60
from an increase in the number of fertile fl orets per spikelet and, sometimes, to the
length or density of the spike, reduction in shattering, and resistance to lodging as
well as to fungal, bacterial and viral diseases and pests. During the course of “the
green revolution”, the semi-dwarf and dwarf varieties were taken to India, Pakistan,
Iran and the Mediterranean basin replacing the numerous land races in every locale.
Today, the dwarfi ng genes have been widely incorporated into most existing
cultivars.
The main achievements in breeding for grain quality have been improvements in
milling and baking characteristics. Certain modern cultivars are easily milled
because the pericarp and seed coat are only loosely attached to the endosperm.
Flour yield is particularly higher in varieties with short, almost spherical grains. To
date, less progress has been made in improving the nutritional value of the grain,
and further efforts are needed, particularly to increase the protein content and rem-
edy defi ciencies in amino acids composition.
From the dawn of agriculture, cultivated wheat was under constant selection
pressure to increase grain yield; prolifi cacy became more important than seed effi -
ciency, since successful seedling establishment in the cultivated fi eld was achieved
by providing the seedlings with optimal growth conditions. According to Evans
( 1981 ), the improvement in grain productivity was achieved through increasing leaf
size and fl ag-leaf area, delay fl ag-leaf senescence, increasing the size of the vascular
system in the spike, advancing fl owering time, increasing rate and duration of grain-
fi lling period, increasing rate and duration of assimilates translocation to the grains,
increasing grain size and grain number per spikelet, increasing spike number per
plant or per unit area. One of the most important changes during cultivation was an
increase in the proportion of the dry matter allocated to the harvested grains (harvest
index). On the other hand, there were few or no signifi cant changes during wheat
cultivation in the photosynthetic capacity per unit leaf area, in growth rate, or in the
accumulated dry weight of the crops (biomass).
Compared to domesticated wheat, wild emmer, subsp. dicoccoides , is character-
ized by a later anthesis and earlier grain ripening. This shorter grain fi lling is appar-
ently the consequence of relatively early and rapid fl ag-leaf senescence occurring
about 2 weeks after anthesis. The degradation of most leaf-proteins at this stage
reduces and eventually ceases completely the capacity for carbohydrates assimila-
tion in the leaves, resulting in a higher N/C ratio in the assimilates translocated to
the grains. Indeed, all wild emmer lines analyzed had high grain protein percentage
(GPP) (Avivi 1977 , 1979a , b ; Feldman et al. 1990 ). High GPP may contribute to
seedling vigor (Millet and Zaccai 1991 ). Under the semi-arid conditions that prevail
in the natural habitats of wild stands, a small number of medium-sized grains with
high protein content suffi ce to ensure rapid germination and successful establish-
ment of the next stand.
Among the traits that were affected by domestication are the storage proteins, in
particular the high molecular weight glutenins whose variability and amounts are
higher in wild than in domesticated tetraploid wheat (Levy and Feldman 1988 ;
1989b ; Laido et al. 2013 ). Recently, a NAC genes from emmer wheat that contributes
to high protein percent, a trait that affects both the nutritive value and the processing
of wheat and was lost during domestication, has been isolated (Uauy et al. 2006 )
M. Feldman and A.A. Levy