Pranee Pattanapipitpaisal and Rillapat Kamlharn

pp. 387 - 393

Abstract

Two hundred and eighty three strains were isolated from rhizoshere-associated soils, from Ubon Ratchathani and
Srisaket province, using Enrichment Media for isolation of Chitinase-producing Actinomycetes agar (EMCA agar). All strains
were screened for chitinolytic activity and sixty eight strains gave significant clear zone on EMCA agar plates. The selected
chitinolytic strains were assayed for in vitro antagonism against Sclerotium rolfsii using cornmeal agar (CMA agar) assay
procedure and the result showed that thirteen isolates have remarkable inhibiting the growth of the fungus and the top five
antagonistic actinomycetes were PACCH 277, PACCH129, PACCH225, PACCH24 and PACCH246, respectively. The result
indicated that these actinomycetes produce chitinase which catalyze the degradation of chitin, resulting in inhibition of S.
rolfsii growth. Their abilities to control the disease development were tested for in vivo biocontrol assay on chilli seedlings.
Two out of thirteen candidate, PACCH24 and PACCH225, antagonists reduced the disease development at 90%. It was
suggested that the ability to inhibit the growth of pathogen in vitro was not related to the disease reduction in vivo. The
strain PACCH24 was further identified as Streptomyces hygroscopicus according to morphological characteristic, cell wall
and cellular sugar analysis and 16S rDNA sequencing. The study implies a novel chitinolytic actinomycete which could be
developed to be a biological agent which would be included as a complement with organic fertilizers in order to control stem
rot disease and promote growth of chilli.