8 ref. Sum. (En)

Several noxious nematodes are associated with yams (Dioscorea spp.) in Jamaica but Pratylenchus coffeae is the only one found infesting yellow yams (D. cayenensis) tubers affected by a dry rot called burning. There was earlier and significantly more sprouting of lightly or heavily dry-rotted yellow yam heads (planting material) which were dipped for 40 min. in a 1.500 ppm Oxamyl solution or lightly dry-rotted undisinfested heads and plants arising from them developed more vigorously (as measured by vine height and leaf size) compared with heavily dry-rotted undisinfested heads. There was significantly less bearing plants in plots planted with the heavily dry-rotted undisinfested heads; greatest gross weights of tubers and of marketable yams were borne in plots planted with lihgtly or heavily dry-rotted disinfested heads and lightly dry-rotted undisinfested heads. Oxamyl or Ethoprop applied 11, 22 and 33 weeks after planting suppressed populations of P. coffeae in soil and roots at 39 weeks but did not influence quantitative production; tubers from Oxamyl-treated plots showed significantly less of the dry rot. The dry rot appears to damage or destroy stem and root primordia resulting in badly affected planting material not sprouting or plants not being vigoruous. Conditions favouring rapid development of the dry rot seem to prevail after heads area planted. Disinfestation supresses populations of the nematodes associated with the dry rot and development of the rot itself. Results suggest that only those yellow yam heads with the least evidence of the dry rot or disinfested heads should be planted. It is recommended that an agency be established to see to the disinfestation of yam planting material in the first instance and eventually be responsible for providing clean planting material