Developing crop descriptor lists - Bioversity International

36 BIOVERSITY INTERNATIONAL TECHNICAL BULLETIN SERIES NO. 13
design – when assessing the descriptors and their diversity, and will
vary according to characterization or evaluation trials.
A useful guide for genebank managers who undertake evaluation
trials on their genetic resources collections is found in Technical
Bulletin No. 4 (IPGRI, 2001). The manual covers the stages involved
in an experimental programme, from the determination of objectives
for each trial, to the methods used for analysis, and provides general
guidelines for managers to adapt to specific crops. It specifically
focuses on evaluation of large collections.
The main issues to consider in the design of an experiment
are:
• Set precise objectives (including background and justification
for the proposed research).
• Experimental design.
• Decide on analysis strategy.
• Select treatments (number of accessions per trial, control
treatments).
• Specify sites (plots and layout).
• Indicate levels of measurement (individual plant, plot or trial
level).
• Collect data and analyse.
10. Scoring, coding and recording of descriptors
In defining individual descriptors, many aspects need to be
considered. The following internationally accepted norms for the
scoring, coding and recording of descriptor states are promoted
worldwide by Bioversity International.
• The Système International d’Unités (SI) units should be used;
the units to be applied for each descriptor are given in square
brackets following the descriptor name.
• The Royal Horticultural Society (RHS) Colour Charts for
colour descriptors is strongly recommended for all ungraded
colour characters (the precise chart should be specified in the
section where it is used). The observation of colour by eye may
compromise accuracy in determining exact colours, depending
on each individual user; a colour chart is a useful tool for
assigning relevant colour codes to different colour states.
• For all quantitative descriptors, it is recommended to use actual
measurements. Where resources are insufficient to take actual
measurements, quantitative characters that are continuously
variable can be recorded on a 1–9 scale, as follows: