Selection of epiphytic yeasts for the biocontrol of Penicillium expansum and Botrytis cinerea in postharvest pears in Patagonia

LUTZ M.C.; LOPES C.A.; SOSA M.C.; SANGORRÍN M.P.

Villa Carlos Paz, Córdoba, Argentina

Congreso; VI Congreso Nacional Sociedad Argentina de Microbiología General; 2009

The valleys of Neuquén and Rio Negro, are the main national producer and exporter ofapples and pears in the country. The “blue mold” caused by <i>Penicillium expansum</i>and the “gray mold” caused by <i>Botrytis cinerea</i> are responsible for the major lossesof fruit in storage. Synthetic fungicides have long been applied for controlling thesemoulds; however, its use is restricted because of the rise of new quality standards for foodand environmental safety. Biological Control using microorganisms adapted to the postharvestenvironment is promising option.With the aim to find potential antagonistic yeasts adapted to the fruits and storageconditions (1-0ºC, 8 months), selective isolation protocols were used. Artificial woundswere caused on pear fruits of cvs Packham´s and D´Anjou obtained from organic andtransition production process. After 150 days, healthy fruit wounds were extracted andmixed in sterile water. Additionally, whole fruits were used for the obtention of epiphiticyeasts. Fifty microliters of each wash water was co-inoculated with a suspension of10³ conidia/mL of <i>P. expansum</i> in new healthy fruits wounds. Fruitswere then incubated at 4°C for 50 days. Aliquots of the same wash waters were used foryeast isolation in GPY and pear juice agar plates at 0ºC. No differences were observedamong the biocontrol percentages obtained with yeast samples from both whole fruit andwounds and from both production processes. Moreover, the same yeast species weredetected in most samples: <i>Aureobasidium pullulans</i>, <i>Crytococcus</i> sp. and<i>Cryptococcus laurentii</i> were the predominant yeasts, while <i>Rodothorulaglutinis</i>,<i>Sporobolomyces roseus</i>,<i>Candida patagonica </i> and <i>Pichiacapsulatta</i> were only found in low proportions.One isolate from each wash waters (only from those exhibiting a biocontrol capacity higherthan 40%) was selected to be tested individually in biocontrol assays against the morevirulent and resistant isolates of both pathogens previously characterized. A total of 34yeast isolates were selected: 10 from fruit surface and 24 from wounded fruit. Twochemical treatments were also included in the study. In all cases, five fruits with onewound in the equatorial zone were inoculated with 20 ul of a suspension of each isolate10⁶ cells/ml and then 10 ul of 10³ or 10⁴conidia/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 activitiesof 100% against <i>P. expansum</i>; however, only eight isolates belonging to<i>Cryptococcus sp.</i>,<i>Cr. laurentii</i>,<i>C. patagonica</i> and <i>P. capsullatta</i>were effective against <i>B. cinerea</i> (with biocontrol from 45 to 66%). Contrarily,chemical fungicides controlled 100% infection by <i>B. cinerea</i> but they were not ableto control <i>P. expansum</i> infections.