Field and laboratory studies of the effect of urea on ascospore production of Venturia inaequalis (Cke.) Wint

Applications of urea after harvest but before leaf-fall restricted perithecial production by Venturia inaequalis. Immersion of detached leaves in urea appeared to be the most effective method of preventing perithecial formation, although spraying attached leaves was equally effective when leaf abscission occurred within a week of treatment. A high nitrogen content within the leaf was one of the major factors contributing to suppression. Urea-treated leaves decomposed rapidly, thus destroying the overwintering substrate for the fungus. When apple plants (clone M. 111) were sprayed in autumn with 5 % urea, followed by a second (pre-bud-burst) application at 2 %, ascospore production in the spring was suppressed. The second treatment appeared to prevent the release of ascospores from mature perithecia.     

Effect of Post-infection Application of Fungicides on the Apple Scab Pathogen, Venturia inaequalis (Cke.) Wint.

The Ergosterol-biosynthesis inhibiting (EBI) fungicides had a prolonged inhibitory effect on the growth and sporulation of the fungus, Venturia inaequalis thereby preventing development of typical apple scab symptoms. Atypical lesions in the form of chlorotic or reddish brown flecks had reduced viable sporulation with deleterious effect on subcuticular hyphae when fungicide was applied beyond 144 h but before 170h after inoculation. Myclobutanil (45μg a.i./ml) had the maximum inhibitory effect on sporulation and colony growth while bitertanol (187.50 μg a.i./ml) showed only a temporary inhibition of fungal growth and sporulation. Ultra-structural studies also exhibited different levels of fungitoxicity by different fungicides when applied 144 h after inoculation.     

Wirkung von Fungiziden auf die Sporulation von Podosphaera leucotricha (Ell. et Ev.) Salm. und Venturia inaequalis (Cooke) Wint

This paper presents the results of 3 year‐long monitoring of crop fields in four ecologically different areas of Ukraine for several phytoviral infections. Various modifications of ELISA were used as main assay to evaluate the spreading of a virus. The technique allowing to determine the frequency of occurrence for a virus of interest is proposed. This technique is based on an identification of viral antigens in crops, accompanying weeds and soil. The differences between the investigated regions on a virus occurrence frequency as well as dynamics of the parameter in relation to crop‐rotation have been revealed. The possibility to use results obtained for predicting phytoviral disease spreading is discussed.     

Genetics of resistance in apple against <Emphasis Type="Italic">Venturia inaequalis</Emphasis> (Wint.) Cke

Apple (Malus × domestica) is the third important fruit in terms of production and consumption worldwide. Apple scab caused by Venturia inaequalis is the most devastating disease of apple. In the apple-growing regions, many fungicides are sprayed to control the disease leading to increase in the production cost. Development of scab-resistant cultivars is the long-lasting solution to control the disease. In apples, more than 20 major scab resistance genes have been identified in various cultivars and few wild relatives. Of all these genes, Rvi6 derived from Malus floribunda has been most extensively used in different breeding programs. Gene for gene interactions of these resistance genes with the avirulence genes from V. inaequalis have been understood in many cases. QTL-based polygenic resistance has also been characterized in apple. Nucleotide Binding Site Leucine-Rich Repeats (NBS-LRR) have been identified from the apple genome and many of them have been characterized from the scab resistance region. Molecular markers associated with most of the major scab resistance genes have been identified and their position has been mapped on different linkage groups. Marker-assisted selection (MAS) can be helpful in speeding up and accurately identifying the scab-resistant parents and progeny. Pyramiding of several major resistance genes can be undertaken for more durable resistance against apple scab. The present paper reviews the Malus-Venturia pathosystem, current status of knowledge about scab resistance genes, and their application in breeding against apple scab.     

A method for the isolation of fungistatic microorganisms active against a slowly growing mold: Venturia inaequalis (Cke) wint

Summary A new cellophane technique is described for the isolation from soil of fungistatic antagonists active against the slowly growing plant pathogenVenturia inaequalis.     

Genetic dissection of partial resistance to race 6 of Venturia inaequalis in apple.

Scab, caused by the fungus Venturia inaequalis, is one of the most important diseases of apple (Malus x domestica). The major resistance gene, Vf, has been widely used in apple breeding programs, but two new races of the fungus (races 6 and 7) are able to overcome this gene. A mapped F1 progeny derived from a cross between the cultivars Prima and Fiesta has bee n inoculated with two monoconidial strains of race 6. These strains originated from sporulating leaves of 'Prima' and a descendant of 'Prima' that were grown in an orchard in northern Germany. 'Prima' carries the Vf resistance gene, whereas 'Fiesta' lacks Vf. A large variation in resistance and (or) susceptibility was observed among the individuals of the progeny. Several quantitative trait loci (QTLs) for resistance were identified that mapped on four genomic regions. One of them was located in the very close vicinity of the Vf resistance gene on linkage group LG-1 of the 'Prima' genetic map. This QTL is isolate specific because it was only detected with one of the two isolates. Two out of the three other genomic regions were identified with both isolates (LG-11 and LG-17). On LG-11, a QTL effect was detected in both parents. The genetic dissection of this QTL indicated a favourable intra-locus interaction between some parental alleles.     

Overwintering of Venturia inaequalis the causal agent of apple scab in relation to weather

Apple leaves collected at East Mailing and bearing colonies of Venturia inaequalis were exposed outdoors from November 1978 to May 1979 at 12 United Kingdom sites. Pseudothecial development and abundance were recorded from samples returned to East Mailing every 2 wk. Pseudothecia matured most rapidly with high rainfall in November and high temperatures in spring. Mature pseudothecia were most abundant with low temperatures in November and low rainfall in spring. In 1979-80 a cross-over experiment, in which scabbed leaves spent either November-January or February-April at a common site, and the other half of the winter at one of five sites, demonstrated the separate effects of weather following leaf-fall and in the spring. Equations for forecasting the time to pseudothecial maturity, but not the numbers of mature pseudothecia, were obtained. Experiments in controlled environments demonstrated the importance of low temperature and high moisture for initiation and early development of pseudothecia, but a controlled increase of temperature in the spring did not result in faster rates of maturation compared with lower temperatures outdoors. Ascospore production from leaves kept in controlled environments in spring was consistently lower than from leaves kept outside.     

Assessment of Sensitivities to Anilinopyrimidine- and Strobilurin-fungicides in Populations of the Apple Scab Fungus Venturia inaequalis

The sensitivity of Venturia inaequalis populations to the anilinopyrimidine fungicides pyrimethanil and cyprodinil was analysed by microscopic in vivo analysis of conidiophore formation. The sensitivity to the strobilurin kresoxim-methyl was analysed using an in vitro germination assay and by determination of the diseased leaf area and conidia produced in vivo. Baseline sensitivities were determined with V. inaequalis populations from control orchards that had never been treated with fungicides. Comparison of the baseline sensitivities with sensitivities of populations obtained from orchards that had received 43 anilinopyrimidine treatments over 4 years, or from an orchard with 54 kresoxim-methyl treatments over 6 years indicated that no resistance to these fungicides has developed at the sites sampled.