Worldwide diversity of endophytic fungi and insects associated with dormant tree twigs

International trade in plants and climate change are two of the main factors causing damaging tree pests (i.e. fungi and insects) to spread into new areas. To mitigate these risks, a large-scale assessment of tree-associated fungi and insects is needed. We present records of endophytic fungi and insects in twigs of 17 angiosperm and gymnosperm genera, from 51 locations in 32 countries worldwide. Endophytic fungi were characterized by high-throughput sequencing of 352 samples from 145 tree species in 28 countries. Insects were reared from 227 samples of 109 tree species in 18 countries and sorted into taxonomic orders and feeding guilds. Herbivorous insects were grouped into morphospecies and were identified using molecular and morphological approaches. This dataset reveals the diversity of tree-associated taxa, as it contains 12,721 fungal Amplicon Sequence Variants and 208 herbivorous insect morphospecies, sampled across broad geographic and climatic gradients and for many tree species. This dataset will facilitate applied and fundamental studies on the distribution of fungal endophytes and insects in trees

Variation in populations of Phytophthora infestans in Finland and Norway: mating type, metalaxyl resistance and virulence phenotype

v2002okDiss. : Ås : Norges landbrukshøgskole, 200

Variation in populations of Phytophthora infestans in Finland and Norway: mating type, metalaxyl resistance and virulence phenotype

vo

Studies on the new nordic population of Phytophthora infestans to improve late blight forecasting and control

vo

Phenotypic variation in Nordic potato late blight populations in year 2003

vokDiss. : Uppsala : Sveriges lantbruksuniversitet, 200

Field-scale molecular testing of virulent potato soft rot Pectobacteriaceae in Norway

Potato soft rot Pectobacteriaceae (SRP) cause large yield losses and are persistent in seed lots once established. In Norway, different Pectobacterium species are the predominant cause of soft rot and blackleg disease. This work aimed to evaluate the potential of real-time PCR for quantification of SRP in seed tubers, as well as investigating the status of potato seed health with respect to SRP in Norway. A total of 34 seed potato lots, including certified seeds, was grown and monitored over three consecutive years. All seed lots contained a quantifiable amount of SRP after enrichment, with very few subsamples being free of the pathogens. A high SRP prevalence based on a qPCR assay, as well as a high symptom incidence in certified seeds were observed, suggesting that current criteria for seed certification are insufficient to determine tuber health and predict field outcomes. Pectobacterium atrosepticum was the most abundant species in the examined seed lots and present in all lots. Consistently good performance of first generation seed lots with respect to blackleg and soft rot incidence, as well as low quantity of SRP in these seed lots demonstrated the importance of clean seed potatoes. Weather conditions during the growing season seemed to govern disease incidence and SRP prevalence more than seed grade. The impact of temperature, potato cultivar and Pectobacterium species on tuber soft rot development were further examined in tuber infection experiments, which showed that temperature was the most important factor in nearly all cultivars. Large-scale quantification of latent infection and predictive models that include contributing factors like weather, infecting bacterial species and cultivar are needed to reduce soft rot and blackleg

Blight management in the Nordic countries

vo

The role of oospores in the epidemiology of potato late blight

Potato late blight (Phytophthora infestans) is a plant disease feared globally by farmers and the potato industry. P. infestans is a heterothallic oomycete with two mating types. Until recently the pathogen was limited to surviving between seasons as living mycelia in its host plant in most parts of the world. This was due to the fact that populations of P. infestans consisted of only one mating type (A1) in all parts of the world except Mexico, the putative centre of origin of the pathogen. Migration of new genotypes from Mexico, including genotypes of the second mating type (A2) has resulted in that now both mating types can be found worldwide. The formation of oospores is only possible if both mating types coexist. Oospores will give the pathogen the ability of surviving for extended periods of time outside its host, for example in the soil. There are reports of oospore formation under field conditions from many parts of the world. Also, in some places oospores are considered as a new, additional inoculum source and as a consequence the onset of late blight epidemics have become earlier. Oospores are formed through sexual recombination. If they act as a source of inoculum, this will increase the genotypic variation in populations of P. infestans leading to an enhanced adaptability of the pathogen. As a consequence, an earlier start of epidemics caused by oospores in the soil and a more aggressive behaviour of the pathogen due to new sexually formed genotypes could make potato late blight even more difficult to control in the futur