Phytophthora cocois B.S. Weir, Beever, Pennycook, Bellgard & J.Y. Uchida, 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 : 32-34

Phytophthora cocois B.S. Weir, Beever, Pennycook, Bellgard & J.Y. Uchida , sp. nov. ( Fig. 6 ). IF550519

Differs from other Phytophthora Clade 5 species in oogonium ornamentation with moderately bullate protuberances. Found in association with Cocos nucifera . The DNA barcode sequence of ITS distinguish P. cocois from all other Phytophthora species.

Etymology: —Latin genitive noun: cocois — of Cocos .

Typification: — USA. Hawaii: Kauai, from diseased fruit (husk) of Cocos nucifera L., J. Y. Uchida H1024 , May 1990, dried culture specimen, holotype PDD 103199 ; ex-holotype living culture preserved in a metabolically inactive state as ICMP 16948 .

Description: —The species is homothallic, with oogonia formed abundantly on V8A. Oogonia are globose with a mean width of 26.2 μm, and ranging between (22.3–)24.8–25–27.3(–35) μm. Oogonium wall ornamentation is mildly bullate, and often less ornamented isolated in host tissue. Oospores nearly fill the oogonia with a mean width of 24.2 μm, and ranging between (19.8–)22.3–24.3–25(–29.7). Antheridia are amphigynous, globose and often strongly reflexed (bent). Antheridial length in fresh host tissue is often longer than isolates in culture. Sporangia are globose to ovoid, papillate and non-caducous. Sporangia have a mean width of 25.4 μm, and ranging between (12.4–)22.4–27.2–29(–35) μm, and a mean length of 38.4 μm, and ranging between (18.6–)31.4–39.6–47.1(–50) μm. Colony morphology after 7 days was very uniform across the isolates tested on most of the media examined. Colonies are loosely aerial. Minimum growth temperature 10°C; maximum 30°C; optimum 22°C. Complete morphometric statistics are presented ( Table 3), and Uchida et al. (1992) provide an original description.

Habitat: —Known on diseased coconut ( Cocos nucifera ) from Hawaii, and Côte d’Ivoire. (Probably also on cocoa ( Theobroma cacao L.) from Côte d’Ivoire.)

Other specimens examined:— USA. Hawaii: Kauai, from diseased fruit of Cocos nucifera , coll. J.Y. Uchida culture H1026 = ICMP 16949; CÔTE D’ IVOIRE. Port Bouet, from nut of Cocos nucifera, De Franque-Ville , culture IMI 360596 = ICMP 19685.

Disease and management: —In Hawaii the disease has killed hundreds of coconut trees. Areas with highly conducive environments have lost most of their trees, thus the disease is now less common than in previous decades. Infected trees, which are identified by dead young leaves, cannot be saved by the application of systemic fungicides. Rapid removal and destruction of infected trees and removal of old leaves and petioles is needed to prevent infection of healthy trees ( Uchida 2004). No other palm in Hawaii has been found to be affected by P. cocois and thus other ornamental palms are planted where coconut fruit is not required.

Figures

FIGURE 6. Phytophthora cocois. A. Death of young coconut fronds is the first common symptom of this disease. The young leaves wilt, dry, and are often bent or drooping into the tree canopy. B. Premature loss of fruits is an early sign of disease. In later stages, fruit rots become more common. Infected green fruits have characteristic “green island” black to brown rots that expand irregularly and frequently form green areas surrounded by darkened diseased tissue. C. internal fruit rot. D. Colony morphology of ex-holotype ICMP 16948 after 10-days incubation at 20°C in the dark. (L–R) Clarified V8 juice agar, MEA, CMA, and PDA. E. Scanning electron micrograph of exholotype ICMP 16948 oogonia showing reflexed antheridium. F–G. Ex-holotype ICMP 16948 (F) and ICMP 16949 (G) oogonia showing some reflexed antheridia and mildly bullate oogonium ornamentation. H. ICMP 16948 Differentiation of the cytoplasm within papillate sporangia into zoospores. I, J. ICMP 16949 sporangia shape variation. Scale bars = 10 μm.