AN EVALUATION OF STREPTOMYCES PATHOGENICITY IN TURNIPPlant pathogenic Streptomyces spp. grow both inter- and intracellularly in host tissue and are good saprophytes. Thus, it is likely that these pathogens produce cell wall degrading enzymes in the process of infection and in saprotrophic growth. Streptomyces spp. isolated from scabby turnips were tested for the ability to grow and produce enzymes on media containing pectin, polygalacturonic acid, or cellulose as a sole carbon source. The production of cell wall degrading enzymes in vitro was tested. Disintegration of inoculated turnip root slices was used as an indicator of enzyme production. Most of the isolates with the highest tissue-degrading tendencies were among the highest enzyme producers; however, many isolates that did not elicit symptoms produced high levels of enzymes, so cell wall degrading enzyme production is not a characteristic unique to pathogenic species. Several Streptomyces isolates that elicited symptoms in turnip either lacked the ability, or caused significantly fewer, symptoms on potato. Seedling inoculations with most Streptomyces isolates resulted in hypocotyl stunting in most varieties. Reduced hypocotyl lengths were also correlated with symptoms on root structures. Inoculated roots were stunted, lacked lateral roots, and exhibited necrosis as compared to controls. Purple Prince turnip showed the most resistance to inoculation with isolates compared to other turnip varieties. Application of the phytotoxins thaxtomin and coronatine also caused stunted hypocotyls and symptoms on roots.
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