Strategies for Developing Core Collections of Safflower (Carthamus tinctorius L.) Germplasm – Part I. Sampling from Diversity Groups of Quantitative Morphological Descriptors

Evaluation data collected from a germplasm collection of 3,250 safflower (Carthamus tinctorius L.) accessions was used to divide the whole collection into six major clusters based on multivariate cluster analysis. The clusters were further grouped into 30 diversity groups based on the geographical origin of the accessions and the plant types. Estimates of the phenotypic diversity of the core samples were obtained through simple random sampling and 5 stratified random sampling strategies. They were compared for varying sampling fractions ranging from 5% to 25% of the whole collection. In the core samples obtained through simple random sampling or stratified random sampling by frequency proportion method or diversity proportion method, the pooled diversity index based on 28 descriptors was close to the diversity of the whole collection. However, when the accessions from different diversity groups were allocated with equal frequency or in proportion to the logarithm of the number of accessions in each group or in proportion to the square root-proportion of the number of accessions in each group, the resultant core samples had higher levels of diversity than the whole collection. About 10–15% of the whole collection was found to be adequate as the core sample size.