Journal of Plant Diseases and Protection最新文献

Heavy metals, such as chromium (Cr), are continuously introduced into the environment through human activities, notably from the excessive use of pesticides, synthetic fertilizers, and irrigation with sewage and industrial wastewater. These substances induce oxidative stress in plants, disrupting crucial morphological and biochemical processes. Seed germination and early plant development are vital stages in the life cycle of plants, heavily reliant on nitrogen metabolism and associated biochemical pathways for energy accumulation. This study aimed to assess the phytotoxic effects of chromium on the growth and biochemical parameters of germinating seedlings from two maize varieties, Pak-Afgoi and Neelem Desi. The findings revealed significant suppression caused by chromium, leading to reduced seed germination rates, embryonic growth, vigor index, and biomass. Nitrogen and protein levels, as well as nitrate reductase activity, were notably affected, with Pak-Afgoi showing lower decreases compared to Neelem. Carbohydrate mobilization and total sugar content also decreased with rising chromium concentrations, although Pak-Afgoi exhibited better nitrogen and carbohydrate utilization rates. Furthermore, oxidative stress markers like hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) indicated damage to growth and biochemical attributes in maize. Interestingly, proline levels increased with higher chromium concentrations, suggesting a protective role in maintaining seedling viability during metabolic disruptions. These results underscore the detrimental impact of chromium on maize growth by altering plant nitrogen and carbohydrate metabolisms and inducing oxidative stress.

The South African blueberry industry has grown consistently over the past few years due to an increase in local and international demand. Like many other crops, blueberries are susceptible to grey mould caused by Botrytis cinerea, resulting in significant reductions in yield. In this study, Botrytis isolates were recovered from symptomatic blueberry fruit, flowers, leaves and undifferentiated buds, but were not found as endophytes in healthy tissues. Phylogenetic analysis of the concatenated glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60) and DNA-dependent RNA polymerase subunit II (RPB2) genes identified 88 isolates as B. cinerea strains as well as a single B. pelargonii strain. The results presented in this study are the first to contribute towards the characterisation of B. cinerea populations in South African blueberry orchards.

Leaf rust, caused by the pathogenic biotrophic rust fungus Puccinia triticina (Pt), is one of the most destructive wheat diseases worldwide; its negative impact on crop yields is exacerbated by increasing temperatures due to climate change. Ascarosides are nematode pheromones that induce resistance to microbial pathogens and pests in a wide range of crops, making them valuable components in biocontrol scenarios. We investigated the effect on infection of various wheat (Triticum aestivum) genotypes with the virulent Pt race 77W × R by ascr#18, the major ascaroside secreted into the rhizosphere by plant-parasitic nematodes. Spraying the leaves with ascr#18 24 h before inoculation with fungal uredospores slowed disease development and resulted in a reduction of the number of rust pustules on treated compared to untreated leaves. Dose–response analysis over the nano- and micromolar range revealed a broad optimum concentration down to 0.01nM ascr#18. Microscopic analysis showed very early arrest of the fungus at the appressorial stage, with associated enhanced local accumulation of H₂O₂ and abortive stoma penetration. Similarly, ascr#18 also induced strong resistance to Pt race PKTTS, confirming its race-unspecific biocontrol activity. The results of this study are consistent with and extend previous research that has shown that ascr#18 activates plant immunity and thus protects plants from pathogens even at very low doses.

Root-knot nematodes (RKNs), Meloidogyne spp., are globally important plant-parasitic nematodes with a very broad host range including cucumber. In this research, we evaluated the nematicidal efficacy of commercial Abamectin-CAP (Vertimec 1.8% EC) versus Iranian-produced Abamectin-IAP (Vertimec 2% EC) compared with Cadusafos (Rugby), Trichoderma harzianum T-22 (Tricuran-P), and chicken manure against the cucumber RKN, Meloidogyne javanica, in commercial greenhouses. We also analyzed the effect of the products and amendment on several soil enzymes because of their significant roles in increasing the rate of decomposition and release of plant available nutrients. The results showed highly significant differences among treatments. The highest reduction of second-stage juveniles (J2) in the soil was recorded for Abamectin-CAP and Abamectin-IAP (93–95%), followed by Tricuran-P (90%), Rugby (82%) and chicken manure (65%). Similar results were obtained for the number of J2 and eggs in the root (94%), root gall indexes (94%), egg mass indexes (74–79%), and reproduction percentage (5.4–8.3%) in the Abamectin-CAP and Abamectin-IAP treatments. Enzyme activity assays showed that Rugby and chicken manure both caused a significant decrease in urease activity, followed by Abamectin-CAP and Abamectin-IAP. The highest alkaline phosphatase activity was observed for Abamectin-IAP and Abamectin-CAP, whereas the highest acidic phosphatase activity was in the Abamectin-CAP treatment. The results form a basis for developing integrated pest management strategies for RKN in cucumber.

Cercospora leaf spot (CLS) disease caused by the ascomycete Cercospora beticola is the most widespread fungal leaf disease in sugar beet. Fungicides of two active ingredient classes, quinone-outside inhibitors (QoIs) and demethylation inhibitors (DMIs), were important tools for CLS control. Over the years, C. beticola has become resistant to QoIs and a sensitivity shift has been reported for DMIs. In this study, the mechanisms causing variation in DMI sensitivity in C. beticola isolates from Europe were analyzed. The CYP51 mutations I387M, Y464S, and L144F were detected in many isolates, and most isolates carried the L144F in combination with mutation I309T. Furthermore, single isolates with other mutation combinations have been found. Wildtype isolates were found in low frequency in all European countries. Isolates that contained L144F showed higher EC₅₀ values than those without L144F. Ranges of EC₅₀ values of different CYP51 haplotypes were overlapping, an indication that other resistance mechanisms are present. Mutation L144F is more frequently encoded by codon TTC (96%) than by TTT (4%), and the usage of codon TTC was correlated with increased EC₅₀ values, this being more pronounced for difenoconazole than for mefentrifluconazole. In addition, it could be observed that the usage of codon GAG for E at amino acid position 170, instead of GAA, was more frequently found in isolates with a higher adaptation compared with haplotypes that did not contain L144F. Overall, GAA was present in 67% of all isolates and GAG in 33%, with an unequal distribution within the haplotypes. These data indicate that target site mutations, especially L144F haplotypes, influence DMI sensitivity and that in L144F haplotypes, L144F codon usage might be responsible for variations within L144F haplotypes. The codon usage for E170 may influence sensitivity and increase EC₅₀ variation of wildtype isolates and isolates with “weak” mutations, but not in L144F haplotypes.

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is one of the most important pests and causes major damage to cultivated plants in Turkey. It has recently become a serious problem in Antalya (southwestern Turkey) due to its high resistance to insecticides used. To address this problem, the present study aimed to evaluate the pathogenicity of five indigenous Beuveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) isolates (BbFn-2, BbKm-2, BbSr-2, BbDs-4, and BbDm-2) with high virulence in previous studies against the pest. All the isolates were tested at five different conidial concentrations (1 × 10⁵, 1 × 10⁶, 1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ conidia mL⁻¹) against the nymphs and adults of A. gossypii using Petri dish and pot trials in the laboratory. The results from the bioassays showed that virulence of the isolates increased significantly with elapsed time up to 10 days after inoculation. All five B. bassiana isolates at the highest concentration (1 × 10⁹ conidia mL⁻¹) caused mortalities ranged from 83.3% to 100% in both nymphs and adults 10 days post-treatment. While the LT₅₀ and LT₉₅ values of the isolates were 1.72–2.12 days and 4.81–8.49 days, respectively, for the nymphs, they were calculated for the adults as 1.65–2.54 days and 4.66–12.93 days, respectively. Results of the phylogenetic analysis showed that these five B. bassiana isolates had high similarities (ranging from 99 to 100%) with the other B. bassiana isolates in GenBank. All the results suggest that above-mentioned five indigenous B. bassiana isolates have significant biocontrol potential against A. gossypii.

One of the most important phytosanitary diseases affecting the production and marketing of the 'Hass' avocado fruit is anthracnose, mainly caused by the fungus Colletotrichum gloeosporioides. This disease is controlled with synthetic fungicides, which can cause harm to humans and the environment. Due to this, safer alternatives have been sought, such as biological control. The objective of this study was to isolate and characterize Bacillus spp. strains that biocontrol C. gloeosporioides in 'Hass' avocado fruits. The isolation, purification, and molecular identification of bacteria with biocontroller capacity was carried out. In vitro and in vivo tests were carried out against the pathogen C. gloeosporioides. Furthermore, the percentage inhibition of spore germination, enzymatic profile, and nutrient assimilation were determined. Forty-three native bacterial strains were isolated from the 'Hass' avocado fruit. The strains that showed the greatest antagonistic capacity in vivo against C. gloeosporioides were Bacillus pumilus AB31, B. thuringiensis AB30, B. thuringiensis AB7, and B. thuringiensis AB21. These strains could produce extracellular enzymes, such as phosphatases, proteases, and β-glucosidase, as well as the assimilation of D-ribose and trehalose. The above favors their antagonistic activity. Four strains of the genus Bacillus (one B. pumilus and three B. thuringiensis) can control C. gloeosporioides in 'Hass' avocado.

Efficacy of two Indian isolates of entomopathogenic nematodes (EPNs) viz., Heterorhabditis bacteriophora MK256358 and Steinernema feltiae MK256355 were tested in laboratory against the larvae of cabbage butterfly, Pieris brassicae. Larval mortality was found directly proportional to initial inoculum level of infective juveniles (IJs). Susceptibility of larvae varied with respect to their variable size. H. bacteriophora MK256358 @ 25 IJs/larva caused 100% mortality to 3rd instar larvae at 72 h but @ 75 IJs/larva, the same mortality was achieved in 48 h. S. feltiae MK256355 @ 100 IJs/larva caused 100% mortality to 3rd instar larvae of P. brassicae at 48 h. H. bacteriophora MK256358 @ 25 and 100 IJs/larva resulted in 100% mortality to 4th and 5th instar larvae, respectively at 72 h, however S. feltiae MK256355 was unable to cause 100% mortality to either 4th or 5th instar larvae at any inoculum level or time period used in the study. LD₅₀ and LT₅₀ values of H. bacteriophora MK256358 were lower than S. feltiae MK256355 indicating that less nematode dose and time is required to kill 50% pest population. Reproduction capacity of nematode within the host was directly proportional to individual larval size and nematode inoculum level and for H. bacteriophora MK256358, it was higher and statistically significant (P ≤ 0.05) from S. feltiae MK256355. Our experimental findings open new avenues for utilization of EPNs against P. brassicae and set the basis for safe insect pest management programme.

Wheat powdery mildew is caused by the fungus Blumeria graminis f.sp. tritici which can lead up to 40% of losses in the grain production. Chemical treatment with strobilurins (Quinone outside inhibitors—QoI) is widely used to control the disease. However, a point mutation in the cytochrome b gene (G143A) of the fungus can provide resistance to strobilurins-based fungicides. Five field samples of the fungus were collected from wheat infected plants, and DNA was extracted for the analysis. The bioassay indicated that all samples were resistant to the strobilurin azoxystrobin 50% (Amistar®, 500 g/kg) in in vivo tests. Molecular analysis (allele-specific PCR and sequenced amplicons) confirmed the presence of both alleles (resistant and susceptible to strobilurins) in all samples. To our knowledge, this is the first report of the presence of strobilurin resistance allele G143A in Blumeria graminis f.sp. tritici in Paraguay.

Spiroplasma citri, the causal agent of citrus stubborn disease (CSD), causes significant losses in citrus crops. An efficient pathogen detection system is critical for epidemiology studies, particularly when a large sample size is involved. In this study, we report the development of an immunomolecular assay, immunocapture real-time polymerase chain reaction (IC-qPCR), targeting the spiralin gene for direct detection of S. citri without DNA isolation. This method can use either plant sample extracts or media in which S. citri was cultivated. The IC-qPCR protocol demonstrated a limit of detection for pure S. citri culture at a Ct value of 36.523 with a 10³-fold dilution factor, making it equally sensitive as qPCR, which exhibited signal disappearance at a 10^–3 dilution (Ct value of 37.484). In contrast, the immunological double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) test produced positive results up to a 10^–2 dilution only. For S. citri-infected citrus samples, the established IC-qPCR protocol had a limit of detection at 36.46 Ct with a 1/64-fold dilution factor, matching the sensitivity of qPCR, where signal disappearance occurred at a 1/64 dilution (Ct value of 37.21). On the other hand, the immunological DAS-ELISA test yielded positive results only up to a 1/16 dilution, with optical density (OD) values of 0.364 and 0.113 for 1/16 and 1/32 dilutions, respectively. The IC-qPCR assay shows no cross-reaction for any other highly related spiroplasma species and bacteria affecting citrus trees including Candidatus liberibacter, Xylella fastidiosa, and Xanthomonas campestris pv. citri. Therefore, IC-qPCR assay provides an alternative quick and very sensitive method to screening S. citri, with the advantage of not requiring any concentration or DNA purification steps while still allowing an accurate diagnosis of CSD.