San Quintin Valley, a 60-mile-long coastal plain (30°30′N, 116°W) in the Baja California Peninsula, is one of the major fresh tomato (Lycopersicon esculentum Mill.) production areas in Mexico with more than 8,000 ha. During the last 10 years, the valley's tomato production has declined because of gray mold and stem canker diseases. Flower rot, reddish brown margins on the leaves and stems, and fruit with a gray mold were observed on field-grown tomato plants (Roma type cv. Tequila) in the autumn of 2003. Severity ranging from 55 to 60% was observed at harvest. Infected tissues were sampled and disinfested by immersion in 1% NaOCl for 1 min, rinsed in sterile water, and placed on malt extract agar at 22°C. Fungal conidia were then transferred to 2% potato dextrose agar (PDA). The resulting fungal colonies were definitively identified as Botrytis cinerea Pers.:Fr. The colonies of B. cinerea were first hyaline and white and became dark gray after 96 h. Mycelia were septate with dark branched conidiophores. Conidia were unicellular, ellipsoid, and ranged from 5 to 8 × 8 to 14 μm. Profuse black sclerotia developed in 7-day-old cultures. Infection site analyses in diseased flowers at different stages during the bloom were done with scanning electron microscopy. Fungal hyphae were located predominantly on the receptacle areas, whereas conidia were located in the ovaries as described previously (3). The identity of B. cinerea was confirmed by a restriction digest with ApoI of the 413-kb polymerase chain reaction amplification product obtained with BA2f/BA1r primers (1) and random amplified polymorphic DNA banding patterns (2). Pathogenicity tests were done by spray inoculation of 1-ml aqueous conidial suspension (106 CFU/ml) on 20 healthy plants during the blossom stage. An equal number of plants sprayed with sterile water was used as the control. Plants were incubated at 20 ± 2°C for 5 days. The fungus was reisolated from diseased flowers and peduncles after surface disinfestation (2.5% NaOCl) and plating on PDA. No symptoms were observed in the noninoculated controls. To our knowledge, this is the first report of B. cinerea causing gray mold disease on tomato in Baja California.
References: (1) K. Nielsen et al. Plant Dis. 86:682, 2002. (2) S. Rigotti et al. FEMS Microbiol. Lett. 209:169, 2002. (3) O. Viret et al. Phytopathology 94:850, 2004.
