Races Of Fungus Research Articles

Unraveling Effects of miRNAs Associated with APR Leaf Rust Resistance Genes in Hybrid Forms of Common Wheat (Triticum aestivum L.)

The fungus Puccinia triticina Eriks (Pt) is the cause of leaf rust, one of the most damaging diseases, which significantly reduces common wheat yields. In Pt-resistant adult plants, an APR-type resistance is observed, which protects the plant against multiple pathogen races and is distinguished by its persistence under production conditions. With a more complete understanding of the molecular mechanisms underlying the function of APR genes, it will be possible to develop new strategies for resistance breeding in wheat. Currently, mainly APR genes, such as Lr34, Lr46, and Lr67, are principally involved in resistance breeding as they confer durable resistance to multiple fungal races occurring under different climatic and environmental conditions. However, the mechanisms underlying the defence against pathogens mediated by APR genes remain largely unknown. Our research aimed to shed light on the molecular mechanisms related to resistance genes and miRNAs expression, underlying APR resistance to leaf rust caused by Pt. Furthermore, the present study aimed to identify and functionally characterize the investigated miRNAs and their target genes in wheat in response to leaf rust inoculation. The plant material included hybrid forms of wheat from the F2 and BC1F1 generations, obtained by crossing the resistance cultivar Glenlea (CItr 17272) with agriculturally important Polish wheat cultivars. Biotic stress was induced in adult plants via inoculation with Pt fungal spores under controlled conditions. The RT-qPCR method was used to analyze the expression profiles of selected APR genes at five time points (0, 6, 12, 24, and 48 hpi). The results presented here demonstrate the differential expression of APR genes and miRNAs at stages of leaf rust development at selected timepoints after inoculation. We analyzed the expression of three leaf rust resistance genes, using different genetic backgrounds in F2 and BC1F1 segregation materials, in leaf tissues after Pt infection. Our goal was to investigate potential differences resulting from the genetic background found in different generations of hybrid forms of the same parental forms. Gene ontology analysis predicted 190 target genes for tae-miR5384-3p and 167 target genes for tae-miR9653b. Our findings revealed distinct expression profiles for genes, with the highest expression levels observed mainly at 6, 24, and 48 hpi. The candidate gene Lr46-Glu2 displayed an upregulation, suggesting its potential involvement in the immune response against Pt infection.

Mycotoxins and Their Impact on Poultry Health and Productivity

They are known as secondary metabolic compounds resulting from fungi. To this day, more than 200 types of mycotoxins have been discovered and diagnosed, and 150 different types of molds producing these toxins have been isolated. The production of mycotoxins is not limited to one group of molds regardless of the compositional classification. Ecological distribution or sex, as these compounds are produced from a diverse group of fungal races when the appropriate temperature and humidity and suitable nutrient medium are available (Danicke, 2002). And that the fungi of the genera of Penicillium, Fusarium, and Aspergillus are among the most important fungi in the field of mycotoxins production at present, and the interest of researchers has focused on many studies on toxins produced from the aforementioned genera (Hammoudi, 2006).

Evaluation of bread wheat germplasm for adult plant resistance to stem rust using artificial inoculation

Wheat stem rust, caused by Puccinia graminis f.sp. tritici, is a major biotic threat to wheat (Triticum aestivum L.) in many wheat-producing countries worldwide, including Ethiopia. The pathogen is capable of continuously evolving new fungal races with high reproductive potential. It can be easily dispersed by wind over large geographic areas, allowing it to attack resistant varieties. Under optimal environmental conditions, it can cause epidemics leading to severe yield losses (up to 100%). A total of 91 germplasms, comprising 81 advanced bread wheat lines and 10 varieties, including the susceptible check Morocco, were planted using an augmented design. The experiment was conducted with artificial inoculation on spreaders to evaluate their slow rusting response against four virulent stem rust races viz. TTKTF, TKKTF, TTKTT, and TTTTF under field conditions at the Kulumsa Agricultural Research Center during the 2022-2023 offseason. Slow rusting resistance at the adult-plant stage was assessed by measuring the final rust severity (FRS) and the average coefficient of infection (ACI). Accordingly, 50 (61.7%) of the advanced lines and 6 (60%) of the released varieties namely Boru, Abay, Shaki, Kakaba, Deka, and Dursa exhibited low levels of FRS and ACI. In contrast, 31 (48.3%) of the advanced lines and 4 (40%) of the varieties showed high FRS and ACI values. The germplasms with low FRS and ACI values were considered to exhibit good slow rusting resistance and could be recommended for release into production and/or used in breeding programs aimed at achieving durable stem rust resistance in Ethiopia.

Virulence of banana wilt-causing fungal pathogen Fusarium oxysporum tropical race 4 is mediated by nitric oxide biosynthesis and accessory genes.

Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most damaging plant diseases known. Foc race 1 (R1) decimated the Gros Michel-based banana (Musa acuminata) trade, and now Foc tropical race 4 (TR4) threatens global production of its replacement, the Cavendish banana. Here population genomics revealed that all Cavendish banana-infecting Foc race 4 strains share an evolutionary origin distinct from that of R1 strains. Although TR4 lacks accessory chromosomes, it contains accessory genes at the ends of some core chromosomes that are enriched for virulence and mitochondria-related functions. Meta-transcriptomics revealed the unique induction of the entire mitochondrion-localized nitric oxide (NO) biosynthesis pathway upon TR4 infection. Empirically, we confirmed the unique induction of a NO burst in TR4, suggesting that nitrosative pressure may contribute to virulence. Targeted mutagenesis demonstrated the functional importance of fungal NO production and the accessory gene SIX4 as virulence factors.

Determination of resistance to yellow rust in new breeding mutant lines of spring wheat at adult plant and seedlings stages

Stripe (yellow, YR) rust bringing about by fungal pathogen of Puccinia striforms Westend Westend. is a serious wheat disease that poses substantial threats to the global wheat yield. Currently, the appearance of virulent fungus races is overcomed restricted by the studed resistance genes of wheat. Seach and identification of new genetic sources with durable resistance genes can allow efficiently to incorporate these target genes into germplasm pools. To increase spring wheat genetic diversity, on the back phone of parental variety Kazakhstanskay-19 (WT) characterizing by rust resistance through physical mutagenesis bythe various gamma irradiation doses, namely 300-, 350-, and 400 Gy, new M3 mutant lines were created. From these new mutant resources, the 75 genotypes having higher yield-associated parameters such as grains number and weight per main spike comparing the parent variety were selected by phenotyping as the adult plant resistant (APR) under rust infected field trial. To measure resistance of these breeding lines at seedling stage by microscopy through the number of haustorial mother cells formation induced by YR treatment with the isolate of Puccinia striforms “Warrior” as temporary responses was carried out. Almost all of spring wheat mutant lines (93.0%, 70 samples from 75 mutant lines) identified as APR to YR had a strong association with SR which is developed on longer time of infection. The most effective dose of irradiation to generate the genetic variation was 350 Gy with mean of 60.08 (p<0.005) according to Anova analysis.

Genetic Variation of Magnaporthe oryzae Population in Hunan Province.

Studies on the population structure and variation of Magnaporthe oryzae in fields are of great significance for the control of rice blast disease. In this study, a total of 462 isolates isolated from different areas of Hunan Province in 2016 and 2018 were analyzed for their population structure and variation tendency. The results showed that from 2016 to 2018, the concentration of fungal races of M. oryzae increased and the diversity decreased; furthermore, 218 isolates in 2016 belonged to ZA, ZB, ZC, ZE, ZF and ZG, with a total of 6 groups and 29 races, in which the dominant-population ZB group accounted for 66.2%; meanwhile, in 2018, 244 isolates were classified into 4 groups and 21 races, including ZA, ZB, ZC and ZG, in which the dominant-population ZB group accounted for 72.54%. In 2018, isolates of ZD, ZE and ZF populations were absent, and the number of total races and isolates of the ZA and ZC groups decreased. Fungal pathogenicity was identified, with 24 monogenic lines (MLs) carrying 24 major R genes. The resistance frequency of R genes to fungal isolates in 2018 decreased significantly, in which except Pikm was 64.5%, the other monogenic lines were less than 50%. Rep-PCR analysis for isolates of Guidong in Hunan also showed that fungal diversity decreased gradually. The influence of R genes on fungal variation was analyzed. The pathogenicity of isolates purified from Xiangwanxian 11 planted with monogenic lines was significantly more enhanced than those without monogenic lines. All the results indicated that in recent years, the fungal abundance in Hunan has decreased while fungal pathogenicity has increased significantly. This study will greatly benefit rice-resistance breeding and the control of rice blast disease in Hunan Province.

Variety-Specific Flowering of Sugarcane Induced by the Smut Fungus Sporisorium scitamineum

Sugarcane smut is the most severe sugarcane disease in China. The typical symptom is the emerging of a long, black whip from the top of the plant cane. However, in 2018, for the first time we observed the floral structures of sugarcane infected by smut fungus in the planting fields of China. Such smut-associated inflorescence in sugarcane was generally curved and short, with small black whips emerging from glumes of a single floret on the cane stalk. Compatible haploid strains, named Ssf1-7 (MAT-1) and Ssf1-8 (MAT-2), isolated from teliospores that formed black whips in inflorescence of sugarcane were selected for sexual mating assay, ITS DNA sequencing analysis and pathogenicity assessment. The isolates Ssf1-7 and Ssf1-8 showed stronger sexual mating capability than the reported Sporisorium scitamineum strains Ss17 and Ss18. The ITS DNA sequence of the isolates Ssf1-7 and Ssf1-8 reached 100% similarity to the isolates of S. scitamineum strains available in GenBank. Inoculating Ssf1-7 + Ssf1-8 to six sugarcane varieties, i.e., GT42, GT44, GT49, GT55, LC05-136 and ROC22, resulted in different smut morphological modifications. The symptoms of floral structure only occurred in LC05-136, indicating that the flowering induction by S. scitamineum is variety-specific. Furthermore, six selected flowering-related genes were found to be differentially expressed in infected Ssf1-7 + Ssf1-8 LC05-13 plantlets compared to uninfected ones. It is concluded that the flowering induction by S. scitamineum depends on specific fungal race and sugarcane variety, suggesting a specific pathogen-host interaction and expression of some flowering-related genes.

Stem and leaf rust-induced miRNAome in bread wheat near-isogenic lines and their comparative analysis.

Wheat rusts remain a major threat to global wheat production and food security. The R-gene-mediated resistance has been employed as an efficient approach to develop rust-resistant varieties. However, evolution of new fungal races and infection strategies put forward the urgency of unravelling novel molecular players, including non-coding RNAs for plant response. This study identified microRNAs associated with Sr36 and Lr45 disease resistance genes in response to stem and leaf rust, respectively. Here, small RNA sequencing was performed on susceptible and resistant wheat near-isogenic lines inoculated with stem and leaf rust pathotypes. microRNA mining in stem rust-inoculated cultivars revealed a total of distinct 26 known and 7 novel miRNAs, and leaf rust libraries culminated with 22 known and 4 novel miRNAs. The comparative analysis between two disease sets provides a better understanding of altered miRNA profiles associated with respective R-genes and infections. Temporal differential expression pattern of miRNAs pinpoints their role during the progress of infection. Differential expression pattern of miRNAs among various treatments as well as time-course expression of miRNAs revealed stem and leaf rust-responsive miRNAs and their possible role in balancing disease resistance/susceptibility. Disclosure of guide strand, passenger strand and a variant of novel-Tae-miR02 from different subgenome origins might serve as a potential link between stem and leaf rust defence mechanisms downstream to respective R-genes. The outcome from the analysis of microRNA dynamics among two rust diseases and further characterization of identified microRNAs can contribute to significant novel insights on wheat-rust interactions and rust management. KEY POINTS: • Identification and comparative analysis of stem and leaf rust-responsive miRNAs. • Chromosomal location and functional prediction of miRNAs. • Time-course expression analysis of pathogen-responsive miRNAs.

Role of Sexual Reproduction in the Evolution of the Wheat Stripe Rust Fungus Races in China.

Experimental and population genetic approaches have reshaped our view of how fungal pathogens reproduce, with consequences for our understanding of fungal invasions. Puccinia striiformis f. sp. tritici, the causal agent of stripe rust, poses a severe threat to wheat production worldwide. The sexual stage of P. striiformis f. sp. tritici was discovered >10 years ago, but how it affects the evolution of the pathogen, especially the emergence of the new virulent races, remains largely unknown. Here, using population genetic analyses, we demonstrate that sexual reproduction plays an important role in the evolution of P. striiformis f. sp. tritici races in China, specifically the newly emerged and devastating race virulent to resistance gene Yr26, which is widely used in China and exerts strong selective pressure on the pathogen population. Association analysis identified six genes encoding secreted proteins as candidates for virulence on wheat cultivars carrying the Yr26 resistance gene. Our results highlight the important role of sexual reproduction and selection exerted by hosts in the emergence of new virulent races in China.

The fungal rat race: mycophagy among rodent communities in eastern Australia

Context Rodents in many parts of the world perform an important ecosystem function as dispersers of mycorrhizal fungal spores. These fungi are vital to nutrient uptake in plant communities, but many of the fungal taxa that form these associations have fruiting bodies that are reliant on animals for their spore dispersal. Aims Numerous studies have focused on the ecological importance of Australian marsupials (especially members of the Potoroidae) for the dispersal of these ecologically important fungi. We chose to focus this study on the role of murid rodents in the dispersal of these fungi in eastern Australia. Methods To compare fungal taxa in murid diets, we trapped rodents in three regions of eastern Australia; our study sites spanned over 2000 km from temperate eucalypt forests to tropical eucalypt and tropical rainforest habitats. We performed microanalysis on all scats to determine whether fungi were consumed and which taxa were being eaten. Statistical analysis was conducted to investigate trends in levels of mycophagy among species and habitats. Key results We examined 10 rodent species, and all were shown to ingest mycorrhizal fungi to varying degrees. The diversity, abundance and specific fungal taxa consumed varied depending on the site and forest type. In drier forests dominated by Eucalyptus spp., the fungal taxa consumed and dispersed were primarily ectomycorrhizal; in wetter rainforest habitats, the fungal diversity consumed was far lower and included primarily vesicular arbuscular fungi. We provide the first evidence of mycophagy by grassland melomys (Melomys burtoni) and Cape York melomys (Melomys capensis). Conclusions Our findings highlight the importance of rodents as dispersers of mycorrhizal fungi across a variety of habitats from temperate to tropical forests of eastern Australia. Implications This study increases the existing knowledge of rodent diets and habitat requirements. It also provides a new angle for mammal conservation efforts, given the vital nature of the ecosystem service provided by these small and frequently overlooked mammals.

Relationship of Colletotrichum lindemuthianum races and resistance loci in the Phaseolus vulgaris L. genome

AbstractAnthracnose caused by Colletotrichum lindemuthianum is one of the most critical diseases in the common bean (Phaseolus vulgaris L.). The characterization and localization of pathogenic fungal races are essential for understanding pathogen population dynamics and developing resistant cultivars. Here, we discussed the relationship between the diversity of C. lindemuthianum and common bean resistance genes against anthracnose disease. Indeed, several studies using a system of 12 differential bean cultivars have been carried out since 1991 to monitor anthracnose, reporting the constant appearance of new races. Colletotrichum lindemuthianum shows high virulence diversity, with 298 races distributed across 29 countries. In Brazil, we identified 89 races, with races 73, 65, and 81 as the most frequent. Moreover, we highlighted the common bean gene clusters, their unique location on chromosomes, and their relationship with races and resistance genes. The genetic mapping studies, molecular markers linked to anthracnose resistance alleles, and the specific races were integrated on the seven‐chromosome map using the reference genome of common bean. Recently, the ease of use of genome sequences and the development of molecular technologies have allowed molecular markers for marker‐assisted selection applied to anthracnose‐resistant cultivars. As a result, it is feasible that Mesoamerican genes Co‐5, Co‐42, Co‐6, Co‐16, and Co‐17, and the Andean genes Co‐12, Co‐14, Co‐Bf, Co‐15, Co‐AC, and CoPv01CDRK are well known to confer resistance to most races reported in Brazil and around the world. Thus, pyramiding these genes through molecular markers can help reduce the time and cost of introducing resistance genes in commercial common bean cultivars.

Occurrence of anthracnose pathogen races and resistance genes in common bean across 30 years in Brazil

Anthracnose caused by Colletotrichum lindemuthianum is one of the most critical diseases in the common bean (Phaseolus vulgaris L.). The characterization and localization of pathogenic fungal races are essential for understanding pathogen population dynamics and recommending strategies to develop resistant cultivars. As resistant genotypes are the most economical and ecologically safe means of controlling plant diseases, there have been efforts to characterize resistance genes in common bean. Several studies using a system of 12 differential bean cultivars have been carried out to monitor anthracnose since 1991, reporting the constant appearance of new fungal races. C. lindemuthianum shows high virulence diversity. The objective of the present study was to review the relationship between C. lindemuthianum races and the common bean pathogenic processes involved in the risk of developing anthracnose disease. As a result, 89 races occurred in Brazil, wherein 73, 65, and 81 of C. lindemuthianum are the most frequent. Furthermore, we built a map with the anthracnose resistance loci, molecular markers, and their respective physical position. The accessibility to the genomes and sequencing technologies permits molecular markers for marker-assisted selection applied to anthracnose-resistant cultivars. This study could be used as a reference for future resistance mapping studies and as a guide for selecting resistance loci in breeding programs aiming to develop common bean cultivars with durable anthracnose resistance.

Experimental Science for the ‘Bananapocalypse’: Counter Politics in the Plantationocene

ABSTRACT The plantation has become a landscape of political impossibility. Its industrial modes of production and scientific management pose existential threats to local lifeways, stymie social justice movements, and unleash persistent ecological harms. This article argues that a renewed scientific sensibility offers a way to expand local strategies for transformative political praxis in the face of other political constraints. It introduces the notion of ‘science-in-vivo’, a method of experimentation that has emerged in the context of Philippine banana plantations ravaged by the ‘incurable’ fungal disease Fusarium Wilt Tropical Race Four, also known as Panama Disease. Literally ‘science within the living body’, the method combines secular and non-secular thought, and gathers human, nonhuman, and extrahuman forces in ways that break down some of the hegemonic antagonisms that define plantation life. It was inspired, originally, by a series of God-given dreams about microbes in the forests of southern Mindanao.

Updated Characterization of Races of Plasmopara halstedii and Entomopathogenic Fungi as Endophytes of Sunflower Plants in Axenic Culture

The management of downy mildew (Plasmopara halstedii) in sunflower, is heavily dependent on genetic resistance, whilst entomopathogenic fungi (EF) can reduce other sunflower diseases. In this work, we characterized P. halstedii from Spain and other countries collected in the past few years. Twenty-three races were identified (the most frequent in Spain being 310, 304, 705 and 715), with an increasing proportion of highly virulent races. Five isolates from countries other than Spain overcame the resistance in RHA-340. In addition, we assessed the efficacy of five EF against downy mildew and their effects on sunflower growth in axenic conditions. None of the entomopathogens reduced disease severity, nor did they have any effect on plant growth when applied together with P. halstedii. In contrast, three EF reduced some of the plant growth variables in the absence of the pathogen. Microbiological and molecular diagnostics suggest that the axenic system and the short experimental time used in this study did not favor the successful establishment of EF in the plants or their potential biocontrol effect. Our results show a shift in P. halstedii racial patterns and suggest that soil as a growth substrate and long infection times are needed for EF effectiveness against downy mildew.

Management of Soil-Borne Fungi and Root-Knot Nematodes in Cucurbits through Breeding for Resistance and Grafting

Soil-borne pathogenic fungi (SBPF) and root-knot nematodes (RKN) co-exist in the rhizosphere and are major pathogens causing root diseases in cucurbits. Current knowledge on soil-borne pathogens of cucurbit crops grown under protected cultivation, their host-pathogen interactions, and mechanisms of resistance has been reviewed. Plant resistance is an effective and sustainable method to control soil-borne diseases and the available resistant cultivars and rootstocks to key soil-borne pathogens are reported. The importance of proper pathogen diagnosis in the right choice of cultivar or rootstock is highlighted because of the specificity in the response of the cucurbit crops to fungal and nematode species and races. Plants protect themselves through common mechanisms of resistance against SBPF and RKN including hardening of their cell walls, pathogenesis-related (PR) proteins, and production of antimicrobial molecules. The activity of some enzymes, such as peroxidases and phenylalanine lyase, is increased after pathogen infection and is higher on SBPF and RKN resistant than susceptible cucurbits. Plant hormones such as salicylic acid, jasmonic acid, and ethylene are involved in the response of cucurbits to SBPF. Most mechanisms of resistance to RKN affect post-infection development of the nematode, which results in a delay or disruption of the life cycle. Traditional and biotechnological tools used for breeding for resistance in cucurbits are described. Grafting is an effective non-host resistance method to control primarily Fusarium wilt but not to control RKN. However, new rootstocks with resistance to both pathogens have been developed recently and their effects on fruit quality and yield stability need additional studies. The impact of grafting on yield in pathogen-infested soils is discussed.

Biodiversity of Pyricularia oryzae Cav. in rice-growing regions of the south of Russia using PCR method.

The purpose of this research by the way of investigating the molecular genetic structure of a highly variable fungal phytopathogen Pyricularia oryzae Cav., to determine effective genes for the development of a strategy for immunogenetic protection against rice blast in conditions of epiphytotic development of the disease in the south of Russia, which would combine high efficacy with both environmental friendliness and resource and energy saving, to ensure country's food security. The knowledge of local pathotype diversity of Pyricularia oryzae Cav. and the (a)virulence genes in rice-growing regions of Russia may allow the prediction of new races and its interaction in local agro-ecology. The identification of virulence gene may become an indispensable theoretical basis for the development of genetic sources with long-lasting resistance to rice blast. Based on molecular and genetic approaches, the genetic structure and biodiversity of the phytopathogenic fungus Pyricularia oryzae Cav. in the south of Russia were considered. The monitoring was studied and it isolated 57 strains of the pathogen from the damaged herbal material collected from the fields in eight agro-ecological rice-growing regions of the Krasnodar Region (Russian Federation): Krasnoarmeysky, Kalininsky, Krymsky, Abinsky, Temryuksky, Seversky, Slavyansky districts, Krasnodar, Rostov Region (Russian Federation)-Proletarsky district and the Republic of Adygea (Russian Federation). A multiplex PCR technique was applied on the basis of fragment analysis to identify the virulent fungal isolates. 33 fungal genotypes with unique genetic profiles were identified among the studied races of Pyricularia oryzae Cav. Their DNA profiles were created. The studied isolates of the pathogen of rice blast were classified using morphological and microbiology cultural features. Based on the phytopathological test using differentiation rice varieties, the quantitative and qualitative composition of (a)virulence genes in fungal races was established. Effective genes for pathogen resistance, which are recommended for breeding programs for the development of rice varieties resistant to rice blast, were identified in the south of Russia.

Apple Scab Disease Severity in the Sais Region of Morocco and its Sensitivity to Three Commercial Fungicides

Apple scab, Venturia inaequalis (Cooke) G. Winter, results in numerous fungicide applications in the Sais region of Morocco. We conducted the study to determine the susceptibility of cultivars through field survey and to evaluate the sensitivity of V. inaequalis to three fungicides using both in vitro and in vivo methods. We surveyed 100 apple orchards and collected two samples. Disease survey showed that the cultivars were highly susceptible to apple scab (grand mean of leaf scab: Golden Delicious, 40.31%; Starking Delicious, 20.45%; and Gala, 18.92%). Results underlined no significant differences between isolates in term of inhibition rate of mycelial growth and averaged disease severity. However, both treatment and concentration were statistically significant. EC50 values ranged from 2.33 µg/ml to 7.40 µg/ml and resistance factor (RF) values of 0.55, 1.02 and 1.79 were obtained for difenoconazole, trifloxystrobin and thiophanate-methyl, respectively. In vivo tests at a concentration of 10 µg/ml on the isolate ViIF using a curative method showed a high efficacy of trifloxystrobin (96.38%), and low efficacy of thiophanate-methyl (29.65%) and difenoconazole (24.62%). V. inaequalis was most sensitive to trifloxystrobin followed by difenoconazole and thiophanate-methyl, respectively. From this work, it was recommended testing more isolates and contact fungicides in order to develop a baseline sensitivity of the pathogen population against commonly used fungicides to treat the disease, as continued usage over time and the introduction of new fungal races may result in a decrease in fungicide efficacy.

Factors Affecting the Vineyard Populational Diversity of Plasmopara viticola.

Vitis vinifera is very susceptible to downy mildew (Plasmopara viticola). A number of authors have suggested different genetic populations of this fungus exist in Europe, each showing a different degree of virulence. Work performed to date indicates this diversity to be the result of different factors. In areas where gene flow is greater and recombination more frequent, the diversity of P. viticola appears to be wider. In vineyards isolated by geographic barriers, a race may become dominant and produce clonal epidemics driven by asexual reproduction. The aim of the present work was to identify the conditions that influence the genetic diversity of P. viticola populations in the vineyards of northwestern Spain, where the climatic conditions for the growth of this fungus are very good. Vineyards situated in a closed, narrow valley of the interior, in more open valleys, and on the coast were sampled and the populations of P. viticola detected were differentiated at the molecular level through the examination of microsatellite markers. The populations of P. viticola represented in primary and secondary infections were investigated in the same way. The concentration of airborne sporangia in the vegetative cycle was also examined, as was the virulence of the different P. viticola populations detected. The epidemiological characteristics of the fungus differed depending on the degree of isolation of the vineyard, the airborne spore concentration, and on whether the attack was primary or secondary. Strong isolation was associated with the appearance of dominant fungal races and, therefore, reduced populational diversity.

Analyzing sequence variation of the Avirulence Avr-Pita1 gene of rice blast isolates, Magnaporthe oryzae in Vietnam

Rice blast disease caused by a filamentous fungus (Magnaporthe oryzae) has been one of the most devastating of all cereal diseases worldwide. The interaction between rice plant, Oryza sativa and the rice blast fungus, M. oryzae is activated by the interaction between protein products of rice resistant genes and fungal avirulence genes. The resistant genes can protect rice from infection of rice blast fungus. However, the resistant genes are usually broken down after several years due to the evolution of new fungal races. Thus, finding rice blast isolates containing the avirulence Avr-Pita1 gene and analyzing the sequence variation of this gene are necessary for further research in reducing rice blast infection. The avirulence Avr-Pita1 gene of 25 rice blast isolates collected from northern, middle and southern Vietnam were amplified and analyzed. The phylogenetic trees were constructed using neighbor-joining and maximum likelihood methods in the MEGA 6.0 program. The results showed that 18 rice blast isolates had the Avr-Pita1 gene and most of them were from middle and southern Vietnam. The results of phylogenetic analysis and polymorphism analysis also showed the diversity of the nucleotide sequence of the Avr-Pita1 gene among the 18 rice blast isolates and differences between Avr-Pita1 of Vietnamese isolates and those from other countries.

Inoculum production and evaluation of temperature and leaf wetness for Passalora sojina inoculation in soybean

ABSTRACT The objective of this study was to develop a methodology for inoculum production and inoculation of Passalora sojina in soybean to assess the reaction to frogeye leaf spot. Thus, sporulation of fungal races was quantified in five substrates under two light regimes. The temperature and the leaf wetness period that resulted in greater infection efficiency were also determined. Petri dishes containing the culture media Oat Flour Agar (OFA), Tomato Juice (FTJ), V8 agar juice (V8), Infant Food (IF) and Potato Sucrose Agar (PSA) plus isolates of P. sojina races 23, 24 and 25 were subjected to 12-h photoperiod and 24-h continuous dark. Inoculated plants were incubated at temperatures of 15, 20, 25, 30 and 35 ºC and leaf wetness periods of 12, 24, 36, 48 and 72 hours. Experimental design was completely randomized with five replicates. There was interaction among isolate, culture medium and photoperiod. The highest sporulation (conidia/cm2) was obtained in the culture media FTJ (race 23) and V8 (races 24 and 25) under 12-h photoperiod. The optimum temperature for the disease development was 27oC under 72 hours of continuous leaf wetness.