Species Diversity and Distribution Characteristics of Calonectria in Five Soil Layers in a Eucalyptus Plantation
by LingLing Liu 1,2,WenXia Wu 1 andShuaiFei Chen 1,*
genus Calonectria includes pathogens of various agricultural,
horticultural, and forestry crops. Species of Calonectria are commonly
collected from soils, fruits, leaves, stems, and roots. Some species
of Calonectria isolated from soils are considered as important plant
pathogens. Understanding the species diversity and distribution
characteristics of Calonectria species in different soil layers will
help us to clarify their long-term potential harm to plants and their
patterns of dissemination. To our knowledge, no systematic research has
been conducted concerning the species diversity and distribution
characteristics of Calonectria in different soil layers. In this study,
1000 soil samples were collected from five soil layers (0-20, 20-40,
40-60, 60-80, and 80-100 cm) at 100 sampling points in one
15-year-old Eucalyptus urophylla hybrid plantation in southern China. A
total of 1037 isolates of Calonectria present in all five soil layers
were obtained from 93 of 100 sampling points. The 1037 isolates were
identified based on DNA sequence comparisons of the translation
elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA),
and histone H3 (his3) gene regions, as well as the combination of
morphological characteristics. These isolates were identified as C.
hongkongensis (665 isolates; 64.1%), C. aconidialis (250 isolates;
24.1%), C. kyotensis (58 isolates; 5.6%), C. ilicicola (47 isolates;
4.5%), C. chinensis (2 isolates; 0.2%), and C. orientalis (15 isolates;
1.5%). With the exception of C. orientalis, which resides in the C.
brassicae species complex, the other five species belonged to the C.
kyotensis species complex. The results showed that the number of
sampling points that yielded Calonectria and the number (and percentage)
of Calonectria isolates obtained decreased with increasing depth of the
soil. More than 84% of the isolates were obtained from the 0-20 and
20-40 cm soil layers. The deeper soil layers had comparatively lower
numbers but still harbored a considerable number of Calonectria. The
diversity of five species in the C. kyotensis species complex decreased
with increasing soil depth. The genotypes of isolates in
each Calonectria species were determined by tef1 and tub2 gene
sequences. For each species in the C. kyotensis species complex, in most
cases, the number of genotypes decreased with increasing soil depth.
The 0-20 cm soil layer contained all of the genotypes of each species.
To our knowledge, this study presents the first report of C.
orientalis isolated in China. This species was isolated from the 40-60
and 60-80 cm soil layers at only one sampling point, and only one
genotype was present. This study has enhanced our understanding of the
species diversity and distribution characteristics of Calonectria in
different soil layers