First Report of Stem and Fruit Infection of Eggplant by Phytophthora drechsleri in Argentina

IRIBARREN, M.J.

PLANT DISEASE

AMER PHYTOPATHOLOGICAL SOC

Año: 2017

0191-2917

Eggplant (Solanum melongena) is a common crop grown along the northeast horticultural belt of Buenos Aires, Argentina. This region is characterized by its humid temperate climate, with precipitations historically above 1000 mm and maximum and minimum average temperatures of 30 °C and 4°C, respectively. Soils are composed mainly of clay which limits drainage. During January-April 2011, commercial eggplant crops in the locality of General Rodríguez (Northern Buenos Aires) developed patches of diseased plants with rots on fruits and stems. Affected fruits had light brown necrotic lesions with an irregular pattern; frequently more than one lesion per fruit was observed. Mummified fruits were also observed. Stems had dark brown necrotic blights. Fruits and stems sampled from three fields were brought to the laboratory, washed thoroughly and disinfected with a 1% bleach solution. Small pieces were removed from the lesion edge, plated on V8 agar (V8A) plates, and incubated at 24°C in the dark for 5 days. Three isolates were transferred to V8A using hyphal tips. Morphological studies were performed on the V8A cultures as well as on plates flooded with tap water. Sporangial morphology was ovoid, persistent, and variable in size, averaging 30 × 45 μm (n = 30). Metalaxyl sensitivity at a 100 ppm dose was also performed. One mycelial plug of each isolate was placed onto the center of a V8A petri dish and incubated for 7 days at 24°C in darkness. Controls included non-colonized V8A plugs. All the isolates resulted sensitive to metalaxyl. Each isolate belonged to the A1 mating type when paired with P. capsici tester isolates, CBS 370.72 and CBS 111.334 (Fungal Biodiversity Centre, CBS, Utrecht, The Netherlands). The isolates produced amphigynous antheridia, and chlamydospores were present but scarce, consistent with P. drechsleri (Erwin & Ribeiro, 1996). Maximum temperatures for growth (37°C) were also performed. Edited sequences of the internal transcribed spacer (ITS) region of the rDNA (GenBank Accession Numbers: KU640191, KU640192, and KU640193) were compared with Phytophthora sequences available in GenBank using the BLASTN search utility (Altschul et al. 1997) and aligned to the data set of Cooke et al. (2000). Sequences of the three isolates matched 100% with GenBank sequences of P. drechsleri (100% coverage, 100% identity and no gaps). Based on these results, the three Argentinian eggplant isolates were identified as P. drechsleri . Pathogenicity tests were completed using three fruits and stems of mature eggplant plants for each isolate. A 5-mm colonized mycelial plug was placed on the organ surface and incubated in plastic boxes for 4 days at 24°C. For the control treatments, organs were inoculated with non-colonized V8A plugs. All inoculated organs developed necrotic lesions 2 to 5 cm long, light brown in fruits and dark brown in stems. Controls remained unaffected. P. dreschleri was consistently reisolated as described above from the inoculated fruits and stems but not from the controls. To our knowledge, this is the first report of eggplant as a host for P. dreschleri in Argentina. Frezzi (1950) reported this species as a pathogen of Chrysanthemum cinerariefolium, Celosia plumosa, Schinus molle, and Solanum lycopersicum in Argentina in 1950.References: S. S. Altschul et al. Nucleic Acids Res. 25:3389, 1997. D. E. L. Cooke et al. Fungal Gen. Biol. 30:17, 2000. D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society Press, St. Paul, MN., 1996. M. J. Frezzi Rev. Invest. Agric. 4:49, 1950.