Evaluation of Colletotrichum gloeosporioides for Biological Control of Miconia calvescens in Hawaii

Abstract

Miconia calvescens (Melastomataceae), from the Neotropics, is a noxious forest weed in Hawaii. We evaluated an isolate of Colletotrichum gloeosporioides that causes leaf spots on Miconia spp. in Brazil for its potential in biological control. Hawaii has no native Melastomataceae genera but does have members of 12 introduced genera. Following Wapshere's centrifugal phylogenetic method (2), eight species of Melastomataceae genera in Hawaii were inoculated in addition to Miconia spp. Naturalized and native Hawaiian members of the order Myrtales also were inoculated to determine host specificity, including Terminalia catappa (Combretaceae); Cuphea hysopifolia and C. ignea (Lythraceae); Arthrostema ciliatum, Clidemia hirta, Dissotis rotundifolia, Heterocentron subtriplinervium, Medinilla scortechenii, Melastoma candidum, Pterolepsis glomerata, and Tibouchina herbaceae (Melastomataceae); Eucalyptus grandis, Eucalyptus microcorys, Eugenia reinwardtiana, Eugenia uniflora, Leptospermum laevigatum, Melaleuca quinquenervia, Metrosideros polymorpha, Psidium guajava, and Syzgium malaccanse (Myrtaceae); Fuchsia magellanica and Oenothera stricta (Onagraceae); and Wikstroemia oahuensis and W. uva-ursi (Thymelaeaceae). All M. calvescens plants were grown from seed collected in Hawaii. Other test plants were grown from seeds or cuttings in artificial potting medium in a greenhouse. Plants had 6 to 8 mature leaves when inoculated. C. gloeosporioides was cultured on 10% potato dextrose agar supplemented with plain agar (35 g/liter) and incubated under constant fluorescent illumination at 20°C. Conidia were harvested by flooding 10-to 14-day-old cultures with sterile tap water, followed by light scraping with a scalpel. Conidial suspensions were adjusted to 106 conidia per ml and applied to both leaf surfaces with a hand-held sprayer. Inoculated plants were kept at 100% relative humidity and 16 to 25°C for 48 h. Four replicate plants and one plant of M. calvescens per species were inoculated. Plants were observed for symptom development for up to 6 weeks. The entire test was repeated once. Lesions were visible after 7 to 10 days. Young lesions had chlorotic halos and expanded in a roughly circular pattern to diameters of 5 to 10 mm. Mature lesions developed necrotic centers, coalesced, and became dry and brittle with age, resulting in extensive leaf necrosis. Defoliation of moderately to severely infected leaves occurred ≈ 30 days after inoculation. With the exception of M. calvescens, C. gloeosporioides did not produce visible symptoms on test plants. The failure of Clidemia hirta, the taxonomic species most closely related to M. calvescens, to become symptomatic was particularly significant relative to the centrifugal phylogenetic concept. The results demonstrate that our pathogen (VIC 19306) is distinct from C. gloeosporioides f. sp. clidemiae (1), which did not infect M. calvescens. We designate our pathogen C. gloeosporioides f. sp. miconiae. Voucher specimens (VIC 19306, Sana, RJ, 24.II.1998, and R. W. Barreto) and cultures are maintained at the Departamento de Fitopatologia, Universidade Federal de Viçosa MG, Brazil. References: (1) E. E. Trujillo et al. Plant Dis. 70:974, 1986. (2) A. J. Wapshere. Ann. Appl. Biol. 77:201, 1974.