Effects of Genetic Factors on Selected Ambrosia Species

1
Effects of Genetic Factors on Selected Ambrosia
Species

• Ana Karim
• Dept. Horticulture and Crop Science

2
Introduction

• The position and fate of each individual in
  a plant population is the result of its genotype,
  its response to the physical environment and its
  competitive interaction with neighbors.
• Fatih and Bazzaz, 1979

3
Intrapopulation gender variation in common
ragweed (Ambrosia artemisiifolia L.)

• When gender variation has been found, researchers
  hypothesized that certain environmental cues are
  the proximate causes.
• Several studies have shown that low moisture has
  induced a change in sex expression, always from
  female to male.
• Insect attack has also influenced sex expression
  Pinyon pines usually monoecious-- following
  chronic herbivore attack, trees did not produce
  female cones and were therefore, functionally
  male.
• McKone and Tonkyn, 1986
• Univ. of Minnesota
• McKone and Tonkyn, 1986
• Univ. of Minnesota

4
Intrapopulation Gender Variation in Common ragweed

• Common ragweed is an annual, wind-pollinated
  species that is native to North America. It is
  common throughout the temperate regions of the
  world.
• Male flowers produced in terminal racemes
• Female flowers produced in axils of bracts
• Ragweed is self-fertile

5
Intrapopulation Variation Experiment

• Field-grown plants were collected from old-field
  abandonment strips(100x20m).
• Plants were oven-dried, shoots were weighed and
  heads counted and sorted by sex for each plant.
• There was considerable variation in seed
  production, weight and male heads.
• Sex of individual plants measured by Lloyds
  (1980) concept of standardized phenotypic
• gender (proportion of and individuals total
  fitness). gender mi/M
• (mi/M (fi/F)
  

6
Results of Intrapopulation Study

• Taller plants were predominantly male.
• In the field, gender was not randomly distributed
  in successional plots.
• Plants were more female in 4-year plots on east
  transect than on east side of 1-year transect.
• Spittlebug treatment used in greenhouse study.
  Gender was related to shoot wt.
• and height. Larger plants were male.

7
Results of Intrapopulation Study
8
Polymorphism Patterns in Ambrosia maritima, A.
artemisiifolia, and A. trifida

• A. maritima an aromatic plant, native to
  southern Europe, Asia minor and Africa.
• Grows in coastal areas, near rivers, canals and
  rice fields.
• Medicinal interest molluscicide from secondary
  root compounds called lactones and
  sesquiterpenes.
• Plant compound also used to treat
  schissomiasis Van De Vijver and Symoens,1989
• Vrije University, Brussels

9
Polymorphism Patterns

• A. artemisiifolia and A. maritima similar
• introduced into Western and Southern Europe
  from North America.
• Protein variation in 21 seed collections of
  three ambrosia species was investigated.
• using isozymes as species level markers
  between the related A. maritima and A.
  artemisiifolia and to assess geographic
  distribution of genetic variation.

10
Origin of seeds obtained for study
Van De Vijver and Symoens, 1989
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Achenes of three ambrosia species
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Allelic Variation
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Polymorphic Variation Results

• Correct identification of species based on ADH
  and 6PGD electrophoretic patterns of seeds is
  possible.
• 25 of the seed collections used in this study
  were incorrectly identified mophologically as A.
  maritima when in reality they A. artemisiifolia,
  introduced weed.

14
Polymorphic Variation Conclusions

• The diversity of morphological characters in the
  leaves, flowers and fruits of A. Maritima reveals
  several population groups on the African
  continent.
• Within a given area (River Nile basin) both inter
  and intrapopulation variation exists.
• Best technique for preservation of germplasm in
  wild plants is genetic conservation (seed
  storage), tissue cultures, cultivation in gardens
  and protection of in situ populations in natural
  habitiats.

15
Effects of Regional Origin and Genotype on
Intraspecific Root Communication in the Desert
Shrub Ambrosia dumosa

• Earlier experiments with A. dumosa has shown that
  the roots of this species has a self/non-self
  recognition capability.
• Laboratory experiments suggested that roots of
  this specie inhibited elongation of roots on
  other Ambrosia plants only, and only after actual
  contact.
• Roots on the same plant did not inhibit each
  other following contact.

Mahall and Callaway, 1996 Univ. of Calif., Santa
Barbara
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Regional Origin and Genotype

• There was an absence of competitive interaction
  among clumped Ambrosia shrubs growin in the
  Mojave Desert.
• This study has as its objective exploration of
  the geographic/genotypic dimensions of the self
  non/self recognition capability of A.
• dumosa roots by comparing the effects of
  encounters between plants collected from Desert
  Center, Calif and Yuma, Ariz.

17
Regional Origin and Genotype Results

• Genetic identity of two interacting plants pose
  an exemption to contact inhibition.
• Genetically identical roots on separate plants
  did inhibit each contact.
• This recognition mechanism may allow individuals
  to avoid direct resource competition and
  partition below ground resources efficiently.

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Rates of elongation of test roots
19
Seedlings of Yuma vs. Desert Center
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Rates of elongation of clones of Ambrosia plants
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Questions ?