A preliminary evaluation of cell and tissue culture methods suitable for screening anthracnose disease reactions in tropical yams

Abstract

Effect of different temperatures (15, 19, 25 and 29 °C), media type (PDA and Czapek Dox agar) and light on sporulation of a Caribbean pathovar of Colletotrichum gloeosporioides f.sp. dioscoreae were studied. Czapek Dox agar and temperature of 25 °C were found to be best conditions for supporting growth and sporulation of this organism. Longterm fungal cultures (2 years axenic culture) did not sporulate effectively under the above conditions unless they were first brought into contact with living tissues of Dioscorea. Methods for inoculation of yams with conidiospores of C. gloeosporioides were developed at the plant, mi-croplant and cell levels. In vitro shoot culture clones showed a similar range of disease reactions to the pathovar as field-grown plants. D. alata showed marked sensitivity to the disease while D. esculenta was the most tolerant species followed by D. composita and D. cayenensis. Dioscorea protoplasts responded differently when cultured in the presence of mycelial culture filtrates and Czapek Dox liquid medium. Glasshouse-raised plants developed anthracnose symptoms only after wounding.