Effect of nitrogen regulation on the epidemic characteristics of intercropping faba bean rust disease primarily depends on the canopy microclimate and nitrogen nutrition

Abstract

Faba bean rust is a serious fungal disease of faba bean caused by Uromyces viciae-fabae (Pers.) J. Schröt in southwest China. The application of nitrogen fertilizer can possibly affect intercropped faba bean and wheat to control faba bean rust disease and increase the productivity of crops. To evaluate the effects of nitrogen levels and intercropping on the occurrence of faba bean rust disease and understand the mechanism involved, field trials in two planting seasons were conducted in 2016–2017 and 2017–2018. Four nitrogen levels ([N0] 0 kg ha −1 , [N1] 45 kg ha −1 , [N2] 90 kg ha −1 and [N3] 135 kg ha −1 ) and two planting patterns (faba bean monocropping and faba bean and wheat intercropping) were used. The epidemic characteristics of faba bean rust were simulated, and the canopy microclimate and nitrogen content in the plant tissues were measured. The results showed that the application of nitrogen significantly increased the maximum disease index ( A ) and the maximum instantaneous epidemic rate ( R max ). The area under the disease progression curve (AUDPC) of monocropped and intercropped faba bean rust was the most deleterious at the N3 level. The application of nitrogen increased the nitrogen content of leaves and the relative humidity of the canopies of monocropped and intercropped faba bean during both planting seasons, while decreasing the temperature and transmittance of light. Compared with monocropping, intercropping significantly increased the yield of faba bean and reduced the AUDPC for faba bean rust disease, and the AUDPC decreased by 22.3–54.7% at the N0-N3 levels with the level of N2 serving as the most effective at reducing disease. Intercropping creates a micro-ecological environment that is not favorable for the occurrence of rust disease by significantly decreasing the relative humidity of the faba bean canopy and increasing the canopy temperature and transmittance of light. Moreover, the N content in the faba bean leaves was reduced and transferred to the pods, thus, enhancing the disease resistance of faba bean. In this study, consideration of the effects on controlling disease and the advantages of increasing yield led us to recommend the application of nitrogen at 45–90 kg ha −1 as the most effective measure to control the occurrence of faba bean rust disease when faba bean and wheat were intercropped. This study provides a basis for the rational application of N fertilizer in faba bean and wheat intercropping systems, which simultaneously control crop disease and enhance crop yield. • N application increased the rust disease severity, and the high N level was the most serious. • Intercropping reduced the rust occurrence, the control effect increased at first and then decreased with N application. • The epidemic of faba bean rust is affected by both canopy microclimate and N nutrition. • Intercropping and applying 45–90 kg N ha −1 fertilizer is the best measure to control the occurrence of rust and increase yield.