Pygmy date palm (Phoenix roebelenii O'Brien), native to Laos and southeast Asia, is one of the most commonly cultivated date palms both indoors and out. In early April 2003, a new and widespread leaf disease was detected on 2- to 3-feet high, potted, pygmy date palms growing in open fields or shade-houses in four commercial nurseries of the eastern Sicily Region of southern Italy. Initial symptoms on infected plants were small, chlorotic spots on blades and edges of leaflets. As spots enlarged, yellow or reddish-brown margins and brown or gray, wrinkled, sunken centers developed. Sometimes, spots or lesions coalesced to cause blight of young expanding leaves or death of apical buds. Botrytis cinerea Pers.:Fr was recovered consistently from sections of infected tissues (disinfected for 1 min in 1% NaOCl and rinsed in sterile water) plated on malt extract agar. On potato dextrose agar (PDA), colonies of B. cinerea were first hyaline, then turned white, and later turned dark gray when spores differentiated. Six- to eight-day-old-cultures developed white sclerotia that turned black after three more days. Conidia in 1-month-old-cultures were hyaline or gray, ovoid, and ranged from 5.2 to 8.8 × 8 to 14 μm (average 6.6 × 9.9 μm). Black microsclerotia were round or irregular in shape and ranged from 0.6 to 2.8 × 0.3 to 2.5 mm (average 1.66 × 0.98 mm) (1). Koch's postulates were performed by spraying potted, 9-month-old pygmy date palms (2 feet high) with a spore suspension (1 × 106 CFU per ml from 15-day-old cultures grown on PDA). Six plants were wounded and inoculated, while six plants were inoculated without wounding. An equal number of noninoculated plants sprayed with sterile water served as controls. All plants were maintained in a humid environment at 20°C. Sunken-leaf and rachis lesions were observed on all wounded and most nonwounded plants within 10 to 14 days after inoculation. Symptoms did not develop on the control plants. Koch's postulates were fulfilled by reisolation of the fungus from affected tissues. A field survey revealed the occasional presence of similar leaf spots on canary island date palms (Phoenix canariensis Hort. ex Chabaud), from which B. cinerea was consistently recovered. The unusually cool and humid weather conditions recorded in Sicily during this disease outbreak were very conducive for occurrence of the B. cinerea infections. Although the disease only occasionally caused death of plants, evidence indicated that B. cinerea reduced commercial value of infected pygmy date palms. B. cinerea was previously recorded in northern Italy on canary island date palm (2) and was recently detected in southern Italy on majesty palm (3). To our knowledge, this is the first report of leaf spot and rachis blight caused by B. cinerea on pygmy date palm.
References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CAB, Kew, Surrey, England, 1971. (2) A. Garibaldi and S. Rapetti. No. 9 Suppl. Flortecnica, 1987. (3) G. Polizzi. Plant Dis. 86:815, 2002.
