Effect of mycorrhizal inoculum and urea fertilizer on diseases development and yield of groundnut crops (Arachis hypogaea L.)

Diseases (rosette virus disease (RVD), Cercospora leaf spot (CLS) and poverty of soils in nutrients are the main causes of groundnut losses (> 60%). Among the methods applied in disease management, the biological method is identified as a priority in crop protection research programs. This study was carried out during the 2001 growing season in Yaounde, Cameroon. The aim was to characterize the development of RVD and CLS on A-26 groundnut variety and also to evaluate yield after mycorrhizal inoculation. A randomized block design with four replicates was used, with two applications of mycorrhizal inoculum. The inoculum contained spores of Glomus sp. and Gigaspora sp. in concentration of 2.10(3) spores. g(-1). A urea treatment and an absolute control were also used. The number of nodules per plant, the root colonization rate (RCR), disease severity and yield were assessed. Results show that RCR was very low in control and urea plots compared to mycorrhizal inoculated plots. Mycorrhizal applications reduced disease infection up to 38.8 and 54.4% respectively, for RVD and CLS. However, plants issued from urea treatment were more stressed and infected. A higher number of nodules (459.1) were recorded on roots of mycorrhizal inoculated plants compared to control and urea treatments which were 218.8 and 237.5 nodules per plant. Mycorrhization of groundnut plants led to a yield increased of up to 628% for dry pods of healthy plants compared to uninoculated plants in control samples. No yield was recorded on infected plants from control and urea treatments, whereas plants infected by RVD and inoculated with mycorrhiza yielded 177.2 Kg. ha(-1) of dry pods. The mains results of this study show that mycorrhizal symbiosis with groundnut roots increased the resistance of plants to RVD and CLS, and positively influenced the physiology of groundnut plants infected by RVD.