Field isolates and laboratory strains of Botrytis cinerea, an ascomycetous fungus causing considerable economic losses, e.g., as "grey mould" of vine, were compared for differences in ploidy level by determining their DNA content per nucleus. Strain SAS56, an ascospore line used routinely for genetic analyses, is probably polyploid, since treatment with benomyl causes a significant reduction in DNA content per nucleus. This conclusion is substantiated by the increased sensitivity of the putative haploid derivatives to mutagens (UV and EMS). Molecular analyses (RAPD) of the haploidized strains indicate a very limited degree of heterozygosis of the parent strain SAS56. Analysis of field isolates of B. cinerea showed that their DNA content per nucleus varied considerably, indicating that aneuploidy/polyploidy is a widespread phenomenon in this species. This can explain both the variability and phenotypic instability of many field isolates of this fungus and the unusual difficulties faced by researchers in recovering stable recessive laboratory mutants. Since the haploid derivatives of SAS56 resemble the parent strain in their parasitic and physiological properties they should provide a good basis for classical and molecular genetic studies.
A model for the genetic structure of grape phylloxera populations in Europe was developed using hierarchical sampling techniques and AFLP-PCR (amplified fragment length polymorphism--polymerase chain reaction) methodology. One-hundred three European and 6 North American phylloxera populations were studied. An additional European sampling set comprising 60 samples was analyzed to study regional subdivision. The populations grouped into two clusters loosely correlated with collection site location. Phylloxera populations collected from northern (above lat 43 degrees) geographic regions were significantly different from southern (below 43 degrees) populations. The northern cluster was more heterogeneous than the southern cluster, possibly reflecting holocyclic versus anholocyclic reproduction. Microgeographic scales of phylloxera genetic structure displayed as much variation within as among host plants. The host plant did not affect the genetic structure of European phylloxera as revealed in two independent experiments.
After inoculation of agar substrates containing resveratrol (an inducible stilbcne characteristic for Vitaceae) with low concentrations (500/cm^) of Botrytis spores, developing germ tubes showed malformations and growth stopped. High density inoculations (10,000/cm-) resulted in apparently normal growth, but stress conditions were indicated by the formation of a large number of sclerotia after 14 days. By contrast, growth of Botrytis and Phomopsis colonies starting from pieces of mycelium was slowed down by resveratrol concentrations < 50 ppm and stopped by higher concentrations. More than 500 ppm (suspensions) induced rhythmical growth; at the front of the mycehum a clear zone appeared, which was free from stUbene crystals but exhibited a brownish pigmentation. In liquid cultures pigmentation but no growth inhibition was observed. It is assumed that resveratrol is oxidized by fungal laccases whose isoenzyme bands can be stained with resveratrol after isoelectric focusing. The different effects of this substrate on fungal growth in liquid and on solid media is explained by the localized action of laccases on solid substances where the radius of diffusion is limited. ZusammenfassungEinfluli von Resveratro! auf Konidienkeimung und Myzelwachstum von Botrytis cinerea und Phomopsis vidcola Keimende Sporen von Botrytis cinerea zeigen auf Agarnahrmedien in Gegenwart von Resveratrol (induzierbares Stilben bei Vitaceen) bei geringer Sporendichte (500/cm') eine Keitnschkuchverformung mit Wachstumsstop; hohere Sporendicbte (10 000/cm') fiihren bei Stilbenkonzentrationen liber 50 ppm -bei zunachst normalem Wachstum -nach 14 Tagen zu einer starken Sklerotienbildung. Von Myzelstiicken ausgehendes radiares Myzelwachstum von Botrytis cmerea und Phomopsis viticola wird dagegen bereits durch Konzentrationen von 10 ppm deutlich verlangsamt und kommt ab 50 ppm ganz zum Stillstand. Sehr boher Stilbengehalt (ab 500 ppm, teilweise wegen der geringen Losiichkeit als kristalline Suspension), fiihrt zu rhythmischem Wuchs, wobei an der Myzelfront stets eine kristallfreie, aber gelbbraun pigmentierte Zone zu beobachten ist. In Fliissigmedien wurde Abbau des U.S. Copyngh. Cle.r.nc. Center Code Stat.m.nt; 093 1-1 785/90/2902-0102$02.50/0
SUMMARYHost-parasite interactions between the grapevine Vitis vinifera L. and the powdery mildew Uncinula necator (Schw.) Burr, were studied by light microscopy and histochemistry, scanning and transmission EM. The lobed appressoria (10/^m diam) of the fungus adhered to the host cuticle because of their shape and the production of a soluble adhesive substance. Each formed a penetration peg (0-3 //m diam) which, after penetration into the epidermal cell, developed into a globular haustorium consisting of a nucleated central body with fingerlike lobes, embedded in a matrix. The surrounding extrahaustorial membrane was derived from the transformed plasmalemma of the host cell. As a defence mechanism the walls of the host cell and neighbouring cells were encrusted with silica and phenolic substances associated with cell wall bound peroxidase activity. Penetration may have been blocked by the formation of a papilla composed of different layers containing carbohydrates, silica and phenolic substances. Cells forming a thick papilla were not infected. In cells with old infections, callose deposits could be observed in walls and/or around the haustorial neck and papilla, and sometimes around the whole haustorium.
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