First record of Phytophthora tropicalis causing leaf blight and fruit rot on breadfruit in Brazil

Abstract

Breadfruit (Artocarpus altilis) has its centre of origin in Malaysia and was introduced by the Portuguese to Brazil, where it is grown mainly in the northeastern states. Its fruit can be used as food, its leaves as cattle fodder and the latex extracted from the fruits and trunk as raw material to produce glue. In 2005, brown necrotic lesions were observed on leaves and fruits of breadfruit grown in the municipality of Itubera, Bahia State, northeast Brazil. A Phytophthora species was isolated from diseased leaf samples on selective medium PARPH (Kanmwischer & Mitchell, 1978). Analyses of morphological characteristics of 5-day-old cultures grown on carrot agar showed a petaloid and sparse aerial mycelium. Observations and measurement of 50 sporangia revealed that they were ellipsoid, 37 µm ± 0·69 (standard error of the mean) × 23·8 µm ± 0·40, caducous with pedicels measuring 61 µm ± 3·08, with a length/width ratio of 1·9:1, mean depth of papillae 4·6 µm ± 0·13, and pore exit of 6·4 µm ± 0·20. Physiological tests showed that the isolate was heterothallic, mating type A1, forming amphigynous antheridia. The isolate was deposited in the Brazilian collection of Phytophthora species under accession number CBP 546. The gene sequences obtained for ITS (accession number AM040496), translation and elongation factor 1α (accession number AM040497) and β-tubulin (accession number AM040498) for isolate CBP 546 showed 99·8, 99·4 and 99·8% identity, respectively, when compared with sequences AJ299733, AY564103 and AY564046, respectively, of P. tropicalis. Pathogenicity tests were performed by inoculating green fruits of breadfruit with 5 mm mycelial discs of 5-day-old cultures of isolates CBP 546 from breadfruit, P. tropicalis CBS 434.91 from macadamia and P. palmivora CBP 232 from cocoa. Inoculated fruits were incubated at 25°C in a humid chamber and lesions were observed 5 days later. The results showed that only P. tropicalis was pathogenic to fruits of breadfruit. This pathogen was reisolated from the lesions onto PARPH medium. These results confirm the identity of isolate CPB 546 as P. tropicalis. Previously P. palmivora was identified as the agent of fruit rot on breadfruit in Micronesia, Western Samoa and India (Trujillo, 1970; Erwin & Ribeiro, 1996). As P. tropicalis was proposed recently as a new species to regroup the isolates of ‘P. palmivora MF4’ (= P. capsici) (Aragaki & Uchida, 2001), it is possible that the pathogen reported by these authors was P. tropicalis. This hypothesis is supported by our pathogenicity tests. This is the first report of P. tropicalis as a pathogen of breadfruit in Brazil.