Phytophthora acaciivora sp. nov. associated with dying Acacia mangium in Vietnam

Abstract

Acacia mangium plantations account for more than 50 % of the exotic plantations in Vietnam. A new black butt symptom was discovered in 2012, followed by the wilting sign in Acacia seedlings in Tuyen Quang Province. Isolations recovered two Phytophthora species, the well-known Acacia pathogen P. cinnamomi, and an unknown species. The new species is described here as Phytophthora acaciivora sp. nov. Phylogenetically this species resides in clade 2d and is most closely related to P. frigida. Phytophthora acaciivora is a heterothallic species, oospores are aplerotic and antheridia are amphigynous. It produces predominantly elongated ovoid, semi papillate, persistent sporangia, no hyphal swellings and no chlamydospores. Optimum temperature for the growth is 25–30 °C and the maximum temperature is over 37.5 °C. Studies are underway to determine the impact of this new species on Acacia plantations in Vietnam.

New and Emerging Insect Pest and Disease Threats to Forest Plantations in Vietnam

“…A number of studies have recommended improvements to nursery hygiene [27,106]. At present, many small forest nurseries are using unpasteurized soil or growing plants on the ground, and there is a high risk that nurseries may be sources of pathogens such as Phytophthora [58]. Silvicultural measures such as improved pruning techniques [28], limiting damage to roots, stems and branches [28,106,107], and diversification of the tree species composition of plantations [108] are opportunities to limit invasions of pests and diseases.…”

“…For the plant pathogens, the ITS1/ITS4 [54] region was used to help identify Fusarium solani [55], the βT1a/βT1b gene region [56] was used for Ceratocystis manginecans [30], and in Phytophthora the primers DC6 [57] and ITS4 were used [58].…”

“…p% of rot disease is 16-20% and DI is 0.2-0.3. This pathogen was first collected in 2013 in an Acacia mangium nursery in the North East [58]. In recent years P. acaciivora has been reported causing damage to Acacia hybrid and A. mangium nurseries in the same region.…”

Root rot pathogens of Cinnamomum cassia in Vietnam

“…cinnamomi and P . parvispora on Acacia (Burgess et al, 2020; Thu, 2016), and an unidentified species on Casuarina (Hoang et al, 2017). As well as having the broadest range of woody host species in Vietnam, P. cinnamomi also has by far the broadest geographical range, being reported from many regions including Tuyen Quang, Lao Cai, Yen Bai, Thanh Hoa, Ba Ria Vung Tau, Dong Nai, Dac Nong and Quang Tri (Jung et al, 2020; Quynh et al, 2017; Thanh et al, 2004; Thu et al, 2013).…”

“…Phytophthora species reported from these hosts are P. colocasiae, P. infestans, P. mekongensis, P. nicotianae, P. palmivora, P. prodigiosa, and P. tropicalis, as well as several unnamed species (Puglisi et al, 2017;Thanh et al, 2004). Phytophthora species that cause disease in plantations of exotic timber in Vietnam include P. acaciivora, P. cinnamomi and P. parvispora on Acacia (Burgess et al, 2020;Thu, 2016), and an unidentified species on Casuarina (Hoang et al, 2017). As well as having the broadest range of woody host species in Vietnam, P. cinnamomi also has by far the broadest geographical range, being reported from many regions including Tuyen Quang, Lao Cai, Yen Bai, Thanh Hoa, Ba Ria Vung Tau, Dong Nai, Dac Nong and Quang Tri (Jung et al, 2020;Quynh et al, 2017;Thanh et al, 2004;Thu et al, 2013).…”