Calonectria species associated with diseased leaves and soils in southern China Eucalyptus plantations

Abstract

Calonectria leaf blight (CLB) is one of the most important diseases of Eucalyptus trees grown in plantations. This disease poses a serious threat to the sustainability of Eucalyptus plantations in southern China. To better understand the causal agents of CLB, we collected samples of diseased leaves and soil from Eucalyptus plantations from nine regions in Guangdong Province where the disease has become a serious problem. A total of 606 Calonectria isolates were purified from the samples, with 399 and 207 originating from diseased leaves and soils, respectively. Phylogenetic analyses utilizing six gene regions resolved 303 isolates in the C. kyotensis species complex and an equal number of isolates in the C. reteaudii species complex. These two complexes were represented by ten known Calonectria species, including C. aconidialis (12.0%), C. curvispora (0.3%), C. hongkongensis (24.8%), C. ilicicola (0.9%), and C. kyotensis (12.0%) in the C. kyotensis species complex, and C. crousiana (1.0%), C. Guangdongensis (0.3%), C. pseudoreteaudii (40.7%), C. queenslandica (7.3%), and C. reteaudii (0.7%) in the C. reteaudii species complex. Pathogenicity tests showed that all species were capable of causing disease on two tested Eucalyptus genotypes, albeit at varying degrees of aggressiveness. Most isolates (98.3%) in the C. reteaudii species complex were from the diseased leaves, indicating that species in this complex are the main causal agents of CLB outbreak. In addition, a significant number of the C. kyotensis species complex isolates (66.7%) from the soil samples could also cause the disease on Eucalyptus leaves.

Wide Distribution and Intraspecies Diversity in the Pathogenicity of Calonectria in Soil from Eucalyptus Plantations in Southern Guangxi of China

“…This is consistent with the results of previous studies showing that Calonectria species in the C. kyotensis species complex, especially C. aconidialis, C. hongkongensis, and C. kyotensis, are the dominant species distributed in the soil of Eucalyptus plantations in southern China [9,[23][24][25]. In addition to soil isolation, C. aconidialis, C. kyotensis, C. hongkongensis, and C. chinensis were also occasionally isolated from diseased Eucalyptus tissues [8,28,55]. Calonectria hongkongensis also caused fruit rot in rambutan (Nephelium lappaceum L.) in Puerto Rico [57].…”

“…In addition to soil isolation, C. aconidialis , C. kyotensis , C . hongkongensis, and C. chinensis were also occasionally isolated from diseased Eucalyptus tissues [ 8 , 28 , 55 ]. Calonectria hongkongensis also caused fruit rot in rambutan ( Nephelium lappaceum L.) in Puerto Rico [ 57 ].…”

“…Several Calonectria species isolated from blighted Eucalyptus leaves and soil in Eucalyptus plantations in China were pathogenic to the tested Eucalyptus genotypes [ 7 , 8 , 9 , 28 , 29 ]. Some of these species were acquired from diseased Eucalyptus tissues (leaves and branches) and soil close to these trees.…”

Evidence of High Genetic Diversity and Differences in the Population Diversity of the Eucalyptus Leaf Blight Pathogen Calonectria pseudoreteaudii from Diseased Leaves and Soil in a Plantation in Guangxi, China

“…is one of the most prominent diseases of Eucalyptus trees in Southeast Asia and South America [1][2][3][4][5][6][7][8]. C. pseudoreteaudii is one of the dominant species isolated from blighted Eucalyptus leaves, especially among some genotypes of E. urophylla × E. grandis and E. urophylla × E. tereticornis in plantations and nurseries in southern China [4,5,[8][9][10]. It is a heterothallic species that resides in the C. reteaudii species complex [6,[10][11][12][13].…”

“…It is a heterothallic species that resides in the C. reteaudii species complex [6,[10][11][12][13]. In China, C. pseudoreteaudii has been recovered from Eucalyptus in Fujian, Guangdong, Guangxi, and Hainan provinces [4][5][6][8][9][10]14]. C. pseudoreteaudii mainly infects Eucalyptus trees that are less than two years old in the high temperature and humidity season.…”