Pathogenicity of Scutellonema bradys populations from different geographical areas in Benin on yam ( Dioscorea spp.)

Abstract

Scutellonema bradys is the most important nematode species affecting yam production in Benin. Two experiments were conducted to assess the variation in pathogenicity of three separate populations of S. bradys (IsoSave, IsoToui and IsoGlaz) on seven yam cultivars of three species: Kpouna, Tabane, TDr131, Moroko ( Dioscorea rotundata), Banioure, Kokoro ( D. cayenensis) and Aloungan ( D. alata). This was done over two consecutive yam growing seasons; 2002–2003 at the International Institute of Tropical Agriculture (IITA) Cotonou Station, Benin experimental farm and 2003–2004 in a farmer's field at Save in central Benin. S. bradys populations were obtained from yam originating from different geographical areas of Save and Toui in the northern Guinea savannah and Glazoue in the southern Guinea savannah, respectively. Four-week-old plants were each inoculated with ca. 1000 S. bradys juveniles and adults in chopped, infected pieces of yam peel. The experiments were harvested at 9 and 10 months after planting, respectively, at IITA and Save. Some differences were observed in the pathogenicity of the different nematode populations, although differences were not consistent between experiments and between yam cultivars. At harvest, in 2002–2003, the various S. bradys populations did not affect tuber weight, number of tubers produced or dry rot severity on the tubers. Highest nematode population density was observed with IsoGlaz, and Banioure was the yam cultivar most susceptible to nematode infestation. In 2003–2004, nematode inoculation reduced ( P ≤ 0.05) tuber weight for yam cv's Aloungan, Moroko and TDr131. Weights of tubers from IsoToui- and IsoSave-inoculated plants were lower than those from control plants. Dry rot severity was more pronounced on cv's Moroko and TDr131 tubers than on cv's Aloungan and Banioure, while no dry rot symptoms were observed on cv Tabane tubers. IsoToui and IsoGlaz caused higher ( P ≤ 0.05) tuber dry rot severity than IsoSave. Differences in nematode population densities occurred across S. bradys populations for cv's Tabane, TDr131 and Aloungan with IsoSave resulting in the highest nematode population densities on cv's Aloungan and TDr131. IsoToui caused the highest percentage weight loss. During 5 months storage, infected tubers lost more ( P ≤ 0.05) weight than uninfected control tubers. The differences in weight loss of infected tubers differed on tubers infected by the various nematode populations. Nematode multiplication during the storage period also differed among populations.