Classification of the guava wilt fungus Myxosporium psidii, the palm pathogen Gliocladium vermoesenii and the persimmon wilt fungus Acremonium diospyri in Nalanthamala

Abstract

Psidium guajava wilt is known from South Africa, Malaysia and Taiwan. The fungus causing this disease, Myxosporium psidii, forms dry chains of conidia on surfaces of pseudoparenchymatous sporodochia, which develop in blisters on bark. Similar sporodochia are characteristic of Nalanthamala madreeya, the type species of Nalanthamala. Nalanthamala, therefore, is the appropriate anamorph genus for Myxosporium psidii, while Myxosporium is a nomen nudum (based on M. croceum). For M. psidii the combination Nalanthamala psidii is proposed. Nalanthamala psidii, the palm pathogen Gliocladium (Penicillium) vermoesenii, another undescribed anamorphic species from palm, two species of Rubrinectria and the persimmon pathogen Acremonium diospyri are monophyletic and belong to the Nectriaceae (Hypocreales) based on partial nuclear large subunit ribosomal DNA (LSU rDNA) analyses. Rubrinectria, therefore, is the teleomorph of Nalanthamala, in which the anamorphs are classified as N. vermoesenii, N. diospyri or Nalanthamala sp. Nalanthamala squamicola, the only other Nalanthamala species, has affinities with the Bionectriaceae and is excluded from this group. Rubrinectria/Nalanthamala species form dimorphic conidiophores and conidia in culture. Fusiform, cylindrical, or allantoid conidia arise in colorless liquid heads on acremonium-like conidiophores; ovoidal conidia with somewhat truncated ends arise in long, persistent, dry chains on penicillate conidiophores. No penicillate but irregularly branched conidiophores were observed in N. diospyri. Conidia of N. psidii that are held in chains are shorter than those of N. madreeya, of which no living material is available. Nalanthamala psidii and N. diospyri are pathogenic specifically to their hosts. They form pale yellow to pale orange or brownish orange colonies, respectively, and more or less white conidial masses. Most strains of Rubrinectria sp., Nalanthamala sp. and N. vermoesenii originate from palm hosts, form mostly greenish or olive-brown colonies and white-to-salmon conidial masses. They form a mono-phyletic clade to which Nalanthamala psidii and N. diospyri are related based on analyses of the internal transcribed spacer regions and 5.8S rDNA (ITS rDNA), LSU rDNA, and partial β-tubulin gene. Few polymorphic sites in the ITS rDNA and β-tubulin gene indicate that Nalanthamala psidii comprises two lineages, one of which has been detected only in South Africa.

• β-tubulin gene
• internal transcribed spacer
• Nalanthamala madreeya
• Nalanthamala squamicola
• Nectriaceae
• nuclear large subunit ribosomal DNA
• phylogeny
• systematics
• wilt disease

We thank Amy Rossman, curator of the herbarium BPI, for the loan of specimens and especially for suggesting the correct basionym of the guava pathogen. We thank Gary Samuels (USDA, Beltsville) and Pierre Evrard (MUCL, Belgium) for providing strains; Barry Manicom for providing a specimen of the guava pathogen; Richard Summerbell (CBS), Walter Gams (CBS), Gary Samuels and two anonymous reviewers for critical comments on earlier drafts of this manuscript; Yu-Ming Ju (Institute of Botany, Academia Sinica, Taiwan) for providing an isolate of N. psidii from Taiwan and locating the type of M. psidii; Jan Dijksterhuis (CBS) for help with scanning electron microscopy; and Charity Ramasodi (University of Pretoria) as well as Arien van Iperen and Mieke Starink (CBS) for technical support. We also thank Aimee Hyten (USDA, Beltsville) for sequencing the ITS rDNA of the isolate from Taiwan. The research was financially supported by the National Research Foundation (NRF), members of the Tree Protection Cooperative Programme (TPCP) and the THRIP initiative of the department of Trade and Industry, South Africa.