Studies on the phyllosphere microflora of tapioca (Manihot utilissima Pohl)

Studies on the phyllosphere microflora of tapioca (Manihot utilissima Pohl.) revealed that incidence of bacteria, fungi, and actinomycetes is indipendent of the variety, but dependent on the age. The bacteria and fungi increased with increasing age of the leaf and were more on mature leaves, whereas no such difference was noticed in the occurrence of actinomycetes. The large majority of the isolates, that were Gram-negative bacteria, was also amino acid-requiring. The chromogenic types occurred in greater abundance. The phyllosphere mycoflora consisted mainly of species of Asperigullus, Penicillium, Mucor, Curvularia, Alternaria, Helminthosporium, Fusarium, Hormicium, and Pullularia, at first three being predominant. There was no correlation between HCN content of leaves and microorganisms in the phyllosphere, Regarding the interrelationship between different groups of microorganisms in the phyllosphere, a positive correlation between fungi and actinomycetes and bacteria and actinomycetes in two (M. 4 and H. 105/44) varieties and a negative correlation for fungi and actinomycetes in one (H. 12/49) were obtained. The effect of leaf exudate and leaf, root, and tuber extracts on the germination of the conidia of three saprobic fungi, viz., Curvalaria sp., Alternaria sp., and Helminthosporium sp. was tested. While the leaf exudate and tuber extracts slightly stimulated the germination of the conidia of the fungi, the leaf extract exerted a selective inhibitory effect on the germination of the conidia of Curvalaria sp., but not on the conidia of Helminthosporium sp. and Alternaria sp.