Climatic mapping to identify high-risk areas for Cylindrocladium quinqueseptatum leaf blight on eucalypts in mainland South East Asia and around the world

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

Eucalyptus spp. are extensively cultivated in southern China because of their adaptability and versatile timber production. Calonectria leaf blight caused by Calonectria species is considered a major threat to Eucalyptus trees planted in China. The GuangXi Zhuang Autonomous Region is the provincial region with the largest distribution of Eucalyptus plantations in China. The present study aimed to expound the species diversity and pathogenicity of Calonectria isolates obtained from the soil of Eucalyptus plantations in GuangXi. A total of 188 Calonectria isolates were recovered from the soil located close to Eucalyptus trees, and the isolates were identified based on the DNA sequence comparisons of the four partial regions of the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA), and histone H3 (his3) genes. The isolates were identified as Calonectria aconidialis (74.5%), C. hongkongensis (21.3%), C. pseudoreteaudii (2.1%), C. kyotensis (1.6%), and C. chinensis (0.5%). The inoculation results indicated that 40 isolates representing five Calonectria species were pathogenic to the three Eucalyptus genotypes. Two inoculated experiments consistently showed that the longest lesions were produced by the isolates of C. aconidialis. Some isolates of C. aconidialis, C. hongkongensis, and C. kyotensis produced significantly longer lesions than the positive controls, but not the isolates of C. pseudoreteaudii or C. chinensis. These results indicated that Calonectria isolated from the soil may pose a threat to Eucalyptus plantations. Some Calonectria isolates of the same species differed significantly in their virulence in the tested Eucalyptus genotypes. The resistance of different Eucalyptus genotypes to Calonectria isolates within the same species was inconsistent. The inoculation results in this study suggested that many Calonectria isolates in each species had different levels of pathogenicity, and many Eucalyptus genotypes need to be tested to select disease-resistant Eucalyptus genetic materials in the future. The results of the present study enhance our knowledge of species diversity and the potential damage caused by Calonectria in the soil of Eucalyptus plantations. Our results also provide new insights into the breeding of disease-resistant Eucalyptus genotypes for controlling Calonectria leaf blight in China in the future.

Diversity and Distribution of Calonectria Species from Plantation and Forest Soils in Fujian Province, China

To meet the growing demand for wood and pulp products, Eucalyptus plantations have expanded rapidly during the past two decades, becoming an integral part of the southern China landscape. Leaf blight caused by various Calonectria spp., is a serious threat to these plantations. In order to explore the diversity and distribution of Calonectria spp. in Fujian Province soils, samples were collected in Eucalyptus plantations and adjacent plantings of Cunninghamia lanceolata, Phyllostachys heterocycle and Pinus massoniana as well as in natural forests. Three hundred and fifty-three Calonectria isolates were recovered from soil samples and they were identified based on a comparison of multilocus DNA sequence data for the act (actin), cmdA (calmodulin), his3 (histone H3), rpb2 (the second largest subunit of RNA polymerase), tef1 (translation elongation factor 1-alpha) and tub2 (β-tubulin) gene regions, as well as morphological characteristics. Six known taxa including Calonectria aconidialis, Ca. hongkongensis, Ca. ilicicola, Ca. kyotensis, Ca. pacifica, Ca. pseudoreteaudii and one novel species described here as Ca. minensis sp. nov. were identified. Of these, Ca. aconidialis and Ca. kyotensis were the most prevalent species, and found in eight and seven sites, and four and five forest types, respectively. Calonectria spp. were most abundant in soils from Eucalyptus stands, followed by P. heterocycle and natural forests. Relatively few species were found in the soils associated with Cunninghamia lanceolata and Pinus massoniana. The abundance of known Calonectria spp. suggests that these fungi have been relatively well sampled in Fujian. The results are also consistent with the fact that most Calonectria diseases are found on Angiosperm as opposed to Gymnosperm plants.

Calonectria pentaseptata Causes Severe Leaf Disease of Cultivated Eucalyptus on the Leizhou Peninsula of Southern China

Eucalyptus (Myrtaceae, Myrtales) trees are widely cultivated for commercial purposes worldwide. Calonectria leaf blight is one of the most prominent diseases associated with Eucalyptus trees grown in plantations in Asia and South America. Recently, symptoms of leaf blight, shoot blight, tree death, and seedling rot caused by Calonectria species have been observed in commercial Eucalyptus plantations and nurseries in Leizhou Peninsula, which is one of the most densely Eucalyptus-planted areas in southern China. Disease samples were collected from 10 Eucalyptus species and a number of Eucalyptus grandis, E. tereticornis, and E. urophylla hybrid genotypes that were planted on plantations at 13 sites and one experimental nursery. A total of 773 isolates of Calonectria were obtained from 683 plantation trees and nursery seedlings. Fifty-five representative isolates from all the surveyed sites and Eucalyptus species/genotypes were selected for molecular identification. These 55 isolates were identified by DNA sequence analyses based on the calmodulin (cmdA), histone H3 (his3), translation elongation factor 1-alpha (tef1), and β-tubulin (tub2) gene regions, as well as a combination of morphological characteristics. The results indicated that these 55 isolates present one single species, Calonectria pentaseptata. Determined by sequences of cmdA, his3, tef1, and tub2 gene regions, only two genotypes were identified among the 55 representative isolates; 54 of these isolates share the same genotype, suggesting that the genetic diversity of Ca. pentaseptata collected during this study was relatively low. A growth study indicated that Ca. pentaseptata is a high-temperature species. The mating test results suggested that Ca. pentaseptata is heterothallic or lacks the ability to recombine to produce fertile progeny. Inoculation results showed that Ca. pentaseptata causes leaf blight and stem rot, resulting in tree death of the two widely planted Eucalyptus genotypes in southern China, and that the two genotypes differ significantly in their susceptibility to infection by Ca. pentaseptata. A selection program to develop Eucalyptus planting stocks with high levels of resistance to Calonectria leaf blight in China during the long-term should be urgently initiated.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Ten new species of Calonectria from Indonesia and Vietnam

Vietnam and Indonesia have rapidly growing and extensive plantation forestry programs, especially of Acacia spp. and Eucalyptus spp. As these plantations expand, the threat from pests and diseases also increases. Calonectria species are among those pathogens causing diseases of trees in plantations and nurseries in these countries. Extensive surveys were conducted across plantations and nurseries of Vietnam and parts of Indonesia, where a large number of Calonectria isolates were retrieved from diseased leaves and soils associated with symptomatic trees. The aim of this study was to identify and resolve the phylogenetic relationships among these isolates using DNA sequence comparisons of four gene regions as well as morphological characters. From a collection of 165 isolates, the study revealed five known and 10 undescribed species. The relatively high diversity of Calonectria species found in this study supports the view that many more species in this genus remain to be discovered in other areas of Southeast Asia.

NOXious gases and the unpredictability of emerging plant pathogens under climate change

Emerging pathogens of crops threaten food security and are increasingly problematic due to intensive agriculture and high volumes of trade and transport in plants and plant products. The ability to predict pathogen risk to agricultural regions would therefore be valuable. However, predictions are complicated by multi-faceted relationships between crops, their pathogens, and climate change. Climate change is related to industrialization, which has brought not only a rise in greenhouse gas emissions but also an increase in other atmospheric pollutants. Here, we consider the implications of rising levels of reactive nitrogen gases and their manifold interactions with crops and crop diseases.

New species, hyper-diversity and potential importance of Calonectria spp. from Eucalyptus in South China

Plantation forestry is expanding rapidly in China to meet an increasing demand for wood and pulp products globally. Fungal pathogens including species of Calonectria represent a serious threat to the growth and sustainability of this industry. Surveys were conducted in the Guangdong, Guangxi and Hainan Provinces of South China, where Eucalyptus trees in plantations or cuttings in nurseries displayed symptoms of leaf blight. Isolations from symptomatic leaves and soils collected close to infected trees resulted in a large collection of Calonectria isolates. These isolates were identified using the Consolidated Species Concept, employing morphological characters and DNA sequence comparisons for the β-tubulin, calmodulin, histone H3 and translation elongation factor 1-alpha gene regions. Twenty-one Calonectria species were identified of which 18 represented novel taxa. Of these, 12 novel taxa belonged to Sphaero-Naviculate Group and the remaining six to the Prolate Group. Southeast Asia appears to represent a centre of biodiversity for the Sphaero-Naviculate Group and this fact could be one of the important constraints to Eucalyptus forestry in China. The remarkable diversity of Calonectria species in a relatively small area of China and associated with a single tree species is surprising.

Migrate or evolve: options for plant pathogens under climate change

Findings on climate change influence on plant pathogens are often inconsistent and context dependent. Knowledge of pathogens affecting agricultural crops and natural plant communities remains fragmented along disciplinary lines. By broadening the perspective beyond agriculture, this review integrates cross-disciplinary knowledge to show that at scales relevant to climate change, accelerated evolution and changing geographic distribution will be the main implications for pathogens. New races may evolve rapidly under elevated temperature and CO2 , as evolutionary forces act on massive pathogen populations boosted by a combination of increased fecundity and infection cycles under favourable microclimate within enlarged canopy. Changing geographic distribution will bring together diverse lineages/genotypes that do not share common ecological niche, potentially increasing pathogen diversity. However, the uncertainty of model predictions and a lack of synthesis of fragmented knowledge remain as major deficiencies in knowledge. The review contends that the failure to consider scale and human intervention through new technology are major sources of uncertainty. Recognizing that improved biophysical models alone will not reduce uncertainty, it proposes a generic framework to increase focus and outlines ways to integrate biophysical elements and technology change with human intervention scenarios to minimize uncertainty. To synthesize knowledge of pathogen biology and life history, the review borrows the concept of 'fitness' from population biology as a comprehensive measure of pathogen strengths and vulnerabilities, and explores the implications of pathogen mode of nutrition to fitness and its interactions with plants suffering chronic abiotic stress under climate change. Current and future disease management options can then be judged for their ability to impair pathogenic and saprophytic fitness. The review pinpoints improving confidence in model prediction by minimizing uncertainty, developing management strategies to reduce overall pathogen fitness, and finding new sources of data to trawl for climate signatures on pathogens as important challenges for future research.

Novel species of Calonectria associated with Eucalyptus leaf blight in Southeast China

Leaf blight caused by Calonectria spp. is an important disease occurring on Eucalyptus trees grown in plantations of Southeast Asia. Symptoms of leaf blight caused by Calonectria spp. have recently been observed in commercial Eucalyptus plantations in FuJian Province in Southeast China. The aim of this study was to identify these Calonectria spp. employing morphological characteristics, DNA sequence comparisons for the β-tubulin, histone H3 and translation elongation factor-1α gene regions and sexual compatibility. Four Calonectria spp. were identified, including Ca. pauciramosa and three novel taxa described here as Ca. crousiana, Ca. fujianensis and Ca. pseudocolhounii. Inoculation tests showed that all four Calonectria spp. found in this study were pathogenic on two different E. urophylla × E. grandis hybrid clones, commercially utilised in eucalypt plantations in China.

Calonectria species associated with cutting rot of Eucalyptus

Decline in the productivity of Eucalyptus hybrid cutting production in the Guangdong Province of China is linked to cutting rot associated with several Calonectria spp. The aim of this study was to identify these fungi using morphological and DNA sequence comparisons. Two previously undescribed Calonectria spp., Ca. pseudoreteaudii sp. nov. and Ca. cerciana sp. nov. were identified together with Ca. pauciramosa. Calonectria pseudoreteaudii resides in the Ca. reteaudii complex and Ca. cerciana is closely related to Ca. morganii. Connected to the discovery of Ca. pseudoreteaudii, species in the Ca. reteaudii complex were re-considered and the group is shown to accommodate two cryptic species. These originate from Australia and are described as Ca. queenslandica sp. nov. and Ca. terrae-reginae sp. nov.

Species concepts in Calonectria (Cylindrocladium)

Species of Calonectria and their Cylindrocladium anamorphs are important plant pathogens worldwide. At present 52 Cylindrocladium spp. and 37 Calonectria spp. are recognised based on sexual compatibility, morphology and phylogenetic inference. The polyphasic approach of integrating Biological, Morphological and Phylogenetic Species Concepts has revolutionised the taxonomy of fungi. This review aims to present an overview of published research on the genera Calonectria and Cylindrocladium as they pertain to their taxonomic history. The nomenclature as well as future research necessary for this group of fungi are also briefly discussed.

Climate change effects on plant disease: genomes to ecosystems

Research in the effects of climate change on plant disease continues to be limited, but some striking progress has been made. At the genomic level, advances in technologies for the high-throughput analysis of gene expression have made it possible to begin discriminating responses to different biotic and abiotic stressors and potential trade-offs in responses. At the scale of the individual plant, enough experiments have been performed to begin synthesizing the effects of climate variables on infection rates, though pathosystem-specific characteristics make synthesis challenging. Models of plant disease have now been developed to incorporate more sophisticated climate predictions. At the population level, the adaptive potential of plant and pathogen populations may prove to be one of the most important predictors of the magnitude of climate change effects. Ecosystem ecologists are now addressing the role of plant disease in ecosystem processes and the challenge of scaling up from individual infection probabilities to epidemics and broader impacts.