Species Diversity, Mating Strategy and Pathogenicity of Calonectria Species from Diseased Leaves and Soils in the Eucalyptus Plantation in Southern China.

Wenxia Wu,Shuaifei Chen

doi:10.3390/jof7020073

Abstract

Many Calonectria species are causal agents of diseases on several forestry, agricultural and horticultural crops. Calonectria leaf blight is one of the most important diseases associated with Eucalyptus plantations and nurseries in Asia and South America. Recently, symptoms of leaf rot and leaf blight caused by Calonectria species were observed in a one-year-old Eucalyptus experimental plantation in GuangXi Province, southern China. To better understand the species diversity, mating strategy and pathogenicity of Calonectria species isolated from diseased tissues and soils, diseased leaves and soils under the trees from ten Eucalyptus urophylla hybrid genotypes were collected. Three hundred and sixty-eight Calonectria isolates were obtained from diseased Eucalyptus leaves and soils under these trees, and 245 representative isolates were selected based on the sampling substrates and Eucalyptus genotypes and identified by DNA sequence analyses based on the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA) and histone H3 (his3) gene regions, as well as a combination of morphological characteristics. These isolates were identified as Calonectria hongkongensis (50.2%), C. pseudoreteaudii (47.4%), C. aconidialis (1.6%), C. reteaudii (0.4%) and C. auriculiformis (0.4%). This is the first report of C. reteaudii and C. auriculiformis occurrence in China. Calonectria pseudoreteaudii was isolated from both Eucalyptus diseased leaves and soils; the other four species were only obtained from soils. MAT1-1-1 and MAT1-2-1 gene amplification and mating type assignment results showed that C. pseudoreteaudii is heterothallic and an asexual cycle represents the primary reproductive mode, C. reteaudii and C. auriculiformis are likely to be heterothallic and C. hongkongensis and C. aconidialis are homothallic. Based on the genetic diversity comparisons for C. pseudoreteaudii isolates from diseased leaves and soils, we hypothesize that C. pseudoreteaudii in soils was spread from diseased leaves. Both the mycelia plug and conidia suspension inoculations indicated that all five Calonectria species were pathogenic to the two Eucalyptus genotypes tested and the tolerance of the two genotypes differed. It is necessary to understand the ecological niche and epidemiological characteristics of these Calonectria species and to select disease resistant Eucalyptus genotypes in southern China in the future.

Highlights

The Eucalyptus (Myrtaceae, Myrtales) plantation area has expanded to more than 5.4 million hm2 in China, accounting for nearly 2.5% of the national total forestry area
Leaf disease with the typical symptoms caused by Calonectria species was observed in one Eucalyptus experimental plantation in GuangXi Province in southern China
These fungi were identified as C. pseudoreteaudii, C. reteaudii, C. auriculiformis, C. hongkongensis and C. aconidialis

Summary

Introduction

The Eucalyptus (Myrtaceae, Myrtales) plantation area has expanded to more than 5.4 million hm in China, accounting for nearly 2.5% of the national total forestry area. China’s Eucalyptus plantations produce more than 30 million m3 timber per year, accounting for more than 33% of China’s total domestic timber production [1]. Eucalyptus plantations are mainly distributed in GuangXi, GuangDong, YunNan, FuJian, SiChuan and HaiNan Provinces in southern China. Leaf blight caused by Calonectria species is considered to be one of the most important diseases in Eucalyptus plantations in southern China [3,18,20]

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