Journal of Phytopathology最新文献

Ustilago maydis, the fungus that causes corn smut disease, leads to significant economic losses in maize cultivars. A key feature of successful plant pathogens is their ability to utilize the plant–pathogen relationship to influence disease progression. Greenhouse experiments examined how pollination and plant genotype affect disease incidence and severity of U. maydis infection. Four U. maydis susceptible maize inbreds (B73, H95, Mo17, and Golden Bantam), and two U. maydis resistant maize-teosinte near-isogenic lines (NIL1 and NIL2) were utilized for this work. Three-hundred and sixty plants (pollinated and unpollinated) from the six plant genotypes were inoculated with U. maydis and assessed based on five phenotypic traits [(1) disease incidence, (2) gall number, (3) gall weight, (4) disease severity, and (5) area under disease progress curve]. All pollinated plants demonstrated significantly (p < .001) lower disease incidence, gall number, gall weight, area under the disease progress curve, and severity in comparison to the unpollinated plants. Both pollinated resistant NILs demonstrated significantly (p < .001) less disease development than the pollinated susceptible maize plants and two unpollinated NILs. Therefore, disease resistance to U. maydis was dependent upon pollination and plant genotype. This provides novel evidence that pollination can significantly improve resistance to U. maydis in different plant genotypes. Enhanced disease resistance observed in the resistant NILs after pollination indicates pollination-mediated resistance is one of the resistance mechanisms functioning in the resistant NILs. Integration of pollination-mediated resistance and resistance introgressed from a maize progenitor will be useful for improving resistance to U. maydis and management of the disease.

Anthracnose is one of the most devastating diseases affecting soybean (Glycine max L. Merril) in India and is incited by the Colletotrichum truncatum species complex. In this study, 33 isolates of Colletotrichum spp. isolates were collected from major soybean-growing states of India. The cultural, morphological and molecular characteristics (Internal Transcribed Spacer rDNA region) of all isolates were demonstrated. Twelve simple sequence repeat (SSR) markers were selected to amplify the genomic DNA of all isolates, to assess the genetic diversity. On the basis of morpho-cultural and molecular characterization of three different Colletotrichum species, C. truncatum, C. cliviicola and C. cholorophyti were identified. Representative Colletotrichum isolates (Ct-Pant, Ct-Gur and Ct-Gag) from each species group were found pathogenic to susceptible soybean variety (PS 1092) and fulfilled Koch's postulates. The SSR genotyping of 33 isolates revealed that all examined SSR markers exhibited a high degree of polymorphism, as indicated by the mean values of 0.51 for polymorphic information content, 1.97 for marker index and 1.99 for resolving power. For each primer, the average number of alleles per locus was 3.58. The results of Jaccard similarity coefficient-based UPGMA (Un-weighted Pair-Group Method with Arithmetic Mean) cluster analysis and principal component analysis showed that isolates of the same species were clustered together, but no clear-cut grouping was obtained on the basis of geographical distribution. Thus, it can be inferred from the study that C. truncatum accessions obtained from various geographical locations of India exhibit substantial genetic variation and a significant level of relatedness.

In 2022, Pyricularia blast-like symptoms were observed in Oplismenopsis najada plants in Argentina. P. oryzae was identified based on its cultural and morphometric characteristics, nucleotide sequencing of ITS1-5.8S-ITS2 amplicons, complemented with phylogenetic analyses, and PCR with Pot2 marker. Koch's postulates were confirmed on O. najada and the Guri INTA CL variety of Oryza sativa. The obtained sequences were deposited in GenBank (ITS: OR741772). The PCR reaction amplified the Pot2 marker, confirming that it is P. oryzae. To our best knowledge, this is the first report of O. najada as new host of P. oryzae worldwide.

The basidiomycete fungus Mycena citricolor hosts on about 80 plant families. The asexual morph causes the disease known as American leaf spot of coffee (Coffea arabica). We isolated and characterized 15 isolates of M. citricolor collected from coffee plants, shade trees and weeds. Cultures on potato-dextrose-agar + yeast extract (PDAY) medium were kept for a week in complete darkness. The cultures were then exposed to light for 7 weeks and co-cultivated with coffee foliar discs, to stimulate the production of gemmifers. We evaluated the speed of growth, appearance, colour of the mycelium and gemmifers production capacity. All isolates conformed to the typical cultural characteristics of M. citricolor, with beige/white thin and slightly aerial mycelium. The whitest isolate was from Persea americana, which had the slowest growth rate in vitro (6.4 mm/day), while the isolate from weed Kalanchoe pinnata was the fastest, with a speed of 9 mm/day. The most gemmifer-producing isolates were those isolated from the coffee cultivar Catimor-Costa Rica 95, Citharexylum donnell-smithii and Cissus verticillata, with over 200 gemmifers per Petri dish. Isolates from Erythrina and Ipomoea nil produced <50 gemmifers on average. The Composite Aggressiveness Index (CAI) was determined on 2-year-old detached coffee branches of the Caturra variety foliage. The least aggressive isolate was from Erythrina poeppigiana (CAI = 0) and the most aggressive was from Kalanchoe pinnata (CAI = 18.87). The isolate from the coffee cultivar Catimor-Costa Rica 95 was more aggressive than that from the cultivar Caturra (CAI = 9.94 vs. CAI = 3.66). Moreover, successful infection occurred only when the apex of gemmae made direct contact with the coffee leaf when using the inoculum derived from C. verticillata and Anredera cordifolia. These results show the variability in the population of the pathogen. This is the first study that characterizes the growth, morphology, reproduction and aggressiveness of M. citricolor obtained from hosts other than coffee. In addition, it is the first to report the use of coffee foliar discs to induce gemmifer production in vitro and to assess and quantify the effect of gemma position when inoculating coffee leaves.

Apples are a popular fruit worldwide and are cultivated in the Xinjiang Uygur Autonomous Region (XUAR) in China. Cytospora canker disease is a serious problem in the apple industry in China. Pathogenicity of all historically recorded Cytospora species from Malus hosts was tested on the leaves and breaches of 13 varieties of apple (Malus domestica) and wild apple (Malus sieversii). Cytospora leucosperma and Cytospora pruinopsis were the most aggressive pathogens on apple and wild apple trees in Xinjiang. Meanwhile, Cytospora leucostoma, Cytospora nivea and Cytospora parakantschavelii were the least aggressive. In addition, Fuji and Golden Delicious were the most Cytospora canker disease-resistant apple varieties and are recommended for future promotion. However, Sitagan and Erzizi were readily infected by Cytospora. Our findings provide a theoretical basis for field disease epidemic monitoring and tailoring disease prevention and control strategies based on the disease resistance of the variety and the aggressiveness of the pathogen.

Plant diseases pose a significant threat to global agricultural productivity and food safety. Early detection and accurate identification of these diseases are essential for effective disease management strategies. Traditional plant disease identification mainly relies on manual observation and experienced expert judgement, which has the disadvantages of being time-consuming, labour-intensive and low efficiency. Given the above problems, this study proposes a method for identifying apple leaf diseases based on a convolutional neural network combining hybrid attention and bidirectional long short-term memory (BiLSTM). Appropriate apple leaf disease samples were selected from multiple public data sets to form an experimental data set. Then, the data set is imported into the improved convolutional neural network for training. Based on the original ResNet18 model, a new convolutional neural network, AppleNet, is constructed by adding a hybrid attention module and modifying the classifier structure. The experimental results show that the average recognition accuracy of AppleNet is 94.66%, which is 2.47% higher than that of the ResNet18 network. In addition, the training time of the model is only slightly increased. The ablation experiment further verified the effectiveness of the model modification. Compared with other advanced models in recognition accuracy and model training time, the superiority of AppleNet is confirmed. This study verifies that deep learning has great potential and application prospects in plant disease identification and provides a new technical solution for intelligent and convenient plant disease identification.

Bacterial leaf blight (BLB) caused by Xanthomonas spp. is an important threat for eucalypt production. Planting of resistant genotypes is the best strategy for eucalypt BLB control. However, selection of resistant clones is challenging since the disease is caused by at least three Xanthomonas species that can be sympatric and cause a range of foliar symptoms. So far, standard area diagrams (SADs) to assess eucalypt BLB severity caused by different Xanthomonas species have not been reported. Here, SADs for eucalypt BLB severity assessment were developed. Plants of five eucalypt genotypes were individually inoculated with different Xanthomonas species and leaves exhibiting lesions varying in colour, shape, and size were digitally scanned for disease assessment. Among 150 scanned leaves, the actual leaf affected area ranged from 0.01% to 55%. Based on these minimum and maximum values and the frequency of severity distribution, the 10 leaves that best represented the distribution of affected leaf area were selected to assemble the SADs. Groups of experienced and inexperienced raters estimated BLB severity on a subset of 50 out of the 150 original leaves without and then with the use of the SADs. Correlation concordance analyses revealed that SADs provided a significant improvement in accuracy, precision and reliability of disease estimates by both rater groups, with higher gains observed for the inexperienced group. The SADs developed in this study will be useful for selection of eucalypt genotypes resistant to BLB under controlled conditions when knowledge on the Xanthomonas species composition is lacking or when local populations are comprised of several species.

Fig mosaic disease (FMD) poses a significant threat to fig (Ficus carica) trees globally. Fig mosaic virus (Emaravirus fici, Family Fimoviridae) is one of the main causes involved in FMD. E. fici has been reported in many countries, including Iran. This research investigated the genetic diversity and distribution of this virus in Kermanshah Province, the third fig-producing region in Iran. In 2021 and 2022, 128 samples, mainly displaying FMD symptoms, were collected from fig trees across nine counties. Using DAS-ELISA with polyclonal antibodies, 86 samples tested positive for fig mosaic virus. The 2-year-old healthy fig saplings grafted with scions from infected trees exhibited mosaic symptoms and tested positive for the virus in DAS-ELISA. Reverse transcription-polymerase chain reaction (RT-PCR) by RdRp-specific primers (E5-s and E5-a) also amplified a DNA fragment with the expected size of about 302 bp from the ELISA-positive samples. Five of the 12 symptomless samples showed positive results in both DAS-ELISA and RT-PCR. This indicates that the absence of symptoms in propagation sources does not imply that they are virus-free. Nucleotide sequences of RT-PCR products confirmed the fig mosaic virus infection. BLAST analysis of 20 samples (GenBank accession numbers OQ552535 to OQ552554) revealed that 19 sequences show high nucleotide identity (93.4%–96.8%) with an isolate from Lorestan Province, Iran (GenBank accession number KT732024). Notably, isolate FM203 showed distinct genetic divergence (86.6%–90.2% nucleotide identity) and shared similarities with some other Iranian isolates, including those from Kermanshah and Mazandaran provinces. Phylogenetic analysis grouped most isolates with the Lorestan isolate, while FM203 was placed in a separate cluster. This study highlighted the widespread presence of fig mosaic virus in Kermanshah Province, emphasizing varying infection rates across different counties, with Dalahoo County (Rijab) showing the highest prevalence.

Pseudostellaria heterophylla, a valuable Chinese herbal medicine, is widely cultivated in China, with a planted area of 5402.7 hm² in Shibing County, Guizhou Province. The occurrence of leaf spot disease represents a significant challenge in the production area. In this study, 30 samples of P. heterophylla exhibiting symptoms of leaf spot were collected from three primary production areas in Guizhou Province. Following isolation and purification, 51 isolates were classified into two genera based on both cultural and conidial characteristics, along with ITS sequence data. Fourteen representative strains were selected for morphological and multigene molecular identification, which revealed that these representative strains were affiliated with Alternaria arborescens species complex (SC), Alternaria tenuissima, Alternaria gaisen, and Sclerotiophoma versabilis. The isolation rates of Alternaria and Sclerotiophoma were 84.3% and 15.7%, respectively. Pathogenicity tests confirmed the identity of the causal agents and demonstrated varying levels of aggressiveness among the different genera and species of pathogens towards P. heterophylla leaves. This study marks the first identification of A. arborescens SC, A. gaisen, and S. versabilis as pathogens causing leaf spot in P. heterophylla in China.

Peach bacterial shot hole is a common global disease of peach trees caused by the pathogen Xanthomonas arboricola pv. pruni (Xap). To preliminarily explore the resistance mechanism of peach bacterial shot hole, leaves of the resistant variety ‘Yanbao’ and the susceptible variety ‘Frederic’ were used as test materials. The contents of total phenols, total flavonoids and lignin were analysed after 1 day of inoculation treatment, and the activities of defence enzymes and cell wall degradation enzymes in the leaves were determined. Furthermore, the resistant substances were screened by combining broad-target metabolomics technology and in vitro antibacterial activity. The results showed that the contents of total phenols, total flavonoids and lignin in peach leaves were related to resistance. The resistant varieties resisted infection by inhibiting the activities of polygalacturonase (PG) and pectin methyl trans-eliminase (PMTE) produced by Xap in peach leaves and increasing the activities of 4-coumarate:coenzyme A ligase (4CL), cinnamic acid-4-hydroxylase (C4H), phenylalanine ammonia lyase (PAL) and peroxidase (POD). A total of six resistant compounds were screened from 85 differential metabolites. The minimum inhibitory concentrations of methyl ferulate (MF), p-coumaric acid (p-CA) and methyl caffeate (MC) on Xap were 0.0625, 00625 and 0.125 mg/mL, respectively, while that of the positive control drug oxytetracycline (OTC) was 0.125 mg/mL. The antibacterial activities of MF and p-CA were better than that of OTC, and MF was equivalent to OTC. In addition, homoeriodictyol, hesperetin and fraxin have certain antibacterial effects. Before inoculation treatment, the contents of MF, p-CA and MC in ‘Yanbao’ were 1.13, 1.24 and 1.96 times higher than those in ‘Frederic’, respectively, while they were 1.29, 1.80 and 1.94 times after inoculation treatment, respectively. During the process of pathogen infection, MF and p-CA in the leaves of resistant peach varieties played a role in inducing resistance, while MC was a component of resistance. The above three cinnamic acid derivatives play an important roles in the resistance of peach bacterial shot hole and are potential control drugs.