Distribution patterns of Calonectria (Ascomycota, Sordariomycetes, Hypocreales, Nectriaceae) species complexes related to diseased leaves and soil habitats during leaf blight outbreak season in Eucalyptus plantations in southern China

Calonectria leaf blight caused by <i>Calonectria</i> species is one of the most important diseases associated with <i>Eucalyptus</i> plantations in Asia and South America. This study aimed to clarify the distribution patterns of <i>Calonectria</i> species residing in different species complexes associated with diseased trees and soils during leaf blight outbreak season in <i>Eucalyptus</i> plantations in southern China. In this study, 482 <i>Calonectria</i> isolates obtained from diseased <i>Eucalyptus</i> trees and soils under these trees in eight sampling sites in three provinces were identified by DNA sequence analyses of <i>tef1</i>, <i>tub2</i>, <i>cmdA</i>, and <i>his3</i> gene regions. Six species residing in three species complexes were identified: <i>Calonectriapseudoreteaudii</i> and <i>C.acaciicola</i> in the <i>Calonectriareteaudii</i> species complex; <i>C.hongkongensis</i>, <i>C.aconidialis</i>, and <i>C.chinensis</i> in <i>C.kyotensis</i> species complex; and <i>C.auriculiformis</i> in <i>C.cylindrospora</i> species complex. The habitats of <i>Calonectria</i> in different species complexes differed, <i>C.reteaudii</i> species complex inhabits in both diseased trees and soils, <i>C.kyotensis</i> species complex only in soils. The Calonectria leaf blight in the sampled regions was caused by species in the <i>C.reteaudii</i> species complex but not by the species in the <i>C.kyotensis</i> species complex. These findings suggest that the species in the <i>C.reteaudii</i> species complex should receive more attention in disease management, as they are the primary cause of the disease in the sampled regions.