History of Plant Breeding

1. History of Plant Breeding David Van Sanford University of Kentucky

2. Origins of Agriculture Harlan (1992) outlined six regions in which agricultural origins occurred We will examine, briefly, the Near East and Meso-America. The Near East serves as a general introduction to self-pollinated species, focusing on common wheat (Triticum aestivum, 2n=6x=42, genomes ABD) Meso-America serves as a general introduction to cross -pollinated species focusing on corn (Zea mays L., 2n = 2x = 20). Ch. 1-3 Fehr Topics 1-3 Murphy

3. The Near East At the eastern end of the Mediterranean Sea, across a broad arching zone of grasslands and open oak-pistachio woodlands called the Fertile Crescent the world’s first agricultural economies emerged between 10,000 and 8,000 years ago (the Neolithic revolution).

5. The Near East Landraces of Self-Pollinated Species The heterogeneous populations grown by Neolithic farmers are called landraces—heterogeneous cultivated forms that evolved from natural populations of plant species.

6. Landraces of Self-Pollinated Species Wheat is a self-pollinated species with low levels of outcrossing. Any given plant in a Neolithic farmer’s field was homozygous at most, or all, loci. In general, seeds harvested from any individual plant faithfully reproduced the parental genotype the following generation. This constancy was maintained through generations in the absence of outcrossing to a different genotype or the occurrence of spontaneous mutations. If a second plant was considered in this Neolithic farmer’s field, the same constancy of genotype from generation to generation occurred. But there was a noticeable difference--this second plant likely had different alleles at many loci when compared locus-by-locus with the first plant.

7. Landraces of Self-Pollinated Species At harvest, the seeds from individual plants were not kept separate, but a conglomeration of seeds from all genotypes in the field was bulked into a seed store. The following season a random sample of this seed was planted. This random sample of seed contained a random sample of the genotypic array found in the field the previous season.

8. The Composition of an Autogamous (Self-Fertilizing) Landrace Population • Contain many genetically distinct homozygous plants—e.g., AABBCC; AABBcc; aaBBcc. They have similar alleles at corresponding loci on homologous chromosomes. • Although these plants exist side-by-side, they remain more or less independent of each other in reproduction. • 3. Plants in these populations are generally fully vigorous homozygotes. Deleterious recessives are rare and are eliminated rapidly. • 4. Prolonged inbreeding is tolerated in the absence of inbreeding depression. •  5. Local adaptation of individuals is high. Reproductive isolation shields adapted gene complexes from breakup through recombination. • As a result, individuals have a low flexibility of response to a changing environment.

9. Homozygous genotypes do not imply a homogeneous population. Landraces of self-pollinating species contain a preponderance of homozygous plants, but they are not homogeneous. Homogeneity in a population exists only if all individuals have the same genotype. Individual loci can be homozygous or heterozygous in a homogeneous population.

10. History of Plant Breeding The Intellectual Landscape • What was the mindset? • How to regard phenotypic variation?

11. Essentialism in BiologyBefore evolution, there existed an essentialist view of biology that proposed all species to be unchanging throughout time. Some religious opponents of evolution continue to maintain this view of biology. The bottom line was--essentialists could not handle intraspecific variation; as a result, they could never be plant breeders.

12. The Significance of Intraspecific Variation Newton’s physical laws were exact and dealt in constancy of the universe and its systems. Scientists assumed that biological laws must have similarly rigid descriptions.

13. The Plant Breeders • Individual plant selections were made within landraces and seed was used to form a) a pure line or b) an improved landrace • 2) Intraspecific crosses were made between cultivars differing in one or two characteristics.

14. Le Coteur, Isle of Jersey, 1830s He observed that progeny from remarkable plants tended to have the same remarkable characteristics. This led to the development of inbred homozygous homogeneous lines from landraces.

16. The Swedish Seed Association Known for utilizing the Pure Line Method is the Swedish Seed Association at Svalof in southwestern Sweden. Nilson in the 1880s, directed a large-scale program of selecting single heads from landraces followed by progeny tests.

17. Early Development of Cultivars Through Hybridization Pringle released an oat cultivar in 1875 in Vermont and Jones released a wheat cultivar in New York in 1893 that resulted from artificial hybridizations. Farrer had notable success during the same period in Australia. Following the rediscovery of Mendel’s laws governing particulate inheritance, the popularity of hybridization to develop breeding populations for cultivar development increased

18. The Influence of Darwin on Plant Breeding Darwin considered intraspecific variation to be fundamental underpinning of evolution. Variation within a single species was no longer considered a distortion of divine creation. This viewpoint replaced the abstract or metaphysical view of variation of the Essentialist. Darwin believed that evolution was like the application of the plant and animal breeder’s activities to nature as a whole.

19. Influence of Mendel Mendel focused on the variation among the offspring of his crosses rather than on an average description of them. He divided progeny into categories, counted offspring in each category, and calculated ratios of individuals in each category. Mendel’s approach was new because he considered the whole population and sought out the underlying mechanisms controlling the variation in the populations.

20. The Confluence of Darwinism, Mendelism and Plant Breeding Genetics could explain how progeny resembled parents, and yet why there was variation among progeny. Organisms resemble parents (thesis) Variation in progeny (antithesis) Genetics (synthesis)

21. Seed Size in Common Bean - Johannsen

22. Landrace – seed size variation Princess Beans Line 1 Line 25 64 35 Mean 43-87 24-47 Range 64 35 Progeny Mean

23. The Pure Line Theory-Johannsen, 1913 • Conclusions: • selection for seed weight was effective; • 2) the original landrace Princess consisted of a mixture of homozygous plants 3) within-line phenotypic variation was environmental in nature and further selection within a pure line will not result in further genetic change Johannsen clarified the difference between phenotype and genotype and gave selection a firm scientific basis.

24. Meso-America--A General Introduction to Cross-Pollinated Species - Maize Current evidence suggests that corn was domesticated from the annual wild grass teosinte (Zea mexicana) in the Balsas River drainage in south central Mexico

25. Monoecious: Staminate (Tassel) and Pistillate (Ear) inflorescences

26. Landraces of Cross-Pollinated Species Corn is a cross-pollinated species with high levels of outcrossing. Any given plant in an Aztec farmer’s field contained both heterozygous and homozygous loci. Heterozygosity occurred only at the loci for which more than one allele was present in the landrace population. The frequency of heterozygosity at a locus depended on the frequency of the different alleles in the population. Seed harvested from any individual plant in an open pollinated landrace did not faithfully reproduce itself the following season It was half-sib seed and the plants it produced the following generation represented the female parent plus the array of male parents that contributed pollen to the female’s silks. The following season a random sample of these seeds was planted. This random sample contained a random array of the genotypes found in the field the previous season.

27. The Composition of an Allogamous (Cross-Pollinating) Population 1. Comprised of a highly heterozygous and heterogeneous plant population--e.g., AaBbcc:AABbCc:AaBBcc:etc. 2. A consequence of open-pollination is the retention of recessive alleles in the population.

28. 3. An open-pollinated landrace has the best potential for evolutionary flexibility. One way to quantify this flexibility is to estimate of Gene Diversity or Polymorphic Index at a locus :   n  Pi(1-Pi) i=1  where n = number of alleles at the locus and Pi the frequency of the ith allele. A locus with two alleles present at frequencies of 0.9 and 0.1 has a polymorphic index of 0.18. If the frequencies are more equitable at values of 0.5 each, say, the diversity measure increases to 0.5.

29. Open-pollination in a heterozygous population promotes effective recombination between linked alleles . • Approximating linkage equilibrium

30. Early Corn Improvement in the United States ( see Troyer (1999). Crop Sci. 39: 601-625) The early corn breeders all practiced a form of mass selection through the selection of desirable open-pollinated ears from superior plants Some open-pollinated cultivars were developed by crossing populations and conducting mass selection on the resulting progenies, eg. Reid Yellow Dent Blount was probably the first to conduct mass selection while controlling the pollen source. He utilized this approach during the 1870s in Tennessee.

35. It took approximately 15 years for the world’s population to grow from 4 to 5.3 billion. The population is expected to reach 9-10 billion in the 21st century. By the last decade of your professional careers the world will be consuming twice the calories per day that were consumed when you were 10 years old.

36. How Will We Feed 9-10 Billion People? • Increase land area devoted to crop production? • Increase yields? • Need to double yields by the end of the 21st century • Huge challenge for breeders • Yield gains are diminishing

37. Plant Breeders – who employs them? Frey (1996); 2205 science person years employed in plant breeding Private sector 68% $340m $148-290,000 per SY University 24% $156m $293,000 per SY USDA 8% $153 $300,000 per SY Agronomic crops (71%), Horticultural crops (29%) Corn (~30%), soybeans (7%), wheat (6%), cotton (6%), temperate fruits and nuts (5%), tomato(4%), forage legumes(4%), and ornamentals(4%) Cultivar development (65%); Germplasm development (18%) Basic research (17%)

38. Consultative Group on International Agricultural Research 1000 scientists of 60 nationalities working in 40 developing countries

39. Sir Roland Biffin