Characterisation of fungal contaminants affecting preservation properties of pirus communis var. bambinella

Abstract

Fungal pathogens cause premature fruit spoilage of Bambinella, a fruit endemic to the Maltese islands, leading to the loss of fruit during the post-harvest phase. The objective of this study was to isolate, characterise and describe the growth kinetics of fungal contaminants of the Maltese June Pear and to produce a quasi-in-vivo model of Bambinella fruit to understand the growth dynamics of fungi on fruit. In total, 358 fungicide-free fruits were collected over 3 consecutive summers. The isolated fungi were identified and counted morphologically and molecularly. Fungi isolated from Bambinella in 2014 and 2015 included Cladosporium ramotenellum, Penicillium lanosum, Penicillium expansum, Alternaria arborescens and Aspergillus sydowii. All isolates are known to be causative factors of fungal disease in pears at various degrees. Mycelium diameter growth rate studies of the isolates were carried out on Sabouraud Dextrose Agar (SDA) at seven different temperatures ranging from 5- 35°C. The data collected was fitted with the modified Rosso model which showed that the optimal temperatures for growth of all the 5 fungi were in the range of 20- 22°C, while growth was slower at temperatures below 10°C and above 30°C. The order of most to least aggressive fungi was found to be: P. expansum, A. sydowii, P. lanosum, C. ramotenellum and A. arborescens. Spore germination studies were also performed for each isolate on in-house prepared Bambinella medium and the percentage of germination at 20°C was calculated. The rate of germination on Bambinella medium appeared to be similar to the rate of germination on SDA, suggesting that the fruit provides ample nutrients for fungal growth. Understanding the growth dynamics of Bambinella fungal pathogens can help in reducing the use of agricultural fungicides, which have been proven to cause clinical azole resistance in fungal organisms causing invasive infections.