89are recessive and complemented by functional copies in the additional genomes.
This was one reason why breeders only used mutation methods when they had
exhausted every other possibility to increase genetic variation. Recently the
TILLING (Targeted Induced Local Lesions in Genomes) approach has contributed
signifi cantly to the effi ciency of mutant discovery. It can be applied in both diploid
and polyploid species, allowing the identifi cation of DNA polymorphism in large
numbers of genotypes, based on DNA sequence differences. Selection for mutant
candidate genes can therefore be made at the molecular level, after which the genes
can be combined to develop new genetic resources for breeding.
TILLING is ideal for common wheat , as this technique allows the detection of
recessive mutations in polyploid species (Comai et al. 2004 ). Slade et al. ( 2005 )
identifi ed 246 alleles of the waxy starch genes in a mutagenised wheat population.
M 4 seeds from the cultivar Cadenza were used to identify mutations through a com-
bination of SDS-PAGE, to analyse granule-bound starch proteins, and TILLING
(Sestili et al. 2010 ). Work has focused on two groups of synthase genes, those
encoding starch synthase II ( Sgp-1 ) and those corresponding to the waxy proteins.
The identifi cation of lines with null alleles for starch biosynthesis genes is a realistic
approach for modifying the wheat starch structure, using traditional breeding to
transfer the mutations into commercial varieties.
Nowadays transgenesis is a potentially important breeding technology to intro-
duce genes for various agronomical traits from wild and cultivated relatives into
wheat. Transgenic wheat production is a two-step process, involving the integration
of foreign DNA and the regeneration of fertile plants, followed by the selection of
a genetically modifi ed cultivar. The fi rst results in transgenic plant development
were obtained using model plants and some important agricultural crops like maize
and rice , while the transformation protocol for small-grain cereals was developed
later. The fi rst fertile transgenic wheat was developed by Vasil et al. ( 1992 ) using a
biolistic method. Agrobacterium -mediated transformation protocols were devel-
oped a decade later for all the major cereal species (Lazzeri and Jones 2009 ). Well-
established transformation protocols are available for wheat and barley with
increasingly effi cient Agrobacterium -mediated transformation techniques, better
integration patterns and improved co-transformation. The increasing number of traits
tested in fi eld trials is proof of the rapid development of the transgenic breeding
technology. Several transgenic wheat and barley transgenic genotypes with agro-
nomically important traits have been submitted for registration (Dunwell 2008 ).
One promising new technology is cisgenesis, which differs from transgenesis
in that DNA fragments from wheat or cross-compatible species are incorporated
into the genome , so cisgenic plants do not contain foreign or modifi ed genetic
material. Cisgenic plants are produced by the same transformation techniques as
transgenic plants. As wheat has many wild and cultivated relatives, the prospects
for developing precision breeding via the cisgenesis technology are excellent.
This technology would be a modern alternative to traditional breeding and would
offer an ideal way of incorporating agronomically important genes from wild and
cultivated wheat relatives into common wheat. Cisgenesis has great potential to
overcome many problems of traditional breeding, such as linkage drag , crossing
3 Wheat Breeding: Current Status and Bottlenecks