Dear all!

Please note this announcement of the next meeting of the Highlands Local
RSS group, which will take place in Aberdeen next week.

As always everybody is welcome!

Claus (local group secretary)

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SPEAKER: Sue Welham (Rothamsted Research)

TITLE: Evaluation of models for late-stage variety evaluation trials

DATE: 20 March 2007
TIME: 4pm (tea/coffee available from 3:40pm).
VENUE: Strathcona Lecture Theatre, Rowett Research Institute, Greenburn
Road, AB21 9SB (See details at:
http://www.rowett.ac.uk/institute/location.html
The Strathcona lecture theatre can be found within Strathcona Hall. This
is the building to your right (opposite from the Reid
Library/Reception), when you come to Greenburn Road from the A96.)

ABSTRACT:
The primary aim of crop variety evaluation programs is to reliably
predict the future performance of potential new varieties relative to
existing commercial varieties. This is achieved through
multi-environment trials (METs), that is, series of field trials
conducted across a range of geographic trial locations and possibly over
several years. Varieties are tested for a range of agronomic traits with
the aim of recommending superior varieties for commercial release.
Usually, a program of METs is established to take varieties through from
the initial selection of potential breeding lines to eventual commercial
release and recommendation to farmers (late-stage variety evaluation
trials). In this talk we are concerned with METs in the latter stages of
this process.

Many models have been proposed for MET data, which can be broadly
classified as one-stage or two-stage analyses (Smith, Cullis & Thompson,
2005). In a one-stage analysis individual plot data from all trials is
combined in a single analysis. In a two-stage analysis variety means are
first obtained from the separate analysis of individual trials (stage
I), and are then combined in an overall mixed model analysis (stage II).
The stage II analysis may be unweighted or weighted to reflect the
relative precision of variety means from each trial. In each case, a
linear mixed model may be constructed to describe the structure of the
data, and this model is usually fitted using REML estimation. Within
this context, variety by environment effects are commonly modelled using
either simple variance components or a factor analytic model.
Within-trial variation may be modelled using either a spatial model or
blocking factors corresponding to the design.

This talk uses the characteristics of real MET data-sets from Australia
and the UK as a basis for a simulation study to evaluate these different
mixed modelling approaches. Results and their implications for the
analysis of late-stage variety testing programs are presented.

Smith, AB, Cullis, BR & Thompson R (2005) The analysis of crop cultivar
breeding and evaluation trials: an overview of current mixed model
approaches. J. Agric. Sci., 143, 1-14.

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  Dr Claus-D. Mayer                    | http://www.bioss.ac.uk
  Biomathematics & Statistics Scotland | email: [log in to unmask]
  Rowett Research Institute            | Telephone: +44 (0) 1224 716652
  Aberdeen AB21 9SB, Scotland, UK.     | Fax: +44 (0) 1224 715349
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