Small pieces of diseased tissue were surface sterilized with 0·5% NaOCl, plated on 2% potato dextrose agar (PDA) at pH 6, and incubated at 22 to 24 ° C. Dense, whitish mycelium developed within 72-96 h. Microconidia were abundant, globose to piriform, 0-1 septate, 4 -10 × 4·5-7 μ m, and formed on unbranched and branched monophialides. Cultures produced a fruity aroma similar to amyl acetate. Spores from 14-day-old colonies that developed on PDA were removed with 4 mL of sterile water. The pathogenicity of the fungus was tested by spraying five healthy inflorescences of tomato with a 5-mL suspension (2 × 10 5 conidia mL -1 of sterile distilled water). Another five healthy inflorescences were sprayed with sterile distilled water. The plants were placed in a growth chamber with a 12-h photoperiod at 22 ± 2 ° C and covered with polyethylene bags that were removed after 3 days when plants were moved to a glasshouse. While control flowers were healthy, all inoculated flowers showed symptoms similar to those observed previously.

The green belt area surrounding the city of La Plata, Argentina, produces more than 70% (around 280 ha) of the lettuce (Lactuca sativa L.) cultivated under greenhouse for fresh consumption in the country. In February 2011, April 2012, and December 2013, butterhead lettuce plants from cv. Lores showing wilt and stunted growth symptoms, red-to-brown discoloration of vascular tissues, and yellow leaves were found in greenhouses in La Plata. Sections of tap root, crown and stem from symptomatic plants showing dark-brown streaking of the vascular tissue were surface sterilized and isolations were made. A total of 21 monosporic isolates obtained from different lettuce production fields were identified as Fusarium oxysporum Schltdl. based on morphological characteristics (2). Vegetative compatibility group (VCG) analysis (1) was conducted on 11 of these isolates and all isolates belonged to the same VCG. To fulfil Koch's postulates, two pathogenicity tests were conducted with these 11 isolates in winter (July 2012) and summer (December 2013). Healthy 20-day-old butterhead lettuce seedlings of two cultivars (Reina de Mayo and Lores in the winter and summer tests, respectively) were inoculated by dipping the roots of each plant in a spore suspension (~3 × 105 CFU ml−1), planted in 1-liter pots containing autoclaved soil and grown in a greenhouse with only natural daylight. Control treatments were prepared by dipping the seedling roots in sterilized distilled water. All inoculated plants showed wilt symptoms 15 to 20 days after inoculation (dai) and 45 to 50 dai in the summer and winter pathogenicity tests, respectively. The delay in the appearance of symptoms observed during the winter test is consistent with the effect of planting date on the development and final incidence of Fusarium wilt of lettuce reported by Matheron et al. (3). No symptoms were observed in control treatments. F. oxysporum was re-isolated from vascular tissues of the stems of symptomatic plants and the formae speciales lactucae J.C. Hubb. & Gerik was confirmed by PCR using the specific primer pair GYCF1 and R943 (4). The identification of only one VCG for the tested isolates agrees with the hypothesis of seed transmission of the pathogen, which might explain the dissemination of Fusarium wilt of lettuce in geographically distant areas (2). Studies are being carried out to determine the race of these Argentinian isolates of F. oxysporum f. sp. lactucae. To our knowledge, this is the first report of F. oxysporum f. sp. lactucae infecting lettuce in Argentina. References: (1) J. C. Correll et al. Phytopathology 77:1640, 1987. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) M. E. Matheron et al. Plant Dis. 89:565, 2005. (4) G. C. Y. Mbofung and B. M. Pryor. Plant Dis. 94:860, 2010.

A new potyvirus, tentatively named cucurbit vein banding virus (CVBV), was identified in crops of cucurbits in San Pedro (Buenos Aires, Argentina). The complete genome sequences of two isolates of CVBV were obtained by next-generation sequencing (Illumina). The genomic RNA consisted of 9968 and 9813 nucleotides, respectively, and displayed typical potyvirus organization. The percentage identity for these two genome sequences, using BLASTn, was 77% to sweet potato virus c and 73% to tomato necrotic stunt virus. BLASTx analysis of the complete polyprotein showed that the most closely related virus is plum pox virus, with 48% amino acid sequence identity for both isolates. Sequence comparisons and phylogenetic analyses indicate that CVBV belongs to a previously undescribed species in genus Potyvirus.

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