Development of sclerotinia in narrowleaf (Lupinus angustifolius L.) and white (Lupinus albus L.) lupin single and mixed crops under different weather conditions in Bryansk region

White rot caused by ascomycetous fungus Sclerotinia sclerotiorum (Lib.) de Bary. is a widely spread disease of many cultivated and wild plants. In the Non Chernozem zone of Russia the epiphytotic development of white rot in white and narrowleaf lupin crops began in 2008 and is related to climate change towards warming. The article presents the first report on dependence between weather conditions in the Non Chernozem zone and white rot infection of white and narrowleaf lupines in single and mixed crops. High significant correlation coefficients have been obtained between air moisture and pods' white rot infection of the narrowleaf lupin in June ( r = 0.95, р = 0.001), and of the white lupin in June and July ( r = 0.90, р = 0.006; r = 0.81, р = 0.026, respectively). High significant negative correlation coefficients between narrowleaf and white lupin yields in single and mixed crops and Sclerotinia infection of pods have been revealed ( r = -0.92, р = 0.003 and r = -1.00, р = 0.002, respectively; r = -0.97, р = 0.000 and r = -0.88, р = 0.122, respectively). The lupin species differed in susceptibility to the pathogen. This work aimed to evaluate the white rot development and harmfulness in white and narrowleaf lupin crops depending on weather of the vegetation season and crop type under the conditions of Bryansk region. The narrowleaf lupin var. Belozernyi 110 and the white lupin var. Dega were cultivated in single crops and in mixed crops with spring wheat var. Iren in 2008-2012, 2014, and 2016 in the North-East of Bryansk region (an experimental field of All-Russian Lupin Scientific Research Institute). Climatic data were received from the meteorological station on the territory of the institute. Lupin plants were infected with white rot mycelium by the wet chamber method. Plants infection was evaluated during the vegetation period (stem and bud formation, flowering and pods' formation stages). The yield of each plot was weighted after the total threshing (a combine-harvester Sampo-500, Sampo Rosenlew, Finland). Intensive pathogen development on the tested lupin species in single and mixed crops was in rainy and warm June-August, at 66.2-80.3 % air moisture. Under rainy, warm and windy conditions white rot spread among plants in lupin crops both by ascospores and by mycelium particles. The first lesion focuses appeared on stems in low field sites and in dense crops. Depressive disease development occurred at air moisture from 54.1 to 60.3 %. White lupin plants were more susceptible to the disease, probably due to the morphological peculiarities of this species. Under favorable conditions for the disease, the incidence of pod infection averaged 15.3-34.8 % in white lupin single crops and 8.4-34.7 % in narrowleaf lupin single crops. Herewith seed yield losses made 14.3-39.2 % and 3.0-34.7 %, respectively. Under dry conditions of 2010, the white lupin infection incidence was 0.3 % in mixed crops with no infection of the narrowleaf lupin observed. The infection of the narrowleaf and white lupins in their single crops made 0.1 and 1.3 %, respectively. The white rot was more harmful for lupin crops upon a combination of sufficient or excessive moisture and optimal temperature in the second part of vegetation. During this period, the pods were formed on the main and lateral stems, and the plant foliation was maximum too. The latter creates favorable conditions for the pathogen inside the crops. Pod infection in lupines decreased significantly in mixed lupin-and-cereal crops, 1.4-1.6-fold for the white lupin, and 1.3-2.3-fold for the narrowleaf lupin. Obviously, the lupin-and-cereal mixed crops create the conditions which are less favorable for the pathogen development and spread, therefore decrease infection of lupin plants and pods.