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7.4 Classifying Environments and Defining Candidate
Sub-Regions
In MET, environments that are similar in terms of genotype response can be grouped
by different methods, and each group may identify a cropping area that is relatively
uniform because genotype x location (GL) interaction effects are limited or negli-
gible. Such areas have been termed by different authors as subregions, subzones,
subareas, macro-environments or mega-environments (Annicchiarico et al. 2005 ).
Based on this, genotypes with specific adaptation can be recommended to specific
sub-regions and genotypes with wide adaptation can be recommended to area with
different environmental conditions. Different sub-regions may be identified not
only within large regions (DeLacy et al. 1994 ; Mohammadi et al. 2010 ) but also
within relatively small regions, as suggested by results from northern Syria
(Ceccarelli 1996 ); Italy (Annicchiarico 1997 ) and northern Italy (Annicchiarico
2002 ); New South Wales (Seif et al. 1979 ; Basford and Cooper 1998 ); Queensland
(DeLacy et al. 1996 ); southwest Canada (Saindon and Schaalje 1993 ); Ontario (Yan
et al. 2000 ); and west of Iran (Mohammadi and Haghparast 2011 ). Subregions may
be defined for variety recommendation: each sub region then coincides with a rec-
ommendation domain, grouping those sites with the same best-performing
genotype(s) (Gauch and Zobel 1997 ). The definition of subregions is not just geo-
graphical, but may also encompass farming practices (e.g. irrigated or rainfed crop-
ping). Subregions have sometimes been defined on the basis of site similarity for
environmental factors that are supposed to be important but are, in fact, chosen
without a definite assessment of their impact on GE interaction (Pollak and Corbett
1993 ). However, additional information on the climatic, soil, biotic and crop man-
agement variables closely related to the occurrence of GE interaction may help
locate geographic boundaries for subregions, besides contributing to the under-
standing of causal factors for the interaction (van Eeuwijk et al. 1996 , 2005 ). The
zoning process should produce subregions that can be defined on a geographical
basis or by other means, such as climatic factors or management practices, in order
to be useful for breeding or cultivar recommendation. In this case, recommenda-
tions concern the whole region. In other instances, individual locations or small
groups of sites may be added to the larger group to form a unique subregion for
breeding or recommendation (Annicchiarico 2002 ).
8 Breeding Methods
Plant breeding has been a key science in improving crop production, with an esti-
mated contribution to productivity increases of around 50 % (Fehr 1984 ). Over the
past decades, it has remained a vibrant science, with continued success in develop-
ing and deploying new cultivars on a worldwide basis (Gepts and Hancock 2006 ).
Q. Sohail et al.