Yield Trends and Genetic Potential

1. Donald N. Duvick Johnston, Iowa Yield Trends and Genetic Potential

2. 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

3. On-farm yields: corn and soybeans in North AmericaBruulsema et al, Better Crops 84 (2000): 9-13

4. On-farm yields: wheat in UKAustin, Crop Sci. 39:1604-1610 (1999)

5. On-farm yields: wheat globalCalderini and Slafer, Field Crops Research 57(1998) 335-347

6. 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

7. 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)

8. Fertilizer N on wheat in UK • Austin, Crop Sci 39:1604-1610 (1999)

9. Fertilizer N on corn in USASource: USDA-ERS:Fertilizer Use and Price Statistics

10. Wheat yields since 1985 • Calderini and Slafer, Field Crops Research 57(1998) 335-347

11. 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

12. Rice yields since advent of “Green Revolution”Pingali, et al., “Asian Rice Bowls, The Returning Crisis? (IRRI, 19970

13. Consequently — • Plant breeding may have to bear a much greater share of responsibility for yield gains in the years to come

14. 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

15. Genetic gain in rice: IRRIPeng et al, Crop Sci. 39:1552-1559 (1999)

16. Genetic gain in wheat: UKAustin, Crop Sci. 39:1604-1610 (1999)

17. Genetic gain in wheat: USAAdapted from Donmez et al, Crop Sci. 41:1412-1419 (2001)

18. Genetic gain in wheat:Mexico (CIMMYT) Reynolds et al., Crop Sci. 39:1611-1621 (1999)

19. Genetic gain in soybeans: USA (Maturity Group II)Wilcox, Crop Sci. 49:1711-1716 (2001)

20. Genetic gain in soybeans: USAWilcox, Crop Sci. 49:1711-1716 (2001)

21. Genetic gain in corn: USAAdapted from Duvick in, Developing drought- and low N-tolerant maize, CIMMYT (1997)

22. Genetic gain in corn: USACastleberry et al., Crop Sci. 24: 33-36 (1983)

23. Genetic gain in corn: USADuvick and Cassman, Crop Sci. 39:1622-1630 (1999)

24. Genetic gain in corn: USA Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

25. Corn: Drought tolerance, USADuvick, personal communication (2002)

26. Drought is drought

27. Drought tolerance, 1930s genetics

28. Drought tolerance, 1990s genetics

29. Wheat: Irrigated performance versus ...S. Rajaram, personal communication

30. Wheat: Drought performanceS. Rajaram (CIMMYT), personal communication (2002)

31. Yield Ceilings? • At what point can on-farm yields go no higher? • Will theoretical “yield potential” calculations predict that point — the yield ceiling?

32. Corn: Yield ceiling?Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

33. Corn: Yield ceiling?Duvick and Cassman, Crop Sci. 39:1622-1630 (1999)

34. Rice: Lowered ceiling?Peng, et al., Crop Sci. 39:1552-1559 (1999)

35. Corn: What ceiling?Source: Iowa Soybean Association (2002)

36. 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

37. 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

38. 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

39. Corn: tassel size, leaf angle • 1930s 1990s

40. Corn: leaf angle • 1930s 1990s

41. 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

42. “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)

43. Increased efficiency • in using (or supplying) soil nutrients: soybeansSpecht, et al., Crop Sci. 39:1560-1570 (1999)

44. 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

45. Tolerance to corn borer (pre-Bt)1940s genetics 1970s genetics

46. 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

47. 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

48. The Future • Will gains continue? • Will they meet global needs? • Will they be for the right crops and right regions?

49. 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

50. 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