Chapter 8 
The Application of Genetics to Plants 
Perspective on plant breeding 
As primitive people moved from hunting and 
gathering to tanning, they learned to identify 
broad genetic ti'aits, selecting and sow ing seeds 
from [jlants that grew faster, proilucetl larger 
fruit, or were more resistant to pests and dis- 
eases. Often, a single trait that appeared in one 
plant as a l esult of a mutation (see Tech. ,\ote 1, 
p. 162.) was selected and bred to increase the 
trait's frequency in the total crop population. 
Mendel’s laws of trait segregation enabled 
breeders to predict the outcomes of hybridiza- 
tion and refinements in breeding methods. (See 
app. II-.-\.) Conseciuentlv , thev achieved breed- 
ing objectives faster and with more precision, 
significantly increasing production. During the 
past 80 years classical applied genetics has been 
responsible for: 
• increased yields: 
• ov ercoming natural breeding barriers; 
• increased genetic diversity for specific 
uses: 
• e.xpanded geographical limits where crops 
can be grown; and 
• improv ed plant quality. 
Since the beginning of the 20th century, plant 
breeders have helped increase the productivity 
(see Tech. Note 2, p. 162.) of many important 
crops for food, feed, fiber, and pharmaceuticals 
by successfully developing cultivars (cultivated 
V arieties) to fit specific environments and pro- 
duction practices. Some breeding objectives 
have met the needs of the local farmer, while 
other genetic improvements have been applied 
worldwide. The commercial development of 
hybrid corn in the 1920’s and 1930’s and of 
"green revolution” wheats in the 1950’s and 
1960's are but two examples of how plant 
breeding has affected the supply of food avail- 
able to the world market. (See Tech. Note 3, p. 
162.) A comparison of av erage yields per acre in 
1930 and UlTv'; in table 24 gives a measure of the 
contribution of genetics.* 
It is im[Dossible to determine exactly to wbat 
degree applied genetics has directly contributed 
to increases in yield, because there have been 
simultaneous improvements in farm manage- 
ment, pest control, and cropping tecbniques 
using herbicides, irrigation, and fertilizers. V'ar- 
ious estimates, however, indicate that applied 
genetics has accounted for as much as 50 per- 
cent of harvest increases in this century. The 
yield superiority of new varieties has been a ma- 
jor impetus to their adoption by farmers. Histor- 
ically, the primary breeding objective bas been 
to maintain and improve crop yields. Other 
'(;. r. Sprague, O. K. .Vlcwander, and J. VV'. Uudley, "Plant Breed- 
ing and (ienelic engineering: A Perspective,” BioScience 30(1): 17, 
1980. 
Table 24.— Average Yield per Acre of Major Crops 
in 1930 and 1975 
Average yield per acre Percent 
1930 
1975 
Unit 
increase 
Wheat 
14.2 
30.6 
Bushels 
115 
Rye 
12.4 
22.0 
Bushels 
77 
Rice. 
46.5 
101.0 
Bushels 
117 
Corn 
20.5 
86.2 
Bushels 
320 
Oats 
32.0 
48.1 
Bushels 
50 
Barley 
23.8 
44.0 
Bushels 
85 
Grain sorghum. . . . 
10.7 
49.0 
Bushels 
358 
Cotton 
157.1 
453.0 
Pounds 
188 
Sugar beets 
11.9 
19.3 
Tons 
62 
Sugarcane 
15.5 
37.4 
Tons 
141 
Tobacco 
. . 775.9 
2,011.0 
Pounds 
159 
Peanuts 
. . 649.9 
2,565.0 
Pounds 
295 
Soybeans 
13.4 
28.4 
Bushels 
112 
Snap beans 
27.9 
37.0 
Cwt 
33 
Potatoes 
61.0 
251.0 
Cwt 
129 
Onions 
Tomatoes: 
159.0 
306.0 
Cwt 
92 
Fresh market . . . 
61.0 
166.0 
Cwt 
172 
Processing 
4.3 
22.1 
Tons 
413 
Hops 
. . 1,202.0 
1,742.0 
Pounds 
45 
SOURCE: U.S. Department of Agriculture, Plant Genetic Resources: Conserva- 
tion and Use (Washington, D.C.: USDA, 1979). 
137 
