Evaluation of in vitro screening methods for assessing anthracnose disease reactions in tropical yams (Dioscorea spp.)
Keywords:Dioscorea, Yams, Anthracnose, In vitro screening
AbstractMethods for inoculation of yams with either spores, mycelia, or mycelial culture filtrates of the pathogen Colletotrichum gloeosporioides Penz. f. sp. dioscoreae were developed at the whole plant, microplant, and cell levels. Microplants showed a similar range of disease reactions to the pathogen to those produced by greenhouse-grown plants. Dioscorea alata cv. 'White Lisbon' showed a marked sensitivity towards the pathogen while D. esculenta was the most insensitive followed by D. composita, D. nummularia, and D. cayenensis/rotundata. Mesophyll protoplasts isolated from the same cultivars of the above species also responded differently to the filtrates of mycelial cultures grown in Czapek Dox liquid medium. The data obtained indicated that leaf tissues of the yams D. esculenta, D. nummularia, and D. composita appeared to withstand test inoculations of the pathogen whereas those of the D. alata cultivar hosts tested (with the exception of 'Kinnabayo') did not. The mechanisms accounting for these differences were not investigated during the current study but their possible relevance to identifying the basis of anthracnose resistance in Dioscorea yams is discussed.