Root and stem rot of Schefflera arboricola in Brazil, caused by Fusarium solani

Schefflera arboricola (octopus tree or local name cheflera pequena) is an ornamental shrub of the Araliaceae from Taiwan. In Brazil it is widely used as a pot plant or in gardens. In March 1998, a disease was observed affecting patches of plants within groups cultivated in the garden of the campus of the Universidade Federal de Viçosa in Viçosa, Minas Gerais. The initial symptoms of leaf chlorosis progressed to leaf drop, browning of stems and death of the above ground parts (Fig. 1). Below ground observations showed that a brown necrosis began in secondary roots and advanced to the base of the stems, by which time complete defoliation had occurred. The bark was shed in plants with advanced necrosis of the root system (Fig. 2).

Tissue fragments taken from the internal parts of diseased plants at the limit of the necrotic areas were surface sterilized and plated on potato dextrose agar (PDA). A Fusarium species was the only fungus obtained, and appeared from most fragments. Single spore cultures from these colonies were grown on carnation leaf agar, to assist identification (Nelson et al., 1983). We have identified the fungus as Fusarium solani based on its morphology (Fig. 3 and Fig. 4), and the symptoms observed in natural and artificial infections, which are similar to those of other diseases caused by F. solani. A typical cream or purple colonies developed on PDA although colony colour is influenced by cultural conditions.

Conidia from one isolate were produced in a potato dextrose broth shake culture at 27 ° C, in the dark. Seven, 8 months-old S. arboricola plants were inoculated by dipping the roots for one minute in a suspension containing 3 x 10⁵ conidia/ml). Roots were injured by light pruning before dipping in the suspension. A similar group of plants were also pruned and the roots immersed in tap water. All plants were planted in individual 4 L pots containing sterile soil and manure mixture (3:1), watered daily, and kept in a glasshouse. After three months two of the inoculated plants had died. The most noticeable feature of the other inoculated plants was a greatly reduced root system and root rot. Leaf chlorosis was observed in some of the inoculated plants. The untreated plants showed no symptoms. Fig. 5 shows a comparison between the two groups. The pathogen was successfully reisolated from the roots of the inoculated plants.

In the United States F. oxysporum was associated with S. arboricola (Miller, 1997), while F. solani was associated with a damping-off of Schefflera actinophylla. A Fusarium sp. was reported to cause damping-off and stem rot of S. arboricola (Farr et al., 1989). Mendes et al. (1998) does not record F. solani in association with S. arboricola. We have found no other records and believe that this is first record of F. solani causing a root and crown rot of S. arboricola.