Arbuscular mycorrhizal fungi

The potential disease suppressiveness of arbuscular mycorrhizal (AM) fungi of various origins on Bipolaris sorokiniana in barley has been investigated. Firstly, a survey considering the occurrence of AM fungi in arable fields in Sweden were conducted with the aim to exploit site specific genetic resources in relation to disease suppressiveness. Arbuscular mycorrhizal fungi were present at all 45 sampling sites surveyed all over Sweden at densities ranging from 3 up to 44 spores per gram air dried soil. The highest spore density was found in a semi-natural grassland and the lowest were found in a cereal monoculture. The AM fungi were then multiplied in trap cultures in the greenhouse with the aim to use these for studying potential disease suppressiveness. Thus, the effects of the AM fungi trap cultures on the transmission of seed-borne B. sorokiniana in barley were investigated, using the trap culture inocula, but also including inocula consisting on spore mixtures. The arbuscular mycorrhizal fungi were able to suppress the transmission of B. sorokiniana in aerial parts of barley plants. The degree of suppression varied with the origin of the AM fungal trap cultures. The trap culture inoculum with the highest suppression of the B. sorokiniana transmission originated from an organically managed barley field with undersown ley. The two spore-inocula with the best suppression of the pathogen originated from fields with winter wheat and spring barley, respectively. Eventually, an in vitro method was developed for studying the effect of AM fungal colonisation of roots on the development of foliar diseases and the reaction of the actual host plant of the disease causing organism. Using the developed method, it was indicated that AM fungal colonisation of barley plant suppressed the development of leaf necroses due to B. sorokiniana. Further in vitro studies on the interaction between B. sorokiniana and arbuscular mycorrhizal fungi showed that B. sorokiniana decrease the germination of the AM fungal spores. In conclusion, AM fungi suppress the development of B. sorokiniana in barley. My data suggest that for biocontrol of B. sorokiniana AM fungi should be considered

High damage potential of seed-borne spot blotch in organically grown spring barley in Denmark

Spot blotch of barley (Bipolaris sorokiniana, perfect state: Cochliobolus sativus) occurs wherever barley is grown but is normally not considered a major problem in Danish barley production. It is therefore not included in routine disease surveys or official variety testing in Denmark. However, recommended seed contamination thresholds are 30% for spring barley and 15% for winter barley. Several spring barley varieties were grown under organic (no seed dressing, mechanical weeding) and conventional (seed dressing with fungicides, herbicide application) production conditions at three sites in Denmark in 2003. The harvested seeds were analysed for contamination levels of seed-borne B. sorokiniana using a blotter method. The percentage of seeds contaminated with B. sorokiniana ranged from about 5 to 95 % and was highly depending on the site, production system and variety. Contamination levels of organically cultivated plots were about twice as high as those of plots receiving conventional treatments. The germinating ability of seeds was highly affected by the level of B. sorokiniana contamination and declined drastically at contamination levels above 60%. This effect appeared to differ among varieties. The 1000-grain weight was not affected by the level of spot blotch contamination of seeds. The results indicate that the importance of spot blotch may be underrated, especially in organic barley production and that the role of varietal resistance should be investigated. More results are expected from ongoing seed analyses

Evaluation of Barley Genotypes Against Spot Blotch Disease in Inner Tarai Region of Nepal

Spot blotch caused by Bipolaris sorokiniana (Sacc. in Sorok.) Shoem. is an important disease of barley (Hordeum vulgare L.). A total of 126 barley genotypes received from Hill Crops Research Program, Kabre, Dolakha having SoluUwa as a susceptible check and Bonus as a resistant check were evaluated as barley disease screening nursery (BDSN) under natural epiphytotic condition at National Maize Research Program, Rampur, Chitwan during winter seasons of 2017 and 2018. The nursery was planted in augmented design. The resistant and susceptible checks were repeated and planted after each 10 tested entries. The unit plot size was 2 rows of one meter length for each genotype planted continuously with 25cm row to row spacing. The seed rate was 100 kg/ha. The recommended fertilizer dose of 23:30:0 N:P2O5:K2O kg/ha was applied. The double digit scale (00 to 99) was used to measure overall foliar infection on the whole plant during flowering, soft dough and hard dough stages. Other agronomic practices were followed as per recommendation. Genotypes B86019-1K-3K-0K3, ACC 2087, ACC 2441, ACC GHv-06816, ACC 1597, ACC 1612, ACC 2059 and ACC 2032 were resistant against spot blotch disease. Similarly, 32 barley genotypes were moderately resistant and rest of the tested genotypes were susceptible to the disease. The selected resistant barley genotypes can be used in crossing program and/or promoted for further testing to develop spot blotch resistant varieties for inner Tarai region of Nepal

Genomic regions associated with common root rot resistance in the barley variety Delta

Common root rot (CRR) caused by Bipolaris sorokiniana is a serious disease constraint in the dry temperate cereal growing regions of the world. Currently little is known about the genetic control of resistance to CRR in cereals. In this study based on a Delta/Lindwall barley population we have undertaken a bulked segregant analysis (BSA) and whole genome mapping approach utilising Diversity Arrays Technology (DArT) to identified quantitative trait loci (QTL) associated with CRR expression. One QTL each was identified on chromosomes 4HL and 5HL explaining 12 and 11% of the phenotypic variance, respectively

Mapping spot blotch resistance genes in four barley populations

Bipolaris sorokiniana (teleomorph: Cochliobolus sativus) is the fungal pathogen responsible for spot blotch in barley (Hordeum vulgare L.) and occurs worldwide in warmer, humid growing conditions. Current Australian barley varieties are largely susceptible to this disease and attempts are being made to introduce sources of resistance from North America. In this study we have compared chromosomal locations of spot blotch resistance reactions in four North American two-rowed barley lines; the North Dakota lines ND11231-12 and ND11231-11 and the Canadian lines TR251 and WPG8412-9-2-1. Diversity Arrays Technology (DArT)-based PCR, expressed sequence tag (EST) and SSR markers have been mapped across four populations derived from crosses between susceptible parental lines and these four resistant parents to determine the location of resistance loci. Quantitative trait loci (QTL) conferring resistance to spot blotch in adult plants (APR) were detected on chromosomes 3HS and 7HS. In contrast, seedling resistance (SLR) was controlled solely by a locus on chromosome 7HS. The phenotypic variance explained by the APR QTL on 3HS was between 16 and 25% and the phenotypic variance explained by the 7HS APR QTL was between 8 and 42% across the four populations. The SLR QTL on 7HS explained between 52 to 64% of the phenotypic variance. An examination of the pedigrees of these resistance sources supports the common identity of resistance in these lines and indicates that only a limited number of major resistance loci are available in current two-rowed germplasm

Mapping spot blotch & common root rot (causal agent: bipolaris sorokiniana) resistance genes in barley

The fungal pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus)causes the foliar disease spot blotch (SB) and the root disease common root rot (CRR). Spot blotch and CRR are serious disease constraints to barley production in warmer growing regions of the world, with estimated yield losses ranging from 30-70% from SB and 15-30% for CRR. Although chemical treatments may assist in controlling spot blotch infections, the most effective and environmentally sound means of control for each disease is breeding for varieties with natural resistance. In Australia, no commercially available varieties offer resistance to either SB or CRR. This study has sought to establish molecular markers that will be useful for selecting for resistance to each of these important fungal diseases. Barley cultivars derived from the breeding line NDB112 have provided durable SB resistance in the North Dakota region of the USA for over 40 years. The robustness of this resistance had not been determined under Australian environmental conditions or with those B. sorokiniana pathotypes present within Australia. To elucidate the genetics of resistance, two seedling and two field trials were conducted on an ND11231-12/VB9524 (ND/VB) doubled haploid (DH) population (180 lines). A molecular map of the ND/VB population was curated in order to provide a firm basis for mapping of resistance loci. Composite interval mapping revealed that different gene combinations are effective at different stages of plant development. Seedling resistance was found to be conditioned by a major locus on the short arm of chromosome 7H and this region was validated in the related population ND11231-11/WI2875*17. A minor quantitative locus on chromosome 5HS was detected in one of the two seedling trials. However, this region requires further investigation to confirm its association to SB resistance in this population. Field resistance to SB in adult plants was found to be associated with two major quantitative trait loci (QTL)on chromosomes 7HS and 3HS; and a putative third minor QTL on chromosome 2HS. The 7H region is common between seedling and field resistance and is the most important locus for the expression of resistance at both stages of plant development. These findings largely concur with genetic studies of this trait in tworowed barley germplasm in North American environments. Common root rot is a difficult disease to phenotype for, and breeding programs will benefit from the identification of molecular markers linked to resistance. Data was provided from field trials of subsets of the population over four years. Using a novel approach combining the efficiency of bulked-segregant analysis with highthroughput Diversity Arrays Technology markers (BSA-DArT), CRR resistance was found to be conditioned by three putative QTL in an unmapped Delta/Lindwall population. QTL were identified on chromosomes 2HS, 4HS, and 7HS. To validate the trait-linkage associations between the DArT markers and the CRR QTL,microsatellite (SSR) markers known to map to the regions identified by BSA-DArT were used. The 2H and 4H regions were validated using marker regression of the SSR markers in most seedling trials, whereas the 7H QTL, which is proximal to the location of the SB resistance QTL in the ND/VB population, was detected in only one seedling trial. The QTL identified in this study offer potential to combat the foliar and root diseases causes by this fungal pathogen. The chromosomal location of QTL for SB and CRR resistance have been found to differ in the ND/VB and D/L populations,which suggests that resistance to each disease is independently inherited. Further research is required to confirm the hypothesis that it is possible to combine resistance to both diseases into a single genotype. Such allelic combinations would provide elite germplasm that would benefit barley breeding programs world-wide

Selection of antagonistic actinomycete isolates as biocontrol agents against root-rot fungi

In this study, actinomycetes isolates, isolated from rhizosphere of wheat (Triticum aestivum L.), were screened for antagonistic activities on certain root rot fungi (Fusarium culmorum, Fusarium graminearum, Fusarium verticilloides and Bipolaris sorokiniana). The  in vitro antagonistic effects of actinomycetes isolates were determined on solid media against fungal pathogens. The inhibition mechanism, effect of application time and pH on inhibition was investigated. The actinomycete isolate 129.01 exhibited a high inhibition ratio of more than 60 % against all fungi. The activity of the isolate 129.01 against root rot fungi was tested under greenhouse conditions. The root rot score (1-10), mean plant height (cm) and mean weight of green part of plant (g) were determined after an incubation period. The root rot score of the infected plants was decreased significantly by this isolate, even if the plants were inoculated with all of the pathogen fungi together (P<0.05). The results indicate that isolate 129.01 could be useful as a biocontrol agent. The assignment of the isolate 129.01 to the genus Streptomyces was supported by 16S rRNA analysis.Fil: Erginbas, Gul. Centro Internacional de Mejoramiento de Maíz y Trigo; TurquíaFil: Yamac, Mustafa. Eskisehir Osmangazi University; TurquíaFil: Amoroso, Maria Julia del R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Cuozzo, Sergio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentin

Root Rot Pathogens of Wheat in South Dakota and Their Affect on Seed Germination and Seedling Blight in Spring Wheat Cultivars

Crown rot and common root rot are the important root diseases in wheat (Triticum aestivum L.) and other cereals causing significant germination and yield losses in the Northern Great Plains and other parts of the world. Bipolaris sorokiniana (Bs) and Fusarium graminearum (Fg) cause common root rot and crown rot respectively, are the important wheat root pathogens that can affect seed germination, seedling establishment and impact crop productivity. A survey was conducted in the year 2014 and 2015 to study the distribution and the prevalence of root rot pathogens in South Dakota. Out of 31 and eight roots samples collected in 2014 and 2015, respectively, F. graminearum was the major pathogen recovered in both years. All the collected samples harbored F. graminearium, and 50% of the samples produced B. sorokiniana. In 2014, 125 isolates of F. graminearum and 62 isolates of B. sorokiniana were recovered from 31 root samples and in 2015, 38 isolates of F. graminearum and eight isolates of B. sorokiniana were recovered from eight root samples. The fungus Gaeumannomyces graminis tritici associated with Take-all was not recovered from the collected samples in both years. Further, we studied the effect of B. sorokiniana and F. graminearum infested seed on germination and seedling establishment (blight) of 11 HRSW wheat cultivars under greenhouse and field conditions (Brookings and Volga). Seeds of 11 hard red spring wheat cultivars HRSW cultivars, Advance, Brick, Briggs, Forefront, Oxen, Prevail, Russ, Select, SD4189, SD4215, and Traverse were infested individually with B. sorokiniana and F. graminearum by spraying with their respected spore suspension. Infested seed from all 11 cultivars were planted in paper cups (10 seeds/cup) filled with sterile vermiculite, using a complete randomized design. Seed germination and seedling blight data was recorded 10 and 20 days’ post planting. The percent germination losses when the seed was infested with F. graminearum ranged from 4 to 33% while the seedling survival rate of the cultivars varied from 48 to 87% and the seedling blight ranged from 7-27% but when seed was infested with B. sorokiniana, percent germination varied from 2-17% with 58 to 96% seedling survival rate and 0-16% seedling blight. We further, planted 100 seeds of seven (2015) and 11 (2016) HRSW cultivars with six different treatments in a split plot design experiment in three replications at two field locations, Brookings and Volga. The treatments included were uninfested seed + untreated (T1), unifested + treated with fungicide (T2), infested (B. sorokiniana) + treated (T3), infested (B. sorokiniana) + untreated (T4), infested (F. graminearum) + treated (T5), infested (F. graminearum) + untreated (T6). Seed germination and seedling blight data were recorded after the germination for three consecutive weeks. Wheat cultivars varied in seed germination and seedling blight to both the pathogens; however, low seed germination was observed in F. graminearum infested seed as compared to B. sorokiniana infested seed at both locations in both years. Cultivars Russ (72%) and Oxen (80%) were highly affected for seed germination and seedling blight to both pathogens whereas Forefront (92%), Select (95%) and Briggs (88%) had the highest germination and the higher seedling survival rate as compared to the other cultivars both under greenhouse and field conditions. The percent germination losses when the seed was infested with F. graminearum ranged from 17-35% while the seedling survival rate of the cultivars varied from 92-99%. In case of the seed infested with B. sorokiniana, germination losses ranged from 2-15% with the only highest germination loss observed in Russ cultivar (32%) with the survival rate of all the cultivars ranged from 91-97%. Fungicide treatment (T3 and T5) significantly increased the seed germination from 14-37% and the seedling blight was also reduced in almost all the cultivars. In another experiment, where oat kernels were used as a source of inoculum, reduction in percent seed germination was observed however, it was not significant

FGB1 and WSC3 are in planta-induced beta-glucan-binding fungal lectins with different functions

In the root endophyte Serendipita indica, several lectin-like members of the expanded multigene family of WSC proteins are transcriptionally induced in planta and are potentially involved in beta-glucan remodeling at the fungal cell wall. Using biochemical and cytological approaches we show that one of these lectins, SiWSC3 with three WSC domains, is an integral fungal cell wall component that binds to long-chain beta 1-3-glucan but has no affinity for shorter beta 1-3- or beta 1-6-linked glucose oligomers. Comparative analysis with the previously identified beta-glucan-binding lectin SiFGB1 demonstrated that whereas SiWSC3 does not require beta 1-6-linked glucose for efficient binding to branched beta 1-3-glucan, SiFGB1 does. In contrast to SiFGB1, the multivalent SiWSC3 lectin can efficiently agglutinate fungal cells and is additionally induced during fungus-fungus confrontation, suggesting different functions for these two beta-glucan-binding lectins. Our results highlight the importance of the beta-glucan cell wall component in plant-fungus interactions and the potential of beta-glucan-binding lectins as specific detection tools for fungi in vivo

Characterization of Bipolaris species, their effects on switchgrass biomass yield and chemical components

Switchgrass (Panicum virgatum L.) is a promising biofuel crop; however, limited attention has been directed toward switchgrass pathogens and their impact on biomass yield. Bipolaris is one of the fungal pathogens that pose a potential threat to switchgrass production in the U.S. This research is focused on the impact of Bipolaris on switchgrass. The research objectives were 1) Assessment of isolates of four Bipolaris species for morphology and virulence diversity on switchgrass and impact on biomass yield, 2) Assessment of Bipolaris infection on switchgrass chemical components, 3) Assessment of switchgrass germplasm for disease resistance, and 4) Genetic characterization of Bipolaris species. Twenty-five representative isolates of Bipolaris oryzae, B. sorokiniana, B. spicifera, and B. victoriae varied in morphology and virulence on switchgrass. Bipolaris oryzae was the most virulent species and B. spicifera was the least. Low, intermediate and high virulence groups were identified across all isolates. Low-virulent isolates had limited negative impact on switchgrass whereas high-virulent isolates greatly impacted switchgrass, even at low inoculum density. High-virulent isolates should be targeted for disease resistance development in switchgrass. However, these virulence groups had similar effect on switchgrass chemical components. Bipolaris infection resulted in a significant increase in ash and lignin contents of switchgrass biomass, and a decrease in carbohydrate content, thereby reducing biomass fitness for conversion to drop-in fuels. Out of the nine switchgrass germplasms screened for disease resistance, six, namely Germplasm A, Germplasm B, Germplasm C, ‘Alamo’ (Bamert), ‘Trailblazer’, and ‘Summer’, were moderately resistant to B. spicifera (LA18) or B. oryzae (SK12), whereas none of the germplasms had resistance to B. sorokiniana (APCNR34) and B. victoriae (JA12). The moderately resistant germplasms can further be explored as resistance donors in breeding programs for development of cultivars with biofuel-valuable traits. Simple sequence repeats markers were developed from a small insert genomic library for B. sorokiniana. Sixteen polymorphic loci used to characterized fifteen B. sorokiniana isolates successfully cross-amplified at least one isolate of B. victoriae, B. spicifera and B. oryzae. These markers are valuable for genetic variability studies of Bipolaris species and a useful tool to formulate breeding strategies for development of resistant switchgrass cultivars