SELECTION OF EPIPHYTIC YEASTS FOR THE BIOCONTROL OF Penicillium expansum AND Botrytis cinerea IN POSTHARVEST PEARS IN PATAGONIA

MARIA CECILIA LUTZ; CHRISTIAN LOPES; MARIA CRISTINA SOSA; MARCELA SANGORRIN

Villa Carlos Paz, Cordoba, Argentina

Congreso; VI Congreso Argentino de Microbiología General; 2009

Sociedad Argentina de Microbiología General

The valleys of Neuquén and Rio Negro, are the main national producer and exporter of apples and pears in the country. The “blue mold” caused by Penicillium expansum and the “gray mold” caused by Botrytis cinerea are responsible for the major losses of fruit in storage. Synthetic fungicides have long been applied for controlling these moulds; however, its use is restricted because of the rise of new quality standards for food and environmental safety. Biological Control using microorganisms adapted to the post-harvest environment is promising option. With the aim to find potential antagonistic yeasts adapted to the fruits and storage conditions (1-0ºC, 8 months), selective isolation protocols were used. Artificial wounds were caused on pear fruits of cvs Packham´s and D´Anjou obtained from organic and transition production process. After 150 days, healthy fruit wounds were extracted and mixed in sterile water. Additionally, whole fruits were used for the obtention of epiphytic yeasts. Fifty microliters of each wash water was co-inoculated with a suspension of 103 conidia/mL of P. expansum in new healthy fruits wounds. Fruits were then incubated at 4°C for 50 days. Aliquots of the same wash waters were used for yeast isolation in GPY and pear juice agar plates at 0ºC. No differences were observed among the biocontrol percentages obtained with yeast samples from both whole fruit and wounds and from both production processes. Moreover, the same yeast species were detected in most samples: Aureobasidium pullulans, Crytococcus sp. and Cryptococcus laurentii were the predominant yeasts, while Rodothorula glutinis,Sporobolomyces roseus,Candida patagonica and Pichia capsulatta were only found in low proportions. One isolate from each wash waters (only from those exhibiting a biocontrol capacity higher than 40%) was selected to be tested individually in biocontrol assays against the more virulent and resistant isolates of both pathogens previously characterized. A total of 34 yeast isolates were selected: 10 from fruit surface and 24 from wounded fruit. Two chemical treatments were also included in the study. In all cases, five fruits with one wound in the equatorial zone were inoculated with 20 ul of a suspension of each isolate 106 cells/ml and then 10 ul of 103 or 104 conidia/ml of the pathogens (minimal infective concentration). Fruits were incubated at 0/-1°C) for 100 days. Fifty-six percent of the total tested isolates showed biocontrol activities of 100% against P. expansum; however, only eight isolates belonging to Cryptococcus sp.,Cr. laurentii,C. patagonica and P. capsullatta were effective against B. cinerea (with biocontrol from 45 to 66%). Contrarily, chemical fungicides controlled 100% infection by B. cinerea but they were not able to control P. expansum infections.