Tropical Plant Pathology最新文献

Bremia species cause downy mildew disease of Asteraceae, in particular in the subfamilies Cichorioideae and Carduoideae. The most notorious species is B. lactucae, which causes lettuce downy mildew. Previously, it was often assumed that this species causes disease on dozens of different host genera, but recent phylogenetic and morphological studies have shown that most species of Bremia are highly host specific and that B. lactucae might be mostly limited to Lactuca sativa and L. serriola. As a first step towards investigating the diversity of Bremia in Iran, ten fresh samples of downy mildew from Carthamus tinctorius and Sonchus asper were collected in 2017 to 2018 from various regions of Ahvaz in the southwest of Iran and subjected to morphological and molecular characterisation. Phylogenetic analyses based on cox2 sequences of mtDNA indicated that these samples represent two sister species of Bremia, B. milovtzovae sp. nov. and B. sonchi, causal agents of downy mildew on C. tinctorius and S. asper, respectively. Morphologically, B. milovtzovae sp. nov. can be readily distinguished from its sister species, B. sonchi, by more elongated conidia and shorter conidiophores.

Abstract

One hundred and seventy-four symptomatic sugarcane samples infected with sugarcane white leaf (SCWL) phytoplasma were collected from sugarcane growing areas in ten provinces across the North, Northeastern and Central plain of Thailand. Genotyping was performed using 16S rRNA and ITS sequence and multilocus sequence typing (MLST) based on six genes including tuf, secY, leuS, secA, AAA1 and groES. The 16S rRNA sequence analysis indicated that the SCWL phytoplasma population showed nucleotide sequence identity of 99.74% to 99.80% to ‘Candidatus Phytoplasma sacchari’. In silico RFLP analysis clustered the strains into 16SrXI-B and 16SrXI-D subgroups. Most strains (77%) were in the 16SrXI-D group, while 16SrXI-B strains were only found in the Northeastern regions. The 16SrXI-D group coexisted with the 16SrXI-B group in Roi Et, Kalasin, and Mookdahan provinces, but it was found alone in Surin province. Multilocal sequence typing showed genetic variations in six genes including tuf, secY, leuS, secA, AAA1, and groES. These variations resulted in the SCWL population being divided into two distinct groups, that are consistent with the 16SrXI subgroups. Additionally, five strains in this population exhibited recombinant DNA in the tuf, secA, leuS, AAA1 and groES genes. This information about the genetic variability of SCWL phytoplasma in Thailand could be used to develop detection methods and monitoring strategies for the disease management.

Abstract

Since its first detection in commercial peanut fields in 1995, both the prevalence and impact on yield of peanut smut disease, caused by the fungus Thecaphora frezzii, have increased significantly. Concurrently, diverse research groups have investigated the disease through various methodologies, enhancing our scientific knowledge base. This study was designed to collate and analyze the literature on peanut smut comprehensively, presenting a detailed scientometric analysis that traces the trajectory of research from the beginning to the current state. To achieve this goal, bibliographic data about the disease was compiled, and metrics were calculated. The analysis revealed that a small proportion of the scientific output was published in peer-reviewed journals, with epidemiology and breeding being the predominant topics. Collaborative efforts played a pivotal role in advancing the study of this disease. The study also pinpointed the most prolific researchers, participating institutions, and the influence of the published work, alongside other trends. However, despite notable progress in peanut smut research, this progress is insufficiently reflected in peer-reviewed literature, posing a challenge for researchers within this domain. Continued studies are vital for the integrated management of peanut smut, to mitigate further yield losses and prevent the pathogen's spread into new production regions.

Ceratocystis wilt, caused by Ceratocystis fimbriata, is the primary disease affecting kiwifruit (Actinidia spp.) and a major constraint for its cultivation and expansion in Brazil. Additionally, the disease poses a threat to other major kiwifruit-producing countries, such as China, Chile, New Zealand, and Italy, where the disease has not been reported on kiwifruit vines yet. In kiwifruit vines, the infection generally initiates through the roots, but pruning wounds can also serve as an entry point for the pathogen. Currently, there is a dearth of proven effective strategies for controlling this disease, and there is no information on the effectiveness of fungicides for preventing C. fimbriata infection on kiwifruit. In the present study, we evaluated the efficacy of four fungicides: metalaxyl + mancozeb, boscalide + cresoxim-methyl, pyraclostrobin, and copper hydroxide, against C. fimbriata isolates. We found that metalaxyl + mancozeb and pyraclostrobin were the most effective in inhibiting mycelial growth in vitro. However, when evaluating these fungicides as pruning wound protectors in two kiwifruit cultivars, these fungicides were not effective, in the method tested. The results found in the in vitro assays can guide the development of chemical control of Ceratocystis wilt in kiwifruit. Furthermore, as none of the fungicides tested here were effective in protecting pruning wounds against C. fimbriata infection in kiwifruit vines, other active ingredients or application methods must be evaluated in upcoming studies.

Soilborne diseases are an increasing threat to agriculture and natural ecosystems. Olive root and crown rot (ORCR) caused by pathogenic oomycete species has recently been reported in several olive-growing countries as an emerging phytopathological problem causing leaf yellowing, defoliation, twig dieback, and the development of wilting followed by decline of olive trees. Within the oomycetes, several Phytophthora and Pythium species have been reported to cause root and crown rot of cultivated and wild olive trees. Studies have shown that the disease is particularly severe in young olive groves located on poorly drained, occasionally waterlogged clay soils. Modernization of olive orchards induced by the introduction of irrigation, planting on more favourable and heavier soils, and intensification may increase the risk to cultivated olive trees. In addition, the potential for the spread of these oomycetes, as well as changes in precipitation patterns with more frequent heavy rains, would facilitate the development of infections in wild olive forests and olive groves. Therefore, this review summarizes the latest findings and advances regarding the causative agents of ORCR, detection and diagnosis tools, symptoms, disease cycle, epidemiology, and potential management strategies.

Plant diseases caused by seed-borne pathogens cause yield and quality losses and threaten seed production of barley (Hordeum vulgare L.) and food security. The aim of this study was to compare common seed health methods for the diagnosis and detection of Pyrenophora species, and to investigate cell wall degrading enzymes (CWDEs), virulence and aggressiveness of the isolates obtained from pre-basic barley seed fields in Iran. Comparing common seed health methods showed that more fungal isolates were recovered from seeds using the agar plate method compared to freezing blotter, osmotic, embryo count, and seed washing tests. A total of 7 fungal species from 5 genera were identified from 30 different samples of various Iranian barley cultivars. Based on morphological and molecular characteristics, the fungi were identified as Pyrenophora graminea, P. teres f. teres, P. teres f. maculata, Alternaria alternata, Fusarium culmorum, F. graminearum, Rhynchosporium commune and Ustilago nuda f. sp. hordei. This study has shown that barley seed samples carry a wide diversity of fungi. The results showed that the 57 % of the total samples were found to be infected by seed-borne fungi. Among the genera, Pyrenophora was the most abundant fungus. Diverse levels of virulence and aggressiveness were observed for various isolates of Pyrenophora species. Analyzing the activity of CWDEs produced by isolates revealed that xylanase activity was more important than cellulase activity for the virulence of Pyrenophora isolates and enzyme activities affect levels of virulence and aggressiveness of isolates. Therefore, these findings suggest that activity levels of xylanase are correlated with variation in virulence and aggressiveness of Pyrenophora isolates on seedings. This is the first report identifying the seed-borne fungi of Iranian barley cultivars in pre-basic barley seed fields of Iran.

Blast disease caused by Magnaporthe oryzae is one of the major challenges to rice crop production worldwide. Wild and related species are potential source of novel alleles or genes for crop improvement especially for biotic stress resistance. This study was designed to characterize blast resistance in a set of wild introgression lines developed in the background of Indian mega rice variety Swarna. The introgression lines (INLs) under this study showed spectra of resistance across the different blast isolates inoculated. Monogenic differential varieties with known specific Pi genes and the susceptible checks were used in phenotyping. This study confirmed the usefulness of the differential system consisting of monogenic varieties and differential blast isolates for the systematic characterization of resistance in novel germplasm and to understand the genetic architecture of blast resistance. Twelve race specific quantitative trait loci (QTL) for partial resistance to disease were detected in these wild introgression lines from O.nivara using composite interval mapping. Of these, 10 were showing resistance to only one isolate each, while QTL detected in chromosome 3 showed resistance against isolates JPF514 and PHL16. While most of the QTLs mapped to previously reported defense related genes whereas two QTLs qBL2.2 and qBL5.1 between RM106—RM5460 and RM5140—RM289 with PVE% of 12.28 and 12.48 respectively are novel with no known blast resistance related genes reported within the locus. This study helps to provide developing the basis for future investigations on race specific or broad-spectrum resistance in rice and related crop species.

Fungicide application is the most widely adopted method to control white mold epidemics in several crops. The objectives of this study were to assess the sensitivity to thiophanate-methyl (TM), fluazinam and procymidone of 238 Sclerotinia sclerotiorum isolates collected during 2014 to 2017 from soybean (n = 77 isolates), dry bean (49), cotton (28), tomato (22), sunflower (17), and other (45) hosts, in different regions in Brazil; to investigate any mutation in the genome of resistant isolates; and to assess the phenotypic stability of resistant isolates. Fungicide sensitivity was assessed using discriminatory doses for TM (5 µg/mL), fluazinam (0.05 µg/mL), and procymidone (0.5 µg/mL). Compared to the controls, the mycelial growth inhibition of the sensitive isolates by fluazinam, procymidone, and TM varied from 76 to 94%; 68 to 96%; and 67 to 98%, respectively. There was no evidence of resistance to fluazinam or procymidone, but 13 isolates from dry bean fields were resistant to TM, all had a mutation at codon 240 (L240F) of the β-tubulin gene. The phenotypic stability of TM resistant isolates was evaluated during and after 10 transfers in culture medium without fungicide. The mycelial growth rate of six TM-resistant isolates reduced with successive transfers, but there was no reversion to a sensitive phenotype. Resistant isolates to TM were more frequently observed in the northwestern region of Minas Gerais state; and there is evidence for altered growth pattern in vitro for resistant isolates. Management of resistant populations must employ fungicides with different modes of actions.

Southern Brazil has witnessed significant outbreaks of leaf blotch disease in barley over the last decade, leading to substantial losses in grain yield and quality. The increasing importance of this disease is mainly attributed to the shift towards cultivars with higher grain yields and superior malting quality, but they are more susceptible to leaf blotch. A field survey was conducted in the major barley-producing areas of Paraná state using DNA barcoding techniques to identify Bipolaris sorokiniana isolates, the causative agent of spot blotch, aiming to determine the extent of pathogenic variability among the isolates. DNA barcoding and phylogenetic analyses were based on internal transcribed spacers 1 and 2 with the 5.8S region (ITS) of rDNA, glyceraldehyde-3-phosphate dehydrogenase (gapdh), and translation elongation factor 1-α (tef1) genes. Out of the 124 isolates examined, which were collected from 20 commercial barley fields each year in 2020 and 2021, 116 isolates were identified as B. sorokiniana and eight isolates as B. gossypina. Koch's postulates confirmed the pathogenicity of B. gossypina in barley, representing a novel occurrence worldwide. The fungus causes the development of elongated brown lesions surrounded by irregular yellow halos, starting at minute points. Subtle differences between these symptoms and spot blotch caused by B. sorokiniana are discussed. This study also assessed the aggressiveness of 16 B. sorokiniana isolates on potted barley grown under controlled conditions, using a visual infection rate (IR) scale ranging from 1 to 9. Significant differences in aggressiveness were recorded among the isolates, with the IR ranging from 5.1 to 7.4 in the cultivar ANA03 and 5.7 to 8.1 in the cultivar Imperatriz. The interaction between the isolates and cultivars was not significant. These findings could support breeding programs aiming to develop cultivars with genetic resistance to spot blotch disease in Brazil.

Chia seeds production has been growing rapidly since mid-2011 when worldwide nutrition experts highlighted the nutritional values of this superfood. However, little is known about the viral diseases affecting this crop can cause yield losses. This study aimed to investigate the epidemiology of cowpea mild mottle virus (CPMMV) in chia crops in northwestern Argentina and to identify and characterize other viruses that infect this crop. Between 2013 and 2021, symptomatic chia leaves and seeds were collected from 480 plants and analyzed for the presence of CPMMV using PTA-ELISA. Transmission through seeds of naturally infected plants was also tested. In addition, total RNA from one CPMMV-positive plant and four CPMMV-negative plants were sequenced by massive sequencing. The results showed that 17% of the chia plants were infected with CPMMV, and the virus incidence varied from 60–80% in the north to 0–5% in the south of the chia-producing fields in the northwestern region, possibly due to variations in the vector population. CPMMV was not detected in any of the 1530 seedlings that developed from the seeds obtained from infected plants. The complete genome of CPMMV was 8180 nucleotides long and shared more than 96.54% nucleotide identity with nine isolates from Brazil and the USA. In addition, the A component of five other begomoviruses were sequenced, including sida mosaic Bolivia virus 2, which is known to infect chia plants, and four other viruses detected in chia for the first time: soybean blistering mosaic virus, tomato mottle leaf distortion virus, tomato dwarf leaf virus, and Euphorbia severe leaf golden mosaic virus. This study also reports the first detection of tomato mottle leaf curl virus in Argentina and the second detection of Euphorbia severe leaf golden mosaic virus in the world. Moreover, this is the second time that an amalgavirus reported to infect chia plants in India, Salvia hispanica RNA virus 1, was sequenced. Overall, this study provides new insights into the epidemiology and molecular detection of CPMMV and other viruses that infect chia crops, which is important for developing effective strategies for the control of these diseases and for maintaining the sustainable production of this important superfood.