Agriculture Reference
In-Depth Information
production that started in the early 1960s has
continued at a steady pace (Fig. 17.1). He et al.
(2001) described wheat management in China as
intensive with high inputs. They listed 36
national and provincial breeding programs, each
employing multiple scientists. Each of these pro-
grams is highly focused and breeds for a rela-
tively small target area. Cultivar replacement has
been rapid, or about four to six times in the past
50 years (He et al., 2001). Over 90% of the grain
in China is used to make steamed bread and
noodles; breadmaking quality has not been part
of the selection criteria until recently (He et al.,
2001). The genetic gain for grain yield was well
documented by Zhou et al. (2007a,b). Improved
cultivars in southern China have shown higher
grain yield, shorter stature, stronger straw, and
increased kernel weight. Characteristics of newer
cultivars in northern China are higher grain
yield, shorter stature, stronger straw, and earlier
heading date.
Total production and genetic gain for grain
yield have been lower in areas that are subject to
erratic abiotic stress such as Australia, Canada,
and the US Great Plains. Cox et al. (1988) com-
pared historic and contemporary cultivars in
six environments and found a wide range in
mean yield and genetic gain among environ-
ments. No relationship existed between genetic
gain and grain yield at a particular location,
but genetic gain was dependent more on the
particular yield-limiting stress factor at that
location. Genetic progress was greater under a
certain stress condition targeted by the local
breeding program. This is supported by the work
of Carver et al. (2001) that showed selection in a
grain-only management system did not necessar-
ily result in genetic gain in a system that included
grazing. Based on this information, the breeding
program integrated grazing into their selection
process.
Figure 17.2 charts the grain yield increase of
three major crops in the US throughout this
past century: maize, wheat, and soybean. Grain
yield of all three crops did not change substan-
tially from 1900 to about 1940 and then began
to increase. In a review of breeding advances
in maize, Duvick (2005) described the trends
in maize yield. Nitrogen fertilizer use started
around 1960 and increased until leveling off in
1985. Hybrid maize production started in the
mid-1930s and by 1945, maize hybrids were
grown on nearly 100% of the maize acres. Duvick
(2005) also reported that genetic gain for maize
yield in the US from 1930 to 2001 was 77 kg ha
−
1
yr
−1
, a value not much different than those
reported for wheat at higher production levels
(Table 17.2).
In 1982, 36 PhD-level scientists worked for
private industry in the US in soybean breeding,
23 in wheat, and 155 in maize (reviewed by
Heisey et al., 2001). By 1994, there were 101
PhD-level soybean breeders in the private sector,
54 wheat breeders, and 510 maize breeders
(Frey 1996). Also in 1994 there were 55, 77, and
35 public soybean, wheat, and maize breeders
(Frey 1996). Perhaps the largest contribution
to maize yields in the US has been the added
investment in research made possible by hybrid
seed sales and the elimination of farmer-
saved seed. In that light, Fig. 17.2 could look
very different if expressed on a per-scientist
basis.
FUTURE PERSPECTIVES
The research encapsulated in this chapter helps
to appraise genetic progress and establish bench-
marks of where wheat breeding is today. It can
also provide direction for the future. As has
been said, “if you keep doing what you have been
doing, you keep getting what you have been
getting.” Plant breeding is an amazing science.
Identify superior progeny, recombine, and select
again. Small incremental changes have moved
wheat yields from 1,000 kg ha
−1
to 3,000 kg ha
−1
in only the past 50 years. Where will yields be 50
years from now? Past experience tells us that if
the current path continues, then world wheat
yields will increase by 40 kg ha
−1
yr
−1
as they have
the past 50 years. But the science which surrounds
wheat breeding is much different than 50 years
ago. As expounded elsewhere in this topic, our
knowledge of a wheat plant continues to expand,
