Journal of Phytopathology最新文献

Cassava mosaic disease (CMD) causes significant losses in cassava production in Africa. The disease is caused by several cassava mosaic geminiviruses (CMGs) and spread through the use of infected plant materials. The infected plants remain infected throughout their vegetative lifecycle as the disease cannot be controlled by standard plant protection measures. Therefore, it is important to develop inexpensive field-based methods that can be easily adopted by small-scale farmers to sanitize geminiviruses-infected stem cuttings used as planting material. This study aimed at eliminating CMGs from infected cassava stem cuttings by use of salicylic acid (SA), hydrogen peroxide (H₂O₂) and hot water (HW) treatments. Eight varieties of CMD-infected stem cuttings were pretreated with SA (1.25, 2.5 and 5 mM), H₂O₂ (0.5%, 1.0% and 1.5%) or hot water (50 and 55°C) at different exposure times before establishment in the glasshouse for evaluation of subsequent plant growth and geminivirus detection. Based on the cassava varieties used for the different treatments, treatment with hot water at 50°C for 5 min and 1.0% H₂O₂ for 12 h were the most effective in eliminating CMGs with an efficiency of 81.7% and 77.8%, respectively. Salicylic acid at a concentration of 5 mM for 6 h eliminated the viruses in 65.1% of the cuttings. The methods tested herein have the potential for producing planting materials with significantly reduced CMD risk for smallholder farmers and the cassava industry to meet their increasing demand. It could also contribute to the global exchange of germplasm for conservation and breeding programs.

Two members of the Araceae broadly cultivated as ornamentals, namely Epipremnum aureum (common name golden pothos or, in Brazil, jiboia) and Zantedeschia aethiopica (common name arum lily or, in Brazil, copo-de-leite), were observed bearing Cercospora leaf spots. The former is a very common garden plant, whereas the latter is an important crop for the flower industry. An examination of the fungus associated with the disease on each plant revealed a very similar morphology which suggested that those might be conspecific. A polyphasic taxonomic study, including phylogenetic analyses based on act, cal and his3 sequences, was conducted. Both isolates from the two aroids were found to belong to the Cercospora apii complex, but were genetically distinct. Cercospora sp. Q was identified as the etiological agent of the leaf spots on E. aureum, whereas the fungus on Z. aethiopica was found to belong to Cercospora sp. G. Inoculations confirmed the pathogenicity of both isolates to their original hosts, and cross-pathogenicity assessments revealed that both isolates were capable of infecting both E. aureum and Z. aethiopica. The limited morphological and pathological distinction between the fungi on these two hosts reflects the continued difficulty in the taxonomic treatment and species delimitation for Cercospora sp. G, Cercospora sp. Q, as well as other provisional code-based Cercospora spp., and other components of the broad C. apii s. lat. complex. The name Cercospora richardiicola (as C. richardiaecola) was mistakenly used for the fungus on Z. aethiopica in earlier publications and this has been corrected herein.

Corynespora leaf fall disease caused by the fungus Corynespora cassiicola is a major leaf disease of Hevea brasiliensis, the commercial source of natural rubber. Different clones of H. brasiliensis show varying levels of sensitivity towards different strains of C. cassiicola. The genetic mechanism behind the differential sensitivity of H. brasiliensis clones has to be identified in order to develop clones resistant to wider range of C. cassiicola strains. The available information on the sensitivity of H. brasiliensis clones is based on the observation of natural infection or infection of detached leaves. In the present study, the sensitivity of seven H. brasiliensis clones towards two strains of C. cassiicola belonging to two different races was determined using a more precise method by artificial infection of the plants under controlled conditions. Strain CLN 16 was found to be more virulent compared with CSB 16, as it induced more severe symptoms in a shorter period. Among the four different stages of leaves, Stage II leaves with copper brown to apple green colour showed higher sensitivity to both strains followed by Stage III leaves with apple green appearance. Among the clones, RRIM 600 had a higher susceptibility towards CSB 16; however, it was the most resistant clone towards CLN 16. Clone PB 350 showed the highest susceptibility towards CLN 16 whereas RRIM 928 showed the highest resistance towards CSB 16. The present study provides a platform for further studies leading to the development of H. brasiliensis clones with resistance towards wider range of C. cassiicola strains.

This research addresses the presence of Elsinoë phaseoli in Kenya, where information on the biology of this pathogen remains scarce. Employing a multifaceted approach, the study demonstrates the steps taken to isolate, identify, and characterize E. phaseoli as the pathogen responsible for scab on common bean. Field observations confirmed scab symptoms, particularly the prominent pod lesions. Elsinoë phaseoli was isolated from common bean using a targeted streaking method on older acervulus-bearing lesions. Morphological examinations revealed a notable diversity within E. phaseoli colonies, consistent with the characteristics of the genus. Molecular identification through ITS-rDNA sequencing confirmed isolate AscoSK1 obtained in this study as belonging to E. phaseoli, offering a robust species differentiation method. Assessing conidium production required the implementation of five different culture methods. An adaptation of the Scheper et al. (2013) method yielded the highest quantity of conidia from 25 colonies spaced at 1 cm apart, with a conidial yield of 5.0 × 10⁶ conidia per 9-cm-diameter Petri dish. A higher conidial yield was attained after the colonies were pre-incubated on potato dextrose agar in the dark at room temperature for 28 days, followed by a transfer to corn meal agar for an additional 2 days at 20°C. This emphasizes the pivotal influence of incubation duration and pre-culture conditions on the process. This research provides insights into the biology of E. phaseoli and introduces an improved method for enhancing in vitro sporulation of the pathogen, setting groundwork for future research and handling.

Castor bean (Ricinus communis) is a crop of great economic importance in Brazil. It is used for producing oil used in the manufacture of cosmetics and biodiesel. The genus Phytophthora contains pathogens with a wide range of host plants, including ornamentals, fruit and vegetable crops. Among the symptoms induced by Phytophthora species are collar and root rot. This study aimed to identify Phytophthora species causing collar and root rot in castor bean seedlings in the Federal District and test their pathogenicity. Samples of symptomatic plants were collected in four satellite cities in Distrito Federal, Brazil. Fourteen isolates were obtained, and they were initially identified through the morphology of reproductive structures. The isolates were subjected to molecular characterization using phylogeny of the sequences from the ITS region and the Cytochrome Oxidase II gene. Ten isolates of the pathogen were tested for pathogenicity on seedlings of two castor bean accessions and species known to be hosts of P. nicotianae. The isolates were identified as P. nicotianae (12 isolates) and P. palmivora (two isolates). In the pathogenicity test, all isolates were capable of causing disease in castor beans. The isolates of P. nicotianae and P. palmivora varied in pathogenicity to other plant species. This is the first report of P. nicotianae causing collar and root rot in castor bean in the Central-West Region of Brazil. It is also the first report of P. palmivora causing diseases in castor beans in South America.

Postharvest diseases in fruits result in significant losses in the agricultural sector. Among these, green mould, caused by Penicillium digitatum, poses a considerable threat to citrus fruits. This study evaluated the potential of Bacillus amyloliquefaciens strain TV-17C as a biological control agent for managing green mould in oranges. Various concentrations of TV-17C in aqueous suspension were applied to naturally infected orange fruits in the packinghouse at two locations (Hatay and Mersin provinces), while the chemical fungicide fludioxonil 230 SC served as a positive control. The application of B. amyloliquefaciens TV-17C at the dosage of 250 mL 100 L⁻¹ reduced green mould incidence by 90.3% and 89.8% in Hatay and Mersin provinces, respectively. Similarly, fludioxonil 230 SC displayed an efficacy of 91.4% in reducing disease incidence. In summary, this study underscores the potential of B. amyloliquefaciens TV-17C as an efficient biocontrol agent against green mould in oranges. Moreover, a positive correlation between higher concentrations and enhanced efficacy was evident. These findings hold promise for the adoption of sustainable disease management practices in the postharvest citrus industry.

The impact of eight pesticides on the transmission of Tomato leaf curl virus (ToLCV) by the whitefly, Bemisia tabaci Gennadius to tomato, Lycopersicon esculentum (Miller), was studied in the field using a randomized block design. Differences in performance were anticipated because these eight insecticides comprise distinct mechanism of action including both contact and systemic. Increased insecticide efficacy is necessary, particularly in regions with conducive weather conditions that support a healthy whitefly population, to effectively manage the population. There is a need to vary the insecticides used in order to reduce the emergence of resistance in the whitefly population due to the extensive usage of a single mechanism of action for whitefly control. The foliar spray of insecticides was done when first incidence of whitefly was noticed in the field with 15 days of interval. The studies on effect of different insecticides in the management of ToLCV disease through the controlling whitefly population, we evaluated that Chlorantraniliprole 8.8% + Thiomethaxam 17.5% SC was effective in sustaining the yield by reducing the incidence of disease and whitefly population during both the years followed by Spirotetramat 11.01% + Imidacloprid 11.01% SC, Thiamethoxam 12.6% + Lambda cyhalothrin 9.5% ZC and Cyantraniliprole 10.26% OD, respectively.

In a previous study, common bean (Phaseolus vulgaris L.) genotypes were selected in the field for reactions to white mould (WM), caused by Sclerotinia sclerotiorum. These genotypes, along with the resistant control A195, were then evaluated in both field and greenhouse (straw test) conditions. The results showed that field trials effectively identified high-yielding WM-resistant genotypes for dry-irrigated conditions. Here we challenge the results of this study with new data and methodology by conducting six sprinkler-irrigated trials from 2015 to 2017 with five genotype groups (G). Three groups comprised genotypes previously studied: G1, seven partially resistant; G4, two intermediately resistant; and G5, three susceptible. G2 consisted of four lines selected for partial resistance in the current study. The resistant control group, G3, comprised the genotypes A195, G122, Cornell605, and Ouro Branco. WM was absent (one trial), or pressure was either low/moderate (two trials) or moderate/high (three trials). The average seed yield ranged from 2207 (G3) to 3178 kg/ha (G1). The contrast G1, G2 versus G3 was nonsignificant for incidence and severity index, indicating that genotypes selected for resistance in the field were as resistant as the resistant control genotypes. Additionally, the groups selected for resistance yielded 43% more and produced 33% less sclerotia weight compared with the control group. Our results reinforce the effectiveness of selecting WM-resistant genotypes using beans originally bred for purposes other than WM-resistance, specifically targeting dry-irrigated areas. Furthermore, our results suggest that the use of genotypes selected for partial resistance reduces inoculum levels in the soil.

Bacterial halo blight (BHB), caused by Pseudomonas coronafaciens pv. garcae (Pcg), is one of the most significant diseases affecting coffee trees worldwide, resulting in considerable damage and notable losses within coffee production systems. Further research into the epidemiology and aetiology of BHB in coffee plants is essential for developing effective management strategies. Understanding the efficiency of each inoculation methodology in inducing symptoms is crucial for advancing this research. Therefore, this study aimed to assess the efficiency of seven Pcg inoculation methods using five concentrations to enhance the highest BHB intensity. The experimental design was a complete randomized block design in a factorial (7 × 5) variance analysis with four replications. The first three pairs of leaves of coffee seedlings of the cultivar Catuaí Vermelho IAC-99 were inoculated and evaluated for the incidence and severity of BHB. The inoculation methods of Pcg by injury provided higher BHB AUDPCI and AUDPCS values. Among these, the inoculum injection and multi-needle wounding at inoculum concentrations of 1.6 × 10⁹ CFU mL⁻¹ demonstrated higher disease intensity.

Pythium tracheiphilum is a narrow host range oomycete first described infecting lettuce in Italy. Subsequently, the pathogen was reported in many other countries. From 2015 to 2019, Pythium isolates were recovered from lettuce plants with symptoms of leaf rot, wilting and vascular necrosis, collected from commercial fields in different rural localities of Brasilia-DF, Brazil. The isolates were identified as P. tracheiphilum based on morphological and molecular genetic analysis. Pathogenicity tests conducted with four P. tracheiphilum isolates confirmed that the isolates were pathogenic to detached leaves of a loose-hearted lettuce cultivar. This is the first report of P. tracheiphilum infecting lettuces in Brazil.