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Chapter 8. Fungal Diseases of Vanilla
Mesak Tombe and Edward C.Y. Liew
Introduction
Diseases of vanilla crop caused by pathogenic fungi have been reported ever since vanilla was commercially cultivated. In vanilla-producing countries such as Indonesia, Madagascar, India, Papua New Guinea, Mexico, and Puerto Rico, diseases caused by fungi are significant constraints to the cultivation of this plant. Until now several fungal genera have been reported to infect vanilla, including Fusarium, Phytophthora, Sclerotium, and Colletotrichum. These attack or infect the stems, roots, leaves, shoots, and fruit of vanilla. However, the disease caused by Fusarium is the most serious and has resulted in crop devastation of epidemic proportion in vanilla farms or plantations in many of the producing countries.
Fusarium Rot of Vanilla
Fusarium rot occurs on the roots, stems, fruit, leaves, and shoots of the plant. However, stem and root infections cause the greatest amount of damage, leading to significant yield loss, and hence the disease is often referred to as stem rot, foot rot, or stem and root rot. In Indonesia, Fusarium rot can infect all parts of the plant from nursery to productive plants but the attack on the stem is most harmful. In light of its significance, a greater emphasis on this disease is placed in this chapter.
Historical Review and Distribution
Fusarium rot, attacking the vanilla crop, has been reported since the crop was cultivated commercially in producing countries, including Indonesia, India, Puerto Rico, the Seychelles, Reunion Island, Madagascar, and Polynesia.
A disease on vanilla was first recorded by Zimmermann in Indonesia in 1903 (Tombe, 1994) when infections on stems and leaves were noted. In 1918, symptoms of a root disease were first noticed in vanilla plantations in Mayagüez, Puerto Rico (Alconero and Santiago, 1969). Tucker (1927) reported that the vanilla root rot in Puerto Rico was caused by a soilborne pathogen called Fusarium batatatis var. vanillae Tucker. In 1925, van Hall (in Tucker, 1927) mentioned the occurrence of a root fungus that caused death of vanilla cuttings in Java, Indonesia. However, the earliest reference associating a Fusarium species to vanilla stem rot in Indonesia was by Soetono (1962), who isolated a species of Fusarium from infected vanilla plants and identified it as F. batatatis Wollenweber.
In the Seychelles Islands, where vanilla was formerly an important crop, the same root disease was present according to a report made by Dupont (1921). The disease description coincided quite closely with that in Puerto Rico (Tucker, 1927). Meinecke (in Tucker, 1927) also observed an undescribed Fusarium attacking the tender tips and young pods of vanilla. Averna-Sacca (1930) reported that the same species of Fusarium was isolated from the diseased vanilla growing in Brazil. However, he stated that the Fusarium pathogen only attacked leaves and stems without any mention of its occurrence on the roots.