During the winter season, Sclerotinia sclerotiorum infects the stem bases of greenhouse‐grown sweet basil plants and, in severe epidemics, it may also infect the shoots. Sclerotia of S. sclerotiorum, and the ascospores that are released from the apothecia that form on them, serve as the inoculum for white mould epidemics. This research aimed to identify cropping parameters associated with lower incidence of white mould in a survey of the main basil‐growing region in Israel, and study cultural methods that might suppress the disease. The survey revealed that this mould, in the main growing area in Israel, has one cycle of infection. Factors associated with increased moisture in the greenhouse were found to be associated with increased levels of the disease. The use of a lower planting density reduced the incidence of white mould in semi‐commercial experimental plots, as well as the severity of the disease on shoots infected by S. sclerotiorum after harvest, in comparison to the commonly used higher planting density, with no negative effect on yield. Mulching the beds with polyethylene effectively reduced disease, and a combination of polyethylene mulch and increased plant spacing reduced disease severity on cut shoots in a synergistic manner. In conclusion, cultural control methods reduced disease incidence under field conditions and severity of the disease on cut shoots.
Sweet basil white mould (BWM, Sclerotinia sclerotiorum) and grey mould (BGM, Botrytis cinerea) are important diseases in Israel and other basil-growing regions. The impact of microclimate on BWM and BGM and on plant sensitivity to these diseases was studied. Disease incidence was evaluated in three field experiments, each consisting of 10-12 polyethylene-covered tunnels. BWM and BGM incidences were correlated with air temperature, relative humidity (RH) and soil temperature data. The incidence of BWM was negatively correlated with high (above >25 or >30°C) air temperatures, RH > 50% and RH > 75% and high (>21 or >24°C) soil temperatures. BGM incidence was negatively correlated with high (>25°C) air temperatures and high (>21 or >24°C) soil temperatures, and positively correlated with RH >65% or >75%. Shoots harvested from plants grown in the walk-in tunnels were inoculated with S. sclerotiorum or B. cinerea under controlled conditions. Severity of BWM and BGM on those shoots was negatively correlated with tunnel air temperatures of >25 and >30°C and soil temperatures >18°C. Thus, high temperatures were related to reduced disease incidence and to reduced sensitivity to the pathogens. Experiments involving potted plants revealed that heating only the root zone suppresses canopy susceptibility to BWM and BGM. These findings indicate that the effect of high greenhouse temperatures involves an indirect systemic effect that renders the host less susceptible to disease. This effect was also observed in harvested shoots that were no longer at the high temperatures, and the effect was systemic.
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