Molecular and morphological characterisation of Scutellonema bradys from yam in Costa Rica and development of specific primers for its detection

The yam nematode, Scutellonema bradys, which can cause dry rot disease of yam (Dioscorea spp.), was recorded for the first time from Costa Rica in four species of yam occurring in the Atlantic and north regions. Morphometric measurements from two populations from each region using ten female and 11 male characters corresponded with previous descriptions of this species. Canonical discriminant analysis of the female morphometric data separated the populations by region, whereas no separation by region was evident using the male data. Analysis of DNA sequences from the ITS region indicated that populations from Costa Rica were monophyletic with S. bradys from West Africa and clearly distinct from other Scutellonema species. No genetic separation by geographic region or Dioscorea species host was observed between Costa Rica populations. Species-specific primers were developed from the ITS region and supported the identity of 17 populations from 15 locations in Costa Rica as S. bradys: 14 populations from D. alata (greater or water yam) and one each from D. trifida (white yampee), D. cayenensis (yellow yam) and D. rotundata (white yam). Yam production in Costa Rica began in the Atlantic region, where the yam nematode was likely introduced from the Caribbean, progressively spreading to other locations through the use of infected vegetative planting material.