EFFICACY OF 4 SEMI-SELECTIVE MEDIA FOR RECOVERY OF XANTHOMONAS-CAMPESTRIS PV CAMPESTRIS FROM TROPICAL SOILS

Four semi-selective media, CS20 ABN, aesculin-trehalose (ET), Fieldhou se-Sasser (FS), and starch-methionine (SM), were compared for efficacy in recovering Xanthomonas campestris pv. campestris from artificially and naturally infested soils. Recoveries of X. c. campestris from soi ls infested with relatively large populations were similar on the four media. The FS and ET media exhibited higher selectivity against backg round saprophytes, whereas enumeration of X. c. campestris on CS20 ABN or SM was often hampered by the overgrowth of background saprophytes. Among three starch-containing media (CS20 ABN, ET and FS media), the zones of starch hydrolysis, characteristic of colonies of X. c. campes tris, were most distinctive for FS medium. This allowed easier identif ication of the target colonies among numerous non-target colonies in t ests with soil containing smaller numbers of X. c. campestris. Althoug h the starch zone was also distinctive on CS20 ABN, this medium was no t as effective as FS because the starch zones were so large that neigh bouring zones fused with each other and many saprophytes formed coloni es within the zones. Overall, FS was most suitable for soil studies in terms of the consistent recovery of the pathogen, the selectivity aga inst saprophytes, and the differentiation from non-target organisms.