Relationship study among soils physico-chemical properties and Monosporascus cannonballus ascospores densities for cucurbit fields in Tunisia

Monosporascus cannonballus is a prominent soil-borne pathogen in the principal Tunisian cucurbits growing areas. One experimental field, was chosen for this study at three growing seasons (A: 2009/10; B: 2010/11 and C: 2013/14), located in the High Institute of Agronomy Chott Meriem (Sousse, Tunisia). The aim of this investigation was to assess the relationship between physicochemical soils properties and spatial distribution of M. cannonballus ascospores densities. The results revealed that ascospores were recovered from all soil subplots at different depths. The highest ascospores density was recorded at 10–20 cm (2.24 ascospores/g soil). At the horizontal distribution, the first (A) and third (C) growing seasons have registered an ascospores level increase with values of 2.13 and 2.17, respectively. Only the first growing season had shown a uniform horizontal distribution. Obtained results revealed an augmentation of the ascospores number at the growing season C with a dissimilar distribution. In general, ascospores densities differed according to the experiments but values were clustered to 1.1–2 ascospores/g of soil which could be favorable for the disease. The physicochemical soils properties analysis at 10–20 cm depth, showed that the soils present a low level of organic carbon and matter, with a pH of 7.78. The soils were mainly sandy, with highly electrical conductivity (2.57 ds m−1), a C/N ratio of 8.11% and silt percent of 4.33%. The principle component analysis (PCA) for the fourteen quantitative traits indicated that the first two PCs explained 57.28%. Four factors exhibited a significant positive correlation with ascospore density; organic matter (r = 0.77), organic carbon (r = 0.74), the mass of nitrogen (r = 0.7) and electrical conductivity (r = 0.61). To control Monosporascus cannonballus in field within IPM strategies, soils physico-chemical properties should be taken in consideration.