Root rot in Cinnamomum cassia (L.) J. Presl. in Vietnam: isolation, identification of causal agents and potential biocontrol agents

Nhu Q Dang

Cinnamomum cassia (L.) J. S. Presl. (Synonym C. aromatica), is an important multipurpose tree, especially for developing countries in tropical and subtropical regions. In Vietnam, there are approximately 160 000 hectares of C. cassia plantations. These contribute to national and regional economies and the livelihood of many thousands of rural families. However, temperature and humidity conditions optimal for the growth of C. cassia, are also perfect for disease development. This research was conducted to improve our knowledge of the cinnamon diseases present in the main plantation regions in Vietnam, determine which Phytophthora species are associated with cinnamon root rot in Vietnam, and test whether endophytes from healthy C. cassia trees can protect them from root rot diseases. Cinnamon is cultivated commercially in the following main provinces Yen Bai, Lao Cai, Lai Chau, Bac Kan, Lang Son, Quang Ninh, Thanh Hoa, Nghe An, Quang Nam and Quang Ngai in Vietnam. Diseased trees were surveyed in Yen Bai - the largest region of cinnamon plantations in Vietnam where four sites were visited and 120 samples from nursery and 160 from plantation trees were processed. After visual inspection, grouping broadly on gross morphological features allowed a selection of putative pathogens for further study. Using morphological and molecular techniques, 167 putative pathogens were isolated and identified. Of these, 40 species of pathogenic fungi, oomycetes, and algae were identified. Twenty were new records for cinnamon in Vietnam, and two were new species of Phytophthora. The two new Phytophthora species from Vietnam were named (P. multibullata QN Dang and TI Burgess and P.× vanyenensis QN Dang and TI Burgess), and in addition, a new species from Christmas Island - P. insulinativitatica QN Dang, G Hardy and TI Burgess and two informal taxa: P. sp. germisporangia and P. sp. awatangi from Papua New Guinea were described. In a study of root rot diseases, samples were collected from four different cinnamon nurseries and plantations in four regions (Yen Bai, Quang Ninh, Thanh Hoa, and Quang Nam), and streams in Yen Bai in Vietnam. These yielded 204 isolates, of which 125 were Phytophthora and 79 species from other oomycete genera. The pathogenicity of 24 Phytophthora isolates was assessed from different locations, including 16 P. cinnamomi, four P. × vanyenensis, and two of each of P. multibullata and P. heveae. This study demonstrated that although P. cinnamomi is the most widespread and commonly isolated species, it is not the only significant root pathogen of cinnamon. Other species such as P. heveae, P. multibullata and P. × vanyenensis are also pathogens of cinnamon. One hundred and thirty-four bacterial and fungal endophytes isolated from healthy cinnamon trees were screened by dual culture in the laboratory to assess their ability to inhibit the growth of P. cinnamomi, P. multibullata, and P. × vanyenensis. Based on their performance in vitro, 12 fungal and 5 bacterial endophytes were screened in the glasshouse for their ability to reduce Phytophthora root rot in cinnamon seedlings. Three fungal endophytes Penicillium citrinum, Xylaria curta, and Clonostachys rosea were shown to have the potential to reduce root rot disease and promote plant growth. The expansion of knowledge of the diseases presents in cinnamon nurseries and plantations in Vietnam, and the possibility of using endophytes as biocontrol agents for Phytophthora root rot will be of significant value to commercial producers of cinnamon in Vietnam.

Root rot in Cinnamomum cassia (L.) J. Presl. in Vietnam: isolation, identification of causal agents and potential biocontrol agents

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