Forest Pathology最新文献

Ash dieback (ADB), caused by the invasive fungus Hymenoscyphus fraxineus, has spread extensively across Europe, resulting in considerable economic and ecological damage to European forests. Resistance screening is crucial for selecting and breeding common ash genotypes that are resistant to the ADB pathogen. This requires a standardised and effective method for infecting ash trees with the pathogen and subsequently measuring the infection success. However, to date, there is a lack of scientifically sound comparisons of available methods. In this study, three different methods for testing the resistance of ash genotypes against H. fraxineus (i.e., stem infections, rachis infections, and spore germination assays) were compared and benchmarked against crown defoliation and stem infection assessments. All three resistance assays were performed on 12 ash genotypes covering a wide intraspecific variation in ADB resistance. Stem infections correlated best with crown defoliation observed in the field. However, this method requires a long preparation time and experimental duration. The easiest and fastest method in terms of preparation and execution was the rachis infection assay. Although not completely equivalent to stem infections, the results of the rachis infection assay significantly correlated with the stem lesion lengths measured. Spore germination assays were also quick to carry out, but the timing of sporulation and the sampling of the leaves, followed by agar-medium preparation, proved to be very difficult to synchronise. Following the very small variations in spore germination rates, there was no significant correlation with the stem lesion lengths measured. To obtain meaningful results on the resistance of ash genotypes to ADB, the stem infection method still proved to be the best and most accurate assay. Although new indirect methods for testing resistance in ash trees are arising (e.g., chemistry, spectroscopy, or genetics), direct resistance testing of ash genotypes remains the basis for resistance and breeding research for ash conservation.

Although Erysiphe sambuci has been documented in Pakistan and China since 1960, detailed asexual characteristics and molecular phylogenetic analyses are still lacking at present. Preliminary morphological identification of Erysiphe species infecting newly collected Chinese Sambucus javanica specimens in this study is in well accord with E. sambuci var. sambuci. Morphological re-examination of the holotype specimen of E. sambuci var. crassitunicatae suggests the chain-like swellings in chasmothecial appendages are not universally present, and the thickened ascus walls are statistically insignificant (1.65–5.2 vs. 1.9–4.5 μm, p = 0.8029) compared with that of E. sambuci var. sambuci found on S. javanica in this study. Molecular analyses of these two varieties demonstrate that there are only three nucleotide variations in the ITS regions and complete identity in 28S sequences. Phylogenetic reconstruction places both taxa within a single clade with 100% bootstrap support, rejecting infraspecific differentiation. Given the integrated morphological and phylogenetic evidence, we propose to formally reduce var. crassitunicatae to synonymy with E. sambuci. Powdery mildew species with mycelioid chasmothecial appendages found on S. javanica and S. adnata in China should be assigned to E. sambuci without any separation into varieties.

Two-needle pine blister rust is caused by Cronartium pini, a fungus that can have one of two forms. One requires an alternate host plant to achieve sexual reproduction and thus complete its life cycle (heteroecious), while the other is able to maintain itself clonally on pines (autoecious). Pine blister rust is widely distributed across Eurasia and may cause significant damage in infected natural forests and plantations. In France, the fungus may cause sporadic, local damage to plantations under certain environmental conditions, such as the presence of wild alternate hosts and particular weather conditions. A recent outbreak of this disease was observed on young pine stands in the Landes forest in South-West France, with prevalence levels reaching up to 80% in some stands. This outbreak emerged contemporaneously with the planting of a large peony field in the middle of young pine plantations. Peonies being one of the many alternate hosts for C. pini, this work aimed to investigate whether the latter was present in its alternating or non-alternating form and to study the relationship between the fungal populations attacking both pine trees and peonies. A total of 522 samples of aecia on pines and 108 samples of uredia on peonies were genotyped in 2021 and 2022 by studying seven microsatellite loci. The results showed that the heteroecious form of C. pini largely predominated in both the populations of the two sites sampled in the Landes forest and at the two more distant sites. In addition, the populations sampled from peonies did not differ genetically from those sampled in the pine plots surrounding them, which suggests that peonies participate in the completion of the biological cycle of C. pini on these sites. On the other hand, the populations in the Landes differ from the populations at the more distant sites in France. This study demonstrates that the establishment of natural hosts in the form of peony crops in the middle of pine plantations allowed the fungus inoculum to multiply in its heteroecious form, to increase the disease pressure and, consequently, the severity of damage to pine saplings. The complete removal of peony plots in late 2023 should help reduce the intensity of the disease in the years to come.

Since the detection in Portugal of the pinewood nematode (PWN—Bursaphelenchus xylophilus), in 1999, annual field surveys have been conducted to monitor its spread. These surveys include sampling symptomatic and dead pine trees, mainly Pinus pinaster Aiton, to assess and control the pine wilt disease. A complementary approach involves the use of chemical lures to capture insect vectors of the genus Monochamus (Coleoptera, Cerambycidae), the primary PWN carriers. The lure used (Galloprotect 2D Plus) includes specific pheromones for Monochamus, but also pine volatiles and bark beetles' pheromones. As part of a collaborative study, insects caught in traps placed in Portugal (969 insects, during 2023) and Poland (272 insects, during 2024) were surveyed for the presence of nematodes belonging to the Aphelenchida. In both countries, Spondylis buprestoides (Coleoptera, Cerambycidae) were caught (195 and 150 insects, respectively) and were found to be the only carrying vector of Potensaphelenchus stammeri (Nematoda: Aphelenchoididae). The general morphology of both females and males agreed with the original description for P. stammeri, namely the male spicules and the conspicuous morphology of the female tail. Molecular analysis, performed by sequencing the partial 18S rDNA gene, a fragment spanning the interspacer ITS1 and ITS2 regions and the partial 28S rDNA gene, further confirmed the results of the morphological analysis. This finding highlights the unique relationship between P. stammeri and the insect S. buprestoides and their large distribution in Europe.

Eucalyptus is one of the most widely grown industrial crops worldwide. This wide distribution comes with many diseases due to the wide exchange of germplasm, and Eucalyptus being a suitable host for indigenous pathogens. Eucalyptus plantations in Uganda are affected by stem canker diseases that have reduced productivity. Therefore, it is crucial to understand the prevalence and distribution of canker diseases among species and clones and regions in order to develop management strategies. A nationwide survey on Eucalyptus canker diseases was conducted in different regions, hereafter clusters, of Uganda. The most prevalent disease in all clusters was Botryosphaeria canker, mainly affecting Eucalyptus grandis, E. camaldulensis and the GU hybrid clone (E. grandis × E. urophylla). However, the most severe disease was Teratosphaeria canker, which affected 50% of the GC hybrid clone (E. grandis × E. camaldulensis). The incidence and severity were highest in the Western and Central Uganda clusters, respectively. The incidence and severity varied significantly with age, with 41% of trees less than 5 years in age being the most affected. Plantations with mixed species, mixed hybrid clones and mixed species with hybrids had the lowest disease incidence and severity compared to monocultures. The findings indicated that, although Botryosphaeria canker was the most prevalent of these diseases, Teratosphaeria canker caused more damage to Eucalyptus plantations in Uganda, with the highest severity recorded in monocultures and clusters characterised by high annual rainfall (1244–1356 mm per year). This information will help Eucalyptus growers carry out site-species matching and select appropriate combinations of species and clones for canker disease management and better yields.