Phytophthora agathidicida B.S. Weir, Beever, Pennycook & Bellgard, 2015

Weir, Bevan S., Paderes, Elsa P., Anand, Nitish, Uchida, Janice Y., Pennycook, Shaun R., Bellgard, Stanley E. & Beever, Ross E., 2015, A taxonomic revision of Phytophthora Clade 5 including two new species, Phytophthora agathidicida and P. cocois, Phytotaxa 205 (1), pp. 21-38 : 29-32

Phytophthora agathidicida B.S. Weir, Beever, Pennycook & Bellgard , sp. nov. ( Fig. 5 ) IF550518

= Phytophthora ‘taxon Agathis’ (PTA) Beever et al. (2009), Phytophthoras in Forests and Natural Ecosystems, nom. inval.

Differs from other Phytophthora Clade 5 species in its oogonium ornamentation with occasional and slightly raised protuberances, and its larger mean oospore diameter (31.9 μm). Found in association with Agathis australis . Differs from P. cocois and P. heveae in its DNA barcode sequence of ITS; differs from all other Phytophthora species in its DNA sequence of the ND1 gene.

Etymology:— Latin noun: agathid - (linguistic stem of Agathis ) and - cida (suffix: one who kills)—the Agathis - killer.

Typification: — NEW ZEALAND. Coromandel : Great Barrier Island, from bleeding lesion on trunk of Agathis australis (D. Don) Lindl. ex Loudon , 23 Mar. 2006, R. E. Beever REB316-14, dried culture specimen, holotype PDD 91595 ; ex-holotype living culture preserved in a metabolically inactive state as ICMP 17027 = WPC P15175 .

Description: —The species is homothallic, with isolates forming oogonia quickly (3–4 days) and abundantly on V8A. Oogonia are globose with a mean width of 31.9 μm, and ranging between (22.2–)29.7–32.2–32.7(–45) μm. Oogonium wall ornamentation is mildly stipulate. Oospores nearly fill the oogonia with a mean width of 27.7 μm, and ranging between (19.8–)25–27.5–29.7(–35) μm. Antheridia are amphigynous, globose some with knots at the base. Sporangia are globose to ovoid-ellipsoid, papillate, borne terminally from long thin branched sporangiophores and could be formed via internal proliferation. Sporangia are non-caducous (although some isolates have a somewhat defined septum near the base of the sporangium, see Fig. 5H ). Sporangia have a mean width of 28.4 μm, and ranging between (12.4–)24.8–27.7–32.2(–50) μm, and a mean length of 39.6 μm, and ranging between (14.9–)32.4–37.5– 47.5(–75) μm. Vegetative hyphae are simple, with slight swellings, and lacking chlamydospores in culture. Colony morphology after 7 days was very uniform across the isolates tested on most of the media examined. Colonies are loosely aerial. On 5% clarified V8-juice agar, there is a weakly stellate radial pattern. Minimum growth temperature 6°C; maximum 25°C; optimum 21.5°C. Complete morphometric statistics are presented in Table 3.

Habitat: —Known only from kauri ( Agathis australis ) trees and associated soil in northern (<38°S) New Zealand’s mixed podocarp broad-leaf forest.

Other specimens examined:— NEW ZEALAND. Northland: Trounson Park , trunk lesion of Agathis australis , 23 Mar. 2010, N. Waipara, culture REB 327-41 = ICMP 18404 ; Northland: Trounson Park , soil under A. australis , 23 Mar. 2010, A. Vannini, culture 327-60 = ICMP 18410 ; Northland: Raetea , trunk lesion of A. australis , 23 Mar. 2010, N. Waipara, culture 327-34 = ICMP 18401 ; Northland: Waipoua Forest, near Tane Mahuta , trunk lesion of A. australis , 23 Mar. 2010, N. Waipara, culture 327-47 = ICMP 18407 ; Northland: Waipoua Forest , trunk lesion of A. australis , 23 Mar. 2010, N. Waipara, culture 327-53 = ICMP 18408 ; Coromandel: Great Barrier Island , from wood of A. australis, Mar. 1972 , P. Gadgil, culture ATCC 32256 = FRI 135 = ICMP 16471 ; Coromandel: Great Barrier Island, Kaiarara , from bleeding lesion on trunk of A. australis , 21 May 2009, N. Waipara, culture REB 326-154 = ICMP 18360 ; Auckland: Pakiri , trunk lesion of A. australis , 18 Nov. 2008, R. E. Beever, REB326-1 = ICMP 18244 ; Auckland: Waitakere Ranges, Cascades , from bleeding lesion on trunk of A. australis , 7 Oct. 2009, R. E. Beever, culture REB 326-221 = ICMP 18358 ; Auckland: Huia , soil under A. australis , 23 Mar. 2010, A. Vannini, culture 327-46 = ICMP 18406 .

Disease and management: —The root and collar rot of kauri (colloquially termed “kauri dieback”) is the subject of a long term management response led by the Ministry for Primary Industries, Department of Conservation, regional councils (Auckland, Bay of Plenty, Northland, Waikato), in partnership with the Tangata Whenua Roopu. Delimitation surveys have confirmed impacts upon kauri of all age classes, in forest remnants and plantations, throughout its geographic range. Phytosanitary measures have been put in place in high-access regional parks to control the spread of the pathogen by foot-traffic, and the use of phosphite to control the disease in planta has also commenced.

Figures

FIGURE 5. Phytophthora agathidicida. A. Kauri stand on steep ridge displaying canopy thinning—“little-leaf” syndrome. There is a progressive dieback of the crown in response to parasitism of the cork cambium. B. Bleeding resin (“kauri gum”) associated with collar-rot of lower trunk. The advancing lesion will spread laterally, eventually girdling the tree. C. Diffuse non-patterned, colony morphology ex-holotype ICMP 17027 after 10-days incubation at 20°C in the dark. (L–R) Clarified V8 juice agar, MEA, CMA, and PDA. D. Scanning electron micrograph of ex-holotype ICMP 17027 oogonia. E. Ex-holotype ICMP 17027 oogonia with amphigynous, tapering bases. F. ICMP 16471 oogonia with amphigynous, sub-globose antheridia (image courtesy of M.A. Dick, Scion). G. ICMP 18407 Differentiation of the cytoplasm within papillate sporangia into acid fuchsin stained zoospores. H, I. ICMP 17027 papillate, globose sporangia. Scale bars = 10 μm.