Genetic Diversity and Pathogenicity of Fusarium oxysporum f.sp. melonis Races from Different Areas of Italy

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis (FOM) is a devastating disease of melon worldwide. Pathogenicity tests performed with F. oxysporum isolates obtained from Italian melon‐growing areas allowed to identify thirty‐four FOM isolates and the presence of all four races. The aims of this work were to examine genetic relatedness among FOM isolates by race determination and to perform phylogenetic analyses of identified FOM races including also other formae speciales of F. oxysporum of cucurbits. Results showed that FOM race 1,2 was the most numerous with a total of eighteen isolates, while six and nine isolates were identified as race 0 and 1, respectively, and just one isolate was assigned to race 2. Phylogenetic analysis was performed by random amplified polymorphic DNA (RAPD) profiling and by translation elongation factor‐1α (TEF‐1α) sequencing. The analysis of RAPD profiles separated FOM races into two distinct clades. Clade 1, which included races 0, 1 and 1,2, was further divided into ‘subclade a’ which grouped almost all race 1,2 isolates, and into ‘subclade b’ which included race 0 and 1 isolates. Clade 2 comprised only race 2 isolates. The phylogenetic analysis based on TEF‐1α separated FOM from the other formae speciales of F. oxysporum. Also with TEF‐1α analysis, FOM races 0, 1 and 1,2 isolates grouped in one single clade clearly separated from FOM race 2 isolates which grouped closer to F. oxysporum f.sp. cucumerinum. RAPD technique was more effective than TEF‐1α in differentiating FOM race 1,2 isolates from those belonging to the closely related races 0 and 1. Both phylogenetic analyses supported the close relationship between the three different FOM races which might imply the derivation from one another and the different origin of FOM race 2.     

Molecular characterization of Rhizoctonia solani isolates the incitant of soybean root rot

Rhizoctonia solani isolates used in this investigation were identified as anastomosis-4 (AG-40), collected from different localities from Assiut governorate in Egypt. Pathogenicity test of seven isolates of R. solani was evaluated on soybean Giza 111 cultivar under greenhouse conditions. All tested isolates were able to infect soybean plants causing root rot with different degrees of severities, isolate No. 1, 2 and 3 showed significantly highest root rot severity, while isolate No. 5 gave the lowest percentage of root rot rating. The sodium dodecyl sulphate polyacrylamide gel electrophoresis patterns were used to compare three isolates of R. solani. There are no variations among R. solani isolates except a few exceptions according to their protein patterns. DNA markers obtained from all isolates showed genetic similarity among different isolates obtained from different geographical regions barring few exceptions. Correlation between DNA patterns of R. solani isolates and their virulence was detected, but no correlation with anastomosis groups (AG).     

Occurrence of Monosporascus cannonballus in Watermelon Fields in Tunisia and Factors Associated with Ascospore Density in Soil

Surveys of 11 watermelon fields throughout production areas of this crop in southern and central regions in Tunisia were conducted in 2007 to determine the aetiology and distribution of watermelon vine decline. Monosporascus cannonballus was isolated from diseased roots in all surveyed fields. All the isolates were identified according to morphological features and confirmed by amplification of a fragment of the ITS region with specific primers. Ascospores of M. cannonballus were recovered from soil in all watermelon fields surveyed and the average population densities ranged from 3.65 to 10.14 ascospores per g of soil. Multiple linear regression analysis revealed that only four of the crop and soil factors evaluated had a significant correlation with ascospore density at the end of the growing season: vertisol vs. other soils, disease incidence, percentage of clay and pH. The pH of the soil showed a strong significant negative linear relationship with ascospore density, while the other three factors correlated positively.     

Race Distribution, Vegetative Compatibility and Pathogenicity of Fusarium oxysporum f. sp. melonis Isolates in Greece

Races and vegetative compatibility groups (VCGs) in Greek isolates of Fusarium oxysporum f. sp. melonis(Fom) were characterized. Three races (0, 2 and 1–2) among 12 isolates tested and two VCGs among 19 isolates tested, were identified. Race 1–2 was the most common and race 1 was not detected. One widespread VCG corresponded to a VCG previously reported from Israel (coded 0138), and included seven isolates of races 0 and 1–2. The other VCG, which was unclassified, included four isolates of races 0, 2 and 1–2. The latter VCG was detected only in a specific melon‐growing location of Evros. The remaining eight isolates tested for VCG did not show positive reactions with other isolates, with each other or with the testers of VCGs 0135 or 0138, although they produced complementary mutants. Using two inoculation methods, the local cv. ‘Golden Head’ was found susceptible to all known Fom races, and especially to race 1–2. These results show the presence of more than one VCG and the widespread distribution of the race 1–2, in Greece.     

Detection of Cochliobolus heterostrophus races in South China

Cochliobolus heterostrophus is the causal pathogen of the southern corn leaf blight (SCLB). There are three known races: race O, race C and race T. To determine which C. heterostrophus races comprise the field population in southern China and to assess diversity of these strains in terms of virulence, 200 isolates from diseased plants were collected in nine provinces/municipalities. All were race O, that is, no race T or race C isolates were found. Sixty race O isolates that sporulated well were chosen for further analysis. Virulence was measured using the integral optical density (IOD) of leaf lesions on four maize inbred lines. UPGMA cluster analysis of AFLP markers was applied to the 60 race O isolates plus control race O, T and C strains. Phylogenetic distribution, geographic location and virulence were not correlated. These results can provide valuable information for guidance in early warning and disease control.     

河北省西瓜枯萎病菌致病性分化及其RAMS分析

本文对50个西瓜枯萎病菌株,(其中46个来自河北省石家庄、保定、唐山等12个西瓜种植区的代表菌株)进行了致病性测定、RAMS(Random amplified microsatellites)扩增和致病类型与RAMS类群的相关性分析。根据鉴别寄主对不同菌株的抗感反应,将50个菌株划分为3个不同的生理小种,即0号、1号和2号生理小种,分别占供试菌株的18%、64%和18%;21个RAMS引物对供试菌株扩增出188条带,其中多态性带134条,占总带数的71%。基于RAMS标记聚类分析,50个菌株被划分为3个类群(RAMSGroups,RGs)。RGI包含来自不同地区的41个菌株,以1号生理小种为主(32个),占该类群的78.1%;RGII包括来自保定、唐山和新疆的3个菌株,均为0号生理小种;RGIII包括张家口、石家庄、保定等地的6个2号生理小种菌株。RAMS类群与生理小种之间存在一定相关性,与菌株的地理来源关系不明显。     

Genetic Variability of Fusarium oxysporum f.sp. ciceris Population Affecting Chickpea in the Sudan

Fusarium wilt caused by Fusarium oxysporum f.sp. ciceris (Foc) is the most important soilborne disease of chickpea in the Sudan and many other countries. A total of 76 Foc isolates from six different chickpea‐growing states in the Sudan have been collected in this study to investigate the genetic diversity of Sudanese Foc isolates. Additional 14 Foc isolates from Syria and Lebanon were included in this study. All isolates were characterized using four random amplified polymorphic DNA (RAPD), three simple sequence repeats (SSR), five sequence‐characterized amplified region (SCAR) primers and three specific Foc genome primers. Based on the similarity coefficient, the results indicated two major clusters included seven subclusters. The isolates from the Sudan were grouped as identified as races 0, 2 and unknown races. The isolates from Syria and Lebanon were grouped together as they identified as races 1B/C and 6, respectively. This study identified a new race Foc (race 0) in the Sudan. The results of this study will be useful for breeders to design effective resistance breeding program in chickpea in the Sudan.     

Race Profiling and Molecular Diversity Analysis of Fusarium oxysporum f.sp. ciceris Causing Wilt in Chickpea

Seventy isolates of Fusarium oxysporum f.sp. ciceris (Foc) causing chickpea wilt representing 13 states and four crop cultivation zones of India were analysed for their virulence and genetic diversity. The isolates of the pathogen showed high variability in causing wilt incidence on a new set of differential cultivars of chickpea, namely C104, JG74, CPS1, BG212, WR315, KWR108, GPF2, DCP92‐3, Chaffa and JG62. New differential cultivars for each race were identified, and based on differential responses, the isolates were characterized into eight races of the pathogen. The same set of isolates was used for molecular characterization with four different molecular markers, namely random amplified polymorphic DNA, universal rice primers, simple sequence repeats and intersimple sequence repeats. All the four sets of markers gave 100% polymorphism. Unweighted paired group method with arithmetic average analysis grouped the isolates into eight categories at genetic similarities ranging from 37 to 40%. The molecular groups partially corresponded to the states of origin/chickpea‐growing region of the isolates as well as races of the pathogen characterized in this study. The majority of southern, northern and central Indian populations representing specific races of the pathogen were grouped separately into distinct clusters along with some other isolates, indicating the existence of variability in population predominated by a single race of the pathogen. The present race profiling for the Indian population of the pathogen and its distribution pattern is entirely new. The knowledge generated in this study could be utilized in resistance breeding programme. The existence of more than one race, predominated by a single one, in a chickpea cultivation zone as supported by the present molecular findings is also a new information.     

Identification of Fusarium species causing basal rot of onion in East Azarbaijan province,Iran and evaluation of their virulence on onion bulbs and seedlings

One of the economically important diseases of onion is the basal rot caused by various Fusarium species. Identification of the pathogenic species prevalent in a region is indispensable for designing management strategies, especially to develop resistant cultivars. Eighty Fusarium isolates are obtained from red onion bulbs on infected fields of East Azarbaijan province. Inoculating the onion bulbs with 38 selective isolates indicated that 17 isolates were pathogenic on onion. According to the morphological and molecular characteristics, these isolates were identified as F. oxysporum, F. solani, F. proliferatum and F. redolens. This is the first report of F. redolens on onion in Iran. On the other hand, the virulence of each pathogenic isolate was evaluated on onion bulbs and seedlings. F. oxysporum which causes severe rot and damping-off was considered as a highly virulent species in both conditions. While, F. proliferatum was considered as the most destructive on onion bulbs. Rot ability of F. solani was not considerable, and only the 4S isolate caused pre- and post-emergence damping-off more than 50%. Finally, F. redolens with less pathogenicity on onion bulbs was identified as the most virulent isolate on onion seedlings, which was explanatory of its importance on farm.     

Virulence Analysis and Race Classification of Xanthomonas oryzae pv. oryzae in China

Two hundred and eighty‐five isolates of Xanthomonas oryzae pv. oryzae were randomly collected from 22 rice‐growing provinces in China. Ninety‐one representative isolates were chosen to assess the differential characteristics of 24 near‐isogenic rice lines containing a single resistance gene or two to four genes. Most isolates were avirulent on pyramided lines, except IRBB51, and hence, the pyramided lines cannot be used as differentials for the virulence analysis of X. oryzae pv. oryzae in China. The 13 rice lines with a single gene were used further to establish a system of races classification of X. oryzae pv. oryzae in China. IR24 and IRBB10 were susceptible to the isolates with several exceptions, whereas IRBB5, IRBB7 and IRBB21 were resistant. Based on the interactions between the isolates of X. oryzae pv. oryzae and the 13 near‐isogenic rice lines, six single‐gene rice cultivars (IRBB5, IRBB13, IRBB3, IRBB14, IRBB2 and IR24) were chosen as differentials, and the 285 tested isolates were classified into nine races. The reaction patterns of the nine races in order were: RRRRRR, RRRRRS, RRRRSS, RRRSSS, RRSSSS, RSRRRS, RSSRRS, RSSSSS and SSSSSS. The race frequencies were 10.18%, 10.53%, 4.91%, 10.18%, 24.21%, 5.96%, 11.23%, 22.46% and 0.35% respectively. The virulence of representative strains of eight Philippine races on 13 rice lines with a single gene was determined and compared with the Chinese races. The frequency distributions of X. oryzae pv. oryzae races were primarily described for the different regions in China.     

Rhizoctonia spp. Causing Root and Hypocotyl Rot in Phaseolus vulgaris in Cuba

Sixty isolates of Rhizoctonia spp. were obtained from Cuban bean fields during the period 2004–2007. Isolates were characterized with different techniques, including nuclei staining, pectic zymogram, PCR–RFLP analysis of the rDNA–ITS region and sequencing of the rDNA–ITS region. The majority of the isolates were identified as multinucleate Rhizoctonia solani isolates, representing two different anastomosis groups (AGs), AG 2‐2 WB and AG 4 HGI; the remaining isolates were binucleate Rhizoctonia isolates and belonged to AG F and AG A. AG 4 HGI isolates were equally distributed in all soil types; AG 2‐2 isolates were more frequently isolated from cambisols, whereas AG F isolates were related to calcisols. Pathogenicity experiments in vitro and in the greenhouse, revealed that binucleate isolates only caused root rot, whereas R. solani isolates were able to cause root rot and hypocotyl rot. Furthermore, differences in virulence level were observed between R. solani and binucleate isolates and among different AGs. Isolates of R. solani AG 4 HGI and R. solani AG 2‐2 WB were the most aggressive, binucleate isolates of AG F were intermediate aggressive, whereas a binucleate isolate of AG A was weakly aggressive. In contrast with other reports about R. solani in bean, web blight symptoms were never observed during this study.     

Characterization of virulent gene locus in the genome of Fusarium spp. causing wilt disease of Psidium guajava L. in India

Wilt of Psidium guajava L., incited by Fusarium oxysporum f. sp. psidii and Fusarium solani is a serious soil borne disease of guava in India. Forty-two isolates, each of F. oxysporum f. sp. psidii (Fop) and F. solani (Fs), collected from different agro climatic zones of India showing pathogenicity were subjected to estimate their virulence factor in terms of analysis using virulent gene-related microsatellite loci. The erratic spread and occurrence of guava wilt in different areas may be due to variable aggressiveness or virulence of different pathogenic isolates in the soil. Out of 10 virulent gene locus related microsatellite markers ofFusarium spp., only six marker viz. Xyl, KHS1, PelA1, PG6/7, CHS1/2 and FMK1/MAPK1 were successfully amplified. This indicates that all the tested Fusarium sp. isolates of guava are having virulence gene in their genome. Microsatellite marker for virulence factor genes of Xyl loci was amplified in both Fop and Fs isolates. Product size of 281 bps was exactly amplified with a single banding pattern in all the isolates of Fop and Fs. It has been observed that other five microsatellite marker for virulence factor genes such as KHS1, PelA1, PG6/7, CHS1/2 and FMK1/MAPK1 were amplified with specific band pattern. PG6/7, CHS1/2 and FMK1/MAPK1 were only amplified in Fop isolates with a product size of 765 bps, 1566 bps; 1010 bps and 1244 bps. PelA1 and KHS1were amplified only in Fs isolates with the product size of 586 bps; 1359 bps, respectively. The results indicate that virulence factor genes are in response to produce wilt disease like symptoms in guava plants and also having pathogenic gene-related locus.     

Pathotypic and molecular evolution of contemporary population of Puccinia striiformis f. sp. tritici in Egypt during 2016–2018

The contemporary races of Puccinia striiformis f. sp. tritici (Pst) in Egypt during 2016–2018 were differentiated based on virulence and molecular patterns. Virulence patterns based on the reaction of the 17 World/European differential sets carrying stripe rust resistance genes (Yr genes) resulted in ten races including four new (first recorded in Egypt) and six old (previously recorded in Egypt). The new races were identified as 64E0 (virulence [V] Yr4, Su), 0E16 (V Yr8, 19), 66E0 (V Yr4, 7, 22, 23, Su) and 4E130 (V Yr2, 6, 7, 25, HVII), while the old were 0E0 (avirulence), 2E0 (V Yr7, 22, 23), 2E16 (V Yr7, 8, 19, 22, 23), 4E0 (V Yr2, 6), 6E4 (V Yr2, 6, 7, 22, 23, 25) and 70E4 (V Yr2, 4, 6, 7, 22, 23, 25, Su). Cluster analysis differentiated Pst races based on virulence frequency to Yr genes. Simple sequence repeat (SSR) markers were used to detect the molecular polymorphism of the Pst races. Clustering separated the old and new races into two groups, indicating their common ancestry since the new races were very distinct from the old races. Although clustering based on virulence revealed some evolutionary patterns, where the new races 64E0 and 66E0 may have probably evolved from the old races (2E16, 2E0, 6E4, 70E4) and the new race 4E130 may be evolved from the joint race 4E0. However, clustering based on molecular patterns indicated that the new races appear to be genetically distinct and may represent an exotic introduction rather than a mutation in isolates of the old races. A weak association between virulence and molecular patterns revealed that they are independent of each other. The SSR markers did not correspond to the virulences in the pathogen. Further studies on the potential virulence genes of the detected Pst virulences are needed.     

Races of Xanthomonas citri subsp. malvacearum,the causal organism of bacterial blight of cotton in northern Nigeria

Xanthomonas citri subsp. malvacearum (Xcm) causes severe qualitative and quantitative losses to farmers in cotton-growing areas of the world. Isolates of Xcm were extracted from cotton seeds obtained from five ginneries located in Funtua, Malumfashi, Gusau and Zaria and standardised to 10^?5?cfu/ml. One isolate per location was used to inoculate three sets of 10 cotton differential lines known to differentiate races of Xcm through possession of B-genes for resistance to bacterial blight. Each cotton differential line was inoculated with the isolates at the six-leaf stage and SDW was inoculated as control. One hundred and sixty pots used were arranged in completely randomised design on the screen house bench. Four different pathogenic races were identified namely race 1, race 12, race 13 and race 16. This confirms the existence of an evolution of the species across northern Nigeria.     

Comparative virulence of Pyrenophora teres f. teres from Syria and Tunisia and screening for resistance sources in barley: implications for breeding

Aims: The aim of this study is to investigate the pathogenic diversity and virulence groups among Pyrenophora teres f. teres isolates, sampled from Syria and Tunisia, and to identify the most effective source of resistance in barley that could be used in breeding programmes to control net blotch in both countries. Methods and Results: One hundred and four isolates of P. teres f. teres were collected from barley in different agroecological zones of Tunisia and Syria. Their virulence was evaluated using 14 barley genotypes as differential hosts. The upgma clustering identified high pathogenic variability; the isolates were clustered onto 20 pathotypes that were sheltered under three virulence groups, with high, intermediate and low disease scores. According to susceptibility/resistance frequencies and mean disease ratings, CI05401 cultivar ranked as the best differential when inoculated with the Syrian isolates. However, CI09214 cultivar was classified as the best effective source of resistance in Tunisia. Conclusions: All P. teres f. teres isolates were differentially pathogenic. CI09214 and CI05401 cultivars were released as the most effective sources of resistance in Syria and Tunisia. Significance and Impact of the Study: National and international barley breeding programmes that seek to develop resistance against P. teres f. teres in barley should strongly benefit from this study. This resistance cannot be achieved without the proper knowledge of the pathogen virulence spectrum and the sources of host resistance.     

Morphological,pathological and molecular characterisation of rice sheath blight disease causal organism Rhizoctonia solani AG-1 IA in Egypt

Rice sheath blight disease caused by Rhizoctonia solani is considered a distractive soil-borne disease of rice production worldwide. The study aimed to determine the causal organism of sheath blight symptoms in Egyptian rice fields. Sheath blight symptoms were first observed in a small area during 2013, 2014 and 2016 seasons, later in a wide area of rice fields in 2016 to 2018 seasons. Pathogen identification was carried out based on morphological traits and internal transcribed spacer sequencing. Thirty-six isolates were identified as R. solani fungus. The isolates exhibited a wide range of variability in their morphological traits and virulence patterns. Five isolates were sequenced and aligned with Chinese isolates with 75–100% identity. This is the first report of R. solani AG-1 IA that associated with rice sheath blight in Egypt. Initiate a breeding program for disease resistance and integrated disease management procedures are important to keep the disease under control.     

Genetic Characterization and Pathogenicity of Rhizoctonia solani Associated with Common Bean Web Blight in the Main Bean Growing area of Argentina

Common bean web blight (WB), caused by the fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris), is among the endemic fungal diseases of major impact in north‐western Argentina (NWA). This study aimed to analyse the genetic and pathogenic diversity of R. solani in Salta, NWA, where 97 isolates were recovered from commercial bean cultivars and wild beans showing WB symptoms in a major bean production area. The isolates were characterized on the basis of specific primers, rDNA‐ITS sequences and morphological characteristics. All the isolates were identified as R. solani AG 2‐2WB, and they exhibited considerable intragroup variation. The phylogenetic tree generated with the ITS sequences confirmed the isolates identification. Aggressiveness of the isolates towards bean seedlings was assessed in the greenhouse. A great variability in virulence was observed among the isolates analysed. On the basis of the disease reaction on foliar tissues, the isolates were grouped into three virulence categories as follows: weakly virulent (30%), moderately virulent (38%) and highly virulent (32%). However, no correlation between virulence and geographical origin was detected. The information generated in this study provides initial data on the population variability of the WB pathogen in north‐western Argentina and represents a valuable contribution to regional breeding programmes aimed to obtain cultivars with durable resistance.     

Relationship of Pseudomonas syringae pv. tabaci races to the rhizosphere of Wisconsin-grown tobacco

Isolates of Pseudomonas syringae pv. tabaci, including 21 strains of the wildfire pathogen and 2 strains of the angular leafspot pathogen, were isolated from 143 rhizosphere and soil samples collected from 11 tobacco fields in Wisconsin. These pathogens were isolated by inoculating rhizosphere and soil washings into tobacco leaves and isolating the bacteria from wildfire or angular leafspot lesions that developed on the leaves. The wildfire isolates were from the rhizospheres of tobacco and Panicum capillare and from soil. While the majority of these were from wildfire-diseased fields, one isolate was from a field without disease symptoms; both angular leafspot isolates were from fields without angular leafspot symptoms. The majority of wildfire isolates were race 1, but three were race 0, and one was a new race. In three fields multiple races of wildfire were found. Both angular leafspot isolates were race 1. Two wildfire and one angular leafspot isolates were from fields where the cultivars were resistant to the races isolated.     

Pathogenic Variability in Colletotrichum lindemuthianum and Evaluation of Resistance in Phaseolus vulgaris in the North-Western Himalayan Region of India

Eightyfive isolates of Colletotrichum lindemuthianum (bean anthracnose) collected from different kidney bean growing areas of a hilly state (Himachal Pradesh) of India, were characterized on the basis of their reaction types on International and CIAT differentials. On international differentials, 12 races viz., Alpha-Brazil, Beta, Gamma and Ind I to Ind IX were characterized. The races designated as Ind I to Ind IX were different from those identified in Europe and USA, thus forming a new race group from the Indian subcontinent. On the CIAT differential set the 85 isolates have been grouped into 19 races. Of these, only races 65 and 73 resembled the North American races. Exotic accessions AB 136 and G 2333 were resistant to all the Indian races. However, race specific resistance has been found in a number of indigenous and exotic genotypes of Phaseolus vulgaris.     

I. Pathogenic variation in fungi and bacteria and mycorrhizal compatibility: Variation in Pseudomonas morsprunorum and the selection of cherry cultivars resistant to bacterial canker

During 1971 and 1972 leaf spot infection caused by Pseudomonas morsprunorum was far more severe on the cv. Roundel than on the normally more susceptible cv. Napoleon, and Roundel supported higher leaf surface populations of the pathogen. This unprecedented reversal in the established field performance of the two cultivars was associated with the presence on the trees of a colony variant (race 2) of P. morsprunorum that differed from the forms of the organism previously described (race 1) in physiological, pathological and phage sensitivity characteristics. In inoculation experiments race 2 isolates showed some specificity for Roundel and race 1 isolates for Napoleon. This difference was reflected in the distribution of the races on trees of the two cultivars growing in experimental plots and commercial orchards. Similar interactions between race and host genotype were observed amongst progeny from breeding programmes and material originally selected for resistance to bacterial canker after inoculation with race 1 proved susceptible to race 2. Three distinct groups of isolates with the colony characteristics of race 2 have been identified and one of these has affinities with Pseudomonas syringae. Group 1 isolates, corresponding to P. morsprunorum and comprising non-fluorescent forms, were the most virulent in pathogenicity tests and accounted for the majority of race 2 infections in the field.