Abstract
The objective of this study was to evaluate the effect of leaf wetness on the severity of septoria leaf spot in sunflower. The experiments were performed in two sowing dates in November and January in Santa Maria, RS. Sunflower inoculation was carried out with the Septoria helianthi isolate, with subsequent assessment of disease severity, progress and cypsela yield. The treatments were composed of different periods of 0, 8, 12, 16, 20, 24, 28 and 32 hours of artificially applied leaf wetness. Variables influencing the disease were observed during the cycle, such as mean air temperature, mean relative air humidity and daily-accumulated rainfall. The greater the leaf wetness the greater the severity and the area under the disease progress curve. Meantime, the healthy leaf area duration has an inverse relation with leaf wetness duration. The yield also decreases with greater leaf wetness duration and the yield reduction reaches 100% in the plants exposed to the longer leaf wetness periods.
Highlights
The sunflower is a crop expanding in the national and world agricultural scenario mainly due to the increasing demand of oil (Backes et al, 2008)
The meteorological variables, daily mean air temperature, daily mean relative air humidity and daily-accumulated rainfall are the main factors that influence the development of septoria leaf spot (Agrios, 2004)
The increase of leaf wetness causes an increase in septoria leaf spot severity, with greatest severity in the experiment sown in January
Summary
The sunflower is a crop expanding in the national and world agricultural scenario mainly due to the increasing demand of oil (Backes et al, 2008). Improving the current low yield levels is important to consolidate the sunflower competitiveness in agribusiness. Low yield is frequently observed due to different adverse factors, which prevent the yield potential expression of the available genotypes. In Brazil, septoria leaf spot on sunflower has not been considered with the proper attention, as there is no availability of tolerant genotypes or recommendation of fungicides along with MAPA (Ministry of Agriculture, Livestock and Supply). In rainy years with El Niño warm phase (Izumi et al, 2014), septoria leaf spot can cause considerable plant damage because of the increase in inoculum dispersion and leaf wetness, leading to significant yield and profit reduction
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