Multi-environment phenotyping of linseed (Linum usitatissimum L.) germplasm for morphological and seed quality traits to assemble a core collection

Linseed or flax (Linum usitatissimum L.) is one of the most ancient industrial crops domesticated for oilseed and natural fiber. India is one of the two proposed centers of origin of linseed and harbours high genetic diversity. The Indian Council of Agricultural Research-National Bureau of Plant Genetic Resources (ICAR-NBPGR) con -serves one of the largest base collections of Linum with around 2800 germplasm accessions at National Genebank, of which 2576 are the unique accessions of cultivated linseed and were characterized for 10 qualitative and 26 quantitative traits and the resultant multi-environment data along with passport information was used to develop a multipurpose core collection. Initially, five different core sets were derived using the core collection assembler tool 'Core Hunter 3' by optimization of average genetic distances between each accession and nearest entry in the core (A-NE) and the average distance between each entry and nearest neighbouring entry (E-NE). These five core sets were subjected to different quality evaluation indices to select one set that best represents the maximum genetic diversity and representativeness present in the entire tested collection. The Core collection-4, developed with weightage of E-NE and A-NE in the ratio of 0.7-0.3 was chosen as the best core collection as it exhibited desirable genetic distance, variance difference percentage (VD; 85%), coincidence rate of range (CR; 91.66%) and variable rate of coefficient of variance (VR; 117.76%), which were more than threshold value of VD (80%), CR (80%), and VR (100%) required for an optimally good core collection. Several summary statistics, Kullback-Leibler distance and Shannon Weaver diversity index indicated similar trait distribution patterns among the chosen core set and the entire collection. Correlogram and principal component analysis revealed that trait associations and their magnitude were conserved for most of the traits in the chosen best core collection. The development of this multipurpose core collection is expected to cater to the needs of linseed breeders and germplasm curators to pave the way for expedited access to genetically diverse and agronomically important material for trait introgression.