FIRST REPORT OF PENICILLIUM ULAIENSE CAUSING WHISKER MOULD ON STORED CITRUS FRUIT IN TUNISIA
W. Rouissi, M. Cherif, A. Ligorio, A. Ippolito, S.M. Sanzani
In a survey carried out in January-July 2014, fruits showing blue and/or green efflorescence, were picked in farms and packinghouses of the northeastern part of Cap Bon peninsula, and brought to the laboratory. On infected fruits P. digitatum and P. italicum coexisted with a morphologically distinct Penicillium spp. This latter was sub-cultured on malt extract agar (MEA) and identified, according to its morphological and cultural characteristics, as P. ulaiense, the causal agent of whisker mould, whose distinctive feature is the ability to form coremia (1-7 mm tall) with white stalks arranged in concentric circles or circular patches (Holmes et al., 1994). Coremia varied in length and shape of stalk and head (e.g. flattened and/or fanlike) and bore sterile tips. A species-specific primer pair (Youssef et al., 2010) amplified a fragment (352 bp) of the intergenic spacer region (IGS) of rDNA from all putative P. ulaiense isolates. For pathogenicity tests, 30 fruits of cv. Valencia late were surface-sterilized with 0.5% sodium hypochlorite, wounded at the equator with a scalpel and the wounds were inoculated with 10 μl of a 105 conidia/ml suspension from a 14-day-old monoconidial culture, or with sterile distilled water (control). Boxes with inoculated and control fruits were stored at 25±2°C and 90-95% relative humidity for 15 days. Control fruit remained symptomless, whereas inoculated fruits developed symptoms identical to the original ones. This is the first report of P. ulaiense causing postharvest whisker mold on stored citrus fruit in Tunisia. It might represent an emerging threat for Tunisian growers and packinghouses, especially those dealing with fruits destined to long- term storage and export.