Weed biology

Weed biology

Gyombiológiai és gyomszabályozási ismeretek modul

• The aim of the subject to train modern weed control knowledge based on biological background.

• Students must know:

– Biological qualities of important weeds, – Ecological claims of important weeds

• We consider stressed educational task forming of integrated approach in weed control.

Main topics

• Definition, classification and adaptation of weeds

• Plant life forms

• Weed survey methods

• Reproduction biology of annual weeds

• Reproduction biology of perennial weeds

• Competition

• Allelopathy

• Herbicide resistance of weeds

Main topics

• Weeds are the greatest biological challenge to agricultural production, whether conventional or organic!

• What makes a plant a weed?

– Cost of weeds

– Why do weeds always win? Biology!

• Get to know the enemy – Anatomy of a weed

• Strategies for weed management

Definition of weed

Definition of weed

• Blatchley 1912: „A plant out of the place or growing where it is not wanted.”

• Robbins et al. 1942: „These obnoxious plants are known as weeds.”

• The European Weed Research Society 1986: „ Any plant or vegetation, excluding fungi, interfering with the objectives or requirements of people.”

• „Weed is a plant or plant parts (stolon, rhizome, tuber, bulb etc.) in any growing stage, which is growing where it is not desired.”

Hunyadi (1974)

Definition of weed

• The most important families in the world :

– Graminaceae

– Compositae} ~ 40%

– Cyperaceae – Polygonaceae – Amarantaceae

– Cruciferae – Fabaceae

– Convolvulaceae – Euphorbiacea – Chenopodiacea

There are about 200.200 plant species in the World, and approximately 6700 species of weeds.

76 species belong to most dangerous weed species of the World, but only 18 have prominent importance.

Importance of weeds

The most important weed familyes of the World Family Number of species

1. Gramineae 44

38%

65%

2. Compositae 32

3. Cyperaceae 12

4. Polygonaceae 8

5. Amaranthaceae 7

6. Cruciferae 7

7. Fabaceae 6

8. Convolvulaceae 5

65%

9. Euphorbiaceae 5

10. Chenopodiaceae 4

Importance of weeds

The most importhant weed familyes of Hungary

Family Number of species

1. Compositae 29

27%

73%

2. Gramineae 24

3. Cruciferae 18

4. Caryophyllaceae 16

5. Fabaceae 13

6. Labiatae 12

7. Chenopodiaceae 11

8. Scrophulariaceae 11

73%

9. Polygonaceae 8

10. Amaranthaceae 4

Importance of weeds

The worst world weeds

Common name Latin name 1. Purple nutsedge Cyperus rotundus 2. Bermuda grass Cynodon dactylon 3. Cockspur grass Echinochloa crus-galli 4. Swampgrass Echinochloa colonum 5. Wiregrass Eleusine indica

6. Johnson grass Sorghum halepense 7. Red baron Imperata cylindrica 8. Waterhyacinth Eichornia crassipes 9. Purslane Portulaca oleraceae

10. Fat-hen Chenopodium album

11. Hairy fingergrass Digitaria sanguinalis 12. Field bindweed Convolvulus arvensis 13. Spring wild-oat Avena fatua

14. Pigweed Amaranthus chlorostachys 15. Spiny amaranth Amaranthus spinosus 16. Yellow nutsedge Cyperus esculentus 17. Hilograss Paspalum conjugatum 18. Itchgrass Rottboellia exaltata

The worst weeds in Hungary

Common name Latin name

1. Cockspur grass Echinochloa crus-galli 2. Field bindweed Convolvulus arvensis

3. Fat-hen Chenopodium album

4. Yellow bristle-grass Setaria glauca

5. Redroot Pigweed Amaranthus retroflexus 6. Creeping thistle Cirsium arvense

7. Black bindweed Bilderdykia convolvulus 8. Common ragweed Ambrosia elatior

9. Field woundwort Stachys annua 10. European dewberry Rubus caesius 11. Common couch-grass Elymus repens 12. Flower of-an-hour Hibiscus trionum

13. Cornflower Centaurea cyanus

14. Green bristle-grass Setaria viridis 15. Field horsetail Equisetum arvense

16. Pigweed Amaranthus chlorostachys

17. Pale persicaria Polygonum lapathifolium

1. Origin of weeds:

- Native

- Adventives

2. Habitats of weeds:

- Weeds adapted to breeding, – Living around the people , – Weeds of crop production^.

Classification of weeds

• Taking of the site

• Exhaustion of water store of the soil

• Exhaustion of nutrient store of the soil

• Decrease of soil temperature

• Suppression of crop plants

• Parasitic weeds

Harmful aspects of weeds (Ujvárosi, 1973)

• Weeds can harbour diseases and pathogenic fungi

• Weeds can propagate pests

• Weeds increase of benefits

• Weeds destroy quality of crop

• Poisonous weeds

• Quarantine and dangerous weeds

Yield losses approach 20% caused by weeds internationally

Harmful aspects of weeds (Ujvárosi, 1973)

Big photosynthetic productivity.

• The most important 10 weeds of the World have C₄ type photosynthesis. It means, that at first step of photosynthesis origins an organic molecule with 4 C atom (PEP).

• Opposite to C₃ type plants, which make 3-phospho- glicerine acid in first step.

Adaptation of weeds

1. Ggrowth and competition

1. Growth and competition

• C₄ plants surpass the C₃ because of:

• big net photosynthesis

• effective water utilization (transpiration coefficient 250-350 g water /dry matter g opposite to C₃ 450-950 g water /dry matter g

• Quick assimilate translocation

• Quick growing up to generative phase.

Adaptation of weeds

Important C₄ weeds:

• Amaranthus retroflexus

• Echinochloa crus-galli

• Setaria spp.(foxtail)

• Digitaria spp.

• Panicum spp.

• Cynodon dactylon

• Portulaca oleracea

• Cenchrus pauciflorus

Adaptation of weeds

1. Ggrowth and competition

1. Ggrowth and competition

-Weeds have rapid seedlings growth and the ability to reproduce when young. (E.g. redroot pigweed can flower and produce seed when less than 8 inches (3.2 cm) tall. Few crops can do this.

- Weeds have quick maturation or only a short time in the vegetative stage. Canada thistle can produce mature seed 2 weeks after flowering.

- Weeds may have dual modes of reproduction. Most weeds are

angiosperms and reproduce by seed. Many also reproduce vegetatively.

Adaptation of weeds

Adaptation of weeds

1. Ggrowth and

competition

Competition for:

-Nutrients -Light

-Water

Results in lower yields and poor crop quality

Adaptation of weeds

2. Reproduction properties

- Weeds have environmental plasticity. Many weeds are capable of tolerating and growing under a wide range of climatic and edaphic conditions.

-Weeds are often self-compatible, but self pollination is not obligatory.

- If a weed is cross-pollinated, this is accomplished by no specialized flower visitors or by wind.

-

2. Reproduction properties

- Weeds resist detrimental environmental factors. Most crop seeds rot, if they do not germinate shortly after planting.

Weed seeds resist decay for long periods in soli and remain dormant.

- Weed seeds exhibit several kinds of dormancy or dispersal in time, to escape the rigors of the environment, and germinate than conditions are most favorable for survival. Many weeds have no special environmental requirements for germination.

- Weeds often produce seed the same size and shape as crop seed, making physical separation difficult and facilitating spread by man. (e.g. alfalfa and Cuscuta spp.)

Adaptation of weeds

2. Reproduction properties

- Some annual weeds produce more than one seed crop per year, and seed is produced for as long as growing conditions permit.

-Each generation is capable of producing large numbers of seeds per plant, and some seed is produced over a wide range of environmental conditions.

-

Adaptation of weeds

2. Reproduction properties

Roots of some weeds are able to penetrate and emerge from deep in soil. While most roots are in the upper foot of soil (e.g. canada tistle roots routinely

penetrate 3 to 6 feet and field bindweed roots have been recorded over 10 feet deep. Roots and rhizomes are capable of growing many feet per year.

- Roots and other vegetative organs of perennials are vigorous, with large food reserves, enabling them withstand environmental stress and intensive

cultivation.

Adaptation of weeds

2. Reproduction properties Build up of soil seed bank

• Seed bank can increase rapidly in one season with fertilization and irrigation and ineffective control

• One weed plant can produce thousands of seeds

• Affected by management

Adaptation of the weeds

3. Allelopathic effect on crop plant

• Black walnut and tomatoes

• Lamb’s quarters roots secret oxalic acid

• Velvetleaf, quackgrass, Canada thistle, giant foxtail, black mustard and yellow nutsedge

• Mechanism: root secretion, decomposition of residues, effects microbial symbionts

Adaptation of weeds

4. Weeds can harbour diseases and pathogenic fungi, esp. crop relatives

• Classic case of wheat rust disease on wheat with alternative host European barberry

• 1970-1990 caused $100 million annually

• Barberry eradication project saved farmers $30 million per year

Adaptation of weeds

5. Can be directly parasitic

• Dodder (Cuscuta spp.) Convolulaceae (Morningglory) Family

• Major problem in West US with alfalfa, clover, potatoes, sunflower

• First germinates root then when finds host becomes parasite

Adaptation of weeds

5. Can be directly parasitic

• Striga is serious problem of corn and sorghum in Africa

• Striga, commonly known as witchweed, is a genus of 28 species of parasitic plants that occur naturally in parts of Africa, Asia, and Australia.

The genus is classified in the family Orobanchaceae although

older classifications place it in the Scropulariaceae.

Adaptation of weeds

Indicate soil characteristics and suitability for crops

6. Indicate soil characteristics and suitability for crops:

• Creeping buttercup, Ranunculus repens, Ranunculaceae Fam.

• Introduced from Europe as ornamental

• Reproduces from seed or rhizomes

• Toxic to cattle

• Could indicate moist soil conditions

Adaptation of weeds

• Enhance soil structure and water penetration

• Improve soil tilts

• Capture nutrients that would otherwise be lost

• Provide habitat for beneficial insects

• Save the soil from erosion and deflation

Benefits of weeds

• The most widely applied life-form scheme is the Raunkiær system.

• Raunkiær plantlife-form: Danish Botanical Society in 1904 - The subdivisions are based on the location of the plant's growth-point (bud) during seasons

Plant life-forms

1. Phanerophytes; 2-3. Chamaephytes; 4. Hemicryptophytes; 5-9. Cryptophytes: 5-6. Geophytes; 7.Helophytes; 8-9.HydrophytesTherophites, Epiphytes

Plant life forms by Raunkiaer

• 1. Woody plants (Phanerophyta) Ph

• 2. Dwarf shrub (Chamaephyta) Ch.

• 3. Partly hidden wintering (Hemicriptophyta) H.

• 4. Hidden wintering (Kriptophyta) K.

– Wintering in soil (Geophyta) G.

– Wintering in water or marsh (Hydatophelophyta) HH.

5. Annual (Therophyta) Th.

Plant life-forms

• Korsmo, E. (1930): Unkrauter im Ackerbau der Neuzeit

• Balázs-Ujvárosi:

• I. THEROPHYTA, T – living for less than13 months annual

• II. HEMITHEROPHYTA, HT – living for two years biennial

• III. HEMIKRYPTOPHYTA, H – overwintering in the ground level

• IV. GEOPHYTA, G – overwintering under the ground

Plant life-forms of weeds

perennial

Weed classification by Ujvárosi (1973)

I. One time blossoming:

- annuals:

T₁ germination in autumn, seed ripening in spring

T₂ germination in autumn, seed

ripening at the beginning of summer T₃ germination in spring, seed ripening at the

beginning of summer

T₄ germination in spring, seed ripening at the end of summer

- biannuals:HT wintering with seed or rosette

II. More times blossoming:

perennials:

- wintering with aboveground and underground shoots (Ph, Ch)

- in winter the aboveground shoots are died (H, G)

Weed classification by Ujvárosi (1973)

Weeds are classified into three categories based on their life history:

Annuals complete their life cycle within one year and reproduce from seed.

Winter annuals germinate in the fall and complete their reproductive cycle in the spring or early summer.

Summer annuals germinate in the spring and set seed in late summer or fall. Summer annuals thrive when summer annual crops like corn or soybeans are

grown.

Weed classification by life cycle

• Biennials live during two growing seasons. The first year consists of vegetative growth, while the second year involves both vegetative and reproductive

growth. Biennials also reproduce from seed. Because these weeds require two years to complete their life cycles, they are found in areas of low soil disturbance such as waterways, pastures, alfalfa, and fence rows.

Weed classification by life cycle

• Perennial plants live for more than two years.

Reproduction can occur by seed production or

vegetatively by structures such as rhizomes, tubers, bulbs, or budding roots. Although perennial weeds are most prevalent in areas of reduced soil

disturbance, some are well adapted to row crops.

Managing perennial weeds is generally more difficult because of their multiple reproductive systems.

Weed classification by life cycle

Life cycle of an annual weed

Winter annual (T-1,2)

Summer annual (T-3,4)

Biannual (HT)

H life form:

• Overwintering organs stand vertically in the soil layer

• H₁: plants with fibrous root-system

• H₂ sarmentose plants

• H₃: these plant’s roots are able to reproduce

• H₄: tap-root unable to reproduce

• H₅: sloped root-stock

Perennials

Perennials (H) Plalife-forms

Overwintering organ:

Short vertical stem on the ground Short as lope stem below ground

Fibrous root-system Taproot

H1 Caltha palustris Ranunculus acer

Runners

H2 Poa trivialis

Ranunculus repens Potentilla sp.

Glechoma hederacea

Reproduction organ Not reproduction organ

H3

Symphytum officinale Taraxacum officinale Rumex obtusifolius

H4 Ononis spinosa Eryngium campestre

H5 Plantago major Artemisia vulgaris Ballota nigra

Perennials (H)

HEMIKRYPTOPHYTA, H₁

Caltha palustris

Perennials (H)

HEMIKRYPTOPHYTA, H₂

Ranunculus repens

Potentilla reptans

Glechoma hederacea

Perennials (H)

HEMIKRYPTOPHYTA, H₃

Symphytum officinale

Rumex obstusifolius Taraxacum officinale

Perennials (H)

HEMIKRYPTOPHYTA, H₄

Eryngium campestre Ononis spinosa

Perennials (H)

HEMIKRYPTOPHYTA, H₅

Artemisia vulgaris

Plantago major

G life form:

• Overwintering and reproductive organs are in the soil

• G₁ : Modified underground shoots → stolon or rhizome

• G₂: modified stem to storage, tuber

• G₃: propagating roots

• G₄: bulb or tuber-bulb

Perennials

Perennial (H, G)

Perennials (G)

GEOPHYTA, G

Overwintering organ:

Long horizontal stem below ground Short vertical stem below ground

Stolons and rhizomes Tubers

G1 Stolons:

Elymus repens Cynodon dactylon Calistegia sepium Rhisomes:

Sorgum halepense Phragmites australis

G2 Mentha arvensis Mentha aquatica Stachys palustris

Creeping roots Bulbs

G3 Cirsium arvense Convolvulus arvensis Asclepias syriaca

G4

Colchicum autumnale Ornitogallum umbellatum Poa bulbosa

Perennials (G)

GEOPHYTA, G₁ with stolons

Elymus repens

Cynodon dactylon

Perennials (G)

Plant life-forms

Sorgum halepense

Phragmites australis

Perennials (G)

GEOPHYTA, G₂ with tubers

Mentha arvensis

Stachys palustris

Perennials (G)

GEOPHYTA, G₃ with creeping roots

Cirsium arvense

Convolvulus arvensis

Asclepias syriaca

Perennials (G)

GEOPHYTA, G₄ with bulbs

Colchicum autumnale Poa bulbosa

Weed survey methods in Hungary

• Measuring method: the plants are cutting from a concrete area and measured by species. It is called for phytomass method, but it is correct when the whole plants are measured together with roots.

• Plant counting: plants are counted by species from a concrete area.

Exact method's

• Braun - Blanquet

• Hult - Sernander

• Balázs – Ujvárosi

• Photography from earth or air

Estimating methods

Resultant of dominance values don’t make a straight line (mathematically not correct).

• Scale values:

1 value = less than 1/20 abundance, 2 value = 1/20 - ¼ abundance,

3 value = 1/4 - 1/2 abundance, 4 value = 1/2 - 3/4 abundance, 5 value = 3/4 - 4/4 abundance.

Braun – Blanquet-scale

• Values of the scale:

1 value = less than 1/16 abundance, 2 value = 1/16 - 1/8 abundance,

3 value = 1/8 - 1/4 abundance, 4 value = 1/4 – 1/2 abundance,

5 value = more than 1/2 abundance.

Hult – Sernander-scale

• The method easy to study and simply to make survey, but needs practice

• We estimate the abundance of different weed species, and finally summed abundance of sampling area

• Mathematically correct and data's are computerized

• Accepted sampling area is 2x2 m²

• Advantage of this method that we can check the data's on the spot

• Values can directly convert to abundance percent.

Balázs – Ujvárosi –weed survey method

Values of the Balázs-Ujvárosi-scale

Values Density % Values Density % Values density %

6 100.00% of survey area 3-4-4 21.87% of survey area 1-2 4.68% of survey area 5-6-6 87.50% of survey area 3-4 18.75% of survey area 1-1-2 3.90% of survey area 5-6 75.00% of survey area 3-3-4 15.62% of survey area 1 3.12% of survey area 5-5-6 62.50% of survey area 3 12.50% of survey area +-1-1 2.49% of survey area 5 50.00% of survey area 2-3-3 10.93% of survey area +-1 1.87% of survey area 4-5-5 43.75% of survey area 2-3 9.37% of survey area +-+-1 1.24% of survey area 4-5 37.50% of survey area 2-2-3 7.81% of survey area + 0.62% of survey area 4-4-5 31.25% of survey area 2 6.25% of survey area 0-+ 0.36% of survey area 4 25.00% of survey area 1-2-2 5.46% of survey area 0 0.10% of survey area

Balázs – Ujvárosi – weed survey method

The weed surveying frame

Early-season weed scouting

• The first key to weed management is proper weed identification. The best method for timely

identification is through field scouting.

• The first reports on weed conditions in a field are needed within two weeks after crop emergence to evaluate herbicide performance and to determine if there is a need for rotary hoeing, cultivation, or post emergence herbicides.

• Earlier scouting will be needed in no-till fields where a knockdown or early preplant herbicide may be

applied.

Weed survey methods

• Identify and record all weed species found.

Determine the severity of the infestation by counting the number of weeds.

• Sample areas get an accurate count of the different weeds present in the field or on the farm.

• Along with weed reports, early soil moisture

observations are important. They serve as indicators of herbicide effectiveness. Adequate moisture is

necessary for effective weed control with all soil- applied herbicides.

Weed survey methods

• Post-emergence herbicides usually are most effective when weeds are young and actively growing.

• The degree of control with these herbicides will vary due to differences in weed species, growth stages, weather conditions, and herbicide application

method.

• To select the best possible herbicide and apply it at the optimum time to maximize control, the manager needs to be able to identify weed seedlings when

they are small.

Weed survey methods

Economic threshold for weeds

• An economic threshold for weeds is the density of a weed population at which control is economically

justified because of the potential for yield reduction, quality loss, harvesting difficulties, or other problems that weeds may cause.

• Broadleaf and grass weeds will compete at different levels of intensity depending upon the

competitiveness of the crop, the tillage system,

environmental conditions, and other weeds present.

• In general, broadleaf weeds are more damaging to a broadleaf crop, while grass weeds are more

competitive in a grass crop.

Weed survey methods

Reproduction biology of weeds

Reproduction Biology of annual weeds

(By: Magyar L., Kazinczi G. 2002 Kazinczi G., Magyar L. 2003)

Reproduction Biology of annual weeds 1. Definition of annual weeds

(Latin: annus, "year")

• Annual weeds are plants that complete their life cycle [from seed to seed] within one growing season, or in less than 12 months

• survive the unfavourable season in the form of seeds

• according the life-form scheme - annual species are Therophytes [Th]

Reproduction Biology of annual weeds

Annual weed species [

] can be classified by their life cycle as follows:

1. Winter annual species emerge in late summer or fall, survive winter, and produce seed during late spring or early summer of the following year

2. Summer annual species emerge in spring or early summer and produce seeds during the same growing season

Reproduction Biology of annual weeds

2. Definition and roles of seeds

• SEED:

- fertilized, mature (ripened) ovule having an embryonic plant

- it stores food material (endosperm or perisperm), and a protective coat (testa) or coats

• Roles of seeds:

1. vehicle for species multiplication 2. dispersal role

3. protection during conditions unfavourable for

germination and development (dormancy; seed bank)

4. temporary source of food for the embryo

5. source for transfer of a new genetic combinations

(diversity)

Reproduction Biology of annual weeds

A typical seed includes three basic parts: (I.) an embryo, (II.) a supply of nutrients for the embryo, and (III.) a seed coat

- The embryo is an immature plant from which a new plant will grow under

proper conditions. The embryo has one cotyledon or seed leaf in monocotyledons, two cotyledons in almost all dicotyledons

- The radicle is the embryonic root

Structure of a seed

Reproduction Biology of annual weeds 3. Seed production of weeds

 extremely fluctuates (e.g Papaver rhoeas: 4-400 capsule/plant)

 can be significantly different between and within species

Seed production of weeds depends on:

• genotype

• environmental factors and their interactions

• time of germination

• intra- and interspecific competition

• pests, hosts, herbicides

• under stress situation the life cycle can shorten

Reproduction Biology of annual weeds

Examples of seed production by common weed species

(Stevens 1932, 1957 )

Scientific Name Number of Seeds

(per plant)

Amaranthus retroflexus 117 400

Chenopodium album 72 450

Portulaca oleracea 52 300 Capsella-bursa pastoris 38 500 Echinochloa crus-galli 7 160 Abuthilon theophrasti 4 300 Ambrosia artemisiifolia 3 380

Sinapis arvensis 1 700

Stellaria media 600

Reproduction Biology of annual weeds 4. Dispersal of weed seeds

- Seed dispersal is the movement or transport of seeds away from the parent plant - Most seed are good travellers, use various forces and agents to transport and

scatter themselves from place to place

What are the purposes of dispersal?

• To reduce competition between the parent plant and the seeds

• To avoid predators and pathogens

• To provide gene flow

• To maintain biodiversity

• It may allow plants to colonize new habitats and geographic regions

Reproduction Biology of annual weeds

Methods and types of seed dispersal

1. Natural: 2. Artificial:

Gravity Machinery

Ballistic (Self-dispersal) Crop seed

Water Livestock

Animal Wind

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Reproduction Biology of annual weeds

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Examples of natural seed dispersal

• Gravity - Most seed of our common crop field weed species have no specialized structures and mechanism

• Water - Seed can be dispersed by water in different ways (float, flooding, movement with surface water - irrigation, rivers, lakes)

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Reproduction Biology of annual weeds

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Examples of natural seed dispersal

• Ballistic (self-dispersal) - the physical and often explosive discharge of seeds from the fruit

• Wind - wings or plumes (pappus) that slow rate of fall

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Examples of natural seed dispersal

• Animals:

A seed eaten by an animal can experience different fates. It can be eaten and dispersed as a viable seed, or be eaten and destroyed by digestion

a./ External way - on the body of animals (barbs, hooks, hairs)

b./ Internal way - via ingestion by animals (birds, mammals)

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Examples of artificial seed dispersal

- Human activities, most important transport mechanism is modern agriculture

- Contaminated crop seed historically has been one of the most important dispersial agents for weed seeds

• Machinery - on equipment

• Crop seeds

• Livestock - feed, hay, straw and manure

• Moving soil for construction and landscaping

Reproduction Biology of annual weeds

How far can weed seeds travel?

(Mohler, 2001)

Agricultural weed seeds can travel over range of distances, depending on the method of transport and the weed species

Reproduction Biology of annual weeds

5. Seed Dormancy

• Dispersal phase usually dormant; dehydrated seeds weight less

(esp. wind dispersal) and are metabolically slower

• Definitions:

Reproduction Biology of annual weeds

• Definitions:

Dormancy can be called as "dispersal in time"

Reproduction Biology of annual weeds

• Significance:

Reproduction Biology of annual weeds

Definitios and terms associated with seed dormancy:

Reproduction Biology of annual weeds

Reproduction Biology of annual weeds The dormancy continuum

•Dormancy is not a simple off-on switch

Reproduction Biology of annual weeds The dormancy continuum

• Level of dormancy changes over time:

- seeds of summer annuals:

are dormant at maturity, and dormancy is released in spring due to low temperatures during winter, whereas high temperatures during summer induce secondary dormancy.

- winter annual species: require higher summer temperatures to release dormancy for germination in autumn

Reproduction Biology of annual weeds

Seasonality of emergence in weed species

• Due to dormancy cycling most weed species germinate at particular times of year

• In general, two-peak emergence differing according to species can be observed

Reproduction Biology of annual weeds Classification of Seed Dormancy

(Baskin - Baskin, 2004)

1. Physiological dormancy 2. Morphological dormancy

3. Morphophysiological dormancy 4. Physical dormancy

5. Combinational dormancy

Reproduction Biology of annual weeds

1. Physiological dormancy

• CAUSE – physiological inhibiting mechanism of germination of embryo prevents germination until a chemical change (hormones, phytocrome,

growth inhibitors) takes place in the seed - divided into 3 levels - (D, I, DN)

• METHOD TO OVERCOME THIS FORM OF DORMANCY – cold (0-10 C^o) and warm (>15 C^o) stratification

• EXAMPLE – most arable weed species belong to this form of dormancy (AMARE, CAPBP, ECHCG)

Reproduction Biology of annual weeds

2. Morphological dormancy

• CAUSE - the seed is immature (underdeveloped) when shed, and a period of growth and/or differentiation is required before germination can take place

• METHOD TO OVERCOME THIS FORM OF DORMANCY – provides favourable conditions for embryo growth and germination

• EXAMPLE – Conium maculatum (CONMA)

Reproduction Biology of annual weeds

3. Morphophysiological dormancy

• CAUSE – Seeds have embryos that are underdeveloped and differentiated as well as a physiologocal component to their dormancy

• METHOD TO OVERCOME THIS FORM OF DORMANCY – these seeds

require time for embryo growth and a dormancy breaking treatment (cold or warm stratification)

• EXAMPLE – some species from the families of Apiaceae, Ranunculaceae, Papaveraceae (PAPRH)

Reproduction Biology of annual weeds

4. Physical dormancy

• CAUSE - The seed have impermeable testas or pericarps, the embryo is therefore dry until the seed coat is broken and water enters

- seed coat may be impermeable to water, oxygen and mechanically resistant

• METHOD TO OVERCOME THIS OF FORM DORMANCY – chemical or physical scarification (abrasion)

• EXAMPLE – commonly in „hard seeds” species from the families Fabaceae, Malvaceae, Chenopodiaceae and Liliaceae

(CONAR, HIBTR, ABUTH)

Reproduction Biology of annual weeds

5. Combinational dormancy

• CAUSE - multiple mechanism, seed have simultaneously physiological (non-deep) and physical dormancy

• METHOD TO OVERCOME THIS OF FORM DORMANCY – a cold or warm stratification treatment of seeds after scarification to permit imbibition

• EXAMPLE – Trifolium repens (TRIRE)

Reproduction Biology of annual weeds Regulation of seed dormancy

• Genotype + Environment = Seed Dormancy

(embryo and mother plant) (macro- and micro-)

Reproduction Biology of annual weeds Regulation of seed dormancy I. Physiological regulation:

II. Role of environmental factors:

- Temperature (diurnal and seasonal fluctuation)

- Light (quality, photoperiod)

- Water availability (moisture)

- Gases (O₂, CO₂)

- Mineral nutrition (nitrate, NO₃)

- Time of ripening and seed position

Reproduction Biology of annual weeds

Relationship between dormancy and phytohormones

• Abscisic acid (ABA)  induces and maintains seed dormancy, inhibits seed germination

• Gibberellins (GA)  promote seed germination

• Cytokinins, Auxins  implicated in promoting seed germination

Physiological dormancy is controlled by the ABA : GA ratio

Reproduction Biology of annual weeds

Photoregulation of seed dormancy

The seeds can detect: - absence or presence

- quality (wavelength composition) - intensity

- duration of light

• Positive, negative photoblastic and light insensitive species Photoreceptor in seeds = PHYTOCHROME SYSTEM

- 5 different Phy (A-E) types of different physiological function

Reproduction Biology of annual weeds

Action mode of Phytochrome

The phytochrome system is the photoreceptor of red light responses

P_R - physiologically „inactive” form - it absorbs red (R; 670 nm) light;

P_FR- physiologically „active” form - it absorbs far red (FR; 730 nm) light

Reproduction Biology of annual weeds

What is a weed seed bank?

Mature seeds are shed from the parent plant and find themselves on the soil surface

• The term „seed bank” is used to describe the reservoir of viable seeds present on the

surface and in the soil

• It consists of numerous seeds many of which are dormant and delay germination until a latter time

• The size of a seed bank in agricultural land varies enormously (between sites, fields and plots) from near zero to as much as 1 million seeds per m²

• It includes

– New seeds recently shed by plants

– Older seeds that have persisted in the soil

Reproduction Biology of annual weeds

Importance of weed seed banks

• It is an indicator of past and future weed problems

• It is the primary source of new infestations of weeds each year

• It gives help to

- learn the dynamics of weed population - predict plant invasion

- plan the methods and strategies of weed management

• Only 1-9 % of the viable seeds produced in a given year develop into seedlings, the rest remain viable and will germinate in subsequent years depending on the depth of their burial

Reproduction Biology of annual weeds

Composition of seed banks

• A few species dominate the seed bank

– They are primary weeds in a cropping system

• Adapted to cropping system

• Resistant to control measures

• Many infrequent species

– Adapted to your area but not to current production practices

– Include

• Newly introduced species

• Species survived previous land uses

Reproduction Biology of annual weeds Types of seed banks

(Thompson and Fenner, 2005)

On the basis of the length of time that seeds survive in the soil a seed bank can be:

• Transient - seeds persist in the soil for less than 1 year

e.g. GALAP, BROMO, CENCY

• Short-term persistent - seeds persist in the soil at least 1 year but less than 5 years

e.g. TAROF, CONCA

• Long-term persistent - seeds persist in the soil more than 5 years

e.g. STEME, CAPBP, CONAR, PAPRH, AMARE _________

• Seed size + morphological feature → The type of a seed bank - small (0,5-1 mm) + flat surfaced seeds = persistent seed bank - large (2-4 mm) + appendage seeds = transient seed bank

Reproduction Biology of annual weeds

What happens to seeds in the soil?

• Active versus dormant (persistent) seed banks

– Active seed bank consists of seeds that are able to germinate

– Dormant seeds make up the persistent seed bank and are able to survive for many years

– Examples:

• Small seeded annual weed seeds without a hard seed coat only persist a couple of years e.g. SET sp., DIGSA

Reproduction Biology of annual weeds

Dynamics of soil seed bank

(inputs to seed bank are shown with black arrows, and losses in white arrows)

Reproduction Biology of annual weeds

Weed seed rain

• Weed seed input (also called seed rain)

• Without seed input the seed bank will rapidly decline

• Local sources of seed predominates

– 95% of seed rain comes from annual weeds growing in field

– Distant sources are important if local seed production is limited

Reproduction Biology of annual weeds

Seed persistence

The longevity of seeds in the soil is highly variable, and depends on species, depth of seed burial, soil type and the level of disturbance

• most long-lived species are annuals

• small seeds tend to have much longer soil lives than large ones

• max. seed viability in the soil e.g. Spergula arvensis: 1600 years (in archaeological digs)

Weed species survival (years)

______________________________________________

Cirsium arvense 21

Chenopodium album 39 Portulaca oleracea 30 Ambrosia artemisiifolia 39 Amaranthus retroflexus 10

Reproduction Biology of annual weeds

Weed seed distribution in the soil

• Majority of seeds in no-till agricultural field is located in the upper 5 cm of soil profile

• In cultivated soils in the upper 15 cm of soil profile

• Cultivation and tillage continuously invert the soil profile

• Bringing up seeds previously buried to the upper soil surface layers more readily germinate

• The type of cultivation is important for distribution (e.g. ploughing buries

seeds below 10 cm)

Reproduction Biology of annual weeds

Tillage effects on weed seed distribution

• Repeated tillage for several years without reinfestation will reduce the weed seed population in soil

• However, if weeds produce many seeds, then it is extremely difficult to completely avoid reinfestation

• Conclusion: allowing weeds to have seeds increases potential problems for many years to come

Reproduction biology of weeds

Reproduction Biology of perennial weeds

• (Latin per, "through", annus, "year")

• A perennial plant or perennial is a plant that lives for more than two years

• Perennials are Herbaceous and Woody perennials (trees and shrubs)

Reproduction Biology of perennial weeds

• Herbaceous perennials grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring from their root- stock rather than seeding themselves as an annual plant does

Perennial weeds

Many invasive weeds are perennials

Perennial weeds

Reproduction of perennials:

• I. Strategies of reproduction

• II. Main asexual forms of reproduction

• III. Factors affecting the regeneration of perennials

Reproduction of perennials

Reproduction of perennials

I. Strategies of reproduction

a) Mainly reproducing by seeds

High seed production and effective seed propagation.

Spreading by seeds but settlement by asexual ways.

Rumex crispus, R. obtusifolius, Ranunculus repens, Mentha arvensis, Achillea millefolium

b) Generative and vegetative forms are equal importance

Tough, hard to kill weeds.

Have to control both the seedling and the daughter plant. Sorghum halepense, Asclepias syriaca, Calystegia sepium

c) Mainly reproducing vegetatively

Weeds of no-or low tillage, or wrong cultivation Stolons can grow 9,9 m a year (ELYRE)

Elymus repens, Cynodon dactylon, Cirsium arvense

Reproduction of perennials

II. Main asexual forms of reproduction

a) Stolons and rhizomes

Reproduction of perennials

II. Main asexual forms of reproduction Stolon

Reproduction of perennials (Elymus repens)

II. Main asexual forms of reproduction Stolon

(Hunyadi et al.1988)

Reproduction of perennials

II. Main asexual forms of reproduction Stolon

Principles of stem growth of common reed (Haslam, 1972)

Reproduction of perennials

II. Main asexual forms of reproduction Rhizomes

Reproduction of perennials

II. Main asexual forms of reproduction Rhizomes

Reproduction of perennials

II. Main asexual forms of reproduction Rhizomes

Reproduction of perennials

II. Main asexual forms of reproduction b) Creeping roots

Root system of Convolvulus arvensis

The reproduction organ never goes above ground

(like rhizomes⁾

Reproduction of perennials

II. Main asexual forms of reproduction b) Creeping roots

Root system of Cirsium arvense

Reproduction of perennials (

Root system of Cirsium arvense

Reproduction of perennials

II. Main asexual forms of reproduction c) Reproducing from taproot

Rootcrown

Axillarybuds leaf

Adventitiousroots

Sideshoot

Lateralroot Taproot

Modified taproot of Rumex obtusifolius

(Hunyadi et al. 1988⁾

Reproduction of perennials

II. Main asexual forms of reproduction c) Reproducing from taproot

Reproduction of perennials

II. Main asexual forms of reproduction

d) Tubers, bulbs, runners

Reproduction of perennials

Tubers and bulbs

Reproduction of perennials

II. Main asexual forms of reproduction

Importance of asexual reproduction:

More nutrients for progeny

Exact reproduction of the parent genotype Small a mount of progeny

No ability to long-distance spread

Reproduction of perennials

III. Factors affecting the regeneration of perennials

1. Periodicity

2. Apical dominance

3. Environmental effects

Reproduction of perennials

III. Factors affecting the regeneration of perennials

1. Periodicity

Periodicity is a seasonal activity of buds on the vegetative organ First observation on Agropyron repens stolons

„Late Spring Dormancy”

(Johnson and Buchholtz, 1957, 1958, 1962,

Confirmed by Hakkanson, 1967; Leakayet al., 1972 and Hunyadi, 1978)

Seasonal activity also descibed on Cynodon dactylon (Hunyadi), Sorghum halepense(Hunyadi) and Phragmites australis (Lukács- Hunyadi)

Reproduction of perennials

III. Factors affecting the regeneration of perennials 1. Periodicity

Seasonal activity of buds on 1-node AGRRE stolon segments

Reproduction of perennials

III. Factors affecting the regeneration of perennials 1. Periodicity

Seasonal activity of budson1-node CYNDA rhizome segments

Reproduction of perennials

III. Factors affecting the regeneration of perennials 1. Periodicity

Seasonal activity of budson1-node PHRAU rhizome segments