Surveys carried out during the spring of 2000, in central Italy showed that systemic Plasmopara helianthi infections occurred in some sunflower fields planted with metalaxyl-treated seeds. Generaly, low incidence of infected plants, ranging from 2% to 26% were observed. Greenhouse tests on sunflower differentials lines showed that the two field isolates of the pathogen obtained during the surveys belong to P.helianthi race 2. Also registered rate o metalaxyl, as seed dressing, confirmed that this fungicide was totally effective in controlling downy mildew infections of both isolates. Some plants of two hybrids were sistemically infected by P.helianthi race 2 in experiments based on artificial inoculation, thus suggesting that due to irregularities in seed production, the commercial seed lots examined are not genetically homogeneous. Laboratory analyses on the metalaxyl amount on treated seeds of ten sunflower hybrids revealed an insufficient seed dressing in most of the hybrids tested. These results confirm that phytosanitary measures like appropiate planting date, crop rotation, application of metalaxyl concentration registered for seed treatment and use of resistant hybrids can at present completely control sunflower downy mildew.
Possibili cause della comparsa di limitati attacchi di Plasmopara helianthi Novot. su girasole.
TOSI, Laura;ZAZZERINI, Antonio;
2001
Abstract
Surveys carried out during the spring of 2000, in central Italy showed that systemic Plasmopara helianthi infections occurred in some sunflower fields planted with metalaxyl-treated seeds. Generaly, low incidence of infected plants, ranging from 2% to 26% were observed. Greenhouse tests on sunflower differentials lines showed that the two field isolates of the pathogen obtained during the surveys belong to P.helianthi race 2. Also registered rate o metalaxyl, as seed dressing, confirmed that this fungicide was totally effective in controlling downy mildew infections of both isolates. Some plants of two hybrids were sistemically infected by P.helianthi race 2 in experiments based on artificial inoculation, thus suggesting that due to irregularities in seed production, the commercial seed lots examined are not genetically homogeneous. Laboratory analyses on the metalaxyl amount on treated seeds of ten sunflower hybrids revealed an insufficient seed dressing in most of the hybrids tested. These results confirm that phytosanitary measures like appropiate planting date, crop rotation, application of metalaxyl concentration registered for seed treatment and use of resistant hybrids can at present completely control sunflower downy mildew.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
