Biological Control of Phytophthora palmivora Causing Root Rot of Pomelo Using Chaetomium spp.

Abstract

Phytophthora diseases have become a major impediment in the citrus production in Thailand. In this study, an isolate of Phytophthora denominated as PHY02 was proven to be causal pathogen of root rot of Pomelo (Citrus maxima) in Thailand. The isolate PHY02 was morphologically characterized and identified as Phytophthora palmivora based on molecular analysis of an internal transcribed spacer rDNA sequence. This work also presents in vitro evaluations of the capacities of Chaetomium spp. to control the P. palmivora PHY02. As antagonists, Chaetomium globosum CG05, Chaetomium cupreum CC3003, Chaetomium lucknowense CL01 inhibited 50~61% mycelial growth, degraded mycelia and reduced 92~99% sporangial production of P. palmivora PHY02 in bi-culture test after 30 days. Fungal metabolites from Chaetomium spp. were tested against PHY02. Results showed that, methanol extract of C. globosum CG05 expressed strongest inhibitory effects on mycelial growth and sporangium formation of P. palmivora PHY02 with effective dose ED50 values of 26.5 µg/mL and 2.3 µg/mL, respectively. It is interesting that C. lucknowense is reported for the first time as an effective antagonist against a species of Phytophthora.

Efficacy of Chaetomium Species as Biological Control Agents against Phytophthora nicotianae Root Rot in Citrus

“…It is particularly notable that the mycelial growth of P. nicotianae KA1 in this study responded more sensitively to the crude extracts of tested antagonists (ED 50 values of 2.6~101.4 µg/mL) than the mycelial growth of P. palmivora did (ED 50 values of 26.5~2,495 µg/mL), which was reported in our previous study [ 9 ].…”

“…The coiling, penetration, and degradation of P. nicotianae KA1 mycelia in response to treatment with all tested Chaetomium species are typical of mycoparasitism. Similarly, all of the Chaetomium species used in this study have been reported to parasitize hyphae and to grow over and degrade P. palmivora colonies [ 9 ]. Hyphae of P. cinnamomi and P. nicotianae can be parasitized and lysed by C. globosum [ 17 ].…”

“…Meanwhile, C. globosum (CG05), C. lucknowense (CL01), and C. cupreum (CC3003), which have all been proven to control P. palmivora -induced root rot in Citrus sp. [ 9 ], were used as antagonists and to produce antagonistic crude extracts.…”

“…Each of the Chaetomium species was tested for antagonism against Phytophthora sp. KA1 using bi-culture techniques [ 9 ]. A 5-mm-diameter mycelial disc from the active growing area of a 5-day-old colony of Phytophthora sp.…”

“…Some of these fungi can act as antagonists against various plant pathogens through the production of lytic enzymes and metabolites [ 6 , 7 , 8 ]. In our efforts to control Phytophthora root rot in Citrus plants, some potent strains of Chaetomium species have been used as BCAs, and we have recently succeed in controlling P. palmivora in vitro using Chaetomium [ 9 ]. However, the applications of these BCAs for the control of Phytophthora species in citrus production are limited because our inadequate understanding of the mechanisms through which Chaetomium species control Phytophthora species.…”