Critical Levels of Dry Rotting of Yellow Yam (Dioscorea cayenensis) Planting Material and Control of Pratylenchus coffeae

Abstract

Of the noxious nematodes associated with yams (Dioscorea spp.) in Jamaica, Pratylenchus coffeae is the only one found infesting yellow yam (D. cayenensis) edible roots affected by a dry rot called "burning." There was earlier and significantly more sprouting of lightly or heavily dry-rotted yellow yam "heads" which were dipped for 40 min in a 1500 p/m oxamyl solution or lightly dry-rotted undisinfested heads and plants arising from them developed more vigorously than heavily dry-rotted undisinfested heads. There was significantly less bearing plants in plots planted with heavily dry-rotted undisinfested heads; greatest gross weights of marketable yams were borne in plots planted with lightly or heavily dry-rotted disinfested heads and lightly dryrotted 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 yields; yams from oxamyl-treated plots showed significantly fewer symptoms of 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 vigorous. Conditions favoring rapid development of the dry rot seem to prevail after heads are planted. Disinfection suppresses populations of nematodes associated with dry rot and development of the rot itself.