ECOLOGY OF MICROBIAL SAPROPHYTES AND PATHOGENS IN TISSUE-CULTURE AND FIELD-GROWN PLANTS - REASONS FOR CONTAMINATION PROBLEMS IN-VITRO

This review compares published surveys of microbial populations in pla nt tissue and cell cultures with the microbial saprophytes and pathoge ns found on field grown plants and microbial populations in the labora tory environment. From this comparison and the measured reduction in c ontamination after improvements in working practices in the laboratory , conclusions can be drawn about the importance of the explant and the laboratory as sources of contamination. Mechanisms of pathogenicity i n vitro are described to explain why bacteria, fungi, and yeasts that are not pathogenic to plants in the field become pathogens in plant ti ssue cultures. Conversely, plant metabolism and its effect on the tiss ue culture environment are described to explain why prokaryotes, virus es, and viroids that cause disease in the field can stay latent in vit ro. Detection methods for latent contaminants in plane tissue cultures are summarized, and the strategies and methods for prevention or trea tment of contamination are discussed.