Abstract
The aim of this study was to evaluate the diversity of yam genotypes concerning their agro-morphological traits based on the Ward-modified location model (Ward-MLM) procedure. 209 genotypes from the commercial production area of the Recôncavo region in the state of Bahia, Brazil were used. Three agronomic traits (length, width and weight of the rhizophore) and two morphological traits (rhizophore shape and skin color) were evaluated. A considerable agro-morphological diversity was detected in the data for the 209 yam genotypes. The Ward-MLM procedure showed that the optimal number of groups according to the criteria of pseudo F and pseudo t2 is four. The separation by genotype groups was associated with their origin from two regions with different soil and climatic conditions. The Ward-MLM procedure has shown its usefulness to detect diversity and cluster genotypes by simultaneous use of morphological and agronomic traits. Key words: Cluster analysis, discriminant analysis, Dioscorea species, Ward-modified location model (MLM).  
Highlights
Yam belongs to the Dioscoreaceae family and to the genus Dioscorea with more than 600 species, ten of which have rhizophores that are used as food (Lebot, 2009; Nascimento et al, 2015)
The aim of this study was to evaluate the diversity of yam genotypes concerning their agromorphological traits based on the Ward-modified location model (Ward-MLM) procedure. 209 genotypes from the commercial production area of the Recôncavo region in the state of Bahia, Brazil were used
The wide range and average in these descriptors between evaluated yam genotypes may suggest the existence of a broad genetic variability that can be used in breeding programs of the species
Summary
Yam belongs to the Dioscoreaceae family and to the genus Dioscorea with more than 600 species, ten of which have rhizophores that are used as food (Lebot, 2009; Nascimento et al, 2015). The species Dioscorea rotundata and Dioscorea cayennensis ( known as Dioscorea cayennensis-rotundata complex) are the most cultivated in the world and account for 95% of yam world production (Obidiegwu et al, 2009; Silva et al, 2014). 90% of domestic production of Dioscorea species stems from the Northeast region, especially the states of Bahia, Paraíba, Pernambuco, Alagoas and Maranhão, where the yam crop represents an important agribusiness (Santos et al, 1998; Santos and Macedo, 2002; Santos et al, 2007a; Silva et al, 2014)
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