Avaliação da resistência à ferrugem (puccinia helianthi schw) em variedades de girassol (helianhus annuus l.)

Abstract

Summary The present study was carried out in Maputo province, at the Eduardo Mondlane University-Faculty of Agronomy and Forestry Engineering and at the Umbelúzi Agricultural Station in the period from July 2005 to February 2006. In this study, we aimed to evaluate the resistance of varieties of sunflower (Helianthus annus L.) to rust caused by Puccinia helianthi Schw in the field and in a controlled environment. To achieve the established objectives, data from field surveys collected in pre-established trials from 2002 to 2004 were used, trials in a controlled environment. For the field trials, the statistical model DBCC "Design of Randomized Complete Blocks" was used, three replications and several varieties, used during the process of crop improvement. For the controlled environment tests, the same design and six varieties were used, namely the varieties MZT TardioX, MZT Precoce4X, MZT Precoce Seleccionado, MZT Tardio Seleccionado, Ala and Agrimo. In a controlled environment, the plants were inoculated with P. helianthi uredospores at a concentration of 106 uredospores/ml of water, eleven days after sowing, when the plants had a pair of true leaves. In this study, the parameters measured were disease incidence and severity. The results were submitted to analysis of variance in the SAS program (System Analisis Statistic) and the means of treatments were submitted to the Duncan test (P <0.05). Depending on the results obtained in the field, it was observed that all varieties had a high incidence, with the Agrimo variety (the most used variety) having an average of 79.8%. Despite this value being high, Duncan's test indicates that the Agrimo variety differs significantly from the other varieties, namely MZT Tardio Seleccionado, MZT TardioX, and MZT Precoce Seleccionado which had 100% incidence and in turn the varieties MZT Precoce 4X and Ward with 98.46% and 97.50% respectively. On the other hand, results in a controlled environment indicate that the varieties Precoce4X and Agrimo are the most susceptible to disease with more than 65.0% of leaf area attacked and the selected MZT Tardio is considered resistant to rust as it was the least infected with 50 ,0% of leaf area attacked.