Studies of genetic diversity in tree species

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Tree seed supply chains
Tree planting on farms in East Africa how to
ensure genetic diversity?
David Boshier,Ian Dawson Ard Lengkeek
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Location of the countries and survey areas
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Nursery sites
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Why bother about genetic diversity?

• adaptation to changing environments
• direct use of genetic resources
• viability of populations in short term
• - seed production
• - inbreeding depression

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Inbreeding depression in Acacia mangium in Sabah

• Seed source
• 1st generation
• 2nd generation
• 3rd generation

• Seedling height (cm)
• 32.5
• 20.7
• 18.1

Sim, 1984
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Theory

• direct impacts
• decrease population size
• increase spatial isolation
• decrease densities
• change local environment

genetic processes genetic drift gene
flow mating - inbreeding selection
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Bottleneck ? genetic drift
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Isolated trees mating patterns?
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Altered mating patterns in farm trees?

• Predictions increased inbreeding
• greater pollen dispersal
• fewer sires
• Isolated farm tree Continuous forest

sires
inbreeding
dispersal
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How many trees to collect from?
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Data collected in a survey of seed-propagated
tree species in tree nurseries from five areas in
East Africa
Survey area (country) Survey area (country) Survey area (country) Survey area (country) Survey area (country) All areas
Kabale (Uganda) Mabira (Uganda) Nairobi (Kenya) Meru (Kenya) Arusha (Tanzania)
Nurseries client data 7 6 9 7 21 16 12 8 22 22 71 59
Cases client data 15 8 26 16 31 25 17 10 54 54 143 113
All species 11 14 16 7 16 43
Indigenous species 3 6 6 1 3 15
Cases indigenous species 4 10 6 2 5 27
Cases five most common species 2 3 11 10 40 66
Cases of unique species occurrence 3 6 6 2 5 22
Single tree collections all species 7 4 8 7 5 31
Single tree collections indigenous species 2 1 2 0 1 6
Seed trees per nursery lot, Nm mean (SD) 3.7 ? 1.8 (3.6) 5.1 ? 2.3 (6.0) 5.8 ? 3.1 (8.9) 5.7 ? 3.1 (6.5) 8.2 ? 3.8 (14.1) 6.4 ? 1.7 (10.3)
Seedlings per nursery lot, Ns mean (SD) 871 ? 712 (1408) 2060 ? 1408 (3661) 787 ? 432 (1228) 1339 ? 1011 (2127) 1543 ? 676 (2535) 1378 ? 401 (2446)
Clients per nursery lot, Nc mean (SD) 12 ? 14 (20) 41 ? 27 (55) 17 ? 9 (22) 81 ? 92 (149) 22 ? 5 (20) 28 ? 10 (53)
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Cupressus lusitanica
Wind pollinated Hermaphrodite, self
compatible 100,000 seed produced per tree
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Calliandra calothyrsus
Bat/moth pollinated Hermaphrodite and male
flowers, Mainly outcrossing 1,000 seed produced
per tree
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Dovyalis caffra
Bird?/insect pollinated Dioecious 270-470 seed
produced per tree
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Sclerocarya birrea male tree being cut as not
producing fruits
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Grevillea robusta

• Self incompatible with protandry
• Fruit set cross-pollination (5.9-17.5)
  gtopen-pollination on farms (0.1-3.3)
• Open-pollinated flower stigmas most no pollen
  or only self-pollen
• Lack of cross-pollen may limit seed production

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Senna siamea

• Insect pollinated
• Hermaphrodite
• Selfcompatible?
• High seed production per tree

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Procurement pathways NGOs compared with CBOs
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Distribution pathways
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Think about and discuss

• Where are bottlenecks to genetic diversity? How
  to overcome these?
• In 5 main species, how does seed production per
  tree influence number of trees seed collected
  from? How species biology affects genetic
  diversity in seed collections?
• How can mixing seed ensure use and maintenance of
  existing genetic diversity? mean Ns/Nc vs mean
  Ns/Nm.
• Advice/training to improve situation? Figs 2-4
  to NGOs and/or directly to communities? What
  specific advice/training?
• How does seed collection and plant production
  occur?
• Are seeds and plants transferred and if so how?
  Does this provide limitations or opportunities?

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Plan objective ensure maintenance of genetic
diversity in the collection supply of seed,
improved nursery practice

• Plan should identify
• influences on genetic diversity(bottlenecks,
  selection, genetic drift) associated with current
  seed collection and distribution paths
• key actors (individuals, institutions), processes
  (what actors do), social limits in seed supply
  chain (policy, trade, institutional, capacity).
  Communication/training needs related to key
  actors.
• Specific actions to improve situation, addressing
  diversity issues in seed system (e.g. practical
  ways to collect distribute seed/seedlings to
  ensure genetic diversity in nurseries material
  planted in field)