The Domestication of Phaseolus vulgaris L.

1. The Domestication of Phaseolus vulgaris L.

2. Taxonomic Overview • Family: Fabaceae/ Leguminosae • Subfamily: Papilionoideae • Tribe: Phaseolae • Phaseolus is a monophyletic genus • Diploid: 2n = 22 x=11 • Predominantly self-pollinating due to papilionaceous, cleistogamous flower structure (some bees)

3. The genus Phaseolus is strictly New World in tropical and subtropical locales. • Documenting Domestication reports range as from Mexico to Argentina • However, two species P. sinuatus Nuttall ex T & G and P. polystachios (L.) BSP are found throughout the Southeastern U.S.A. (Radford, 1964)

4. Importance to Humans • Fabaceae is one of the most important plant families; has been for millenia • Includes other domesticates such as: Cicer arietinum L. “Chick pea” Arachis hypogaea L. “Peanut” Lathyrus odoratus L. “Sweet pea”

5. Phaseolae also includes: Glycine max (L.) Merr “soybean” Vigna unguiculata (L.) Walp. --> 4 ssps “Cowpea, Black-eyed pea, Yardlong bean, Catjang” • Phaseolus includes 5 domesticated species: P. vulgaris L., P. lunatis L. (“lima bean”), P. acutifolius A. Gray (“tepary bean”), P. coccineus L. (“runner bean”), P. polyanthus Greenman. • Of these, Phaseolus vulgaris L. is the most important vegetable protein source for humans!

6. Diversity!

7. History • Native to Central/South Americas • Arrived in Spain & Portugal from Central America in 1506 after the “discovery” of the “New World.” • Accessions from the Andes started arriving in Europe after 1532. • Reached Germany by at least 1543, as evidenced by a description in a German herbal.

8. Mystery of Domestication! • Role of introgressive hybridization of P. vulgaris and P. coccineus in Mexico (bumblebees!)? • Domesticated twice?! • How many species are we dealing with here??

9. Role of Hybridization • Discussed in article at some length; hybridization b/t P. coccineus and P. vulgaris resulting in P. polyanthus? • Also, proposed by Freytag in 1955 that gene flow from P. coccineus could be responsible for the larger seed size in Mesoamerican varieties as opposed to Andean varieties. (Gepts and Khairallah both report the Andean varieties to have larger seeds.)

10. Domesticated Twice?! • Archaeological Evidence • Molecular Evidence

11. Archaeological Evidence • Supports two events of domestication because: 1. Domesticates appear before evidence for cultural contact b/t Meso- & Andean-America (occurred ~2000-1000 yrs BPE) (Gepts et al., 1986) 2. Distinct varieties matching varieties today found in sites. 3. Wild P. vulgaris grows in both regions. (Kaplan, 1980)

12. Earliest evidence in Mesoamerica found in Coxcatlan Cave of Tehuacan Valley, dating to 5,500-7,000 yrs BPE • Earliest evidence in Andes dates to 8,000 yrs BPE, found in Guitarrero • Wild remains were found in Mesoamerica, but not in Andes (all sites located outside of natural growth of wild P. vulgaris.)

13. Molecular Evidence • Wealth of evidence! • Focus mainly on: 1. Phaseolin types (protein markers) 2. RFLP diversity 3. mtDNA analysis (for you, Phil!) • Following table is from Gepts, 1996

15. Phaseolin Types • Authoritative article on this subject is Gepts et al., 1986 • Analyzes phaseolin variations b/t Andean & Mesoamerican wild plants as well as landraces using 1-D SDS-PAGE and 2-D IEF-SDS/PAGE on 106 wild forms and 99 landraces

16. Wild forms: Mexico: M, S (nearly all M) Guatemala: same as Mexico Peru: S, T (mainly T) Brazil, Argentina: T Domesticated: Mexico: S (2 T) Colombia, Guatemala, Costa Rica: S (1 T) Ecuador: S, T, C (1 C) Peru: few S, lots T, 2 C, 2 H, 1 A Bolivia, Chile, Argentina: T, C, few S, 2 H. Condensed Results from Gepts, 1986 on Phaseolin Distribution

17. RFLP Diversity • Looked at Velasquez & Gepts, 1994 • Digested genomic DNA four ways: one time each with three different restriction enzymes, EcoRI, EcoRV, and HindIII, and one time with all three. • Generated diagrams based on Nei’s distances.

18. Nei’s Distance Diagrams, Velasquez & Gepts, 1994

19. Mitochondrial DNA Analysis • Khairallah et al., 1990. • Examined 23 Malawian landraces • Digested mtDNA with 8 restriction endonucleases, HaeIII, BamHI, DraI, EcoRI, HindIII, PstI, SalI, XhoI. • 2 distinct mtDNA groups were discovered, corresponding to the two nuclear DNA groups. • However, a high level of mt genome homogeneity • Demonstrates divergence before domestication!

20. How Many Species Are We Dealing with Here?? • Evidence supports that P. vulgaris is at least in the process of speciation • Two divergent gene pools repeatedly identified • Gepts & Bliss, 1985 demonstrated F1 hybrid lethality b/t Meso- and Andean-American varieties • 3 gene pools? Islam et al., 2002

21. Map of Type Distribution of Wild Phaseolus vulgaris Gepts, 1996

22. Wild forms: Mexico: M, S (nearly all M) Guatemala: same as Mexico Peru: S, T (mainly T) Brazil, Argentina: T Domesticated: Mexico: S (2 T) Colombia, Guatemala, Costa Rica: S (1 T) Ecuador: S, T, C (1 C) Peru: few S, lots T, 2 C, 2 H, 1 A Bolivia, Chile, Argentina: T, C, few S, 2 H. Condensed Results from Gepts, 1986 on Phaseolin Distribution

23. Nei’s Distance Diagrams, Velasquez & Gepts, 1994

24. Sources • Freytag, G. F. (1955) Variation of the common bean in Central America. Unpublished thesis, Henry Shaw School of Botany, Washington Univ., St. Louis, MO. • Gepts, Paul. (1996) Origin and evolution of cultivated Phaseolus species. In: B. Pickersgill and J.M. Lock (eds). Advances in Legume Systematics 8: Legumes of Econoic Importance, pp. 65-74. Royal Botanic Gardens, Kew. • Islam, F.M.A., et al. (2002) Genetic variability in cultivated common bean beyond the two major gene pools. Gen. Res. Crop Evol. 49: 271-283. • Kaplan, Lawrence. (1981) What is the Origin of the Common Bean? • Khairallah, M.M. et al. (1990) Mitochondrial DNA polymorphisms of Malawian bean lines: further evidence for two major gene pools. Theor. Appl. Genet., 80: 753-761. • Velasquez, Viviana L. Becerra and Paul Gepts (1994) RFLP diversity of common bean (Phaseolus vulgaris) in its centres of origin. Genome, 37: 256-263.