265East Asia around 2000 B.C., North and South America in the 1500s A.C. (Heiser
1990 ) and Oceania in the late 1700s A.C. (Macindoe and Brown, 1968 ). Wheat
became then a worldwide crop and its adaptive capacity and plasticity resulted in
several landraces and cultivars adapted to the most diverse temperature, photope-
riod, altitude and cultural practices (Bennet 1970 ).
The first scientific breeding started in the nineteenth century when the earlier
breeders started selecting and crossing landraces and cultivars from different origins
and genetic pools and obtained the combinations that led to superior varieties.
Especially successful cases of different genepool uses shall include the Italian
breeder Strampelli, who in the first decades of the twentieth century include in his
crossing block foreign lines like the Japanese variety Akakomugi (Salvi et al. 2013 ).
The crosses between Italian landraces, breeding lines and Akakomugi resulted in
the introgression of new alleles for phenological adjustment and suitable agronomi-
cal types– such as Rht8c for short straw and Ppd-D1 for photoperiod insensitivity–
in the Italian gene pool. The varieties developed by Strampelli, such as Ardito and
Mentana became the backbone of most of the new varieties developed in the
Mediterranean countries and distant countries like China and some South American
countries (Dalrymple 1986 ; Lupton 1987 ; Yang and Smale 1996 ). A similar
approach was followed by the Nobel laureate Norman E. Borlaug in the 1950s with
the Norin-10/Brevor cross that, with the introduction of the Rht-B1 and Rht-D1
dwarfing alleles, further reduced plant height preventing lodging when the crop was
subjected to increased fertilization and irrigation; the efforts of Borlaug and his
team led to what is commonly known by “The Green Revolution” (Worland and
Snape 2001 ; Borlaug 2008 ). These cases could be considered among the most suc-
cessful human introgression of suitable alleles from a different genepool that led to
important increases in crop productivity. Allele introduction from different primary
genepools is still nowadays one of the main sources of diversity and traits of interest
(Reif et al. 2005 ). Crosses between winter and spring varieties – two genepools that
used to remain isolated from one another due to geographical and physiological
barriers – have been widely used by national and international breeding centers like
ICARDA and CIMMYT to obtain new high yielding wide adapted varieties.
The usefulness of the primary gene pool in wheat improvement has been and is
still nowadays undeniable. However, with the advances in hybridization and bio-
technological techniques during the first decades of the 20thcentury, new genepools
became available for breeders. The wide genetic diversity of wheat wild relatives
that had evolved separately for thousands of years and whose natural hybridization
with common wheat normally results in weak progeny and partial or totally sterility
is still available. The introgression of new alleles, chromosomes or entire genomes
of these relatives has become one of the main sources of diversity and new alleles
nowadays. One of the most successful introgressions of wild genomic regions into
a modern wheat variety was curiously not the result of a directed cross made by a
breeder but a casual hybridization occurred in a farmers’ field. The wheat/rye
1RS.1BL translocation allowed CIMMYT wheats – particularly the ones related to
the Veery group of varieties– to increase their above-ground biomass yield, number
of spikes per unit area, grain weight and test weight (Villareal et al. 1992 ). With this
Breeding and Genetic Enhancement of Dryland Crops