Alien Introgression in Wheat Cytogenetics, Molecular Biology, and Genomics

95

The artifi cial synthesis of hexaploid wheat is an excellent tool to widen genetic
variability and to select genotyp e s with new agronomical properties (Fig. 3.4 ). The
fi rst attempts to develop synthetic hexaploid wheats through the artifi cial hybridi-
sation of durum wheat [ Triticum turgidum ssp. durum (Desf.) Husn.] with Aegilops
tauschii Coss. were published by McFadden and Sears ( 1944 ). In the early 1990s,
synthetic hexaploid wheats were backcrossed to many CIMMYT and global elite
breeding lines. The advanced backcross lines are popular with breeders worldwide
due to their excellent levels of resistance to biotic and abiotic stresses , and in some
cases, high grain quality. The successful incorporation of genetic diversity from
the wild relatives of wheat has created wheats containing more variation (Rajaram
2001 ).
Synthetic-derived lines were compared with their recurrent parent in fi eld experi-
ments conducted in the mid-1990s near Ciudad Obregon, Sonora, Mexico. More
than 80 % of the synthetic-derived lines were signifi cantly superior to their recur-
rent parent for kernel weight. Eight lines had signifi cantly higher grain yield com-
pared with their recurrent parent. The grain yields of superior lines were up to 11 %
higher than those of their recurrent parents. A strong association between grains
m −2 , biomass, spikes m −2 , grain and biomass production rates and grain yield was
observed in all the populations (del Blanco et al. 2001 ).

Triticum turgidum Aegilops tauschii

F1 hybrid*

(2n=3x=21, ABD)

*Treated with

Colchicine

Synthetic hexaploid wheat

(SHW)

(2n=6x=42, AABBDD)

Bread wheat

F1 X Bread wheat

X

x

2n=6x42, AABBDD

BC1F1---BC1Fn

Synthetic backross

derived lines (SBL)

Fig. 3.4 Production scheme of synthetic backcross derived lines (after Ogbonnaya 2011 )

3 Wheat Breeding: Current Status and Bottlenecks