Abstract
The Sclerotinia sclerotiorum (Lib.) de Bary fungus is a necrotrophic and polyphagous pathogen with soybean crop as one of its most important hosts. However in order to occur epidemics caused by such a pathogen it is necessary that the climatic conditions, mainly air temperature and relative humidity be favorable to the occurrence and development of the disease. The current research aimed to assess the incidence and severity of S. sclerotiorum in soybean plants grown in Arapoti, PR, Brazil, as a function of different plant populations, row spacing, and microclimate. The experiment was conducted in a naturally infested area. The experimental design adopted was a randomized block in a factorial combination with 4 row spacing (0.35, 0.45, 0.60, 0.75 m) and 4 plant populations (150, 200, 250; 300 thousand plants per hectare), totaling 16 treatments and 4 replications. Throughout the current study we performed 4 assessments of incidence and severity. Local climatic conditions were favorable for the incidence and severity of the pathogen. Mean air temperature, rainfall, relative humidity and leaf wetness duration, monitored during all experimental period, favored the development of the pathogen in the experimental field. Yield and 100 seed weight did not show fluctuations as a function of variations on the incidence and severity of white mold in soybean crop fields. Nevertheless, crop yield was higher under a reduced spacing, whereas the 100 seed weight showed the highest values under the lowest plant population treatment.
Highlights
Soybean is grown in Brazil on a large scale
Faced with the aforementioned outcomes and observations reported in the literature, the aim of the current research was to evaluate the incidence and severity of white mold for soybean crop grown in the Paraná State, southern Brazil, in relation to plant populations, row spacing, and local meteorological variables in order to arrive at a reduction in the production costs for growers and to guarantee the sustainability of agriculture at the studied site
In order for the infection to be successful, ascospores released by sclerotium of S. sclerotiorum need an exogenous source of energy coming from the senescent flowers and other senescent organs of the plant (ABAWI; GROGAN, 1979; BOLAND; HALL, 1988)
Summary
Soybean is grown in Brazil on a large scale. The development of diseases is one of the greatest problems faced by growers because this can trigger significant losses in relation to yields and increased production costs of the grain and seeds, mainly due to the utilization of agrichemicals in crop fields. Among the pathogens that possess the capacity to cause diseases in soybean plants, the Sclerotinia sclerotiorum (Lib.) de Bary fungus is one of the most significant. S. sclerotiorum is a necrotrophic and polyphagous pathogen possessing a vast spectrum of hosts, roughly 408 agricultural crops, of which the most important in terms of economic are soybean, common beans and cotton (BOLAND; HALL, 1994; BOLTON et al, 2006). This pathogen has been disseminated all over Brazil, with a large spread in the south, center-west and southeast states, and some areas of the northeast of the country (JULLIATTI et al, 2013). The fungus in question has a natural ability to form resistance structures, named sclerotium, which can survive in the soil for a period of time, varying from 3 to 8 years, even under adverse environmental conditions (STEADMAN, 1983; BOLTON et al, 2006)
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