MOLECULAR AND MORPHOLOGICAL CHARACTERIZATION OF Colletotrichum gloeosporioides CAUSING ANTHRACNOSE DISEASE OF WHITE YAM (Dioscorea rotundata Poir) IN THE TOLON DISTRICT OF NORTHERN GHANA AND ITS MANAGEMENT WITH PLANT EXTRACTS

Abstract

The anthracnose disease caused by Colletotrichum gloeosporioides is a major constraint to yam production worldwide. The harmful effects of synthetic fungicides on the environment have necessitated the use of eco-friendly alternatives. This study investigated the incidence and severity of anthracnose disease of laribako and pona yam varieties in the Tolon District of Ghana, and also characterised C. gloeosporioides isolates associated with infected laribako and pona crops. Phytochemical analysis was conducted on Azadiratcha indica, Balanites aegyptiaca, Jatropha curcas and Khaya senegalensis seeds, Icacina oliviformis leaves and Capsicum spp. (Legon 18 variety) fruit extracts which were tested in vitro and in vivo for their potency in managing yam anthracnose disease. The C. gloeosporioides isolates were characterised using PCR techniques with the primer pairs ITS1/ITS4, NS1/NS2, CgInt/ITS4, CgLac-f/CgLac-r, CaGlu-f2/CaGlu-r2 and Ca-f1/ Ca-r2. The antifungal activities of 10, 25, 50, 75 and 100% concentrations of each of the plant extracts against C. gloeosporioides were assessed in vitro using the food poison technique. The fungitoxicity of the plant extracts against yam anthracnose disease was assessed under field conditions through foliar application of 75 and 100% concentrations of each plant extract. The anthracnose disease incidence and severity of D. rotundata crops recorded for the 2016 and 2017 cropping seasons in the Tolon District increased significantly (P ≤ 0.05) from July to September. Generally, the 2016 cropping season recorded higher disease incidence and severity than 2017. The C. gloeosporioides isolates produced characteristic band sizes on ITS1/ITS4, NS1/NS2, CgInt/ITS4 and CgLac-f/CgLac-r. None of the isolates produced a band on CaGlu-f2/CaGlu-r2 and Ca-f1/ Ca-r2. The phytochemical analysis revealed alkaloids, anthraquinones, cardiac glycosides, flavonoids, phlobatinnins, saponins, steroids, tannins and terpenoids. Contents of total phenols, flavonoids, tannins and alkaloids varied among the plant extracts. Each of the plant extracts significantly (P ≤ 0.05) inhibited the mycelia growth and spore germination of C. gloeosporioides. The plant extracts also reduced the incidence and severity of anthracnose disease and enhanced vine length, shoot and root dry weights, and tuber yield. This showed that potentially these extracts can be used to produce formulations for the management of anthracnose disease of yam.