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

LUTZ, C.; LOPES, C.A.; SOSA, C.; SANGORRIN, M.P.

Córdoba, Argentina

Congreso; VI Congreso Argentino 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 Penicillium expansum and the“gray mold” caused by Botrytis cinerea are responsible for the major losses of fruit instorage. 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 andenvironmental safety. Biological Control using microorganisms adapted to the post-harvestenvironment 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 of 103conidia/mL of P. expansum in new healthy fruits wounds. Fruits were then incubated at4°C for 50 days. Aliquots of the same wash waters were used for yeast isolation in GPYand pear juice agar plates at 0ºC. No differences were observed among the biocontrolpercentages obtained with yeast samples from both whole fruit and wounds and from bothproduction processes. Moreover, the same yeast species were detected in most samples:Aureobasidium pullulans, Crytococcus sp. and Cryptococcus laurentii were thepredominant yeasts, while Rodothorula glutinis, Sporobolomyces roseus,Candidapatagonica and Pichia capsulatta 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 104 conidia/ml of the pathogens (minimal infectiveconcentration). Fruits were incubated at 0/-1°C) fo r 100 days. Fifty-six percent of the totaltested isolates showed biocontrol activities of 100% against P. expansum; however, onlyeight isolates belonging to Cryptococcus sp.,Cr. laurentii,C. patagonica and P. capsullattawere effective against B. cinerea (with biocontrol from 45 to 66%). Contrarily, chemicalfungicides controlled 100% infection by B. cinerea but they were not able to control P.expansum infections.