Forest Pathology最新文献

Platycladus orientalis is widely distributed in China and is an excellent afforestation tree with uses for timber, medicinal, ornamental and landscape purposes. Branch blight was observed on cypress plants in Zhejiang Province of China. Three fungal isolates (CSAL1, CSAL2 and CSAL3) were obtained by tissue isolation from diseased samples. The isolates were identified as Alternaria alternata based on morphological characteristics and a multi-gene phylogenetic tree constructed by combining sequences of the internal transcribed spacer (ITS), large subunit ribosomal RNA (LSU), glyceraldehyde-3-phosphate dehydrogenase (gapdh), translation elongation factor 1-alpha (tef 1) and Alternaria alternata major allergen (Alt a 1). The pathogenicity of the isolates was confirmed by fulfilling Koch's postulates. To the best of our knowledge, this is the first report of A. alternata causing branch blight on P. orientalis in China.

Calonectria leaf blight is among the most prevalent diseases affecting planted Eucalyptus in Southeast Asia. Calonectria reteaudii was recently identified as the main causal agent of a localised epidemic in Malaysia, and a number of isolates were collected from diseased leaves and soils associated with symptomatic trees. This provided an opportunity to gain a better understanding of the pathogen ecology, particularly the relationship between soil and phyllosphere inoculum sources. A set of eight polymorphic SSR markers was used to genotype 21 isolates from leaves and 23 isolates from soils collected beneath infected trees. In addition, mating types of all isolates were identified using PCR-based diagnostic mating-type primers. Low genotypic diversity was found in both the leaf and soil populations of C. reteaudii. However, the isolates from diseased leaves exhibited higher levels of genotypic and genetic diversity compared to those from associated soils. All multilocus genotypes identified in the soil isolates were also represented in the leaf population. While all isolates from the soil were of the MAT1-1 mating type, both MAT1-1 and MAT1-2 were identified in isolates from the diseased leaves, but the MAT1-1/MAT1-2 ratio deviated significantly from a 1:1 ratio. The high level of clonality observed for the isolates suggests that conidia are most likely the primary source of pathogen dispersal. The results also suggest that isolates of C. reteaudii from the soils collected beneath heavily infected trees likely originated from the phyllosphere and not vice versa.

The vital activity of Erysiphe alphitoides, as a major foliar fungal pathogen, causes the most important biotic stress; being chronic disease, this fungal infection spreads throughout the oakeries in Europe. In some cases, this epiphytotic is considered as the main reason for the slowdown in the natural recovery of the common oak population in Europe. The pathogen has the greatest impact on seedlings, resulting in their mortality. We revealed a clearly confirmed unfavorable impact of powdery mildew on all critical and calculated indicators of the Kautsky curve in the infected Quercus robur leaves. Regardless of the type of oak forest, an influence of the fungal pathogen on photosynthetic processes in annual seedlings has been established. In conditions of E. alphitoides-caused biotic stress, Q. robur seedlings experienced violations of the photosynthetic apparatus, progressed over time and depended on the damage severity. The powdery mildew was confirmed to affect most of the plant physiological traits studied. In oak seedlings with the leaf surface damaged by powdery mildew more than 50%, alterations in the chlorophyll fluorescence induction were revealed, quite different in their intensity and direction, compared to the healthy (fungi-unaffected) leaves. This suggests that all the studied parameters might be used as indicators of the most stressed state of common oak seedlings.

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.