Plant disease最新文献

Apiospora marii (syn. Arthrinium marii) is an ascomycete recently associated with olive tree dieback in Italy and Spain. In this study, a quantitative PCR (qPCR) and a digital droplet PCR (ddPCR) were developed for its detection. Considering the sequences available in GenBank, the ITS region was selected, and two primer/probe sets (AM135 and AM158) were generated. The optimization of the PCR conditions showed that 60°C was the best annealing temperature and 500/250 nM was the best primer/probe concentration in both assays. Under these conditions, 1 fg μl^-1 of A. marii DiSSPA_A1 DNA was detectable by qPCR, corresponding to a Cq value of 32 for AM135 and 33 for AM158. The same concentration was the lowest detected in ddPCR, corresponding to 0.20 and 0.12 c μl^-1, respectively, for AM135 and AM158. The specificity of both primer/probe sets was tested in qPCR and ddPCR using the DNA of microorganisms commonly associated with olive wood and different olive cultivars. Untargeted amplifications were observed using the DNA of some isolates, and consequently the PCR reaction was stopped at the 37th cycle. The primer/probe set AM158 showed the best performance, and it was used for the validation in qPCR and ddPCR using the DNA extracted from healthy, artificially inoculated, and naturally infected olive trees in the field. Both positive amplification and A. marii colonies were always obtained from samples artificially inoculated and from naturally infected olive trees in the field. The diagnostic tools can be used for monitoring A. marii and will be particularly helpful for evaluations on plant propagation material and to investigate aspects of the fungus's lifestyle.

Cryptostroma corticale, the fungus causing sooty bark disease, is a threat to Acer species in Europe and North America. Furthermore, the conidiospores of this fungus are a threat to the health of highly exposed persons or immunocompromised humans. For the detection of C. corticale, species-specific primer pairs ccITS1f/ccITS1r and ccITS2f/ccITS2r were developed and published in 2017. Here we show that these primers are not completely specific for C. corticale. They detect also the closely related species Biscogniauxia grenadensis var. macrospora and B. cinereolilacina. These species are distributed in similar regions to C. corticale, and furthermore B. grenadensis var. macrospora has a similar host range to C. corticale. Therefore, for an unambiguous diagnosis of C. corticale, positive results of the primers ccITS1f/ccITS1r and ccITS2f/ccITS2r should be verified with a sequence analysis of the ITS region or a morphological investigation.

Cladosporium rot is an emerging postharvest disease of blueberries and table grapes in the Central Valley of California. To determine the causal agent(s), 308 isolates of Cladosporium spp. were collected from decayed blueberries and table grapes exhibiting Cladosporium rot symptoms. Phylogenetic analyses of the internal transcribed spacer, actin gene, and translation elongation factor 1-alpha gene, combined with morphological characterization, identified 12 Cladosporium species: C. anthropophilum, C. asperulatum, C. cladosporioides, C. delicatulum, C. floccosum, C. limoniforme, C. macrocarpum, C. ramotenellum, C. subtilissimum, C. tenellum, C. tenuissimum, and C. xylophilum. Ten species were identified with the three most prevalent species being C. asperulatum, C. cladosporioides and C. macrocarpum, accounting for 23.2, 18.9, and 34.1% of the isolates from blueberries, respectively. Seven species were identified with the three prevalent species being C. cladosporioides, C. limoniforme, and C. ramotenellum, accounting for 55.6, 22.9, and 18.1% of the isolates from table grapes, respectively. The optimal temperature for mycelial growth was 20°C for all isolates, except for C. tenuissimum that grew faster at 25°C. Although the species composition differed between the two fruit crops, pathogenicity tests on the fruit inoculated with representative isolates of each species showed that all 12 Cladosporium species were able to cause Cladosporium rot on both fruits. Delineation of species compositions responsible for Cladosporium rot will help develop control methods targeting specific pathogens.

Globodera pallida is a quarantine pest of potato in Idaho, which is being eradicated through use of soil fumigants. Planting trap crops may be helpful for eradication efforts. Globodera pallida requires a hatching factor, without which eggs remain dormant for decades. Trap crops for G. pallida induce hatch but prevent development thereby reducing populations. Prior research suggests that quinoa (Chenopodium quinoa) is a nonhost which induces hatch. Several varieties of quinoa ('Biobio', 'Cherry Vanilla', 'French Vanilla', 'Kailey', 'Oro de Valle', and 'Red Head') were evaluated for G. pallida host status and hatching effect. All quinoa varieties under evaluation were found to be nonhosts that caused greater hatch than bare soil, but less than potato. Quinoa was further assessed as a trap crop in comparison to Solanum sisymbriifolium, a known highly effective trap crop for G. pallida. These trap crops were also investigated in rotation with resistant or susceptible potato. Results from greenhouse and field trials showed that when in rotation with the susceptible potato 'Russet Burbank', quinoa reduced G. pallida progeny cysts by 37 to 40%, while S. sisymbriifolium reduced G. pallida progeny cysts by 82 to nearly 100%. Rotating quinoa, S. sisymbriifolium, or barley to the resistant potato variety 'Innovator' resulted in a G. pallida reproduction factor of nearly zero or zero. As a trap crop, quinoa is not as effective as S. sisymbriifolium but does cause reduction of G. pallida. Ultimately, a resistant potato variety in rotation is also a valuable control measure.

Orobanche cumana predominantly infects sunflower but often occurs in tomato fields in Xinjiang, China. However, it is suspected that the parasitic populations to those two host crops are different species or biotypes. The present study seeks to elucidate this issue through comparison of differences in morphology, genetics, and parasitic ability between populations from different host sources. A field survey showed that the infestation level in sunflower fields was remarkably higher than in tomato fields. Consistent with this, cross-infection experiments showed a preference for sunflowers by O. cumana. Among populations from different hosts, although those populations displayed significant morphological differences, which may stem from regional variations, the main genetic variation occurred within rather than between hosts (Gst = 0.10), with frequent gene exchange among host populations (Nm = 4.52). Populations from different geographical origins exhibited significant differences in morphological traits, with environmental factors such as latitude playing a crucial role in shaping the external morphology of O. cumana. There was low interpopulation variation but high intrapopulation variability (Gst = 0.42) among geographical populations. Genetic distance correlates with geographic distribution, suggesting distance-based isolation among populations (Nm = 0.69). This result indicates substantial genetic potential, which could facilitate the differentiation of more virulent races, posing a greater threat to host crops. It can be concluded that broomrape populations, distributed across various geographical locations and parasitizing both sunflowers and tomatoes, indeed belong to the same species, O. cumana, and that tomatoes serve as an opportunistic host for O. cumana in Xinjiang, China.

Tobacco leaf spot is a major challenge for tobacco leaf production, and the phyllosphere of tobacco is the main habitat for many pathogens. In this study, tobacco leaves with typical symptoms were sampled, and morphological and molecular biological methods were used to identify pathogens. Illumina high-throughput sequencing and Biolog-ECO were used to investigate the composition and carbon metabolic capacity of the microorganisms in the tobacco leaves. A total of 24 fungal isolates were obtained, including one taxon each of Diaporthe, Paramyrothecium, Botrytis, Phoma, and Mortierella; six each of Fusarium and Epicoccum; four of Trichoderma; and three of Alternaria. Six genera of bacteria were isolated: Bacillus, Pantoea, Enterobacter, Pseudomonas, Prolinoborus, and Atlantibacter. Pathogenicity tests revealed that four isolates of Epicoccum and three isolates of Alternaria were pathogenic, and the leaf spot symptoms induced by coinfection with members from these two groups were similar to those observed in the field. These pathogens were identified as Epicoccum latusicollum and Alternaria alternata through multigene analysis. High-throughput sequencing analysis showed that the dominant fungi in diseased tobacco tissues were Alternaria and Epicoccum, and the dominant bacteria were Pseudomonas, Paenibacillus, and Pantoea. In carbon source utilization tests, where various carbohydrates were the main carbon sources, the utilization capacity of phyllosphere microorganisms in diseased tobacco leaves was lower than that in healthy leaves. The combined application of culture-dependent and independent methods provided comprehensive insights into plant disease diagnosis and tobacco phyllosphere microorganism community composition and metabolic function.

Panax notoginseng (Burk.) F. H. Chen, a valuable Chinese herb in Yunnan Province, is highly susceptible to leaf spot disease caused by Boeremia linicola. However, effective control methods for leaf spot in P. notoginseng remain limited. We surveyed understory P. notoginseng populations in Lincang, Lancang, and Xundian, where the incidence rate reached up to 80%, and the disease index was as high as 25 in severe cases. We found that B. linicola can be transmitted through the air and overwinter in infected leaves and soil, with conidia and pycnidia serving as the primary infection source. The optimum growth conditions for the in vitro culture of the pathogenic isolate B. linicola LYB-2 were 20°C and pH 5.0. We also screened potential control agents using plate and colony-inhibition assays. Among the tested agents, tetramycin exhibited 38.56 to 74.67% inhibition against LYB-2, with a half-maximal effective concentration (EC₅₀) of 0.60 mg/liter. Trichoderma atroviride and T. harzianum exhibited inhibition rates of 52.48 and 44.19%, respectively, while Bacillus subtilis reached 78.45%. Field tests demonstrated significant inhibitory effects of B. subtilis, T. atroviride BH-10 preparation, and 0.3% tetramycin, achieving 72.56, 71.3, and 70.2% inhibition, respectively. This study provides a theoretical foundation for ecofriendly management of P. notoginseng leaf spot disease while also establishing a critical scientific basis for disease prediction and sustainable control strategies.

Botrytis spp. cause major economic losses for small fruit growers in Washington and Oregon, the top blueberry- and red raspberry-producing states in the U.S. Pre- and post-harvest fruit rots are conventionally managed through repeated within-season applications of fungicides from various Fungicide Resistance Action Committee (FRAC) groups. As such, monitoring fungicide resistance profiles of Botrytis spp. from small fruit fields is crucial. To this end, in 2022 and 2023 a total of 708 and 305 Botrytis isolates were obtained from blueberry (WA and OR) and red raspberry (WA) fields, respectively. These isolates were screened against technical grade fungicides at discriminatory doses using in vitro conidial germ tube growth assays. Across years, isolates from blueberry showed varying resistance frequencies to fungicides tested: boscalid (60%; FRAC 7), fluopyram (49%; FRAC 7), fluxapyroxad (38%; FRAC 7), isofetamid (21%; FRAC 7), pyrimethanil (19%; FRAC 9), cyprodinil (4%; FRAC 9), pyraclostrobin (68%; FRAC 11), azoxystrobin (62%; FRAC 11), and fenhexamid (34%; FRAC 17). Botrytis isolates from red raspberry displayed the highest resistance frequency to fluopyram (79%), followed by pyrimethanil (31%), boscalid (30%), fluxapyroxad (22%), isofetamid (21%), and cyprodinil (6%). Cross-resistance was prevalent for fungicides in FRAC group 11 and for various fungicide combinations within FRAC group 7. The unique fungicide resistance patterns seen here compared to previous studies in the Pacific Northwest and elsewhere highlight the need for ongoing fungicide resistance monitoring in small fruits.

Trichosanthes kirilowii has long been cultivated for application in traditional Chinese medicine. In this study, we identified two isolates of zucchini green mottle mosaic virus (ZGMMV; species Tobamovirus cucurbitae) from T. kirilowii plants. We determined the complete genome sequences of ZGMMV isolates named ZGMMV-GL-1 and ZGMMV-GL-2. Each ZGMMV genome was 6517 nucleotides (nt) in length, with only a single nucleotide variation detected between two sequences. Sequence analysis revealed that the ZGMMV isolates from this study shared 88.07%-91.62% nucleotide identity with five other ZGMMV isolates deposited in GenBank. Phylogenetic analysis indicated that ZGMMV isolates can be clustered into two distinct groups; our two isolates shared the highest sequence similarity with the ZGMMV isolate from Nanning (GenBank accession no. MF066176) and clustered within Group Ⅱ. The coat protein (CP) gene was cloned from ZGMMV-infected T. kirilowii samples, and the CPZGMMV was expressed using the pET28(a) vector. Specific polyclonal antiserum CPZGMMV was generated by immunizing rabbits with the purified protein, and its sensitivity was determined to be satisfactory. Leveraging the high accuracy and sensitivity of the CPZGMMV antiserum, we developed a rapid, precise, and scalable diagnostic method for ZGMMV. Then, we constructed the full-length cDNA clones (ZGMMV-GL-1 and ZGMMV-GL-2). Additionally, the ZGMMV cDNA infectious clones from T. kirilowii were also able to infect Nicotiana benthamiana and Cucumis sativus systemically, inducing rough-textured and curled leaves in N.benthamiana, mosaic symptoms in C. sativus and T. kirilowii. In this study, we produced an antiserum against the ZGMMV coat protein and developed a sensitive, rapid and reliable diagnostic assay, which lays a technical foundation for the detection and monitoring of ZGMMV. Therefore, the establishment of the ZGMMV infectious clone facilitates further research on viral protein functions, plant-pathogen interactions, and the formulation of effective ZGMMV management strategies.

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, significantly impacts global Brassica napus (canola/rapeseed) production. Because current management relies heavily on timely chemical and cultural methods, developing host resistance is critical to reduce dependence on fungicides and ensure long-term control efficacy. This study aimed to develop a reliable field protocol using S. sclerotiorum-infected inoculum to induce SSR in B. napus and evaluate partially resistant genotypes identified in controlled environments. Several experiments were conducted to evaluate and optimize inoculation techniques on six B. napus cultivars in a series of laboratory, greenhouse, and field experiments. Of the 12 inoculum carriers assessed, the red rice inoculum was selected for further evaluation in the field because of its efficacy as demonstrated in detached-leaf and whole plant assays and its low cost, reliability of production, and ease of application. Using the field inoculation method developed in this study, we found that the semiwinter Japanese lines 'Chikuzen,' 'Chisaya,' and 'Norin28' had partial SSR resistance under field conditions, suggesting a correlation between glasshouse and controlled-environment stem-inoculation assays and whole plant field screens. It also supports the use of these three cultivars as parental lines for future breeding populations containing SSR resistance alleles. The nondestructive, high-throughput field screening methodology developed in this study enables large-scale, reliable screening of B. napus genotypes under various field conditions using cost-effective, easily sourced red rice inoculum applied uniformly to create consistent disease pressure, and it can include multiple isolates.