Interaction Of Barley Yellow Dwarf Virus and Fusarium culmorum (W. G. Sm.) Sacc. in Winter Wheat

The barley yellow dwarf virus (BYDV) epidemics, which occurred predominantly in northern Germany in 1988–90 and caused unusual yield losses of wheat, prompted our study on interactions of BYDV and Fusarium culmorum. At the late stages of plant development (EC 55/65) infections with BYDV resulted in a lower yield reduction of wheat plants than infections with F. culmorum. Combined infections at flowering resulted in severer yield reduction, indicating additive effects of the two pathogens. However, if wheat infected by BYDV at stage EC 25/35 was secondarily inoculated with the fungus at EC 55/65 the yield was less reduced than in combined infections at EC 55/65. Our results proved that the susceptibility of wheat plants to F. culmorum is increased when infection by BYDV takes place during the late stages of growth. These results correspond to observations during 3 years of the epidemic in Germany. In these years BYDV was spread mainly during the late spring, resulting in a severe secondary infection by the fungus. From the results of these investigations it may be concluded that during the years of BYDV epidemic the yield of wheat was reduced to an economically important extent because of the fungal infection, which was favoured by the virus infection.     

Genetic determination of variability of barley doubled haploids inoculated with Fusarium culmorum (W.G.Sm.) Sacc. with regard to mycotoxin accumulation and reduction in yield traits

The genetic determination of variability of barley doubled haploid (DH) lines in regard of their susceptibility to Fusarium head blight caused by Fusarium culmorum was studied. The susceptibility was evaluated in 3-year field experiment on the basis of reduction in yield traits and myotoxin accumulation in infected kernels. The following traits were analysed in inoculated and control plants: kernel number and weight per ear, 1000-kernel weight, percentage of plump kernels (>2.5 mm), deoxynivalenol (DON) content and nivalenol (NIV) content of kernels. On the basis of the obtained data, heritability coefficient (ratio of genotypic to phenotypic variance) was assessed, and genetic parameters as well as the number of effective factors were estimated. Heritability coefficients calculated from two-way analysis of variance, i.e.regarding the influence of years and year x genotype interaction, appeared to be exceptionally low and ranged from 5.2% for the reduction in plump kernels to 38.2% for the reduction in 1000-kernel weight. In the case of mycotoxin accumulation about 60% of the observed variability in NIV concentrations and 30% in DON concentration resulted form genetic differences among lines. Additive effects of genes were important for all the analysed traits. Significant effects of dominance and dominance x dominance were observed for 1000-kernel weight and percentage of plump kernels. Moreover, it was found that the observed variability in yield trait reduction resulted from segregation of 5-6 effective factors, DON contents from 4 factors, while NIV content from 5 factors.     

The influence of sucrose and wheat root exudates on the germination and growth of conidia ofFusarium culmorum (W.G.S.M.) Sacc

Summary It is shown in these studies that the germination of the conidia ofFusarium culmorum (W.G.Sm.) Sacc. is influenced by both constitutive and exogenous factors. In a dense suspension, selfinhibited spores are induced to germinate by dilution with distilled water and by suspending in either sucrose solution or wheat root exudates. The exudates not only stimulate conidial germination but also promote subsequent growth of the fungus. The significance of this in pathogenesis is discussed.     

Cellulolytic and Pectolytic Activity of Cylindrocarpon destructans (Zins.) Scholt. Isolates Pathogenic and Non-Pathogenic to Fir (Abies alba Mill.) and Pine (Pinus sylvestris L.)*

In studies on cellulolytic and pectolytic activity of C. destructans, it was found that only one of the twenty isolates studied exhibited cellulolytic activity. The total activity of this isolate was similar in media with CMC and powdered cellulose. The specific activity was, however, two times higher with powdered cellulose. All isolates identified as pathogenic to fir and to pine produced pectolytic enzymes. Not all of them, however, exhibited exo- and endo-PMG activity. In general, an increase of total activity of exo-PMG was accompanied by an increase in the specific, activity. Of the non-pathogenic isolates, only one did not show pectolytic activity. The results of our studies have revealed that there exist no significant differences in pectolytic activity between the isolates pathogenic and non-pathogenic to fir and pine. Also, the isolates belonging to both groups were not cellulolytic except one non-pathogenic.     

Pathogenic Variation of Fusarium Isolates Associated with Head Blight of Wheat in Australia

This paper examines the level of pathogenic diversity in Australian Fusarium pseudograminearum and Fusarium graminearum isolates for head blight from the assessment of 51 wheat germplasm lines, barley, triticale, rye, maize and sorghum plants. A set of nine putative wheat differentials were selected and assessed with 10 F. graminearum and 12 F. pseudograminearum isolates. Isolates of both species were pathogenic on all the wheat germplasm lines, barley triticale and rye. The isolates differed largely in a quantitative way with only small differential effects and were statistically demarcated into three pathogenicity groups: low, intermediate and high. Such distribution patterns suggest that wheat germplasm lines employ different resistance mechanisms to each group of isolates and the three pathogenicity groups may have different mechanisms controlling pathogenicity. The aggressiveness of F. graminearum and F. pseudograminearum isolates on the wheat germplasm lines were marginally correlated (r = 0.40). Durum wheats were ranked as the most susceptible while Sumai 3, Ituo Komugi, Sotome A, Sotome and Nobeokabouzu komugi were consistently grouped as resistant by both species. These findings reiterate the need to consider pathogen variability in the screening, selection and improvement of resistance to head blight in wheat.     

Histopathology of Oil Palm Seedlings Infected by, Pathogenic Fusarium oxysporum Isolates from Africa

Oil palm seedlings (one-leaf stage) grown from Malaysian seed were inoculated with six African isolates of Fusarium oxysporum f. sp. elaeidis and one African isolate of Fusarium oxysporum var. redolens. All the isolates induced similar symptoms and anatomical responses in the inoculated palms. The pathogen invaded the root, bulb, leaf bases and leaves in that sequence. In the root and bulb, infection resulted in plugging of xylem elements with mycelium, conidia, tyloses and gums, disintegration and plugging of phloem tissues, disintegration of plugged vascular elements forming gaps and cavities, and collapse of cortical tissues leading to the isolation of the infected vascular tissues. Formation of hypertrophic or hyperplastic cells in the xylem parenchyma was not observed. Anatomical changes in the infected leaf bases and petioles were similar to those occurring in the infected bulb; except that tyloses were formed less frequently. Generally there was no sign of the pathogen in the wilted leaf blade, but the epidermal, hypodermal and mesophyll cells appeared shrunken or to have collapsed. No hyphae or anatomical changes were observed m the tissues of symptomless inoculated palms.     

Moniliformin Accumulation and other Effects of Fusarium avenaceum (Fr.) Sacc. on Kernels of Winter Wheat Cultivars

Accumulation of the mycotoxin moniliformin (MON) and other effects on kernels were examined in 13 Polish winter wheat cultivars inoculated with F. avenaceum (Fr.) Sacc. isolate ATCC 64451. Kernels from inoculated ears were divided into three fractions: Fusarium damaged kernels (FDK), kernels with black point symptoms (BPK) and healthy looking kernels (HLK). The average moniliformin content (mg/kg) was highest in chaff (11.69), lower in infested kernels (FDK + BPK) (2.70) and lowest in HLK (1.16). The mean level (mg/kg) of moniliformin in kernels (total sample) ranged from 0.78 in cv. Liwilla to 3.84 in cv. Gama. Moniliformin levels in chaff were correlated ( r = 0.5322) with the average metabolite concentration (mg/kg) in kernels, and ranged from 4.97 in chaff of cv. Roma to 22.9 of cv. Alba. The moniliformin concentration in kernels (total sample) was highly correlated with the level of the metabolite in diseased kernels. This is the first report of the relationship of black point symptoms with F. avenaceum colonization of kernels and moniliformin accumulation.     

Evaluation of Durum Wheat Genotypes for Resistance against Root Rot Disease Caused by Moroccan Fusarium culmorum Isolates

Fusarium culmorum is one of the most important causal agents of root rot of wheat. In this study, 10 F. culmorum isolates were collected from farms located in five agro-ecological regions of Morocco. These were used to challenge 20 durum wheat genotypes via artificial inoculation of plant roots under controlled conditions. The isolate virulence was determined by three traits (roots browning index, stem browning index, and severity of root rot). An alpha-lattice design with three replicates was used, and the resulting ANOVA revealed a significant (P < 0.01) effect of isolate (I), genotype (G), and G × I interaction. A total of four response types were observed (R, MR, MS, and S) revealing that different genes in both the pathogen and the host were activated in 53% of interactions. Most genotypes were susceptible to eight or more isolates, while the Moroccan cultivar Marouan was reported resistant to three isolates and moderately resistant to three others. Similarly, the Australian breeding line SSD1479-117 was reported resistant to two isolates and moderately resistant to four others. The ICARDA elites Icaverve, Berghisyr, Berghisyr2, Amina, and Icaverve2 were identified as moderately resistant. Principal component analysis based on the genotypes responses defined two major clusters and two sub-clusters for the 10 F. culmorum isolates. Isolate Fc9 collected in Khemis Zemamra was the most virulent while isolate Fc3 collected in Haj-Kaddour was the least virulent. This work provides initial results for the discovery of differential reactions between the durum lines and isolates and the identification of novel sources of resistance.     

Chemotyping of Fusarium graminearum and F. culmorum Isolates from Turkey by PCR Assay

Fusarium graminearum and F. culmorum are the major causal agents of Fusarium head blight in Turkey. They produce trichothecenes such as deoxynivalenol (DON), nivalenol (NIV) and their several acetylated derivatives, 3-acetyldeoxynivalenol (3-ADON) and 15-acetyldeoxynivalenol (15-ADON). In this study, a total of thirty-three isolates of F. graminearum and F. culmorum were collected from various regions and three different hosts. They were identified by amplification of tri5 gene cluster. Totally 32 isolates, 21 of F. culmorum and 11 of F. graminearum, were determined as DON chemotype, while only one F. graminearum isolate (1F) was detected as a NIV. A 282 base pair (bp) band for tri13 gene and also ranging from 458 to 535 bp bands for tri7 gene were amplified in all DON producers’ genomes. Further analysis of DON chemotype based on tri3 gene amplification showed that all isolates of F. graminearum displayed 15-ADON sub-chemotype. They yielded a 863 bp amplicon. Similarly, 3-ADON sub-chemotype was identified in F. culmorum’ isolates except F13. As a result of tri3 gene assay, it was produced a 583 bp fragment in these twenty isolates. It is the first report that a F. graminearum isolate depicts NIV chemotype in agricultural regions of Turkey. According to our findings, DON chemotype is predominating in our country. Also, it is presented that most of the F. graminearum isolates have 15-ADON sub-chemotype, while all F. culmorum’s belong to 3-ADON which possess full length amplicon of tri7 gene.     

Metabolic activities of the sugarbeet pathogens Fusarium solani (Mart.) Sacc. and Sclerotium rolfsii Sacc. under pyramin stress

Effects of different concentrations of active ingredient of the herbicide pyramin on metabolic activities of Fusarium solani and Sclerotium rolfsii were examined. High concentrations of this herbicide (1000 and 2000 g mL^-1 for F. solani and 100 and 200 g mL^-1 for S. rolfsii) had inhibitory effects on the metabolic activities of both fungi. These were demonstrated by significant decreases in growth, and increases in rates of CO₂ evolved, O₂ consumed and keto acids produced. These were accompanied by increased rates of sugar, nitrate and inorganic phosphorus absorption as well as lowered rates of synthesis of carbohydrates and insoluble nitrogenous (including protein) and phosphorus (including RNA-P and DNA-P) compounds. In addition, rates of excretion of both nitrogen and phosphorus fractions by the mycelial mats were increased.A concentration of 25 g mL^-1 exerted little or no effect on the metabolic activities of these fungi, although S. rolfsii was somewhat sensitive to this concentration.     

RAPD Characterization of Fusarium oxysporum Isolates Pathogenic on Argyranthemum frutescens L.

The random amplified polymorphic DNA (RAPD) technique was used to analyse total genomic DNA of 10 isolates of a new Fusarium oxysporum pathogenic on Argyranthemum frutescens (Paris daisy), by comparing them with representatives of the formae speciales basilici, chrysanthemi, cyclaminis, dianthi, gladioli, lilii, lycopersici, melonis, pisi, radicis‐lycopersici, tracheiphilum, and a non‐pathogenic isolate of F. oxysporum. A close genetic relatedness was observed among most of the new isolates from A. frutescens. These isolates also shared RAPD markers with the tested representatives of the forma specialis chrysanthemi. A single isolate among those tested from diseased A. frutescens was placed in a different cluster, which included representative isolates of forma specialis tracheiphilum. All the new isolates from A. frutescens, with the exception of the single divergent one, could be identified by their characteristic amplification profile, using selected random primers. A rapid protocol for DNA extraction directly from fungal colonies grown on Fusarium selective medium allowed the complete analysis in less than 4 h.     

Competitive Aggressiveness in Binary Mixtures of Fusarium graminearum and F. culmorum Isolates Inoculated on Spring Wheat with Highly Effective Resistance QTL

Fusarium head blight (FHB) caused by Fusarium graminearum and F. culmorum is a devastating disease with high effects on grain yield and quality. We developed spring wheat lines incorporating the highly effective FHB resistance quantitative trait loci (QTL) Fhb1 and Qfhs.ifa‐5A. Whether these QTL lead to competition within Fusarium populations in the field resulting in isolates with higher aggressiveness has not been analysed. The aims of this study were to determine (i) the aggressiveness potential of F. graminearum and F. culmorum isolates, (ii) competition effects of these isolates in binary mixtures and (iii) the stability of resistant hosts. Six F. graminearum, two F. culmorum isolates and seven binary mixtures containing these isolates were tested for their aggressiveness and mycotoxin production at two locations in South Germany in 2007 and 2008. Host lines were four spring wheat lines containing the resistance QTL Fhb1 and/or Qfhs.ifa‐5A or none of them and one standard variety. Re‐isolates were sampled from plots inoculated with the binary mixtures to identify the percentage of each isolate in the mixture by simple sequence repeat markers. Resistant host lines reacted as expected and had a high stability to all isolates and mixtures. Only less important host × mixture interactions were detected. Aggressiveness among isolates and mixtures was significantly different. Type and amount of mycotoxin and high single isolate aggressiveness were not necessarily advantageous in the mixture. However, both F. culmorum isolates outcompeted F. graminearum isolates. Significant deviations from the inoculated 1 : 1 proportions occurred in 34 of 49 cases, illustrating that competition effects appeared in the mixtures. These differences depended mainly on the year and not on the level of host resistance. We conclude that resistance should not be affected by the Fusarium isolates and mixtures.     

Chemical constituents of Medinilla septentrionalis (W. W. Sm.) H. L. Li (Melastomataceae)

Our phytochemical investigation of the whole plants of Medinilla septentrionalis (W. W. Sm.) H. L. Li led to the isolation of five tannins (1–5), five phenolic acids and phenolic acid derivatives (6–10), four flavonoids (11–14), two triterpenes (15 and 16), and one hydantoin derivative (17). The structures of the obtained compounds were identified using spectrometric methods (¹H NMR, ¹³C NMR and MS). This is the first study reporting on the chemical constituent of M. septentrionalis and the chemotaxonomic relationships between Medinilla and other genera of Melastomataceae.     

Analysis of Genetic Diversity of Fusarium oxysporum f. sp. phaseoli Isolates, Pathogenic and Non-pathogenic to Common Bean (Phaseolus vulgaris L.)

Twenty isolates of Fusarium oxysporum from Brazil, pathogenic and non‐pathogenic to common bean, were analysed using random amplified polymorphic DNA (RAPDs) to study the genetic diversity. RAPD analysis using 23 oligonucleotides resulted in the amplification of 229 polymorphic and 7 monomorphic DNA fragments ranging from 234 to 2590 bp. High genetic variability was observed among the isolates, with the distances varying between 8% and 76% among pathogenic, 2% and 63% among the non‐pathogenic and 45% and 76% between pathogenic and non‐pathogenic isolates. The analysis of genetic distance data showed that the pathogenic isolates tended to group in one group and the non‐pathogenic in another. The genetic distance values of 30% among the pathogenic isolates in cluster A are compatible with the genetic distance values observed within the physiological races, but the distance values among the pathogenic isolates in clusters B and G are not compatible with the distance values observed within the race. Although our results are preliminary, it was not possible to exclude the existence of more than one race of this fungus in Brazil.     

Detoxification of Benzoxazolinone Allelochemicals from Wheat by Gaeumannomyces graminis var. tritici, G. graminis var. graminis, G. graminis var. avenae, and Fusarium culmorum

The ability of phytopathogenic fungi to overcome the chemical defense barriers of their host plants is of great importance for fungal pathogenicity. We studied the role of cyclic hydroxamic acids and their related benzoxazolinones in plant interactions with pathogenic fungi. We identified species-dependent differences in the abilities of Gaeumannomyces graminis var. tritici, Gaeumannomyces graminis var. graminis, Gaeumannomyces graminis var. avenae, and Fusarium culmorum to detoxify these allelochemicals of gramineous plants. The G. graminis var. graminis isolate degraded benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benzoxazolin-2(3H)-one (MBOA) more efficiently than did G. graminis var. tritici and G. graminis var. avenae. F. culmorum degraded BOA but not MBOA. N-(2-Hydroxyphenyl)-malonamic acid and N-(2-hydroxy-4-methoxyphenyl)-malonamic acid were the primary G. graminis var. graminis and G. graminis var. tritici metabolites of BOA and MBOA, respectively, as well as of the related cyclic hydroxamic acids. 2-Amino-3H-phenoxazin-3-one was identified as an additional G. graminis var. tritici metabolite of BOA. No metabolite accumulation was detected for G. graminis var. avenae and F. culmorum by high-pressure liquid chromatography. The mycelial growth of the pathogenic fungi was inhibited more by BOA and MBOA than by their related fungal metabolites. The tolerance of Gaeumannomyces spp. for benzoxazolinone compounds is correlated with their detoxification ability. The ability of Gaeumannomyces isolates to cause root rot symptoms in wheat (cultivars Rektor and Astron) parallels their potential to degrade wheat allelochemicals to nontoxic compounds.     

Expression of Resistance of Wheat to Fusarium graminearum and F. culmorum Under Various Experimental Conditions

The resistance ranking was very similar under different periods of incubation except the 17 and 24 h variants under plastic bags and with the presence or absence of Bayleton treatment. Very similar ranking was recorded also in the tests where four plot replicates were used, e.g. the reaction severity was so close in different plot replicates that one plot per genotype seemed to be enough for serial resistance tests. The significant plot × genotype interaction shows that relative resistance ranking may vary to some extent, but basic changes do not occur. Also similar cultivar reactions were observed at different levels of disease severity resulting from inoculation with isolates differing in pathogenicity. An average reaction to these levels is closer to the genetically determined resistance. Analysis of the behaviour of a cultivar at different disease severity levels helps to predict the field behaviour of a given genotype. The Bayleton treatment was ineffective against scab, although there was some interaction with cultivars.