Post on 22-Dec-2015
Crop yields increase annually in many nations
Changes in cultural methods (e.g., fertilizer kinds and amounts, plant density, and weed control) are responsible for about 50% of yield gains
Genetic improvements are responsible for another 50% of the yield gains
The culture-to-genetics ratio varies from crop to crop and region to region
Yield gains from cultural inputs may be leveling off
In industrialized countries — Environmental concerns mitigate against
further increases in application rates for fertilizers and/or herbicides and insecticides
Weed control is nearly absolute, although it could be less effective in the future as weeds develop resistance to intensively used herbicides
DEDHAM, Iowa — By the time the Raccoon River winds through the western hills here, passing corn fields and livestock pens before reaching Des Moines miles to the east, it is so polluted the city has to put it through a special nutrient filter to meet government standards for drinking water.
The culprits are not industrial plants or mines belching toxins into the river. They are Iowa farms, which send fertilizer and animal wastes into the groundwater and into the river. (New York Times, February 10, 2002)
Fertilizer N on corn in USASource: USDA-ERS:Fertilizer Use and Price Statistics
Nitrogen used on corn, rate per fertilized acre receiving nitrogen, selected States
y = -0.1521x2 + 603.57x - 598764R2 = 0.9009
0
20
40
60
80
100
120
140
160
1960 1965 1970 1975 1980 1985 1990 1995Year
N, lb/A
Yield gains from cultural inputs may be leveling off
In developing countries — Intensive production inputs may have adverse
agro-ecological impact In high-yield regions, reduced or no yield
increase from increased applications of fertilizer
Rice yields since advent of “Green Revolution”Pingali, et al., “Asian Rice Bowls, The Returning Crisis? (IRRI, 19970
Consequently —
Plant breeding may have to bear a much greater share of responsibility for yield gains in the years to come
Genetic yield gains continue in most crops
Gains primarily are in grains and legumes grown for the commercial market
Gains primarily are for crops bred by professional breeders, public and private
Gains in yield to date have not been materially aided by biotechnology
Gains in yield are linear and show little or no sign of leveling off
Genetic gain in wheat: USAAdapted from Donmez et al, Crop Sci. 41:1412-1419 (2001)
Genetic Gain: Wheat in Great Plains
y = 33.38x - 62039R2 = 0.9227
2000
2500
3000
3500
4000
4500
5000
5500
1920 1940 1960 1980 2000 2020
Year of Introduction
Genetic gain in corn: USAAdapted from Duvick in, Developing drought- and low N-tolerant maize, CIMMYT (1997)
y = 0.0763x - 141.76R2 = 0.8813
5
6
7
8
9
10
11
1930 1940 1950 1960 1970 1980 1990 2000
Year of Hybrid Introduction
Yield at optimum density per hybrid
Corn: Drought tolerance, USADuvick, personal communication (2002)
y = 0.0708x - 132.16R2 = 0.8867 2001
y = 0.0822x - 151.24R2 = 0.8371 1992
4
6
8
10
12
14
1920 1940 1960 1980 2000Year of Hybrid Introduction
Yield at optimum density per hybrid 1992
2001
Wheat: Irrigated performance versus ...S. Rajaram, personal communication
PROGRESS IN YIELD WITH YEAR OF RELEASE IN IRRIGATED DEMONSTRATION PLOTS. SONORA 98-99
R2 = 0.7296
2
3
4
5
6
7
8
9
10
1940 1950 1960 1970 1980 1990 2000 2010
RELEASE YEAR
YAQUI 50
SONORA 64
UP 301
SIETE CERROS
SONALIKA
PAVON
SERI M82
DEBEIRA
BACANORA T88
ARIVECHI M92
CUMPAS T88
SHANGHAI 4
HUITES F95
R2 = 0.73
RATE OF PROGRESS:
89.6 kg/ha per yearor2% increase in yield per year
Wheat: Drought performanceS. Rajaram (CIMMYT), personal communication (2002)
Progress in yield from more than 200 trials in drought affected and semi-drought affected locations globally.
100
105
110
115
120
125
130
135
140
145
150
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Year
Yield less than 2.5 t ha-1
Yield between 2.5 and 4.5 tha-1
r2 = 0.63
r2 = 0.39
Yield < 2.5 t ha -1Rate of progress 2.27% per year
Yield 2.5 - 4.5 t ha-1Rate of progress 2.33% per year
ESWY SAWYT SAWY
Yield Ceilings?
At what point can on-farm yields go no higher?
Will theoretical “yield potential” calculations predict that point — the yield ceiling?
Corn: What ceiling?Source: Iowa Soybean Association (2002)
Iowa Master Growers Champion Non-irrigated
y = 0.0099x3 - 58.854x2 + 116170x - 8E+07R2 = 0.9235
0
50
100
150
200
250
300
350
400
450
1950 1960 1970 1980 1990 2000 2010Year of Contest
Bushels per acre
Yield potential: theoretical or practical
Theoretical calculations require assumptions that may become outdated as farming practices change
Estimates of practical yield potential require constant updating also, as farming practices change
An eternal constant: Farmers want more yield and greater stability of yield
How to increase practical yield potential?
Change plant architecture Improve “harvest index” Increase “crowding comfort” Increase efficiency in utilizing soil
nutrients Increase tolerance to disease and insect
pests Increase tolerance to abiotic stress
Plant architecture
Rice, wheat and corn now have more upright leaves
Corn has smaller tassels Rice and wheat are designing
“New Plant Type” to have larger panicles/spikes and larger stems
Harvest Index
Rice and wheat have increased harvest index since 1960s, but no further change is expected
Corn has not increased harvest index (when genotypes are at optimum density)
Rice, wheat, soybeans, and corn currently increase yield by increasing biomass and thereby increasing the number of grains/kernels per unit area
“Crowding comfort”: Soybeans
“As the plant population increased from 33 to 50 to 100 plant m-2 the yield of new (post-1976) cultivars became increasingly greater than that of the old (pre-1976) cultivars.” (Specht, et al., Crop Sci. 39:1560-1570. 1999)
Increased efficiency in using (or supplying) soil nutrients: soybeans
Specht, et al., Crop Sci. 39:1560-1570 (1999)
Tolerance to disease and insect pests
Conventional breeding has been effective and will continue to be effective in providing resistance to most disease and insect pests
Durable resistance is the greatest need Biotechnology, e.g. with transgenics, can produce
resistance in some cases where none is found in the crop species or its near relatives
Molecular biology, longer term, will produce theory and genetics for improved durable resistance
Tolerance to abiotic stress
For all crops, increased yield is associated with increased tolerance to abiotic stresses such as: Too hot Too cold Too wet Too dry Too much shade Too few nutrients
Tolerance to abiotic stress
There is no completely stress-free environment
Therefore to breed for more tolerance to any stress is to breed for higher yield as well as for more stable performance
No cultivar is perfect, therefore possibilities to breed for improved yield are always present
The Future
Will gains continue? Will they meet global needs? Will they be for the right crops
and right regions?
Yields can (will?) continue to climb, but ... The cost per unit of improvement has risen
consistently during the past 100 years Enthusiasm for production agriculture including
plant breeding consistently declines (in the non-farm population of the rich countries)
Funding for public sector plant breeding (and for public agricultural research in general) consistently declines worldwide
Yields can (will?) continue to climb, but ... Attitudes toward private sector plant breeding
polarize toward condemning it or assuming that “it can do it all”
Widespread fear of genetic engineering for plant breeding is transforming into a fear of plant breeding in general
Gains cost more
Thus we seem to require increasingly greater numbers of maize breeders to maintain a constant rate of improvement in yield.” (Duvick, in Genetic Contributions to Yield Gains of five Major Crop Plants. CSSA. 1984)
Higher yields not needed “The biotechnology industry claims it holds the
answer to world hunger: high technology to increase production. But according to the United Nations Food and Agriculture Organization (FAO), this badly misstates the problem. There is no shortage of food in the world. Per capita food production has never been higher.” Advertisement in New York Times, October 11, 1999, by Turning Point Project, a coalition of more than 60 non-profit organizations.
Funding declines “Expenditures on agricultural
research in the public sector, including the International Agricultural Research Centers (IARCs) have stagnated and in some cases, declined sharply in recent years.” (Maredia and Byerlee, Agricultural Economics 22:1-16. 2000)
Parasite or protector? “… government does the costly, basic and
innovative research, while big companies pick up the profits in the marketplace.” (Fowler and Mooney, “Shattering: Food Politics, and the Loss of Genetic Diversity”. 1990.”
“Some question the need for continued public funding [of agricultural research], thinking that … the private sector will do the job.” (Pardey and Beintema, Slow Magic. IFPRI Policy Statement. 2002)
Plant breeding = genetic engineering?
“Recently, in the state of Washington, usually known for its progressive policies, strawberry plots and greenhouses belonging to Washington State University have been savaged, even though they contained not one single transgenic plant! In fact, nobody at that university has ever conducted transgenic research on strawberries.” (Lurquin, The Green Phoenix, A History of Genetically Modified Organisms. 2001)
Can breeding meet the challenge?
Predicted rates of increase in food demand during the next 50 years tend to be larger than measured genetic gains in yield during the past 50 years
Future food needs are greatest in regions where breeding progress has been slowest
But with adequate political and economic support, yield gains could be greatly increased in the most needy regions
Can breeding meet the challenge?
Plant breeding cannot do the job alone
It must be preceded and under-girded by the proper political and economic climate
Tailor breeding to the place and people
Breeding techniques suited for commercial agriculture in industrial countries will work also for commercial agriculture in developing countries
But many farming people (2 billion?) in “traditional agricultural areas” (poor land, poor economy) do not farm commercially and have different and highly diverse needs for variety improvement.
Participatory plant breeding may be best suited for such “traditional” farmers
Participatory Plant Breeding Several variations, all emphasize
decentralization strong farmer participation on-farm testing
Professional breeders advise but do not dictate
Goal is to produce varieties that meet local farmers’ needs that farmers can reproduce
What about biotechnology?
Biotechnology will not enable spectacular increases in yield in the near term
Biotechnology will be essential over the long term to help yield gains keep in step with global food needs
Biotechnology in the near term will be more useful in developing countries than in industrial countries, if it can help breeders add badly needed kinds of disease and insect resistance
What about biotechnology? Biotechnology’s greatest contribution to plant
breeding will be to increase the depth of knowledge about gene action and how to modify it to suit needs of farmers
Biotechnology causes contrasting social problems at present; it arouses fears and raises hopes in two types of people: Type 1: great fear of repressive monopolies Type 2: great hope of high profit margins Both types may be wrong
In conclusion: Plant breeding, properly supported and wisely conducted,
can help to increase food production in step with diverse needs of a growing global population
Breeding must be done with care to produce products
That farmers want and can eat and/or sell That grow well where the farmers farm That respond well to the way the farmers farm
As breeders would say: Pay attention to GxE