Thanks for forwarding this Gerrit,

I cannot agree more on Abraham Singels' comment and I have the exact experience with breeders and geneticist in a private sector. We are all from different disciplines such as soil, crop physiology, genetics, agronomy, engineering, climate and meteorology, just name a few, but one common and unique character among us is we all believe we need to use system approach to integrate all kinds of knowledge into models to solve complex issues in crop systems.

The crop models have been developed for several decades and been successful in various applications. However, one week area in crop models is crop genetics exactly as Ken mentioned in his last email ("That is the part of modeling that we are not particularly good at, or finished with, at the present state of crop modeling." and "That means more genetic coefficients than we currently use in the models."). I also totally agree what Ken said "...it is easy to say all this, but it will be difficult to obtain such more detailed coefficients, as we are short on data and on real understanding of some of those issues." I have the same feeling too sometimes. But here what I want to say is let us face it and make effort: Let us build up a communication channel with crop genetics and breeders, learn from them, bring them in crop modeling community, understand their point of view while also let them understand where we come from. Through this, I hope we may close the gap sooner.



Jun


-----Original Message-----
From: DSSAT - Crop Models and Applications
[mailto:[log in to unmask]]On Behalf Of Gerrit Hoogenboom
Sent: Friday, February 06, 2004 8:04 AM
To: [log in to unmask]
Subject: Fwd: Re: Genetic coefficients


>Hi
>To add to the discussion on so called genetic coefficients.  We at the SA
>Sugar Association have spent some effort in trying to formulate "genetic
>coefficients" (some plant breeders really get excited when this term is
>used because they use the term for very different parameters and feel that
>it creates confusion) for sugarcane that capture genetic characteristics
>and by implication exclude environmental effects.  Preliminary studies
>showed that very few of the coefficients that we have investigated seem
>stable across environments.  This implies that (1) the data  is too
>variable and that measurements are not adequate or (2) the coefficients do
>not truly capture the gene action as it manifests in phenotype.  Many of
>these coefficients refer to phenotypic events such as thermal time to leaf
>emergence or maximum leaf size etc. and are far removed from the actual
>genetic control of processes in the plant.  They are convenient in many
>instances but could be quite misleading.  I agree with Ken and believe
>that these coefficients should be viewed as attempts at understanding the
>true genetic control of growth and development.  We could learn a lot from
>how these coefficients vary between environments.  It is interesting to
>see how different crops are approached e.g. soybeans (Hoogenboom & White,
>Agron.J. 95:82-89) has succeeded in very closely capturing genetic control
>of development by formulating coefficients in terms of gene presence or
>absence.  To do that with a crop like sugarcane would be extremely
>difficult because of its polyploidy -  we therefore have to formulate
>coeff's in terms that are a few levels removed from the actual control by
>genes.
>
>In summary I think that as we try and unravel genetic and environmental
>control of plant processes, the models of these processes and the
>parameters that we use to represent genetic traits will improve to more
>closely represent reality.  Where coefficients do exhibit variance across
>environments, that reflects lack of knowledge in some cases, or - a
>realization that further refinement to achieve closer representation of
>reality will not achieve significant improvement in model applications.
>
>Our preliminary efforts are documented in
>Zhou, M., Singels, A. and Savage, M.J., 2003. Physiological parameters for
>modelling differences in canopy development between sugarcane cultivars.
>Proc S Afr Sug Technol Ass 77:610-621
>Donaldson, R.A., Redshaw, K.A. and  Singels, A., 2003.  In search of
>parameters to model cultivar specific canopy development. Proc S Afr Sug
>Technol Ass 77:605-609
>
>     Thanks for the opportunity to be part of this stimulating dicussion.
>
>Abraham Singels
>SA Sugar Association Experiment Station
>Mount Edgecombe
>


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