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An exact micro-plot experiment was conducted to determine the effect of fungicides (treatments: Sandofan Manco 64 WP, Penncozeb 80 WP, Tanos 50 WG; Tanos 50 WG applied three times; Tanos 50 WG, Penncozeb 80 WP, Tanos 50 WG) on the severity of late blight and early blight in three potato cultivars and on the composition of fugal communities colonizing potato leaves. The tested fungicides significantly reduced the intensity of late blight and early blight. The efficacy of fungicidal control was affected by weather conditions and potato cultivars. The highest efficacy (30–36%) against late blight and early blight was noted in potato plants cv. Aster sprayed with Sandofan Manco 75 WG, Penncozeb 80 WP, Tanos 50 WG and Tanos 50 WG applied three times in the first year of the study. Sandofan Manco 75 WG, Penncozeb 80 WP, Tanos 50 WG, and Tanos 50 WG and Penncozeb WP 80 used alternately during the last two last growing seasons were most effective in late blight control in potato cv. Tara and Salto. In these cultivars, early blight was best controlled with Tanos 50 WG applied three times, and Tanos 50 WG and Penncozeb 80 WP used alternately. The lowest counts of Alternaria spp. – the causal agent of early blight – were isolated from potato leaves in the above treatments.
In an exact micro-plot experiment, potato plants of three cultivars were sprayed at 10-day intervals with the following fungicides: Sandofan Manco 64 WP, Penncozeb 80 WP and Tanos 50 WG; Tanos 50 WG applied three times; Tanos 50 WG, Penncozeb 80 WP and Tanos 50 WG (control treatment without fungicides). After five-month storage, the incidence of common scab (Streptomyces scabies) was determined on 100 tubers selected randomly of particular treatments, according to a nine-point scale (percentage infection index). The symptoms of late blight (Phytophthora infestans) and dry rot (Fusarium spp.) were evaluated in 5 kg samples for each treatment (percentage of the mass of infected tubers). Fungi were isolated from tubers at the laboratory. The applied fungicidal control insignificantly affected the severity of infection caused by S. scabies only in the last year of the study. Potato tubers from fungicide-treated plants showed weaker symptoms of infections caused by P. infestans and fungi of the genus Fusarium. The abundance of pathogens colonizing potato tubers was lower in fungicide treatments.
A field experiment was carried out (2004–2005) to determine the effect of seed potato treatment with the fungicides Dithane M 45 75 WG, Prestige 290 FS and Vitavax 2000 FS, and the biocontrol agent Polyversum on the severity of stem infection of three potato cultivars, Vineta, Irga and Wawrzyn caused by Rhizoctonia solani and Colletotrichum coccodes. Untreated seed potatoes were planted in the control plots. Disease severity was assessed using a four-point scale, at the following potato developmental stages: beginning of leaf yellowing, end of leaf yellowing – beginning of tuber ripening. The communities of fungi colonizing potato stems was also determined (the fungi were cultured on Potato Dextrose Agar medium). Seed potato treatment with the fungicides Dithane M 45 75 WG and Vitavax 2000 FS, and the biocontrol agent Polyversum significantly reduced the symptoms of rhizoctoniose and anthracnose on the stems of the studied potato cultivars. Prestige 290 FS showed the weakest protective effect. The lowest number of C. coccodes and R. solani isolates were obtained from the stems grown from seed potatoes treated with Vitavax 2000 FS and Polyversum.
An exact field experiment was conducted to determine the effect of chemical dressing of tubers with Dithane M 45 75 WG, Prestige 290 FS and Vitavax 2000 FS, and biological dressing with Polyversum on the occurrence and intensity of rhizoctoniosis and anthracnose on the tubers of three potato cultivars (early cultivar Vineta, late cultivars Irga and Wawrzyn). The composition of communities of fungi colonizing potato tubers was also determined. The chemical and biological dressing of tubers significantly decreased the infection by rhizoctoniosis on tubers (except for Prestige in 2004) and the percentage of tubers with microsclerotia. Dithane M 45 75 WG and Vitavax 2000 FS were the most effective in protecting potato tubers against the tested pathogens. The infection rate of tubers of cv. Wawrzyn by Rhizoctonia solani and cv. Vineta by Colletotrichum coccodes was significantly higher, as compared with the other cultivars. The highest decrease in the population size of the causal agents of rhizoctoniosis and anthracnose was stated on tubers treated with Dithane M 45 75 WG and Vitavax 2000 FS. R. solani was completely eliminated in the objects with biological dressing treatment.
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