Australasian Plant Pathology最新文献

Coffee leaf rust (CLR) poses a significant threat to coffee crops worldwide, including those grown in Brazil. CLR thrives in climatic conditions ideal for coffee cultivation, which results in its constant presence in Brazilian coffee farms. The intensity of CLR exhibits variations as affected by interannual and spatial climate variability that shape epidemics. The aim of this study was to determine the agro-climatic favourability zones for CLR occurrence in the major coffee-producing regions of Brazil based on region-specific agro-climatic conditions. Climate data spanning from 1961 to 2015 at 46 sites were selected to represent the major coffee-producing regions. Using a CLR infection rate model, daily simulations were performed to calculate the cumulative infection rate (CIR) for each site and growing season, starting from 1^st October to 30^th June of the following year. Based on the CIR values, the sites and seasons were categorised into five favourability classes: Very Low, Low, Medium, High, and Very High. An Agro-Climatic Favourability index (ACFav_index) was developed, considering the frequency of seasons falling within each favourability class. A map displaying four distinct favourability zones across the studied regions was then obtained and showed that most of the traditional coffee-growing areas fell within the Medium to High Favourability zones for CLR. The obtained map, delineating CLR favourability zones, holds practical value for coffee growers, consultants, and policymakers alike. It can guide the selection of CLR-resistant coffee cultivars for new cultivation areas and aid in the development of effective disease control strategies.

Arecanut is an important commercial plantation crop in India, and many farm families depend solely on the arecanut industry. In July 2018, immature nuts were shed heavily due to fruit rot disease in the Western-Ghats region. Though the symptoms were suggestive of common fruit rot disease, they appeared to be unusual. The associated pathogen was isolated from the infected tissue using the standard isolation technique, and an oomycete fungus was consistently isolated from infected nuts. Based on the colony and spore morphology, the pathogen was identified as Phytophthora sp. and by multi-gene sequencing (ITS, β-tub, TEF-1α, and Cox-II) confirmed it as Phytophthora parsiana. The pathogenicity of the isolate (P25) was established by inoculating healthy arecanut fruits with the pin-prick method. To our knowledge, this is the pioneering work that represents the first report of Phytophthora parsiana infecting arecanut in Western-Ghats of Southern India.

The pulse crops widely cultivated in South India for their protein rich grains are negatively affected by whitefly-transmitted begomoviruses (genus Begomovirus, family Geminiviridae) causing yellow mosaic disease (YMD). Here, YMD-inducing begomoviruses were characterized from cultivation areas in Tamil Nadu, South India, with complete sequences of seven DNA-A and eight DNA-B components determined. The pairwise nucleotide sequence comparisons for complete DNA-A showed that both mungbean yellow mosaic virus (MYMV) and mungbean yellow mosaic India virus (MYMIV) were present. The comparisons of nucleotide sequences of YMD begomoviral isolates revealed the presence of five groups of DNA-B components, which showed only 81–88% identity in the common region with their cognate DNA-A. The recombination analysis revealed significant events in the the non-coding and coding regions in DNA-B components, which were predicted amongst the MYMV isolates and between MYMV and MYMIV sequences. The partial tandem repeat constructs of MYMV and MYMIV DNA-A and DNA-B isolates (GenBank Accession Nos. KC911721, KC911724, AF142440 and AF126406) were infectious in blackgram (Vigna mungo), which showed typical YMD symptoms. Also the blackgram genotypes showed different levels of susceptibility and tolerance under experimental inoculation with MYMV and MYMIV. From the results, it is inferred that MYMV and MYMIV have occurred in mixed infection in blackgram.

In 2016 and 2017, circular and irregular leaf spots on globe artichoke (Cynara scolymus) were observed in seven locations of the Mediterranean region of Türkiye. In a preliminary microscopic examination, fungal spores in the leaf spots were similar to the genus Cladosporium. However, three different methods (direct transferring, agar-plate, and blotter) were used for isolation of possible causal agent(s) of those leaf spots. Based on morphological and molecular data (ITS and Actin), fungal colonies isolated from those leaf spots belonged to Cladosporium cladosporioides and Cladosporium pseudocladosporioides. Pathogenicity tests were fulfilled using globe artichoke seedlings of cv. Bayrampaşa in a greenhouse. In addition, to detect prevalence of the leaf spots on globe artichoke, surveys were conducted in 79 commercial fields in two consecutive years. As a result, mean disease incidence was 17.4% in 2016, while it was 24.4% in 2017. The results of the present study suggest that Cladosporium cladosporioides and Cladosporium pseudocladosporioides are associated with the leaf spots on globe artichoke. Cladosporium was previously reported to be associated with leaf spots on sycamore fig, papaya, pecan, wheat, eggplant, tomato and ladies palm. To the best of our knowledge, this is the first record of Cladosporium species causing leaf spots on globe artichoke in the world.

Cryphonectria hypovirus 1 (CHV1), as a biological agent, has a great potential for controlling of chestnut blight. CHV1 infects Cryphonectria parasitica, the causal agent of chestnut blight, via horizontal transmission, subsequently weakening the pathogen’s virulence. C. parasitica has a vegetative incompatibility system that restricts the transmission of CHV1 between different vc types, but not completely. This study aimed to determine the horizontal transmission of CHV1 between the vc types related to the C. parasitica population in Aydın Province. The two CHV1 infected isolates, Zgl709, and Fr22, which belong to EU-1 and EU-12 vc types, respectively, were used as the virus donor isolates in the horizontal transmission test. Thirty offspring single ascospore isolates, representing 16 vc types, which were obtained from the sexual cross between a local EU-1 and a local EU-12 isolate, served as the recipients. CHV1 was transmitted 100% if the donor and the recipient were from the same vc type. The average transmission rate between the donor EU-1 (Zgl709) and the recipients from different vc types was 13.6%. Fourteen recipient isolates from 8 vc types (EU-3, EU-4, EU-7, EU-8, EU-25, EU-26, EU-28, and EU-30) were successfully converted to hypovirulent by the donor EU-1. The average transmission rate between the donor EU-12 (Fr22) and the recipients from different vc types was 7.5%. Only 5 recipient isolates from 4 vc types (EU-4, EU8, EU-29, and EU-30) were converted to hypovirulent by the donor EU-12. There was no transmission of CHV1 between EU-1 and EU-12, which are the two dominant vc types present in Aydın Province.

A fungus that resembles Chrysoporthe sp. was found associated with Eucalyptus mini-stumps in clonal mini-gardens in Brazil causing severe losses. The symptoms observed were wilt that evolves into partial or complete drying and death of the canopy, and lesion in the xylem of the mini-stumps. The primary objectives of this research were (i) to determine the causal agent of the wilt disease using morphological and molecular analyses; (ii) to assess the pathogenicity of the isolates on various commercial clones of Eucalyptus; and (iii) to evaluate the impact of temperature on the pathogen’s development. Through phylogenetic analyses of sequences from the Internal Transcribed Spacer, actin, and β-tubulin genes, Chrysoporthe cubensis was identified as the causal agent responsible for the wilt disease. All six tested Eucalyptus clones exhibited susceptibility to the pathogen, with clone CNB 007 demonstrating higher susceptibility and clones CNB 005 and CNB 030 displaying comparatively lower susceptibility. Furthermore, the development of the isolates varied depending on the Eucalyptus clone, with higher temperatures favouring pathogen growth. Notably, the less susceptible clones exhibited greater sensitivity to elevated temperatures compared to the more susceptible ones. This study represents the first report of C. cubensis causing wilt disease on Eucalyptus mini-stumps worldwide.

Dickeya solani associated with other members of Pectobacterium spp. and Dickeya spp. (Pectobacteria) causes the destructive potato blackleg in the Iranian province of Isfahan. The seed tuber dispersal ability and better adaptation of D. solani to warm climates raise major concerns about the spread and establishment of the pathogen across the country. Therefore, monitoring of the target pathogen on potato seeds and diseased plants is necessary to make effective decisions to limit the spread of the pathogen. However, the similarity in symptom development and phenotypic characteristics of Pectobacteria makes it difficult to distinguish D. solani in the collected samples. The aim of the present study was to develop a reliable PCR-based method for the specific detection of D. solani in naturally infected samples. In ERIC-PCR genotyping of different species and subspecies of Pectobacteria, a distinct PCR product around 950 bp was amplified only in D. solani strains. The amplicon was cloned, sequenced, analyzed and found to be highly homologous to the ugpC-1 gene sequence. Based on the sequenced fragment, a primer pair (DSF1/DSR2) was designed that allowed the specific amplification of a 895 bp band from the isolates of D. solani, but not from non-target Pectobacteria and other bacterial species tested in the present study. The approximate limit of detection of the PCR assay has been estimated to be approximately 2.7 × 10⁴ CFU/ml. The developed D. solani specific PCR assay can likely serve as a valuable method for various purposes.