First Report of Foliar Infection of Cabbage by Phytophthora drechsleri in Argentina

IRIBARREN M.J.; GONZÁLEZ B.A.; VÉLEZ, M.L.; GRESLEBIN, ALINA G.; STECIOW, M

PLANT DISEASE

AMER PHYTOPATHOLOGICAL SOC

Año: 2012 vol. 96 p. 1830 - 1830

0191-2917

Cabbage (Brassica oleracea var. capitata L.) is a popular crop grown alongthe northeast horticultural belt of Buenos Aires Province, Argentina. Inthe summer of 2010, fields in this region remained flooded for longperiods due to frequent and intense precipitation (560 mm from Januaryto March). Commercial cabbage crops in the cities of Luján and GeneralRodríguez developed patches of diseased plants that were stunted andwilted. Affected plants had necrotic areas in the crowns and roots.Symptoms expanded to the upper stems, leaving vascular tissuesexposed. During April 2010, samples from 2 fields were brought to the laboratory where the stems were washed thoroughly and disinfected witha 1% bleach solution for 2 minutes. Small pieces (5 mm in diameter)were removed from the lesion edge, plated on V8 agar (V8A) plates, andincubated at 24°C in the dark for 5 days. Four isolates were transferred toV8A using hyphal tips. Morphological studies were performed on the V8Acultures as well as plates flooded with tap water. Sporangia wereobpyriform, nonpapillate, persistent, and variable in size, averaging 44 ×28 μm. Each isolate belonged to the A1 mating type when paired with P.capsici tester isolates, CBS 370.72 and CBS 111.334 (Fungal BiodiversityCentre, CBS, Utrecht, the Netherlands). The isolates producedamphigynous antheridia, and chlamydospores were present but scarce.Maximum temperatures for growth (37°C) were also performed. Editedsequences of the internal transcribed spacer (ITS) region of the rDNA(GenBank Accession Nos. JQ653300, JQ653301, JQ653302, and JQ653303)were compared with Phytophthora sequences available in GenBank usingthe BLASTN search utility (1) and aligned to the data set of Cooke et al.(2). Sequences of the four isolates (strains 2: R-cai-cuello-col-3, 3: R-caicuello-col-18, 4: R-AN-col-1A and 5: R-AN-col-1B) matched 100% withGenBank sequences of P. drechsleri (100% coverage, 100% identity andno gaps). Based on these results, the four Argentinian cabbage isolateswere identified as P. drechsleri (3). Pathogenicity tests were completedusing three detached heads of mature cabbage plants (B. oleracea var.capitata) for each isolate. A 5-mm colonized mycelial plug of theappropriate isolate was placed on the main vein of the outermost leaves.For the control treatments, three heads were inoculated withnon-colonized V8A plugs. The inoculated and control heads of cabbagewere incubated in plastic boxes wrapped in black nylon bags at 24°C for 4days. Broccoli (B. oleracea var. italica) and cauliflower (B. oleracea var.botrytis) were also tested following the same procedure. All heads ofcabbage, broccoli, and cauliflower developed necrotic lesions 2 to 4 cm indiameter and a dark grey color. Control heads of each plant remainedgreen. P. dreschleri was consistently reisolated as described above fromthe inoculated heads, but not from the control heads. To our knowledge,this is the first report of cabbage as a host for P. dreschleri in Argentina.Frezzi (4) reported this species as a pathogen of Chrysanthemumcinerariefolium, Celosia plumosa, Schinus molle, and Solanumlycopersicum in Argentina in 1950.