Pathogenic Susceptibility of Cashew (Anacardium occidentale L.) to Twelve Isolates of Colletotrichum sp Present on Six Weeds in Cashew Orchards in Côte d'Ivoire

Abstract

Cashew nuts are one of the agricultural products that contribute significantly to Côte d'Ivoire's economic development. However, cashew nut production in Côte d'Ivoire is threatened by anthracnose. Reducing anthracnose proliferation factors could reduce its impact on cashew trees. The aim of the study was to assess the virulence of Colletotrichum sp. isolated from weeds in cashew trees. It assessed the pathogenicity of 12 isolates of Colletotrichum sp.  extracted from six weeds on cashew plants. The inocula were prepared by scraping the mycelium of each fungus in 10 ml of sterile distilled water. The spore suspension was collected and calibrated at 4.6.106 conidia/ml using a Malassez cell. This suspension was applied by spraying to the leaves of 30-day-old cashew plants. The parameters assessed were symptom incidence and severity index. All isolates tested induced symptoms characteristic of anthracnose on cashew plants. There was a significant difference between isolates in terms of their virulence. The highest incidence of 90% was obtained on plants inoculated with the ColE2 isolate and the lowest incidence of 30% was obtained on plants inoculated with the ColN3 isolate. The highest severity index of 7.66 was obtained on plants inoculated with the ColE3 isolate and the lowest severity index of 2.00 was obtained on plants inoculated with the ColN3 isolate. These results show that Daniellia oliveri (Rolfe), Vitellaria paradoxa (G), Micuna pruriens (L.), Blighia sapida (K. Koenig), Albizia zygia (DC) and Pterocarpus erinaceus (Poir) are hosts of anthracnose in cashew orchards in Côte d'Ivoire. Their integration into cashew pathogen control strategies is necessary.