Loquat is a minor fruit tree crop, mainly cultivated for internal markets, currently with nearly 140 ha planted in the V region of Chile. A canker disease has been observed frequently affecting 2 to 4% of trees in small orchards during the most water-demanding months, when plants are water-stressed. Symptoms start at the bases of the trees where a dark brown wood discoloration is observed underneath the bark, along with bark cracking around the cankers. As cankers continue to expand, foliage becomes chlorotic to light brown, and partial to complete defoliation occurs along with dieback of branches and twigs. Crown samples, taken from three symptomatic trees, were collected and thoroughly washed in tap water. A total of 15 small wood pieces (5 mm long segments) selected from the margins of cankers were washed and disinfected with 10% household NaOCl, rinsed with sterile distilled water, and plated on potato-dextrose agar (PDA, DIFCO). Plates were incubated for 5 days at 22°C in darkness. All wood pieces yielded white colonies of coenocytic mycelium. PDA plugs (5 mm diameter) obtained from pure cultures were incubated in sterile distilled water for 4 days at 23°C with a 12-h photoperiod. Sporangia, chlamydospores, and oospores developed; sporangia were ovoid, papillate, terminally borne, with an average length and width of 34.88 (41.57 to 27.76) μm and 29.97 (31.23 to 22.59) μm, respectively, a L/B ratio of 1.29 (1.33 to 1.23), and papilla of 3.39 ± 0.76 μm. Chlamydospores and oospores had an average diameter of 36.77 (46.47 to 27.01) μm and of 24.49 (31.18 to 22.04) μm, respectively. Based on this morphology, these isolates were tentatively identified as Phytophthora cactorum (Lebert & Cohn) Schroeter (Erwin and Ribeiro 1996). To confirm the identification, the internal transcribed spacer (ITS) sequence of ribosomal DNA of isolate 996 was amplified using the ITS6/ITS4 primers and its sequence (GenBank accession no. KX257260) showed 100% identity with P. cactorum strain KJ755110 from GenBank. Pathogenicity studies were conducted on five 1-year-old loquat plants cv. Golden Nugget with P. cactorum isolate 996. Plants were wounded at the crown region and inoculated with a 0.6 cm mycelium plug obtained from PDA plates. Wounded plants (5) served as controls. Plants were cultivated for 4 months under semicontrolled glasshouse conditions (24 to 28°C) with extensive watering during the first month, decreasing the frequency of watering through the other months of culture. Lesion length, stem diameter, and root fresh weight were determined after the conclusion of the experiment. A reddish brown lesion developed around the inoculation site on trunks. Root fresh weights and stem diameters were reduced by 53% and 20%, respectively, in inoculated plants. Inoculated plants died within 3 to 4 months following inoculation. Noninoculated controls remained healthy. P. cactorum was reisolated from 100% of the inoculated plants, fulfilling Koch’s postulates. Thus, P. cactorum may cause trunk and stem rot of loquat, and this is the first report in Chile. P. cactorum has been previously reported in Taiwan and Perú (Hurtado-Gonzales et al. 2009), and also on several fruit crop trees in Chile (Latorre 2004). © 2016, American Phytopathological Society. All rights reserved.
