Assessment of IBPGR morphological descriptors in determining pattern within crop germplasm collections

A series of experiments, using barley (Hordeum vulgare L. emend, Bowden) as an example, were designed to test whether or not the IBPGR taxonomic minimum descriptor lists ensure adequate diversity for subsequent research. This hypothesis was tested using additional taxonomic and physical measurements into the IBPGR minimum taxonomic data set, and a variety of protein polymorphs (SDS-PAGE and leaf esterases) as the impartial and independent descriptors. Pattern analysis was identified as the most appropriate method of describing germplasm diversity, and was applied to the various data sets to establish (i) the inherent diversity distribution in the DSIR world barley collection and (ii) the identification of descriptors most useful in discriminating between accessions. The IBPGR Barley Descriptor List has a set of morphological descriptors that are recommended as the minimum required for the description of barley germplasm. With the exception of spike density, the current study confirmed these descriptors are only moderately useful in discriminating between accessions. Seven additional easily scored morphological descriptors were identified as useful in discriminating between accessions and are recommended for inclusion in an updated version of the IBPGR Barley Descriptor List. These additional morphological descriptors are: growth habit, awn colour, glume colour, stem colour, seed weight, test weight, and purple auricle. Congruence between the various distribution patterns established the level of agreement between the IBPGR minimum descriptor data set and the additional physical and chemical description. Generally, there was a poor level of agreement between patterns of diversity detected by the IBPGR minimum descriptors and genetic markers of both additional morphological and biochemical origin. This lack of congruence clearly shows the IBPGR minimum descriptors are inadequate predictors of global pattern and therefore of a species total diversity.