Stem blight of southern highbush blueberry (SHB) results in premature plant mortality and has been identified by Florida blueberry growers as the economically most important disease for the industry. In 2007, plants with stem blight and dieback symptoms were sampled at 4-month intervals from two farms located in Alachua and Polk Co., FL. In all, 30 cane samples (stem blight) and 30 crown segments (dieback) were collected at each sample date and each location. In total, 360 samples were collected; fungal species in the family Botryosphaeriaceae were isolated from 85% of the samples. Based on morphology and phylogenetic analysis of the internal transcribed spacer region and elongation factor 1-α (EF1-α) sequences, two dominant species recovered from SHB in Florida were identified: Lasiodiplodia theobromae and Neofusicoccum ribis. Species isolation was independent of location, symptom type, and time of year. Additional samplings are needed to investigate population change over multiple years and in the rest of the southeastern United States. Breeding for resistance and management of stem blight and dieback in Florida should focus on these two fungal species.

Stem blight of southern highbush blueberries has been attributed to Botryosphaeria dothidea (2). Symptoms include necrotic branches with attached leaves and brown discoloration of the vasculature extending the length of the affected branch. A 2007 field survey of stem blight in Florida resulted in isolates of the previously reported B. dothidea and Neofusicoccum ribis and isolates of unreported Lasiodiplodia theobromae (2). Isolates of L. theobromae were identified to species level by morphological characterization (3). Identity was confirmed by comparison of rDNA sequences of representative isolates (GenBank Accession No. FJ882072) to reference sequences (99% similarity to Accession No. EF622074) (1). Seven, fresh, pruning wounds on southern highbush blueberries cv. Misty were inoculated with a 10-mm V8 juice agar plug of isolate MixFC-6 taken from the margin of a 3-day-old colony. Seven wounds were inoculated with a sterile agar plug. All plugs were attached to the wounds with Parafilm. Mean lesion length 14 days after inoculation was 8.6 ± 2.4 cm. The pathogen was reisolated from the margin of lesions and identified by colony growth characteristics on potato dextrose agar. No lesions were observed on control plants. To our knowledge, this is the first report that stem blight of southern highbush blueberries in Florida can be caused by L. theobromae. References: (1) A. Alves et al. Fungal Divers. 28:1, 2008. (2) F. L. Caruso and D. C. Ramsdell. Compendium of Blueberry and Cranberry Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (3) P. W. Crous et al. Stud. Mycol. 55:235, 2006.

In July 2013 in coastal (Santa Barbara County) California, commercial plantings of southern highbush blueberry (Vaccinium corymbosum) developed symptoms of a previously undiagnosed disease. Symptoms consisted of reddening and wilting of foliage, with leaves and small twigs later drying up. The bark of diseased branches was discolored and sunken; removal of this bark revealed a brown discoloration of the underlying wood. Approximately 5% of the planting was affected. When placed on acidified potato dextrose agar (A-PDA), surface disinfested pieces of symptomatic wood consistently yielded one type of fungus. On A-PDA, isolates produced extensive white aerial mycelium that turned dark gray after 4 to 5 days and formed pycnidia after 21 days. Three single-spore isolates were grown on PDA for 21 days for morphological and molecular characterization. Conidia were hyaline, smooth, and ellipsoid with round apices and truncated bases. Conidia measured 13 to 20 × 5 to 7.5 μm (n = 50; mean 16.7 × 6.1 μm), with a length/width ratio of 2.73. After 25 days, conidia became biseptate with a darker middle cell. rDNA sequences of the internal transcribed spacer (ITS) region of the isolates (GenBank KJ126847 to 49), amplified using primers ITS1 and ITS4 (5), were 99% identical to the holotype isolate of Neofusicoccum parvum Pennycook and Samuels (3) by a BLAST query (GU251125). Partial sequences of the translation elongation factor 1-alpha (EF1-α) gene (KJ126850 to 52), obtained using primers EF728Fa and EF986R (5), were 99% identical to N. parvum (GU251257). To demonstrate Koch's postulates, 14-day-old colonies of the three N. parvum isolates were grown on A-PDA. Using three blueberry cultivars (Abundance, Jewel, and Snowchaser), slits were cut beneath the epidermis of branches 1 cm diameter or less; one colonized agar plug (6 mm diameter) was placed into each cut and the epidermis was resealed with Parafilm. Ten inoculations (one inoculation per branch; two branches per plant) were made for each isolate and each cultivar; inoculated plants were maintained in a greenhouse. After 10 to 14 days, leaves on inoculated branches turned red and wilted, bark above and below the inoculation sites turned brown, and vascular tissue beneath the bark was also brown. After 21 days, diseased areas became sunken. N. parvum was recovered from all inoculated branches of all cultivars and matched the characteristics of the original isolates. Control branches, inoculated with sterile agar plugs, did not develop any symptoms and N. parvum was not isolated. This experiment was repeated with similar results. Many Botryosphaeriaceae species, including N. parvum, are associated with canker and dieback symptoms on blueberry worldwide (2). To our knowledge, this is the first documentation of stem blight caused by N. parvum on blueberry in CA. Blueberry is a rapidly expanding industry in the state, with 960 ha planted in 2005 increasing to 2,830 ha in 2012 (1). Drought stress predisposes plants to stem blight caused by Botryosphaeriacease species (4); therefore, expansion into arid areas of CA could increase the incidence and severity of N. parvum. References: (1) N. Amer. Blueberry Council. 2012 World Blueberry Acreage & Prod. Rept., 2013. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., online publication, ARS, USDA. Retrieved February 5, 2014. (3) S. R Pennycook and G. J. Samuels. Mycotaxon 24:445, 1985. (4) W. A. Sinclair and H. H. Lyon. Diseases of Trees and Shrubs, Second Edition. Comstock Publ. Assoc. 2005. (5) B. Slippers et al. Mycologia 96:83, 2004.

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