehmer) Westling on pomegranates (3). Complex fruit trade networks result in a large variety of fruit from different countries being retained together in storage or holding facilities (34). In addition, citrus and pome fruit are sometimes re-packed in the same facility to remove decaying fruit. This practice can p...

Postharvest decay of nectarine and plum caused by Penicillium spp.

“…The isolates were the same as used by Louw and Korsten (2014). Isolates of P. expansum (P.eC and P.eP), P. crustosum (P.cC and P.cP), Penicillium solitum Westling (P.sC and P.sP) and P. digitatum (P.dC and P.dP) were selected from each chain (the last letter of the isolate code denotes the chain: C, citrus; P, pear).…”

“…Handling and inoculation of fruit for trials were similar as described by Louw and Korsten (2014;. Pathogenicity was determined by inoculating (6 x 10 4 conidia/ml) five 'Sunburst' nectarines and five 'ARC PR-4' ('African Rose') (2011/12) plums with each Penicillium spp.…”

“…Lemon and pear fruit were added to compare infection of nectarine with that of alternative hosts. Some of these host-pathogen associations were recently reported (Louw and Korsten 2014; and potentially serve as cross-contamination sources for stone fruit in the fresh produce chain.…”

“…Cultures were purified and observed for phenotypic similarities. A single culture from any of the two to three fruit was preserved (water -and cryo-preservation) and identified by PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) assay and sequencing, as described by Louw and Korsten (2014;. PCR-RFLP allowed for molecular grouping of the Penicillium spp.…”

“…These factors create an environment at risk to inoculum build-up, crosscontamination, cross-infection and ultimately losses. Risk can be higher at the end of a season (higher inoculum loads) and end of the fresh produce chain (increased susceptibility of older/riper fruit) so that even non-host pathogens can become a threat (Vilanova et al 2012a;2012b;2014;Louw and Korsten 2014;. For instance, when citrus increase inoculum levels of P. digitatum in a facility where pears are handled, P. digitatum can reach the pears via aerial dispersal or other means of cross-contamination, cause decay and contribute to losses (Louw and Korsten 2014;.…”