Search

When cultivating pumpkin crops in most agricultural regions of the world, one of the most aggressive diseases is real powdery mildew, the damage of plants in which, under optimal soil and climatic conditions for the pathogen, reaches 100%. In the open and protected ground, among the cultivated representatives of the Cucurbitaceae family, the most widespread and harmful are the species Sphaerotheca fuliginea (Schlecht ex Fr.) Poll and Erysiphe cichoracearum f. sp. cucurbitacearum (DC ex Merat). In regions where both phytopathogens are present, mixed infections may occur, making identification difficult, and, accordingly, further plant protection measures. The pathogens of this powdery mildew of pumpkin crops have different requirements for temperature and humidity. During the growing season, there may be a change in species composition when conditions change, for example, when a new season begins. Symptoms of the disease in the form of a white or yellowish powdery plaque in the form of rounded spots (mainly on the leaves) can manifest themselves at all stages of plant development, the susceptibility of which increases by the beginning of fruiting. According to biological characteristics, S. fuliginea and E. cichoracearum are obligate biotrophic pathogens, unable to exist independently without living photosynthetic tissue, except for the wintering (sexual) stage of teleomorphs in the form of globular kleistothecia. At this stage, it is not difficult to differentiate pathogens by the morphology of kleistothecium. When analyzing the plant material of melons with the naked eye, S. fuliginea and E. cichoracearum cause similar symptoms of damage, but by microscopy these organisms can be distinguished by a complex of morphological characteristics. Taxonomically significant features are: the location of the mycelium, the formation of conidia (single or chain), the presence or absence of noticeable fibrosin bodies, the features of the appressoria, the size and shape of the conidia, as well as the position and type of their sprout tubes. The works of Russian and foreign scientists have shown the possibility of determining the types and physiological races of pathogens using an indirect method: reactions to differentiator plants. To date, about 30 physiological races of the pathogen Podosphaera xanthii (Sphaerotheca fuliginea) and 2 races of E. cichoracearum are known. However, this method does not always correlate with the methods of molecular analysis. Determination of the species composition of powdery mildew pathogens is a starting point for the development of a further strategy for the cultivation of pumpkin crops and in breeding work for resistance to this disease.

Eight red chicory (Cichorium intybus L. var. silvestre Bisch.) cultivars were screened for plant characteristics, yield, resistance to Erysiphe cichoracearum and their persistence of bolting over a two-year period (2002 and 2003 growing seasons) in central Slovenia. On two years with meteorologically different conditions the highest total and marketable weight of heads (i.e. total weight – weight of removed damaged leaves) were obtained from cv. 'Averto', followed by cv. 'Mesola' and 'Rubino'. The most compact heads in both years, were produced by cv. 'Palla rossa-super'. Less productive cultivars of red chicory were on average the most infected with the powdery mildew caused by E. cichoracearum. In 2002 the fungus occurred in a substantially larger extent than in 2003, which was less favourable for spread of the pathogen. The higher temperatures, prevailing in summer 2003, presumably promoted a greater percentage of bolting in plants. Among eight cultivars studied through two years, cv. 'Castel Franco', 'Averto' and 'Mesola' drew no incidence of bolters.

The occurrence of Erysiphe cichoracearum (Ec) and Sphaerotheca fuliginea (Sf), causal agents of cucurbit powdery mildewin the Czech Republic (CR) was studied in the period of 1995-2001. Nearly 800 leaf samples with disease symptomswere microscopically examined. Ec is the predominating species, detected on 98% of locations. It was accompanied by Sfon 24% of locations. The occurrence of Sf as the only powdery mildew species was proved on 2% of locations. Recentoccurrence of Sf in the CR corresponds with data on Sf fast spreading and prevailing on cucurbits in West and SouthEurope. However, Ec is the strongly predominating powdery mildew species largely distributed throughout the country.The hyperparasitic fungus Ampelomyces quisqualis was detected on 30% of samples.