We got agro-morphological and genotypical data. We would like to define a core collection. I would like to know which means to use for the agro-morphological data and Why.
It may depend on the crop and marker used. However, irrespective of the two, the best way is to define the most important agro-morphological or economic traits. This is dependent on the intended goal of the core collection, i.e., for breeding, conservation, genetic diversity etc. I think it may be good to classify the collections using these economic traits followed by marker data. The two data set may provide clear pattern of associations of the collections to make selection or decision.
Kindly refine your question. It seems you are interested in how to highlight key characters. If you are, then analyse you collected data using PCA and depending on the character cluster, you can then highlight those characters as key agronomic characters for the crop plant of interest.