Influence of Cephalosporium diospyri and environment on Botryodiplodia theobromae canker development in Platanus occidentalis

Abstract

Many sycamore (Platanus occidentalis L.) trees were killed throughout East Texas, during the Summers of 1973-1975, by the combined effects of Cephalosporium diospyri Crandall and Botryodiplodia theobromae Pat. Botryodiplodia cankers and dieback were associated with Cephalosporium wily symptoms. A highly virulent and a lowly virulent strain of B. theobromae were isolated from sycamore trees. The lowly virulent strain colonized inoculated sycamore seedlings but did not produce cankers, in most cases, unless the seedlings were either under the influence of water-stress or Cephalosporium wilt. The highly virulent strain produced cankers on water-stressed and non-water-stressed seedlings but cankers were much larger on water-stressed seedlings. Botryodiplodia theobromae did not cause cankers on sycamore seedlings at 20C, but almost 100% canker development was observed on seedlings inoculated with the fungus and maintained either a 30 or 35C growth chamber. The fungus grew faster on 0.8% wood chip agar at 30C than it did at 35C but larger cankers were produced at 35C than at 30C. Sycamore bark and sapwood did not inhibit growth or spore germination of B. theobromae. New wounds on sycamore stems were better infection courts for B. theobromae conidia than old wounds, but wound 5 mm below excised twig tips were the best for canker and dieback establishment. Canker development from B. theobromae conidia is stimulated by a reduction in water content of stems. Botryodiplodia theobromae is highly sensitive to benomyl (1-butylcarbamoyl-2-benzimidazole carbamic acid methylester) and thiabendazole [2-(4-thiazolyl) benzimidazole]. Fungicide concentrations of 0.5 ug/ml completely inhibited growth of the fungus.