Tropical Plant Pathology最新文献

Stem rust is one of the most important foliar diseases of wheat crops. This study was conducted to identify pathogenic variation in wheat stem rust fungus (Puccinia graminis f.sp. tritici) population and evaluation of wheat cultivars to emerging dominant races. For handling diseased samples, major wheat growing areas were selected by multistage sampling technique. Accordingly, 4 zones and 6 districts were selected to get representative disease isolates for race analysis. Hierarchical cluster analysis was done to classify cultivars. Fifty seven single pustules of stem rust were isolated from 86 samples, analyzed using twenty stem rust differentials genes and designated to six races. Among identified races, TKKTF was dominant accounting for 38 % of the isolates followed by TKTTF containing 21.1% of the isolates. TTKTT was the most virulent race identified in current study, 95% of Sr genes susceptible including Sr24, an effective stem rust resistance gene to several stem rust races so far encountered in Ethiopia. The cultivars were classified into 4 hierarchical clusters based on their infection reaction. Among 22 cultivars, four showed low infection type (IT) to race under evaluations. The current statuses of rust race warrants the intimate use of gene edition technology that is a fast track for rust mitigation. Moreover, breeding for stem rust should include screening of resistance genes in wild relatives, wide wheat germplasm to develop varieties tolerant to new and emerging races.

The genus Fusarium is largely known due to its economical relevance, affecting several agronomically important crops. The pineapple fusariosis, caused by F. guttiforme, is among the most important diseases in pineapple (Ananas comosus var. comosus (L.) Merrill Cppens & Leal) worldwide, causing seedling and fruit losses estimated in 20% and 40%, respectively. Because this pathogen can potentially induce 100% production losses, studies seeking efficient and long-lasting disease management strategies are required. This study aimed to assess the Fusarium species diversity associated with pineapple fusariosis in the North region of the state of Rio de Janeiro, Brazil. Symptomatic pineapple fruit were collected from different producing areas, and 20 Fusarium isolates were obtained through indirect isolation. The proper fungal species identification was carried out based on nucleotide sequences of the translation elongation factor 1α (tef1) and β-tubulin (tub2) genomic regions. Also, the aggressiveness of Fusarium isolates was evaluated through inoculation of fruit and leaves of the susceptible pineapple cultivar Pérola. The Bayesian phylogenetic analysis reinforced that Fusarium guttiforme was the only species identified infecting pineapple in the North of Rio de Janeiro, with the new isolates forming a monophyletic group with a previously reported F. guttiforme isolate. Although the close genetic relationship observed among tef-1α and β-tub2, at 99.1-100.0% nucleotide identity, differences in aggressiveness were observed. All isolates of F. guttiforme caused lesions on leaves and fruits; however, nine isolates stood out as more aggressive towards fruit, and two as more aggressive on the leaves. The F. guttiforme isolates identified here can be used as inoculum sources to evaluate putative genetic resistance in pineapple breeding programs.

Litchi downy blight, caused by Phytophthora litchii, presents significant challenges to litchi production, storage, and transportation. Previous studies have shown that coumoxystrobin exhibits effective inhibitory activity against P. litchii. Salicylhydroxamic acid (SHAM), an alternative respiratory pathway inhibitor, is commonly used to evaluate the efficacy of cytochrome respiratory pathway inhibitor like coumoxystrobin against fungal phytopathogens in vitro. In this study, the toxicity of SHAM on various developmental stages of P. litchii, including mycelial growth, sporangial germination, zoospore release, and cystospore germination, was assessed. The EC₅₀ values for SHAM were determined as 166.72, 150.69, 333.97, and 240.91 μg/mL, respectively. Subsequently, the activity of coumoxystrobin against P. litchii was assessed in the presence of SHAM at a concentration of 50 μg/mL, which showed slight inhibition below 20% for all four developmental stages. The addition of SHAM significantly improved the inhibitory activity of coumoxystrobin against P. litchii at different stages, with reductions in EC₅₀ values ranging from 7.55- to 122.92-fold. Moreover, respiration assays revealed that a concentration of 5 μg/mL coumoxystrobin inhibited P. litchii mycelial respiration to a lesser extent compared to the combined effect of coumoxystrobin and SHAM. SHAM also enhanced the control efficacy of coumoxystrobin against phytophthora blight development on litchi leaves. Previously, we reported that coumoxystrobin effectively controls postharvest downy mildew on litchi fruit. Consequently, coumoxystrobin holds promise as an agent for litchi downy blight control in the field and after harvest. Furthermore, similar to previous studies, SHAM, an alternative oxidase (AOX) inhibitor, was found to significantly enhance the activity of the two aforementioned QoI fungicides against P. litchii, both in vitro and in vivo. This suggests that further exploration of AOX inhibitors and the role of AOX in plant diseases could contribute to the rational use of QoI fungicides and improve control efficiency for plant diseases.

The surveys for the occurrence of leaf rust (Puccinia triticina) in wheat-growing areas of India were conducted from 2019–2022. The leaf rust appeared sporadically late in the season, and major outbreaks were not recorded. Twenty-nine pathotypes were identified in 963 wheat leaf rust samples analyzed. Pathotype 52 (121R60-1; MHTKL) comprised 55.7% of the population, followed by 77–5 (121R63-1; THTTM), and 52–4 (121R60-1,7; MHTKL) in 19.4 and 10.1% of the samples, respectively. The remaining 30 pathotypes were observed in 14.8% of the pathotyped samples only. The field population of P. triticina was avirulent on Lr9, Lr19, Lr24, Lr25, Lr29, Lr32, Lr39, Lr45, Lr47, and Lr80. A considerable genetic diversity for leaf rust resistance was found in 42 wheat varieties recommended for cultivation from 2020–2022. Twelve Lr genes (Lr1, Lr2a, Lr3, Lr10, Lr13, Lr23, Lr24, Lr26, Lr34, Lr37, Lr46, and Lr68) were inferred in 37 varieties. Among these Lr13, and Lr23 were observed in 13 varieties each followed by Lr10 in 11 varieties, and Lr26 and Lr1 in 5 varieties each. The presence of Lr24, Lr34, Lr37, Lr46, and Lr68 was confirmed through molecular markers. In controlled polyhouse studies, the slow-leaf rusting was observed in five wheat varieties (DBW327, HD3293, HD3298, HD3369, and VL2041) whereas 26 of the 31 varieties conferred race-specific adult plant resistance. These findings would help to further streamline the future resistance breeding program in the Indian subcontinent and strategic management of wheat leaf rust.

The root-lesion nematode, Pratylenchus brachyurus, is a migratory endoparasite with highly polyphagous behavior, able to parasitize a broad variety of plant species, including economically significant crops such as soybean, wheat, corn, rice and cotton. Due to its wide range of hosts, ability to survive for an extended period of time in the absence of a host, asexual reproduction, and global distribution, Pratylenchus brachyurus causes a significant impact in various production systems. The symptoms caused by this nematode are characterized by stunted plants, while infected roots become partially or totally darkened (necrotic) due to extensive lesions in the tissues. The nematode is widespread in many countries, including Brazil, where it has been reported in the central area of the country, particularly in the Cerrado region, and has been arising as an important phytosanitary threat to soybean production. Consequently, this pest requires special attention in its management in various agricultural systems. This review comprehensively describes various aspects of P. brachyurus, including its biology, symptoms, and a compiled and updated source of information regarding the spread and damage caused by P. brachyurus, with a focus on Brazilian agriculture. Additionally, the review provides insights into future approaches that offer promising solutions to this problem.

Purple blotch of onion, a significant disease affecting major onion cultivating regions globally, is often linked with Alternaria species. In this study, symptomatic onion leaves from 11 different fields in Southern Punjab, Pakistan were sampled, resulting in the acquisition of 25 Alternaria isolates. Six isolates were chosen for DNA sequence analysis, which involved the amplification of three DNA regions: internal transcribed spacer (ITS), glyceraldehyde 3‐phosphate dehydrogenase (GAPDH), and the major allergen gene Alt a1. Our findings indicated the presence of two distinct Alternaria species, with A. alternata demonstrating the highest disease severity on the susceptible cultivar, ‘Phulkari’. In vitro bioassay results revealed that the methanolic leaf extract of Datura stramonium exhibited the most significant antifungal activity (68.52%), outperforming Mentha piperita (43.13%) and Calotropis procera (40.16%). Greenhouse experiments showed that aqueous extracts of D. stramonium reduced disease severity by 43.75% and 46.23% when used as a protective measure, and by 41.95% and 38.43% when used as a curative measure in two consecutive years. The D. stramonium methanolic extract was fractionated using organic solvents, revealing varying degrees of antifungal activities: n-butanol (99.31%), chloroform (68.76%), n-hexane (50.56%), and ethyl acetate (62.60%). GC–MS analysis of the n-butanol fraction identified nine compounds, primarily alkaloids. From identified compounds, scopolamine (15.23%), atropine (14.42%), apoatropine (9.55%), 2-methoxy-4-vinylphenol (2.33%) are already reported for their biological activity. Our findings suggest that D. stramonium extracts have potential as an alternative disease control agent against purple blotch of onions.

In Brazilian soybean production, the main annual yield losses are caused by nematodes. One of the principal plant-parasitic nematodes is the root-lesion nematode, Pratylenchus brachyurus. Resistance is among the major tools to manage nematodes, but the correct characterization of genotypes is a challenge. Several factors contribute to accurate phenotyping for nematode resistance, including the density of inoculum, the age of the plant at inoculation, and the timing of plant evaluation. Therefore, the objective of this study was to suggest standardizing the initial inoculum population and plant age at the time of P. brachyurus inoculation. We evaluated the population dynamics of P. brachyurus in a susceptible soybean cultivar until the 100th day after the inoculation based on the nematode reproduction factor (RF) weekly assessment. RF values were low at 30 DAI, and only after 51 DAI, the reproduction of P. brachyurus was sufficient to ensure more precise RF values in the susceptible soybean evaluated. Soybean plants inoculated at different plant ages (0, 10, and 20 days after planting) and inoculum densities (200, 400, 800, 1,600, and 3,200 nematodes per plant) were assessed 70 days after inoculation (DAI) to RF. Based on our data, we recommend that for an accurate classification of soybean genotypes in relation to resistance or susceptibility to P. brachyurus, inoculation should be conducted with 200 to 800 nematodes per plant within 7 to 15 days after sowing, and the evaluation should be done at least 70 days after inoculation.

We hypothesized that foliar-applied fungicide for white mold (WM) management, especially when associated with partially resistant genotypes to WM, could reduce the incidence of common bean seed-borne Sclerotinia sclerotiorum. Seeds from three irrigated field trials with low/moderate, moderate or high WM pressure were evaluated using the Neon test. In these trials, genotype (partially resistant, intermediate resistant, or susceptible to WM) was combined with fluazinam (0, 1, 2, or 3 applications). The fungicide-genotype interaction was nonsignificant for the seed infection frequency of S. sclerotiorum, partially refuting our hypothesis. However, compared to no fungicide application, two applications resulted in a 6.5-fold reduction in the seed infection frequency, indicating that fungicide applications may contribute to reducing seed infection by this fungus.

Wilt disease complex is the most important disease of chickpeas (Cicer arietinum L.) in the production areas from Mexico. Disease symptoms include root rot, yellowing, wilting, poor growth, discoloration of vascular tissues, and death of plants. This study aimed to identify the fusarioid species associated with chickpea wilt in northwest Mexico by the combination of phylogenetic analyses and morphological characterization, as well as to determine their pathogenicity and aggressiveness on chickpea seedlings. A total of 80 isolates of fusarioid fungi were obtained from symptomatic plants of 16 chickpea fields distributed in Sinaloa and Sonora, Mexico. Subsequently, a subset of 41 isolates representing the range of geographic origin was selected for further morphological characterization, phylogeny, and pathogenicity tests. Phylogenetic analyses of partial fragments of the translation elongation factor 1-alpha (tef1-α) and RNA polymerase second largest subunit (rpb2) genes were used to determine the identity of 26 Fusarium isolates and 15 Neocosmospora isolates to species level. Pathogenicity tests were performed on chickpea seedlings (cv. Blanco Sinaloa) under greenhouse conditions. Phylogenetic analyses of 41 fungal isolates of this study allowed the identification of Fusarium languescens (51.2%), Neocosmospora falciformis (36.6%), F. nirenbergiae (7.3%), and F. verticillioides (4.9%). All fungal isolates were found to be pathogenic on chickpea seedlings and a significant difference in aggressiveness was observed.

Foot rot disease caused by Phytophthora capsici is one of the most destructive diseases of black pepper in Vietnam and worldwide. However, other oomycete species such as P. tropicalis and Pythium deliense reported as serious threats to black pepper in India have also been recorded on this plant. The population of oomycetes occurring in black pepper plantations in Vietnam and their pathogenicity have not been investigated in the last decade. To this end, two hundred fifteen oomycete isolates were collected from the root rots and rhizospheric soil of black pepper in the Central Highlands and the Southeast region of Vietnam. Of these, 23 isolates were representatively chosen based on their origin and morphology for DNA sequence analysis of the internal transcribed spacer region, then 11 isolates were further selected for the translation elongation factor 1-alpha and the beta-tubulin gene analyses. Morphology and molecular analyses indicated that P. capsici, P. cinnamomi, P. heveae, P. nicotianae, P. parvispora, P. tropicalis, Phytopythium vexans, and a new species candidate Phytopythium sp. were identified among oomycete isolates. Of these, P. capsici and P. tropicalis could be the prevalent species in black pepper plantations in studied areas. The inoculation tests demonstrated that P. capsici, P. nicotianae and P. tropicalis were pathogenic on both leaves and roots of black pepper. Phytopythium vexans was pathogenic on root only. Meanwhile, P. cinnamomi, P. heveae, P. parvispora and Phytopythium sp. were non-pathogenic.