Association of Erwinia Spp. with the Rhizosphere of Crops and Weeds in the Peruvian Jungle

Abstract

In the Chanchamayo Valley, Peru (800–1200 m) where jungle has been cleared over several decades to establish tropical plantations and pasture, visibly healthy crops and weeds were sampled and processed to detect the presence of Erwinia spp. in the rhizosphere, on the rhizoplane, and within roots and stems. Rhizosphere and rhizoplane subsamples were incubated in a pectate-enriched medium at 26C for 84 h, diluted, and plated on crystal violet pectate (CVP) medium. Root and stem sections were surface disinfested, macerated and plated on CVP. Sample fields were at the International Potato Center San Ramon Station where potatoes have been grown in rotation with cover crops and in fields of four farms where potatoes had never been grown. Erwinia spp. were identified by standard biochemical tests and pathogenicity on tuber slices. At the San Ramon Station, 28% of 200 samples yielded Erwinia spp., whereas isolations were successful from 22% of 282 specimens from fields where potatoes had never been grown before. Most isolates (95%) were E. carotovora pv. carotovora (Ecc), which was isolated from 57% of rhizosphere samples and 42% rhizoplane samples.