Mool Chand Singh
Inspection and identification of weeds
In order to prevent the introduction of serious exotic weeds or of biotypes of existing weeds with their material, all imported plant/plant materials are subjected to critical examinations and only healthy material is released. Samples are examined for weed seeds by sieving through sieves of different pore sizes. Then they are critically and thoroughly examined using available standard methods such as-
Visual examination
Working samples are spread in a thin uniform layer on a clean white drawing sheet or in a white enamel tray and examined with the help of illuminated magnifier and all weed seeds are collected. Weed seeds are segregated into different types on the basis of their shape, size, colour, texture and the presence of any attachment. Segregated weed seeds are kept in screw caped vial and reference is written on the vial.
Microscopic examination
If the seeds are extremely small in size then stereoscopic binocular is used for weed seeds detection the seeds are placed in a glass Petri dish and examined under stereoscopic binocular
Page | 165 microscope and weed seeds are segregated from the crop seeds with the help of forceps or camel hair brush.
Identification of weed seeds
Seed identification is a specialised field of taxonomy that has been developed over the past 50 years to meet the problem of labelling the crop and weed seed. Accurate identification of weed seeds is necessary for the correct labelling of weed seed and also for correct quarantine action. This requires skill and good judgement on part of seed analyst making the examination .The seeds of some kinds of plants are sufficiently distinctive that they are not easily confused with these of other kinds and their identification posses no problems .There are many groups of plants, however, in which seeds of one species may closely resemble those of another species. In some cases one of these may be a crop plant and the other an undesirable or noxious weed like mustard and Argemone mexicana seeds.
Aids for identification
- With naked eyes, if seeds are large enough.
- Hand lens, if seeds are not clearly visible with naked eyes.
- Binocular microscope for extremely small seeds.
- Identification manual with colour photographs, drawings & description of important characteristics.
Identification techniques
Identification on the basis of morphological character
A collection of identified weed seeds is maintained as reference. The intercepted weed seeds are compared with reference collection for identification. Weed seeds are also identified on the basis of morphological characters by consulting identification keys.
Clues for identification
Following morphological characters of the seeds are more useful clues for identification.
- Shape - Size
- Peculiarities of surface structures like smooth or rough, pitting grooves, sculpturing.
- Colouring characteristics of hilum (attachment scar) , mainly its shape, size and position
- Other noticeable characters like wings/ pappus , spines, awns, hairs.
Page | 166 - Sometimes similar external morphological characteristics of different families or genera make identification difficult. hence ,internal character are examined for proper identification .These internal clues include:-
- Endosperm: amount, position and shape.
- Absence of endosperm.
- Embryo: size, shape, cotyledon, development, position, textures, thickness and inner markings of seed wall.
Identification on the basis of vegetative and floral characters
If the weed seeds could not be identified on the basis of morphological characters, such seeds are grown in net houses in isolation under strict plant quarantine conditions to observe various vegetative and floral characters and on the basis of these characters, the weed species are identified.
Weed species of Quarantine significance to India
Government of India has strengthened the existing system and brought into force, the new Plant Quarantine (Regulation of Import into India) Order 2003. Enforcement of this order is mainly intended to prevent the introduction and spread of exotic pests that are destructive to the country. According to the special provisions for Quarantine weeds (clause 3(12) and (Schedule VIII) of Plant Quarantine (Regulation of Import into India) Order 2003, no consignment of seed or grain contaminated with Quarantine weeds shall be permitted unless devitalized. Thirty-two weed species, which are listed in Schedule VIII are Allium vineale, Ambrosia maritima, Ambrosia psilostachya, Ambrosia trifida, Apera-spica-venti, Bromus secalinus, Cenchrus tribuloides, Centaurea diffusa, Centaurea maculosa, Centaurea solstitialis, Cichorium pumilum, Cichorium spinosum, Cordia curassavica, Cuscuta australis, Cynoglossum officinale, Echinochloa crus-pavonis, Froelichia floridana, Helianthus californicus, Helianthus ciliaris, Heliotropium amplexicaule, Leersia japonica, Matricaria perforatum, Polygonum cuspidatum, Proboscidea lovisianica, Salsola vermiculata, Senecio jacobaea, Solanum carolinense, Striga hermonthica, Thesium australe, Thesium humiale and Viola arvensis.
References
Akhtar J, B Singh, A Kandan, P Kumar, D Chand, AK Maurya and SC Dubey (2017) Interception of pathogens during quarantine processing: an effort towards safe introduction of oilseed and vegetable Brassicas germplasm in India. J Oilseed Brassica 8: 120-130.
Albrechsten SE (2006) Testing Methods for Seed-transmitted Viruses: Principles and Protocols. CAB International, Wallingford, UK, 268 p.
Ayoub SM (1981) Plant Nematology-An Agricultural Training Aid. Nema Aid Publications.
Bhalla S, VC Chalam, A Lal and RK Khetarpal (2009) Practical Manual on Plant Quarantine.
National Bureau of Plant Genetic Resources, New Delhi, India p. 204 + viii.
Page | 167 Bhalla S, VC Chalam, B Singh, K Gupta and SC Dubey (2018) Biosecuring Plant Genetic Resources in India: Role of Plant Quarantine. ICAR-National Bureau of Plant Genetic Resources, New Delhi, 216 p +vi. ISBN 978-81-937111-1-8
Bhalla S, VC Chalam, Z Khan, B Singh and SC Dubey (eds) (2018) Potential Quarantine Pests for India in Tropical and Sub-tropical Fruit Crops. ICAR-National Bureau of Plant Genetic Resources, New Delhi, India. 510 p +x. ISBN 978-81-937111-0-1
CAB International (2007) Crop Protection Compendium CAB International, Wallingford, UK.
Chalam VC and RK Khetarpal (2008) A critical appraisal of challenges in exclusion of plant viruses during transboundary movement of seeds. Indian Journal of Virology 19 (2): 139-149.
Chalam VC, DB Parakh and AK Maurya (2017) Role of viral diagnostics in quarantine for plant genetic resources and preparedness. Indian Journal of Plant Genetic Resources 30 (3): 271- 285.
Chalam VC, S Bhalla, B Singh and Rajan (eds). 2012. Potential Quarantine Pests for India in Grain Legumes. National Bureau of Plant Genetic Resources, New Delhi, India. 324 p. + xii.Chalam VC, K Gupta, S Bhalla, Rajan and RK Khetarpal (2009) Training Manual on Biosecurity and Biosafety: Policies, Procedures and Issues. National Bureau of Plant Genetic Resources, New Delhi, India, 392p.
Chalam VC, SC Dubey, C Murali Krishna, S Bhalla and Kuldeep Singh (eds.) (2018) Transboundary Movement of Living Modified Organisms: Strengthening Capacities of Enforcement Agencies.
ICAR-National Bureau of Plant Genetic Resources and Ministry of Environment, Forest and Climate Change, New Delhi, India. vi+159 p. ISBN 978-81-937111-2-5
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10.1002/9780470290125.ch8
Kandan A, J Akhtar, B Singh, D Pal, D Chand, PC Agarwal and SC Dubey (2016) Application of loopmediated isothermal amplification (LAMP) assay for rapid and sensitive detection of fungal pathogen, Colletotrichum capsici in Capsicum annuum. J. Environ. Biol.37: 1355- 1360.
Kaura A (1959) A new transparency method for detecting internal infestation of grain. Grain Storage News Letter, 1(1): 12.
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KiranR, KandanA, Kumar P, SinghD, AkhtarJ, SinghB and Dubey SC (2019). Development of species-specific primers for detection of Xanthomonas campestris pv. campestris causing black rot of crucifers. Journal of Environmental Biology 40: 105-110.
Kumar P, R Kiran, A Kandan, J Akhtar, B Singh, K Nair and SC Dubey (2017) Detection of
Xanthomonas campestris pv. campestris in imported germplasm of cabbage during post entry quarantine. Indian Phytopath.70: 413-417.
Page | 168 Lal A and VK Mathur (1988) Seed health testing for plant parasitic nematodes. In: Proc. Seed Sci. &
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Mathur SB and Olga Kongsdal (2003) Common Laboratory Seed health Testing Methods for Detecting Fungi. Common Laboratory seed Health Testing Methods for Detecting Fungi.
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Southey JF (1986) Laboratory Methods for Work with Plant and Soil Nematodes. MAFF, HMSO London. 202 pp.
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