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<span style="font-size: 12.0pt; font-family: ";Arial";,";sans-serif";; mso-fareast-font-family: Calibri; mso-fareast-theme-font: minor-latin; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">The yam mosaic virus (YMV) and the yam mild mosaic virus (YMMV) are pathogens affecting the yam (<em>Dioscorea </em>sp.). This work presents the results of a serological and molecular study for the diagnosis of potyvirus in field samples and micro cultures, within the framework of a phytosanitary programme. Potyvirus was detected in 70% (175/250) of leaf, tuber, or micro culture samples using the ELISA DAS indirect technique. Twenty weeds associated with yam growing were serologically positive. In the field, plants expressed mottling symptoms with different degrees of chlorosis and some cases of wrinkling at the edges of the leaf. A flexuous virus, having a size estimated as being 740nm x 12 nm, was identified in an extract which was within the limits for potyvirus using the immunosorbent electron microscopy (ISEM) technique. The coat protein (CP) was determined as having 26Kd, 28Kd and 31Kd weight in different isolates by Western Blott. YMMV was amplified by RT-PCR and IC-RT-PCR using specific primers. A 250pb fragment was obtained from leaves as well as tubers and also from tubers from two generations obtained from the Ñ22 (P, F1, F2) plant. YMV was detected in one sample. Results show the presence of YMMV, YMV and a mixture of potyvirus in those isolates analysed. This is the first report concerning the presence ofYMMVin Colombia and its identification by the IC-RT-PCR technique. This is the first report concerning potyvirus in weeds associated with yam, identifying such plants as being viral reservoirs and thus increasing the risk of infecting neighbouring susceptible crops. The results strengthen yam crop phytosanitary programmes.</span>