271date or yield (Hernandez-Segundo et al. 2009 ), and (iii) stress index determined
with crop models (Chapman et al. 2000 ).
7.3 Specific vs. Wide Adaptation
There are two possible strategies for a plant breeder interested in developing variet-
ies which show a low GE interaction, namely (i) the subdivision of a heterogeneous
area for which the varieties are being bred into smaller regions such that each of
them has a more homogeneous environment and its own characteristic varieties, and
(ii) the introduction of varieties which show a high degree of stability in perfor-
mance over a wide range of environments (Annicchiarico et al. 2005 ). However, the
first strategy can also encounter large interactions of genotypes with locations even
within a sub-region and even within the same location over seasons. In recent
decades, various programs run at international research centres have modified their
breeding strategy to produce genotypes suitable for cropping in less favourable
areas. A specific adaptation strategy has been pursued for barley improvement at the
ICARDA, with selection under conditions similar to those in the target environment
(favourable or drought-stressed), and with implications extending also to elements
of the breeding strategy, such as the choice of genetic resources and variety type. A
“shuttle breeding” procedure- alternate selection in drought-stressed (unfavourable)
and irrigated (favourable) environments- was established for the selection of widely
adapted germplasm at CIMMYT. However, the possibility of GE interaction
between environments of similar ecological potential (based on crop mean yield)
may lead to the definition of different sub-regions also within unfavourable and
moderately favourable areas. For this reason, barley breeding at ICARDA began
producing specific material for different sets of drought-prone countries; rice breed-
ing at the International Rice Research Institute (IRRI) defined specific plant ideo-
types for several different ecosystems; and wheat breeding at CIMMYT is attempting
a compromise between a wide adaptation prospect and the opportunity to breed
specifically for 12 different mega-environments (Braun et al. 1996 ). The specific
adaptation strategy is receiving increasing attention in developing countries, some-
times in combination with participatory plant breeding schemes. The participation
of farmers can: i) support the multilocational selection work; ii) allow for exploiting
possible specific adaptation effects even within sub region; iii) contribute to enhance
the biodiversity of material under cultivation, thereby improving production stabil-
ity; and iv) facilitate the seed supply to farmers via local seed systems. For small
farmers in relatively poor countries, such systems may be far more important than
formal seed systems (Annicchiarico et al. 2005 ; Ceccarelli 2015 ).
Breeding and Genetic Enhancement of Dryland Crops