Weed Biology, Ecology & Physiology of weed, Weed & Crop Competition, Allelochemicals, their Nature & Impact, Weed-Seed Physiology

1. Presented by
Minakshi R. Neware
Ph.D Agril. Botany (P. Phy.)

2. Biology, Ecology & Physiology, Weed & Crop
Competition, Allelochemicals, their Nature &
Impact, Weed-Seed Physiology
Course No.- PP 607
Credits- 1+1=2
Submitted to
Dr. D. V. Durge
Professor
Department of Agricultural Botany,
Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola

3.  Unwanted plant
 Any unwanted plant that originated under a
natural environment and in response to
imposes, evolved and continue to do
activities. (Aldrich & Kremer 1997)
 Accounts not more than 1% of the total plant
species on the earth.

4.  Reduction in crop yield
 Loss in crop quality
 Weeds as reservoirs of pests and diseases
 Interference in crop handling
 Reduction in land value
 Limitation of crop choice
 Loss of human efficiency

5. Class - Angiospermae ( Flowering plants)
Sub classes – i) Monocotyledonea
ii) Diacoltyledonea
Weed seed germination
Factor affecting : - - Moisture
- Temperature
- Oxygen
- Light
- Chemical inhibiters in soil
- Depth of burial
- Tillage

6. Sr.
No.
Crop Critical Period
1 Rice 10-20 DAE
4-6 weeks after transplanting
12th weeks of crop growth
2 Maize 2-3 weeks of emergence
3 Sugarcane 4-16 weeks after planting
4 Potato 3-4 weeks after planting

7.  Annuals – Trianthema spp., Chinopodium album, Amaranthus viridis
- Propagate by seed/ Spores – Ferns (Rao, 2000)
- Easy to control
- Very persistent
 Biennials – Dacus carrota, Taraxacum spp., Adenanthera echinata
1st yr – Vegetative growth
- Tap root system
- development of food storage organ
2nd yr – Flowering
- Seed production
 Perennials – Johnson grass, Sorghum halepense
- Propagated both seed & vegetative
- Having underground storage organs
- Very aggressive & competitive weed (Walia, 2003)

8. Weed seed Dissemination
Natural
- Wind
- Water
- Animals
- Forceful dehiscence
Artificial
- Tillage equipments
- Farm machinery

9.  Largely influenced by climate, edaphic ( Soil) & abiotic factors
 Affects occurrence, abundance, range & distribution
 Mechanisms - Higher seed production rate
- Asexual propagation
- Rapid dispersal
- Crop weed association
- Continuous use of single herbicide
results in weed resistance

10.  Vegetative plant propaguales
 Prolific seed production
 Ability of vegetative propaguales under adverse
 Seed dissemination & dormancy
 To resist any detrimental effects of the
environment

11.  Rapid expansion of tall, foliar canopy
 Horizontal leaves under overcast condition
 Obliquely slanted leaves under sunny condition
 Large leaves
 C4 photosynthetic pathway
 Low leaf transmissivity of light
 A climbing habit
 Leaves forming mosaic leaf arrangement for best light interception
 High allocation of dry matter to built tall stem
 Rapid extension in response to shading
 Early & fast root penetration of a large soil area
 High root density
 High root- shoot ratio
 High root length/ root weight
 High proportion of actively growing root
 Long & abundant root hair
 High uptake potential

12.  Rudimentary embryo
 Mechanically resistant seed coat
 Impermeable seed coat
 Excessive presence of inhibitors
 Tuft of hair

14. 1. Crop growth and yield is affected
2. Crop suffers from nutritional deficiency
3. Leaf area development is reduced
4. Yield attributes will be lowered
5. Reduce the water use by the crop
6. Affect the dry matter production
7. Lowers the input response
8. Causes yield reduction
9. Pest and disease incidence will be more

15.  Timing of weed emergence
 Growth habit
 Growth rate
 Weed density
 Duration of weed growth
 Characteristics of weed species
 Characteristics of crop species
 Cropping practices
 Climate
 Soil factors

16.  Allelopathy = allelo + pathy (“Mutual harm”/
“Suffering”)
 Allelopathy – Beneficial or harmful effect
 Allelochemicals – Biochemicals releases by
crop or weed.
 Processes – Leaching, root exudation,
volatilization, residue decomposition, other natural and
agricultural processes.

17.  Low molecular weight
 Acetate and amino acids are basic component
 Volatile
 Content- amino acids and derivatives,
polypeptides, purines necleosides, toxic gases
(HCN, NH3) and variety of other chemicals (Rice,
1984).

18. Mode of Action Allelochemicals Assay species Refrences
O2 evolution in
photosynthesis
Sorgoleone Solanum tuberosum Nimbal et al., 1996(a)
Chlorophyll
accumulation
Phenolics
Ferulic, Artemisinin,
pcoumaric Acids
Vigna unguiculata
Lemna minor
Dakshini and
Dakshini, 1992
Stiles et al., 1994
Inhibition of electrons
between Qa and Qb
Sorgoleone Spinacia oleracea Stiles et al., 1994
Depletion plasma
membrane
Dehydrozaluzanin Cucumis sativus Galindo et al., 1999
Perturbation of water
uptake
Juglone Glycine max Hejl and Koster, 2004
HPPD Juglone, Sorgoleone A. thalian,
Arabidopsis thaliana
Meazza et al., 2002
PS II efficiency Parthenolide,
Artemisinin
Algae Yang, 1996

19.  Interfere with cell elongation
 Interfere with photosynthesis
 Interfere with respiration
 Interfere with mineral ion uptake
 Interfere with protein and nucleic acid metabolism

22. a) Plant factors
i. Plant density
ii. Life cycle
iii. Plant age
Eg. - Parthenium, allelopathy occurs during its
rosette & flowering stage.
iv. Plant habit
v. Plant habitat
b) Climatic factors
i. The soil & air temperature
ii. Soil moisture
c) Soil factors: Physico-chemical and biological properties
d) Stress factors: Abiotic and Biotic stresses

23. Allelopathic Plants Impact
Intercropping of black walnut with
corn
Reduced corn yield by production of Juglone
allelochemical from black walnut
Intercropping of Leucaena with
other crops
Reduced yield - wheat & turmeric
Increase - Maize & Rice
Rye, Fescue & Wheat Suppressed weed when use as cover crop
Broccoli Residue interfere in growth of other cruciferous
crops
Sunflower & Buckwheat Reduced weed pressure when use as cover crop
in Fava bean
Tifton burclover Inhibit growth in wheat
Sunnhemp Inhibition of vegetable seed germination
Wild oat Affect germination & early seedling growth in
wheat
Datura Affect germination & growth in sunflower

24.  Root exudation of maize inhibits the growth of Chenopodium album
 The cold water extracts of wheat straw when applied to weeds reduce
germination and growth of Abutilon sp.
 Extract of leaf leachate of decaying leaves of Polygonum contains
flavonoides - Germination, root and hypocotyls growth of weeds like
Amaranthus spinosus
 Inhibitor secreted by decaying rhizomes of Sorghum halepense- Growth
of Digitaria sanguinalis and Amaranthus sp.

25. Weed species Source of toxin Afflicted crop
species
Reference
Abutilon theophrasti Residue, seeds Radish, corn,
soybean, tomato
Gressel and Holm,
1964
Bhowmik and Doll,
1984
Acalypha indica Extract Bajra Murthy and Zakharia,
1980
Ageratum conyzoides Extract, leachate Wheat Sugha1979
Chuihua, Fei, and
volatile Shoushan,
1999
Agropyron repens Extract, residues Bean, soybean,
alfalfa
Weston and Putnam,
1986
Allium vineale -- Oat Osvald, 1950
Alternanthera triandra Root washings Soybean, groundnut,
blackgram
Tiwari et al., 1985
Amaranthus blitoides Extract, residue Barley, wheat Qasem, 1994b,
1995b
Amaranthus dubius Extract, leachate, Beans, corn, sorghum Altieri and Doll, 1978
Amaranthus palmeri Extract, residue, Cabbage, carrot,
onion, sorghum
Bradow and Connick,
1987; Menges, 1988
Amaranthus spinosus Living plant Coffee Vander Veen, 1935

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