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Influence of Temperature, Light Intensity, and Isolate on the Development of Neofusicoccum parvum--Induced Dieback of Eugenia, Syzygium paniculatum

Syzygium paniculatum (Myrtaceae) is an important plant in the South Florida ornamental industry. Known as eugenia in the trade, the plant was relatively free of diseases before Hurricane Wilma (2005). Since then, a serious dieback disease has become prevalent in local nurseries, especially during late summer. Symptoms included wilting and death of terminal and lateral branches, and vascular discoloration in dead and dying branches and the main stem. Several fungi were isolated from diseased plants, but Neofusicoccum parvum was usually the only fungus isolated from symptomatic tissue. Most isolates were sterile, but all that were tested produced significant (P < 0.05) dieback on, and reduced growth of, the cultivar Monterrey Bay. Glomerella spp. and a Pestalotiopsis sp. that were recovered from asymptomatic portions of diseased plants and Mycoleptodiscus terrestris recovered from healthy liners of Monterrey Bay did not cause dieback symptoms in pathogenicity studies or affect host growth. In incubator studies, N. parvum caused significant external symptoms, vascular discoloration, and mortality at 25 and 30°C; in general, only vascular symptoms developed at 20°C and no symptoms developed at 15°C. Thus, temperature may be associated with the seasonal development of this disease. Significant differences in disease development were not observed under a wide range of light intensities (2,000 to 300 μmol s^-1 m^-2). S. paniculatum is a new host record for N. parvum.