ABSTRACT
Different Phytophthora species are responsible for causing one of the most important diseases of cacao, the black pod rot, and P. palmivora, well distributed worldwide, is the predominant species. Morphology and aggressiveness of 100 isolates of P. palmivora, collected from farms in 13 municipalities of the cacao growing region in Bahia State, were evaluated for three consecutive years. Leaf discs from the clones Scavina 6 (SCA-6), resistance standard, and SIC-23, susceptibility standard, were inoculated with suspensions of each of the isolates obtained from the Phytophthora Collection “Arnaldo Gomes Medeiros” of Cacao Research Center/CEPLAC, at the concentration of 3.0 x 105 zoospores/mL. A pathophysiological scale was used to evaluate the infection seven days after inoculation. Colony appearance and sporangium and chlamydospore production of each isolate were evaluated; the structures of 61 isolates were measured, and the type of compatibility of the 100 isolates was determined. Reaction of the two cacao clones to the isolates of P. palmivora had a great variation, demonstrating different degrees of aggressiveness among isolates. Such aggressiveness is not related to the site or the year of collection, since more and less aggressive isolates were obtained in the same municipalities and years of collection. There was also a variation in the morphology of colonies. Ellipsoid to ovoid sporangia had a mean size of 28.3 - 50.5 x 18 - 36.7 ?m, short pedicels (1.5 - 4.4 ?m) and length-width ratio ranging from 1.1 to 2.2. Globose, terminal or intercalary chlamydospores ranged from 18.4 - 43.5 µm in diameter. All 100 isolates were A2 compatible. The observed variability in the aggressiveness of P. palmivora isolates will have implications for the epidemiological studies and the selection of genotypes resistant to P. palmivora.
Keywords
Black pod rot;
Theobroma cacao
; Variability; Morphometric characterization; Pathogenicity
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