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- Title
Quantitative studies on downy mildew ( Peronospora destructor Berk. Casp.) affecting onion seed production in southern Uruguay.
- Authors
González, Pablo; Colnago, Paula; Peluffo, Sebastián; González Idiarte, Héctor; Zipitría, Javier; Galván, Guillermo
- Abstract
Onion downy mildew (Dm) symptoms and damage on seed production fields in southern Uruguay were quantified during two seasons as the progress of incidence, severity, and as the effect of the level of seed-stalks infections on seed yield and quality. In addition, the effects of two plantation dates and two plant densities on Dm were studied in a factorial experiment. Maximum incidence along the season ranged from 15 to 65% in four commercial fields in 2005 and two fields in 2006. Maximum severity ranged from 4.5 to 9.3% of leaf area affected in 2005, and 0.35 to 1.17% in 2006. Whereas Dm incidence varied among studied fields, disease progress as Dm severity varied mainly between studied years. Crop rotation, crop vigour and plant density were identified as major factors affecting Dm variation in the field. Intensive fungicide schedules did not control Dm when other conditions favoured the disease. A high level of Dm severity defined as large necklace spots on seed-stalks significantly reduced seed yield in comparison with healthy seed-stalks in 2005, as well as seed yield and germination in 2006. Weight of 1,000 seeds was not significantly reduced by Dm infections on seed-stalks. Six genera of fungi were recovered from seeds harvested on highly infected seed-stalks ( Stemphylium, Fusarium, Alternaria, Penicillium, Aspergillus and Botrytis), but not Peronospora. Late planting date and low plant density had significantly lower Dm incidence and severity. This finding questioned the early planting dates and high densities previously recommended in order to achieve high yielding crops. The combination of several practices to reduce initial inoculum, susceptibility status of the host, and environmental conditions promoting the disease is discussed as forming a basis for effective disease control.
- Subjects
URUGUAY; ONION diseases &; pests; SEED industry; PLANT stems; PLANT spacing; CROP rotation; FUNGICIDES; STEMPHYLIUM; FUSARIUM
- Publication
European Journal of Plant Pathology, 2011, Vol 129, Issue 2, p303
- ISSN
0929-1873
- Publication type
Article
- DOI
10.1007/s10658-010-9697-7