ISOLATION AND SELECTION OF BACTERIA AND YEASTS ANTAGONISTIC TO PREHARVEST INFECTION OF AVOCADO BY COLLETOTRICHUM-GLOEOSPORIOIDES

Bacteria and yeasts were isolated from leaves, flowers and fruit of av ocado trees that had not been sprayed with pesticides for several year s. Of the 1050 microorganisms isolated, 37% inhibited mycelial growth of Colletotrichum gloeosporioides on potato dextrose agar. Many of the se organisms also significantly reduced spore germination of the fungu s on cellophane overlaying weak sugars agar and a greater proportion o f yeasts than bacteria were more effective. Some bacteria and yeasts a lso reduced spore germination of the pathogen on avocado leaf disks. T he predominant group of suppressive bacteria was Bacillus spp., and th e antagonistic yeasts included Aureobasidium spp. and a variety of pin k and white colony types. Antibiotic resistant isolates of Bacillus, c arbendazim resistant isolates of two yeasts and an Aureobasidium sp. w ere sprayed on avocado leaves and survived for at least 2 months on th e phylloplane. On the basis of performance in these tests, isolates wi th biocontrol and colonization potential were selected and tested for their capacity to provide disease control on fruit. In repeated tests, several bacteria and yeasts consistently reduced lesion development a nd lesion size on detached avocado fruit when applied prior to inocula ting fruit with the pathogen.