Morphological and molecular identification of Phytophthora tropicalis causing black pod rot in Mexico

Figures & data

Fig. 1 (Colour online) Isolation of Phytophthora tropicalis from cacao pods. (a) Cacao pod with black rot; (b) internal damage in the cacao pod; (c) cacao pod endodermis infection; and (d) Phytophtora sp. isolate recovered from infected tissue, grown in PDA at 28°C for 5 d

Table 1. Morphological features of Phytophthora tropicalis, Phytophthora palmivora and Phytophthora capsici.

Feature	Phytophthora tropicalis PtCa-14	Phytophthora palmivora P0255^a,b	Phytophthora capsici P3605^c,d
Colony morphology (Growth per day in mm)
PDA	Chrysanthemum shape and appressed 9.3 ± 0.32	With no distinctive pattern. Some colonies with slight chrysanthemum pattern.	With no distinctive pattern to light chrysanthemum pattern
SDA	Chrysanthemum shape and appressed 1.3 ± 0.32	ND	ND
Corn meal agar (CMA)	Sparse aerial hyphae 6.3 ± 0.57	NA	ND
Chocolate Agar	Chrysanthemum shape to petallate 6.43 ± 0.35	NA	ND
V8	Chrysanthemum shape to petallate 6.8 ± 0.41	With no distinctive pattern. Some colonies with slight chrysanthemum pattern.	With no distinctive pattern to light chrysanthemum pattern
Sporangial characteristics
In solid media	Not present	Present	Present
Shape	Papillate, caducous with long often curved pedicels, which presented ovoid, obovoid, pyriform, ellipsoidal, produced in water cultures	Sporangia papillate; caducous whit short pedicel: spherical predominantly ellipsoid with a broad base,	Sporangia are caducous subglobose, ovoid, obovoid, ellipsoid, fusiform, pyriform, to distorted shapes sometimes with tapered bases
Papillation	P, BP	P (conspicuous papillate).	P, SP occasionally with two or three apices
Average length (μm)	36.761 ± 4.45	45.3	32.8–65.8
Average breadth (μm)	23.097 ± 2.92	29.8	17.4–38.7
Sporangiophores characteristics
Shape	Simple sympodial or umbellate whit long pedicels	Simple sympodial are characterized by short.	Unbranched, irregularly branched, and occasionally simple sympodial with short, medium, and long pedicels
Average pedicel length (μm)	130.08 ± 38.23	5	35−138
Average papilla size (μm)	3.39 ± 0.86	ND	ND
Chlamydospores characteristics
Production	Not present in solid media, produced in water cultures globose, terminals or intercalary	Chlamydospores are abundantly produced in agar and water cultures, globose and subglobosas, terminal or intercalary.	Production of chlamydospores in some isolates is conditioned to some extent by the choice of cultural methods (Uchida and Aragaki 1985). Rare or Absent were terminal or intercalary
Chlamydospores size (μm)	24.09 L ± 3.37 26.23 W ± 0.62	16–50 L 16–45 W	28–29 L 22–52 W
Hyphal characteristics
Hyphae pattern	Short torulose	Coralloid torulose	Some isolates in aqueous cultures and are globose, subglobose, produced individually or catenulate
Hyphal swelling	Absent	Present	Present
Hyphae (µm)	6.11 ± 1.00	ND	ND

P, papillate. BP, bipapillate. SP, semipapillate. ND, No data. L, length. W, wide.

Values are the mean of 50 repetitions ± SD.

^aMchau and Coffey (1994); ^b Brasier and Griffin (1979); ^c Mchau and Coffey (1995); ^d Leonian (1922).

Fig. 2 (Colour online) Colony morphology of Phytophthora tropicalis PtCa-14 in different media. (a) PDA; (b) SDA; (c) corn flour; (d) chocolate; and (e) V8. Stellate to petallate colony pattern after the phytopathogen was grown for 5 d at 28°C. No sexual structures were observed

Fig. 3 (Colour online) Phytophthora tropicalis PtCa-14 observed by transmission electronic microscopy. (a) Sporangia showing sympodial with long pedicel and umbellate sporangiophores; (b) attachment of sporangiosphores is in close and simple sympodial arrangement; (c) sporangium typically papillate, ellipsoid; (d) chlamidosporas with base bulbous. Polymorphism sporangia; (e) sporangia limoniforme; (f) ellipsoid sporangia; (g) bi-papillate/tulbinate; (h) elongate; (i) release of zoospores with water; and (j) chlamydospore. Magnification: a, b, 20X; c, d, g, 40X; e, f, h, i, j, 100X

Fig. 4 (Colour online) Phylogenetic analysis of Phytophthora species, comparing the concatenated molecular markers ITS/coxII/TEF-1a/beta tubulin with maximum likelihood using the model GTR+I+G. The bar represents the differences among the sequences. The sequences were gathered from the Phytophthora database (http://www.phytophthoradb.org/)

Fig. 5 (Colour online) Pathogenicity assays of Phytophthora tropicalis PtCa-14 using pear fruits and cacao pods. (a-c) pear fruits, 5 d after inoculation with strain PtCa-14; (d) uninoculated pear fruit; (e) peach fruit, 3 d after inoculation with train PtCa-14; (f) uninoculated peach fruit; (g-i) cacao pods, 7 d after inoculation with strain PtCa-14; (h) uninoculated cacao pod

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