Tropical Plant Pathology最新文献

Sesame (Sesamum indicum L.) is one of the most important oilseed crops in tropical and subtropical regions of the world. Iran is the 16^th sesame producer in the world. Despite long cultivation of sesame and the presence of charcoal rot disease for decades in Iran, comprehensive studies has not been performed on the causal agents of charcoal rot and disease management. The purpose of this research was to identify Macrophomina species causing charcoal rot in major sesame -growing areas of Iran. Samples were collected from sesame plants and two dominant weeds of sesame fields, Amaranthus retroflexus and Convolvolus arvensis, with symptoms of charcoal rot from five provinces of Iran: Bushehr, Fars, Khuzestan, Hormozgan, and Kohgiluyeh & Boyer-Ahmad. All isolates were identified as M. phaseolina based on morphological characters. Molecular identification was performed by phylogenetic analysis of ITS-rDNA and tef1-α regions. All isolates from sesame were confirmed as M. phaseolina while isolates from A. retroflexus and C. arvensis were identified as M. euphorbiicola. The reaction (resistant/susceptible) of eight commercially important sesame cultivars to M. phaseolina and M. euphorbiicola was evaluated under greenhouse conditions. All M. phaseolina isolates caused charcoal rot on root, crown, and stem tissues while M. euphorbiicola-inoculated sesame cultivar were asymptomatic. In this research, we concluded that Behbahan and Dashtestan cultivars could be suggested as the preferable and superior cultivars for cultivation in areas under infestation by M. phaseolina in the South and Southwest Iran.

Southern South America's main winter cash crop is wheat (Triticum aestivum L.). Wheat stripe mosaic virus (WhSMV, Benyviridae) cause soil-borne wheat mosaic disease (SBWMD) in Brazil, and is a recurrent threat that reduces grain yields in southern Brazil and Paraguay. For many years, field tests in Brazil have used visual evaluations of symptom severity to measure how wheat cultivars respond to this virus and even the genetic inheritance of resistance. The WhSMV genome sequencing process made it feasible to detect and quantify the virus just recently. This research aims to determine a correlation between the severity of symptoms and virus titer by measuring WhSMV in wheat cultivars by RT-qPCR using the absolute quantification technique. In a field with a history of the SBWMD, seven cultivars were assessed in order to confirm the symptom manifestation (severity scale), plant height, and grain yield. Primers were designed and developed the RT-qPCR technique to relate visual notes of symptoms (the disease index) with the virus titer. The virus was found in all genotypes and variations between the visual severity and viral titer in the plants were detected, indicating that viral replication is not the only factor affecting the intensity of symptoms in this pathosystem.

Black scurf/stem canker disease, caused by the basidiomycetous fungus Rhizoctonia solani Kühn, became one of the major constraints to potato production worldwide. R. solani isolates of AG-3 are considered the main causal organism of black scurf, characterized by the presence of sclerotial bodies on the surface of potato tubers. R. solani limits the potato plants growth by developing cankers on sprouts, stems and tubers which make tubers ugly due to the appearance of corky spots and elephant hide symptoms on the tubers. To stop the establishment of disease, early detection and precise identification of pathogens are important components of an integrated disease management system. The present review summarizes the current knowledge about symptomology and epidemiology of black scurf, methods for early and accurate detection of black scurf pathogen/s, and molecular basis of potato–R. solani interaction. Elaborative and up-to-date information on various management options including cultural, chemical, biological, genetic manipulation and nanotechnological approaches and their effectiveness for managing black scurf are discussed. Genetic approaches that show promise for the control of black scurf include the development of transgenic lines by overexpressing or silencing pathogenesis-related (PR) genes and genome editing to develop lines with lower susceptibility to the disease is discussed.

The causative agent of olive knot disease is Pseudomonas savastanoi pv. savastanoi (Psv), a member of the P. syringae complex that causes aerial tumors rather than the foliar necrosis and cankers typical of most members of this complex. Following its occurrence in Duhok and Ninevah provinces in Iraq in 2021–2022, this work sought to isolate and characterize Psv using conventionaland molecular methods, and phylogenetic analysis for the first time in Iraq. All 140 bacterial isolates tested negative for Levan production, Oxidase activity, Pectolytic activity on potatoes, and Arginine dihydrolase activity in the LOPAT (levanase test, pectolytic activity, and arginine hypersensitive reaction) assays. The bacteria were Gram-negative, hypersensitive to tobacco, and did not produce spores. Using PCR-based diagnostics and the sequence of iaaL, the phylogenetic placement of fourteen Psv strains were determined. Together with Psv strain LMG5385 (KM593985) in one clade, the phylogeny showed that all fourteen of the Iraqi isolates were grouped together. As a result, it appears that the Psv present in these two Iraqi provinces are monophyletic.

This study assessed the efficacy of five active ingredients (boscalid, carbendazim, cyprodinil, fluazinam, and fludioxonil) at five concentrations (0.01, 0.10, 1.00, 10.00, and 100.00 mg/L a.i.) against nine Macrophomina isolates (M. phaseolina: CMM1556, CMM4748, and CMM4764; M. pseudophaseolina: CMM2163, CMM4815, and CMM4767; and M. euphorbiicola: CMM2158, CMM4868, and CMM4867). We evaluated daily mycelial growth, growth inhibition percentage, and the effective concentration that inhibits 50% of the radial mycelial growth (EC₅₀). Additionally, the in vivo impact of fluazinam and fludioxonil on the incidence and severity of root rot and vine decline, as well as melon plants biometrics, were determined. Increasing fungicide dose resulted in a higher percentage of mycelial growth inhibition, with the most favorable outcomes observed at 100.00 mg/L a.i. for all tested products. Overall, the Macrophomina isolates exhibited greater tolerance to boscalid (EC₅₀ = 13.40 mg/L a.i.), followed by cyprodinil (EC₅₀ = 1.18 mg/L a.i.), carbendazim (EC₅₀ = 0.05 mg/L a.i.), fluazinam (EC₅₀ = 0.03 mg/L a.i.), and fludioxonil (EC₅₀ = 0.03 mg/L a.i.). The latter two demonstrated high efficacy in vitro. While none of the products achieved complete control of the fungus in vivo, the lowest incidence and severity of root rot and vine decline in melon plants were 28.57% and 0.29, respectively, in plants inoculated with M. euphorbiicola and treated with fludioxonil. For the other species and isolates, fluazinam exhibited better control, resulting in reduced mass loss and root length.

Cymbidium mosaic virus (CymMV) is one of the most important viruses causing economic losses in orchids. The complete genomic sequences of three CymMV isolates collected from Guangdong Province, namely, CymMV-GDFS1, CymMV-GDFS2 and CymMV-GDFS3, were obtained via cloning, sequencing and assembling to clarify the variation and recombination of CymMVs. The mutation analyses of CymMV isolates demonstrated that the gene variation in CymMV followed the order of RdRp >TGBp1 > TGBp2 > TGBp3 > CP. Amongst them, RdRp had the most mutation sites, whereas TGBp3 had the least one. Moreover, the gene mutation of CymMV showed an obvious preference, the main type of mutation was the base transition of T→C or C→T. Notably, a recombinant event was detected in the RdRp gene of CymMV-GDFS1. The complete sequences of the three CymMV isolates shared more than 97% identities at nucleotide levels, phylogenetic relationship analyses revealed that the three CymMV Guangdong isolates belonged to subgroup A. This study provides a theoretical basis for the study of the evolution and pathogenicity of CymMV.

Metalaxyl is the most widely used fungicide to control Phytophthora diseases. A detached leaf bioassay was developed to quantify metalaxyl efficacy using metalaxyl-sensitive (CbP01) and metalaxyl-resistant (CbP03) isolates of Phytophthora palmivora as biological indicators. The linearity of pathogen growth on metalaxyl-treated leaves ranged from 1.6–200 ppm. This assay was applied to determine metalaxyl efficacy on durian leaf after foliar spraying and soil drenching at concentrations of 2 and 4 g/l. Metalaxyl applied as foliar spray inhibited the growth of CbP01 up to 80% for 30 days after application and up to 62–65% inhibition 60 days after application. Soil drenching strongly inhibited the growth of both CbP01 and CbP03 isolates with inhibition greater than 90% for at least 60 days after application. Although soil drenching was more effective than foliar spraying in controlling P. palmivora, soil drenching with 4 g/l metalaxyl resulted in seedling death within 15 days after application. This simple bioassay to evaluate the efficacy and persistence of metalaxyl in planta is beneficial for designing and optimizing metalaxyl application with maximum efficiency and minimum negative impacts on human health and the environment.

White mold, caused by the fungus Sclerotinia sclerotiorum, is one of the most destructive diseases on soybean worldwide and deserves attention regarding its management. In this regard, the hypothesis that spraying nickel (Ni) on soybean plants could increase their resistance against white mold, considering its involvement in the catalytic process of several enzymes and as a constituent of many biomolecules, was investigated. The photosynthetic performance (chlorophyll (Chl) a fluorescence parameters and photosynthetic pigments pools (chlorophyll a + b and carotenoids), concentrations of malondialdehyde (MDA), phenolics, and lignin as well as the expression of defense-related genes [phenylalanine ammonia-lyase (PAL1.1, PAL1.3, PAL2.1, and PAL3.1), chitinase (CHIA1), chalcone isomerase (CHI1B1), lipoxygenase (LOX7), metalloproteinase (MMP2), isochorismate synthase (ICS1 and ICS2), urease (URE), pathogenesis-related protein 1 (PR-1A), and nitrate and nitrite reductase (NIR1-1 and INR-2)] were assessed in plants noninoculated or inoculated with S. sclerotiorum and non-sprayed or sprayed with Ni. Mycelial growth of S. sclerotiorum was inhibited by Ni in vitro. White mold severity for Ni-sprayed plants decreased due to higher foliar Ni concentration, less MDA concentration, a great pool of photosynthetic pigments, and a more preserved photosynthetic apparatus compared to plants non-sprayed with Ni. Higher concentrations of phenolics and lignin linked to up-regulation of PAL1.3, PAL2.1, PAL3.1, CHI1B1, and PR-1A genes for Ni-sprayed plants were important to increase their resistance against white mold. These results highlight the potential of Ni for white mold management in the context of more sustainable agriculture that must prize adequate plant mineral nutrition.