Disease Note.

Recent Outbreak of Bark Canker Caused by Melanconis modonia on European Chestnut in Northern Portugal. C. G. Abreu, Departamento de Proteccao de Plantas, Universidade de Tras-os-Montes e Alto Douro (UTAD), 5000 Vila Real. Portugal. Plant Dis. 80:1301. Accepted for publication 25 July 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1301B.

Diffuse cankers caused by Melanconis modonia Tul. (anamorph Cory-neum modonium (Sacc.) Griffon & Maubl.) have been recorded previously in Portugal, but only on bark that is senescent or when chestnuts are weakened by biotic and abiotic factors (1). A widespread and unexpected outbreak of a diffuse canker on young chestnuts occurred in spring and summer 1995 in northern Portugal. The disease was recorded by UTAD Plant Protection Department and field advisers of the Regional Agriculture Service in the nonirrigated chestnut-growing areas of Bornes, Padrela, Penela, and Vila Real. Observation of conidia from sporulating acervuli and the isolation from the margin of depressed lesions on acidified potato dextrose agar revealed that M. modonia was consistently associated with the cankers. The acervulus was black at maturity with oblong to fusiform conidia that had 5 to 6 septa and measured 40.1 to 60.2 × 12.9 to 17.6 urn. The most affected chestnut orchards were surrounded by new plantations of hybrid chestnuts (Castanea crenata x C. sativa) that are very susceptible to the disease under the weather and crop conditions of Portugal (1). Additionally, a commercial chestnut nursery reported severe problems with the same bark canker in 1995 on CA 90, Marigoule, and Marsol hybrids. In September 1995, a survey at the nursery indicated that up to 75% of the hybrids were infected by M. modonia. This resulted in the entire chestnut field being abandoned and a significant monetary loss to the nursery. The infected neighboring hybrids are suspected of providing primary inoculum and the very dry conditions during the past 4 years in the main chestnut areas probably predisposed the new European chestnut orchards to the fungal infection.