Core collection of sorghum: I. Stratification based on eco-geographical data

ICRISAT conserves a large (36 719 entries) collection of sorghum [Sorghum bicolor (L,) Moench] accessions in India, This collection comprises cultivated and wild sorghums acquired over the past 25 years from 90 countries. However, it is difficult to characterize and assess a large collection with limited time and resources. To facilitate maintenance, assessment, and utilization of the collection, we considered the establishment of a core collection using stratified sampling strategies. Results from a study of the morpho-agronomic diversity were used to describe the genetic structure of the collection. Morphological traits, including days to flowering and plant height, can be affected by daylength variation, These two characters were highly correlated with latitudinal and racial distributions of landraces. Thus, stratifying the entire collection for response to photoperiod, estimated by flowering date and plant height, was indicative of a major source of specific adaptation within the collection, This stratification resulted in tour clusters. which described the sensitivity of genotypes to photoperiod within the latitudinal range where selection was carried out by farmers, These four clusters may serve as the basis for a random stratified sampling to establish cores in this collection.