Influence of cover crops on the development of some soil-borne plant pathogens

Abstract: The suppressive effects of different cover crops on soil-borne plant pathogens and the diseases caused by these, were investigated in greenhouse trials. Four different cover crops and three soil borne pathogens were studied as model organisms. The cover crops were: oilseed radish (Raphanus sativus), mustard (Sinapsis alba), rye (Secale cereale) and Westerwold ryegrass (Lolium multiflorum). The pathogens were: Sclerotinia sclerotiorum, Fusarium culmorum and Rhizoctonia solani.The study was carried out in 84 boxes in the greenhouse, with 28 boxes per pathogen with four replicates. The cover crops were grown in pathogen inoculated soil for eight weeks, and then cut, chopped and incorporated into the soil. Potencial pathogen inhibition was analysed by recording apothecia on the soil surface for Sclerotinia and by using bio-tests in barley for Fusarium and potato for Rhizoctonia.Apothecia analyses showed a delay of ten or more days in S. sclerotiorum apothecia formation with ryegrass as the cover crop, whereas no effect was observed for the other three crops. This suggests that ryegrass can be a useful tool in the management of S. sclerotiorum. Sclerotinia infections are significant in oil-seed rape, which is particularly susceptible in the flowering stage but not later. If apothecia release can be delayed by one week or more, the susceptible stage of the plant may have passed and oil-seed rape infection can thus be avoided.None of the tested cover crops suppressed disease development of Fusarium and Rhizoctonia in the bio-tests.Overall, I conclude that ryegrass can be use against S. sclerotiorum to delay the apothecia formation. However, there was no evidence that any of the other tested cover crops species can be used to control soil-borne pathogens. More studies are required to explain the mechanisms delaying apothecia formation in that particular case and how they can be exploited for the purposes of crop protection.