From 1998 through 2002, commercial chives (Allium schoenoprasum) in coastal California (Monterey County) were damaged by an undescribed disease. Initial symptoms were chlorosis and tan-colored necrosis at the leaf tips; as the disease progressed, extensive tan-to-light brown discoloration extended down affected leaves, resulting in their death. The damage prevented growers from harvesting affected crops. Stems of the chive plants were unaffected. Diseased plants continued to grow new leaves that subsequently became infected. A fungus was consistently isolated from symptomatic leaves. Isolates grown on potato dextrose agar (PDA) in petri plates incubated at 24°C under fluorescent lights produced extensive mycelial growth without conidia. However, on onion leaf straw agar (2), the isolates produced abundantly sporulating colonies with conidiophores and conidia typical of a Botrytis species. Conidiophores rarely exceeded 1 mm long. Ellipsoidal conidia measured 11 to 17 × 5 to 8 μm. On green bean pod agar (4), the isolates produced a few, black, irregularly shaped sclerotia measuring 1 to 2 mm in diameter. Morphological comparisons were made on PDA between five chive isolates and isolates of the following Botrytis species known to infect Allium species (1): B. aclada BA5, B. allii BA3, B. byssoidea ATCC 60837, B. cinerea from an onion seed crop, B. porri 749, B. squamosa 392, and B. tulipae GC-1. B. elliptica strain MARLI-3 was also compared with the chive isolates. Chive isolates produced floccose, off white-to-light tan mycelium, lacked sporulation (except where mycelium contacted the edge of the plastic petri dish), and did not form sclerotia on PDA, thereby resembling B. byssoidea. Identification of the chive isolates as B. byssoidea was confirmed by ApoI restriction fragment length polymorphism digests of a 423-bp PCR amplicon obtained from each of the five chive isolates and the eight known Botrytis species (1,3). Pathogenicity of the chive isolates of B. byssoidea was confirmed by spraying a conidial suspension (1 × 105 conidia/ml) of each of 12 isolates onto chive (cv. Fine Leaved) and onion (A. cepa cv. Southport White) plants until runoff, incubating the plants in a humidity chamber at 24 to 26°C for 48 h and then maintaining the plants under ambient light in a greenhouse. After 6 to 8 days, inoculated chives and onions developed symptoms similar to those observed in the field and B. byssoidea was reisolated. Noninoculated control chives and onions sprayed with distilled water did not develop symptoms. The experiment was conducted three times and the results were the same. To our knowledge, this is the first report of a leaf blight of chive caused by B. byssoidea in North America. After 2002, the commercial chive plantings were placed on farms further east in Monterey County away from the coast. The disease has not been observed since this move to a drier climate.
References: (1) M. I. Chilvers and L. J. du Toit. Online publication. doi:10.1094/PHP-2006-1127-01-DG. Plant Health Progress, 2006. (2) L. A. Ellerbrock and J. W. Lorbeer. Phytopathology 67:219, 1977. (3) K. Nielsen et al. Plant Dis. 86:682, 2002. (4) A. H. C. van Bruggen and P. A. Arneson. Plant Dis. 69:966, 1985.