ENUMERATION OF BACTERIAL AND YEAST COLONISTS OF APPLE FRUITS AND IDENTIFICATION OF EPIPHYTIC YEASTS ON PEAR FRUITS IN THE PACIFIC-NORTHWESTUNITED-STATES

A procedure for the isolation of diverse culturable microflora for the estimation of the population size of yeasts and bacteria on the surfa ce of pome fruits is described. Maximum numbers of morpholgically dist inct colonies of both yeasts and bacteria were recovered from apple fr uit surfaces when fruits were shaken for 5 min in sterile phosphate bu ffer plus tween, sonicated for 5 min, and aliquots of the buffer plate d onto diluted yeast malt agar and diluted nutrient broth agar, respec tively. The yeast and bacterial populations on the surface of unspraye d Golden Delicious apple fruits were approximately 8.0 x 10(3) and 9.5 x 10(4) colony forming units (cfu) per cm(2), respectively. The densi ties of yeasts on the surface of pear fruits collected from Yakima, Wa , Cascade Locks, Medford, and Hood River, OR, were approximately 7.3 x 10(3), 6.4 x 10(3), 4.1 x 10(3), and 9.9 x 10(2) cfu . cm(-2), respec tively. The highest number of morphologically different yeast isolates were recovered from pear fruits from Cascade Locks and Hood River, Or egon and Yakima, Washington. Aureobasidium pullulans was present on fr uits in all pear orchards sampled whereas Cryptococcus albidus and Rho dotorula glutinis were isolated from 80% of the orchards. Other yeasts colonizing pear fruit surfaces in 20-60% of the orchards were Cryptoc occus infirmo-miniatus, Cryptococcus laurentii, Debaryomyces hansenii, Rhodotorula aurantiaca, R. fujisanensis, R. minuta and Sporobolomyces roseus.