Phylogeny,distribution and pathogenicity of Lasiodiplodia species associated with dieback of table grape in the main Brazilian exporting region

Botryosphaeria dieback is an important disease of table grape in the São Francisco Valley, the main Brazilian exporting region. The objectives of this study were to identify species of Lasiodiplodia associated with botryosphaeria dieback of table grapes in the São Francisco Valley, investigate the prevalence and distribution of the species in the region, and evaluate their pathogenicity and virulence in green shoots of table grape. A total of 112 Lasiodiplodia isolates were obtained from 14 vineyards, located in Casa Nova, Juazeiro and Petrolina. Fungal identifications were made using phylogenetic analysis based on partial sequences of translation elongation factor 1‐α (EF1‐α) and internal transcribed spacer (ITS) sequences, in combination with morphometric characteristics of conidia. Eight species of Lasiodiplodia were identified: L. brasiliense, L. crassispora, L. egyptiacae, L. euphorbicola, L. hormozganensis, L. jatrophicola, L. pseudotheobromae and L. theobromae. Except for L. crassispora, L. pseudotheobromae and L. theobromae, all the other species are reported for the first time on grapevine worldwide. The distribution of Lasiodiplodia species differed between the three table grape populations of São Francisco Valley. All Lasiodiplodia species isolated in this study were present in the population of Casa Nova and Lasiodiplodia theobromae was the most prevalent. All species of Lasiodiplodia were pathogenic on detached green shoots of grapevine, with L. brasiliense being the most virulent.     

Urban London plane tree dieback linked to fungi in the Botryosphaeriaceae

Since the first report of the stain canker agent Ceratocystis platani in 2001 in Geneva, dieback of London plane trees (Platanus × acerifolia) has focused greater attention and an epidemiological monitoring has been implemented, as part of a compelling state directive for stain canker management. Genetic identification was carried out in order to ascertain the presence or absence of C. platani. We report here observations recorded between 2011 and 2013, of samplings from a total of 6 plane trees in 4 locations. Identification of bacteria and fungi was performed by sequencing of the rDNA ITS region for fungi, and of the 16S rRNA gene for bacteria. Fungi belonging to the Botryosphaeriaceae species occurred in almost every sampling, whereas Ceratocystis platani was only isolated in 2 trees. The 4 botryosphaeriaceous species, Diplodia mutila, Dothiorella sp., Diplodia seratia and Neofusicoccum parvum, could be responsible for the observed plane cankers, while other fungi could participate in the dieback symptoms. Since these species have been reported as canker agents on other tree species in Europe, artificial infections were carried out with pure cultures of Dothiorella sp., Diplodia mutila and Neofusicoccum parvum on young plane trees. Only Neofusicoccum parvum managed to provoke cork canker symptoms after a few months, but D. mutila and N. parvum were found in internal necrotic tissues. This is the first report of Dothiorella sp., Diplodia mutila and Neofusicoccum parvum associated with plane tree dieback in Switzerland and the first report of pathogenicity of Neofusicoccum parvum in plane trees. This survey showed that most cases of plane tree dieback in the Geneva region were not caused by C. platani and that other fungi could be responsible for similar symptoms.     

Diseases on Eucalyptus species in Zimbabwean plantations and woodlots

Zimbabwe embarked on planting Eucalyptus species in the early 1900s. Based on a robust breeding programme, it has become a major source of seed for other countries in and outside Africa. Tree health surveys conducted on Eucalyptus in some east and southern African countries over the past two decades have revealed several important fungal diseases that were previously not known in the region, but little is known regarding these problems in Zimbabwe. The aim of this study was to identify important Eucalyptus diseases across Zimbabwe's agroclimatic regions. Morphological characteristics and DNA sequence data were used to identify pathogens collected to species level. Widespread stem canker diseases, caused by species belonging to the Botryosphaeriaceae and Teratosphaeriaceae, and leaf spot diseases caused by fungi in the Capnodiales, were identified. Armillaria root and stem rot was restricted to a single site in the Eastern Highlands. Fungi that could cause canker or blue stain of timber were isolated from recently harvested stumps and included species of Ceratocystis and Ophiostoma. This study is the first to identify Eucalyptus pathogens to species level in Zimbabwe and we report for the first time the presence of the stem canker pathogen T. gauchensis in southern Africa. The results will provide a foundation for the formulation of future disease management strategies in the country.     

Botryosphaeriaceae species causing canker and dieback of English walnut (Juglans regia) in Italy

English walnut (Juglans regia) is an important nut crop worldwide and is currently considered emerging in Italy. Botryosphaeriaceae fungi cause symptoms including cankers, discoloration and dieback, and several species are reported across the world on walnut. In this study, symptomatic trees from an orchard in Southern Italy showing branch dieback, cankers, wood discoloration and gummosis were surveyed. Three different fungi from the Botryosphaeriaceae were consistently isolated from symptomatic tissues. Representative isolates were characterized using morphological and molecular approaches based on conidial morphology, optimum growth temperature and the comparison of DNA sequence data from the ITS, tef1‐α and tub2 loci. Three species were identified: Botryosphaeria dothidea, Neofusicoccum mediterraneum and Neofusicoccum parvum. Pathogenicity tests on detached fruits and potted plants showed that all three species were pathogenic. To our knowledge, this is the first report of these Botryosphaeriaceae species causing canker and dieback on English walnut in Italy.     

Pruning quality affects infection of Acacia mangium and A. crassicarpa by Ceratocystis acaciivora and Lasiodiplodia theobromae

Pruning (singling) is a common silvicultural practice in commercial Acacia plantations because these trees tend to have multiple stems. The wounds resulting from pruning are susceptible to infection by pathogens. Ceratocystis acaciivora and Lasiodiplodia theobromae have been shown recently to be important pathogens of A. mangium in Indonesia, where they are commonly associated with wounds on trees. The aim of this study was to determine the impact of different wound types on infection of A. mangium and A. crassicarpa by these two pathogens. Isolates of C. acaciivora and L. theobromae, found to be the most pathogenic in a prior study, were used to inoculate pruning wounds. Results showed that pruning conducted in a manner to reduce stem damage, resulted in lower levels of fungal infection. Where pruning resulted in tearing of the bark, there were higher levels of infection and disease occurred even without artificial inoculation. Inoculation of pruning wounds with C. acaciivora and L. theobromae showed that both fungi have the potential to cause disease. However, C. acaciivora was most virulent. Results of this study showed conclusively that careful pruning will result in lower levels of disease in young A. mangium and A. crassicarpa plantations.     

Botryosphaeriaceae occurring on native Syzygium cordatum in South Africa and their potential threat to Eucalyptus

Eight species of the Botryosphaeriaceae (canker and dieback pathogens) were identified on native Syzygium cordatum in South Africa, based on anamorph morphology, ITS rDNA sequence data and PCR-RFLP analysis. The species identified were Neofusicoccum parvum, N. ribis, N. luteum, N. australe, N. mangiferae , Botryosphaeria dothidea, Lasiodiplodia gonubiensis and L. theobromae . Their pathogenicity on S. cordatum seedlings and a Eucalyptus grandis  ×  camaldulensis clone was determined in glasshouse inoculation trials. Isolates of all identified species, except one of N. mangiferae , were more pathogenic on the Eucalyptus clone than on S. cordatum . Some of the species that cross-infected these hosts, such as N. ribis, N. parvum and L. theobromae , were amongst the most pathogenic on the Eucalyptus clone, while B. dothidea and L. gonubiensis were the least pathogenic. Results of this study illustrate that species of the Botryosphaeriaceae from native hosts could pose a threat to introduced Eucalyptus spp., and vice versa .     

High genetic and virulence diversity detected in Neofusicoccum luteum and N. australe populations in New Zealand vineyards

Genotypic and virulence diversity of Neofusicoccum luteum and N. australe isolates recovered from grapevines displaying symptoms of dieback and decline in New Zealand were investigated. The universally primed PCR (UP‐PCR) method was used to investigate the genetic diversity of 40 isolates of N. luteum and 33 isolates of N. australe. Five UP‐PCR primers produced a total of 51 loci from N. luteum and 57 from N. australe with a greater number of polymorphic loci produced in N. australe (86%) compared with N. luteum (69%). Analysis of UP‐PCR data showed both species found in New Zealand vineyards were genetically diverse at both the inter‐ and intra‐vineyard levels with only a single pair of clonal isolates in N. luteum. Cluster analysis of UP‐PCR data produced four genetic groups in N. luteum and 10 in N. australe (P < 0.05). For both species, there was no relationship between the genetic groups and the origin of isolates. The mean genetic diversity (H) of N. luteum was less than for N. australe, being 0.1791 and 0.2417, respectively. Pathogenicity assays of both species using isolates from either the same or different genetic groups inoculated onto either green shoots or grapevine trunks, showed virulence diversity within the population; however, no correlation was identified between genetic groups and virulence.     

Drought × disease interaction in Eucalyptus globulus under Neofusicoccum eucalyptorum infection

Eucalyptus species are widely spread over the world, being extensively planted and exploited by industries. Drought and pathogens are known to affect the establishment and productivity of Eucalyptus plantations worldwide. The aim of this work was to evaluate the pathogenicity of Neofusicoccum eucalyptorum in drought‐stressed and well‐watered E. globulus plants. The effect of a previous drought priming step and the role of water status at the time of inoculation were evaluated. Lesion length, plant growth and physiological parameters (relative water content, water potential, photosynthetic pigments and lipid peroxidation) were determined. The results indicate that water‐stressed plants were more susceptible to N. eucalyptorum than non‐stressed ones. However, this response was particularly relevant when the plants were inoculated while water limitation was already occurring. Moreover, drought‐primed plants were slightly more resistant to fungal infection than the non‐primed ones. This study reinforces the importance of exploring drought × disease interaction in Eucalyptus and the underlying physiological responses involved in plant performance.     

Susceptibility of grapevine pruning wounds to infection by Lasiodiplodia theobromae and Neofusicoccum parvum

The susceptibility of 1‐ and 2‐year‐old grapevine wood to botryosphaeria canker caused by Lasiodiplodia theobromae and Neofusicoccum parvum was evaluated in California in two seasons. In the 2007 dormant season, pruning‐wound susceptibility was highest when wounds were inoculated immediately after pruning in December (80% of pruning wounds were infected in Chardonnay for both fungal species and 75% and 98% in Cabernet Sauvignon for N. parvum and L. theobromae, respectively). In the 2008 dormant season, pruning‐wound susceptibility was highest in November in Chardonnay (86% and 93% for N. parvum and L. theobromae, respectively) and in December in Cabernet Sauvignon (71% and 75% for N. parvum and L. theobromae, respectively). The lowest infection rates (13–35%) were observed when vines were pruned and inoculated in March in both dormant seasons and for both cultivars. Susceptibility of pruning wounds did not differ significantly (P = 0·7612) between 1‐ and 2‐year‐old wood and consequently, pruning‐wound protection treatments should be applied to all wounds. In conclusion, grapevine pruning wounds were susceptible to infection by L. theobromae and N. parvum to varying extents throughout the dormant season in California (November–March), but, overall, susceptibility of pruning wounds was highest when inoculations were done immediately after pruning and decreased significantly as the interval between pruning and inoculation increased. Results of this study suggest that pruning grapevines in late winter (March) in California would significantly reduce the risk of infection by L. theobromae and N. parvum.     

Susceptibility of Eucalyptus hybrid clones to Botryosphaeria canker in Uganda

ABSTRACT

The study assessed the susceptibility of the nine commonly grown Eucalyptus clones to Neofusicoccum species associated with Botryosphaeria canker in Uganda. The inoculation trials indicated that susceptibility of Eucalyptus hybrids differed significantly (p = .000), clones GU609, GU7, GC578, and GC796 exhibiting a higher tolerance than GC784, GC550, GU8, GC514, and GC540. The results further revealed that N. parvum was more pathogenic than N. kwambonambiense. The generated information can be exploited in sustainable forest management by expanding the growing of tolerant hybrids in areas with high Botryosphaeria canker disease pressure.