Biological Control of Brassicales Ring Spot Disease Caused by Alternaria brassicicola Using Antagonistic Yeasts

T his research investigated the biological control of Ring Spot Disease of Brassicales caused by Alternaria brassicicola, which is an agriculturally important pathogen, using antagonistic yeasts. One hundred fifteen yeasts were isolated from 38 fruits and vegetable leaves. A total of twenty-nine yeast isolates showed the inhibitory activity of A. brassicicola more than a value of 50% by the dual culture method. The result showed that three antagonistic yeast isolates Y107, Y123, and Y16 showed high inhibitory percentages at 75.00%, 73.52%, and 70.33%, respectively. Interestingly, these yeasts inhibited spore germination of A. brassicicola after 12 h within the range of 80.90 to 90.26%. Subsequently, the efficacy of the selected antagonistic yeast against Ring Spots Disease on cabbage seedlings (Brassica oleracea L. var. capitata) and Pak choi (Brassica chinensis L. var. chinensis) was tested in the greenhouse. The result indicated that antagonistic yeast isolate Y107 inhibited the disease at 72.75% and 71.42% in Cabbage seedlings and Pak choi, respectively. However, the efficacy of isolates Y123 and Y16 were not significant in disease inhibition in both Cabbage seedlings (66.67% and 66.08%) and Pak choi (69.83% and 68.92%). Additionally, the antagonistic yeast isolates were identified by phylogenetic analysis of the D1/D2 domain of the large subunit ribosomal RNA (LSU) gene. Yeast isolates Y16 and Y123 were identified to Kurtzmaniella quercitrusa, while isolate Y107 was Hanseniaspora thailandica.