Plant Domestication PDF

BIOB38: Plants and Society 1-2. Origin of agriculture 3-6. Plant domestication 7-10. Green Revolution & its legacy 11-14. Plants that feed the world 15-16. Plants that please the palate 17-18. Plants that heal the sick 19-20. Plants that hook the mind and body 21-22. Plants the...

BIOB38: Plants and Society 1-2. Origin of agriculture 3-6. Plant domestication 7-10. Green Revolution & its legacy 11-14. Plants that feed the world 15-16. Plants that please the palate 17-18. Plants that heal the sick 19-20. Plants that hook the mind and body 21-22. Plants the world thirst after 23-24. Plants of warmth and strength Plant domestication 3-4. Altered plant traits 5-6. Methods of domestication Domestication "Domesticated races show adaptation, not indeed to the animal's or plant's own good, but to man's use or fancy.“ Charles Darwin Needed for domestication: heritable variation in wild populations (desirable traits). Selection (by humans), time Introduction Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Plant fitness and seed dispersal Wild plants tend to have adaptations for seed dispersal. Without adaptations: most seeds/fruits deposited very close to the mother plant → ____________________________ → ____________________________ 1. Reduction of seed dispersal Reduction of seed dispersal: a good thing for farmers Grass seeds as human food. Impossible to collect once fallen off the plant 1. Reduction of seed dispersal Reduction of dispersal Grasses Corn (maize), wheat, rice, barley, rye, spelt, millet, etc. Legumes Soybean + all other beans, lentils, peas, chickpeas 1. Reduction of seed dispersal Loss of seed dispersal in grasses Mechanism and scientific evidence? 1. Reduction of seed dispersal Key to understanding: wild grass architecture 101 When seeds ripe: cells inside spikelet in the rachis undergo Grass seed programmed cell death → rachis falls apart (= shattering) into individual spikelets → dispersal of spikelets (+ seed) away from parent plant → formation of a smooth abscission layer at the spikelet bottom 1. Reduction of seed dispersal Shattering versus non-shattering: 2 genes control this Naturally occurring, rare recessive mutations (bad for a plant in its wild, native setting): no seed dispersal Absence of abscission layer, no controlled cell death of rachis Good for farmers: seeds do not fall on the ground → not lost! Early farmers slowly selected non- shattering genotypes 1. Reduction of seed dispersal More likely incorporation of non-dispersing mutants – how? Ripe seeds: more nutrients → early farmers collected seeds from yellow plants Wild-type: ripe seeds more likely fallen off on ground Mutant plants: ripe seeds still on plant, no shattering Wild meadow  Same mix Field next season next year Most seeds eaten Some seeds kept to sow Nice hypothesis! Scientific evidence? 1. Reduction of seed dispersal Evidence for spread of non-shattering mutants: barley lower-most portion Spikelet remnant, Fossil evidence at digs in Fertile Crescent: partial spikelets → edge Smooth edge visible Wild-type: smooth lower-most portion edge as result of Spikelet remnant, predetermined cell death Mutant: frayed Modified from Fuller. 2007. Annals of Botany 100: 903-924 Rough edge (rough) edge 1. Reduction of seed dispersal Evidence for spread of non-shattering mutants: barley 10,000 y BP 9000 y BP 8000 - 6000 y BP 4000 y BP Archeological sites (Fertile Crescent) Modified from Fuller. 2007. Annals of Botany 100: 903-924 1. Reduction of seed dispersal Spread of non-shattering mutants: other food grasses Barley Wheat Rice Purugganan and Fuller. 2009. Nature 457: 843-848 1. Reduction of seed dispersal Stiff rachis → threshing necessary to get seeds Outcome of Threshing with animals domestication: stiff rachis, seeds not released Manual threshing 1. Reduction of seed dispersal Stiff rachis → threshing necessary to get seeds Mechanical threshing 1. Reduction of seed dispersal  Teosinte: wild ancestor of → Corn Shattering Non- wildtype shattering, domesticated corn Seeds fallen off rachis 1. Reduction of seed dispersal Beans Wild-type Domesticated Seeds remain in (Explosive) opening to eject seeds seed pod 1. Reduction of seed dispersal Peas Domesticated peas need (manual) shelling (pre- mechanical): Whole family had to help! Pea shelling in Italy in early 20th century 1. Reduction of seed dispersal Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Increase in seed size Barley (also wheat) Rice Bean late late mid early early Fertile Crescent China India Mechanism? Modified from Fuller. 2007. Annals of Botany 100: 903-924 2. Increase in seed size and number Measurement of 1000s of seeds, only keep large ones? Seeds are small… NO! 2. Increase in seed size and number Solution to increase in seed size: sowing into tilled soil 2. Increase in seed size and number Small versus large seed vs emergence After tilling, seeds are sown into grooves & covered with soil Larger seeds are more likely to emerge (more reserves) Over time, larger seeds make up majority of the gene pool ☺ Run out of food reserves before start of photosynthesis Soil Germinating large seeds Germinating small seeds 2. Increase in seed size and number Larger seeds: more vigor, more likely emergence Zhu et al. 2009. Rangeland Econ. Manag. 62: 337-344 2. Increase in seed size and number Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Increase in seed number Cultivated barley Wild barley Seeds in 6 rows Seeds in 2 rows Wild and cultivated millet 2. Increase in seed size and number  Teosinte Corn 2. Increase in seed size and number Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Dormancy, definition State of quiet, inaction (“wait and monitor the environment”) -No growth, no germination -Wait for good environmental conditions Bad conditions = frost and heat/drought 3. Loss of dormancy Scenarios without dormancy: no seedling protection Summer Fall Germination of Winter seedling Young seedling Winter-cold faces the harshest of climates seasons Solution: don’t germinate before the harsh season, stay Flowering Ripening of seeds Seed dispersal DORMANT Fall Winter Spring Summer Summer-dry climates such Young seedling faces the as Medi- harshest of seasons terranean (winter-wet) Germination of Flowering Ripening of seeds Seed dispersal seedling 3. Loss of dormancy Dormancy in winter-cold climates: wild plants Seeds will only germinate after experiencing winter (aka in the spring) They need at least 3 weeks of 0 to -4◦ C Snow to germinate once spring comes =vernalization Shorter period? Probably not the full winter → don’t risk germination… Seeds ‘can count days and sense temperature!’ Seed at soil level Snow acts as insulation, typical winter temps : 0º C 3. Loss of dormancy Dormancy in summer-dry climates: wild plants Seeds will only germinate once summer is over Trigger: correct change of day length: photo sensitivity! Winter-spring-summer: day length increases Summer-fall-winter: day length decreases ☺ Seeds perceive day light and its relative durational change 3. Loss of dormancy Dormancy & the spread of crops into different climates Farmer Ali leaves the Fertile Crescent (1: summer dry) moving to Spain (also summer dry) and does agriculture Most of his wild seeds germinate in the fall (well adapted for Fertile Crescent: wild type, photo sensitive) Small proportion: naturally occurring mutants, missing genes to assess day- length change (= photo-neutral). Seeds germinate whenever they get Summer dry Summer dry moist (no dormancy) 1 3. Loss of dormancy Ali spreads agriculture to Spain Spain: Mediterranean, also summer-dry (matches 1) Ali sows seeds mid winter (best season to sow) and harvests normal yields, as in the Fertile Crescent. Both seed types (WT, M) yield harvest Seeds sown Harvest Summer Wild type (photo-sensitive) dry Summer dry Mutant (photo-neutral) 1 3. Loss of dormancy Farmer Ben spreads agriculture to England England: winter-cold (mismatch to Fertile Crescent) Ben sows seeds in the spring (best seasonal choice) and harvests very little. Only photo-neutral mutants yield harvest Winter Seeds sown Yield Yield cold Next season Summer dry Summer dry No germination of photo-sensitive seeds in the spring (no harvest), but in the fall (freezing death) → domestication: change of gene pool to photo-neutral seeds 3. Loss of dormancy Loss of photo-sensitivity needed in winter-cold climates Wheat, barley Chickpea, lentil Winter-cold Winter-cold Central Europe X Central Europe Summer-dry Summer-dry Summer Mediterranean Mediterranean dry Loss of photo-sensitivity: No loss of photo-sensitivity: transfer into Central Europe no transfer into Central Europe No chickpeas & lentils in winter- cold Central Europe 3. Loss of dormancy Loss of dormancy: a good thing for farmers! Possibility to move from one type of climate to another Farmer is in control when to sow (in the best local season): all sown seeds (mutants) will germinate without needing to overcome any dormancy Once domesticated (loss of photosensitivity), originally summer-dry crops can be gown anywhere, including in Canada (winter cold) Seeds sown Harvest 3. Loss of dormancy Dormancy in domesticated plants: gone Wild Domesticated Wild & domesticated beans bean bean planted at the same time: domesticated beans germinate quickly, wild ones wait for correct break to their dormancy Domesticated rice Wild rice Oka, National Taiwan University and International Rice Research Institute 3. Loss of dormancy Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Wild: perennial → domesticated: annual Perennial wild relative Annual domesticated crop Hordeum jubatum Barley (H. vulgare) Cicer anatolicum Chickpea (C. arietinum) Avena macrostachya Oat (A. sativa) Pennisetum purpureum Pearl millet (P. glaucum) Oryza rufipogon Rice (O. sativa) Sorghum propinquum Sorghum (S. bicolor) Glycine tomentella Soybean (G. max) No fruiting in year 1 Harvest in year 1 Need to wait for year 2 Leventin and McMahon. 2008. Plants and Society. McGraw-Hill. 4. Life cycle: mostly shortened to annual Wild and domesticated rice Common wild ancestor Evolved into two species Wild Wild perennial annual Oryza Oryza rufipogon nivara Hybridization btw the two species Cultivated Two most common rice cultivars Annuals O. indica O. japonica http://http-server.carleton.ca/~bgordon/Rice/papers/mori2000.htm 4. Life cycle: mostly shortened to annual Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Wild → domesticated sunflower: ease of harvest Many small One/few large flower heads flower head Sunflower effect Harlan. 1995. The Living Fields. Cambridge University Press. Pg. 199. 5. More compact growth habit Sunflower effect Wild type: lots of small flower heads Domesticated: one or few large heads Harlan. 1995. The Living Fields. Cambridge University Press. Pg. 199. 2. Selective breeding, aka mass selection Teosinte → corn: sunflower effect Many small Few large female cobs female cobs Teosinte Corn 5. More compact growth habit Wild → domesticated (soy) beans: more compact 5. More compact growth habit Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Increased palatability: fewer toxins (2ary compounds) Reduction in toxic or unpleasant compounds Rosenthal and Dirzo. 1997. Evol. Ecol. 11: 337-355 6. Increased palatability Wild → domesticated lima bean Wild: contains toxic cyanogenic glycoside Domesticated: much decreased or absent 6. Increased palatability Wild → domesticated nightshades (Solanaceae) Wild: contains toxic alkaloids Domesticated: much decreased or absent 6. Increased palatability Species of the nightshade family (Solanaceae) Still contain some toxic alkaloids Issue for some compromised, food-sensitive people 6. Increased palatability Wild → domesticated squash Wild: contains toxic alkaloids Wild squash: bitter Domesticated: much decreased or absent Cultivated squash 6. Increased palatability Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Flavor, texture, color, cooking time, use, shelf life 7. Diversification Flavor, texture, color, cooking time, use Dent Corn Pop Corn Flint Corn Flour Corn Sweet Corn Waxy Corn 7. Diversification Flavor, texture, color, cooking time, use Rice 7. Diversification Flavor, texture, color, cooking time, use Russet: Red: White: Potato baking, boiling, French fries steaming, boiling, roasting, au gratin, scalloped mashing, boiling, steaming, au gratin, roasting Yukon gold: Blue: Fingerling: mashing, steaming, boiling, steaming, baking, boiling baking, boiling, roasting baking, roasting 7. Diversification Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Ingenious solution: flowers Manipulation of environment to pick up and move pollen from one individual to another → outcrossing Outbred Inbred BIOC37 Plants: White clover Life on Edge 8. Propagation: sexual to clonal But: outcrossing/random mating likely… … results in unwanted new genetic variation … breaks up desirable genetic lines (cultivars) Reduction of seed dispersal watering down of Increase in seed size & number Loss of or Loss of dormancy Shortening of life cycle More compact growth habit ↑ palatability & diversification Wanted: fixation of selected traits: change reproductive system to selfing or no sex 8. Propagation: sexual to clonal Early days of domestication More desirable Field surrounded by wild ancestors of cultivated plants domesticated cultivar Less desirable wild-type Random outcross mating, btw cultivar & wild-type plants → desirable traits: lost Goal: no x mating Hard to control! Next-best goal: selfing 8. Propagation: sexual to clonal Outcrossing ancestor → selfed domesticated cultivar Outcrossing Selfing Fixation of good Chasmogamy (open- Cleistogamy (closed- genotypes flower pollination) flower pollination) and traits 8. Propagation: sexual to clonal Selfing flowers in cultivars (ancestors: mostly outcrossed) Rice Bean Wheat Peanut Barley Flax Oats Sesame Chickpea Chilies Pea Tomato Cowpea Okra Lentil etc Soybean Fixation of good genotypes 8. Propagation: sexual to clonal Open-pollinated flowers, but vegetative propagation Farmer propagates crops asexually Rhizomes: potato, ginger, taro, cassava Stolons (runners): strawberry Rooting of branches: banana, coffee, cocoa, tea, pine apple, sugar cane Grafting: grape, apple, pear, peach, apricot, cherry, almond, orange, olive Fixation of good genotypes 8. Propagation: sexual to clonal Open-pollinated flowers, but vegetative propagation: rhizomes Plant reproduces asexually through rhizomes (clonal reproduction: genetically identical) and sexually through seeds (mix of mom and dad) Cultivar with good traits X Wildtype with bad traits Offspring with worse traits than cultivar Because many plants can be propagated clonally, it does not matter if seeds carry bad genes: seeds are not used to regenerate a field 8. Propagation: sexual to clonal  Potato Cassava Ginger Sex. reprod. Propagated asexually through rhizomes (= modified stems below ground) → Fixation of good genotypes 8. Propagation: sexual to clonal  Sex. Strawberry: seeds and stolons (runners) reprod. Propagated asexually through cutting stolons (= modified stems above ground) → Fixation of good genotypes 8. Propagation: sexual to clonal Sugar cane: stem cutting Sugar cane produces seed, but it is propagated asexually through cutting stems into pieces which regrow into adults → Fixation of good genotypes 8. Propagation: sexual to clonal Sugar cane: clonal monocultures 8. Propagation: sexual to clonal Banana: stem cutting wild Stem Sucker Sucker domesticated Sucker Sterile! Sucker → Fixation of Regrown from good stem cutting genotypes with a sucker 8. Propagation: sexual to clonal Grapes (wine): grafting High Prize quality winning yield grape Grape plants grow new branches every Hardy substrate year ‘forever’ → Fixation of good genotypes 8. Propagation: sexual to clonal Grafting also incredibly important in fruit trees Different genotypes/species grafted onto one tree → Fixation of good genotypes 8. Propagation: sexual to clonal Open-pollinated flowers, but vegetative propagation Mostly through rhizomes or stolons, rooting of branches, or grafting Rhizomes: potato, ginger, taro, cassava Stolons (runners): strawberry Rooting of branches: banana, coffee, cocoa, tea, pine apple, sugar cane Grafting: grape, apple, pear, peach, apricot, cherry, almond, orange, olive Fixation of good genotypes 8. Propagation: sexual to clonal Altered plant traits 1. Reduction of seed dispersal 2. Increase in seed size & number 3. Loss of dormancy 4. Life cycle: mostly shortened to annual 5. More compact growth habit 6. Increased palatability 7. Diversification 8. Propagation: sexual to clonal Individual characteristics Character wild domesticated Seed dispersal High Low Seed size & # Few, small Many, bigger Seeds need vernalization Common None Photoperiod sensitivity Sensitive Insensitive Lifecycle Often perennial Often annual Growth habit Any Stunted, compact Secondary compounds Many Reduced Propagation Mostly sexual Vegetative and outcrossed and asexual Plant domestication 3-4. Altered plant traits 5-6. Methods of domestication