Physical Purity Testing 

Physical purity analysis tells us the proportion of pure seed component in the seed lot as well  as the proportion  of  other crop seed, weed seed and inert  matter by weight  in percentage for which  Seed Standards have been prescribed. Thus, it helps in: 

i. Improving the plant stand (by increasing the pure seed component).

ii.Raising a pure crop (by eliminating  other crop seed and weed seeds). 

iii. Raising a disease free-crop (by eliminating  inert matter).

iv. In the use of seed drill  (by selecting uniform particles).

 There is a need for physical purity analysis for:

a) Seed Certification or Seed Law Enforcement Agencies to judge  that the seed lot conforms to the prescribed standards.

b) Seed processing plants for using right kind of processing equipment.

c) Physical purity analysis is a pre-requisite for germination test because 'pure seed' component is used for germination testing.

 Objective

The  primary   objective   of  physical  purity   analysis  is  to  determine

 i) the percentage composition  by  weight  of  the sample being  tested and by inference the composition  of  seed lot 

 ii)  The  identity  of  various  species of  seeds and  inert particles  constituting   the  sample. The  definition   of  the  various  physical  purity components in the ISTA Rules are as follows:

Pure Seed

The pure seed shall refer to the species stated by the sender, or found to Predominate the test, and shall include all botanical varieties and cultivars of that species (even if immature, undersized shriveled disease or germinated providing. They can be definitely identified as of that species) unless transformed into visible fungal-sclerostia, smut balls or nematode galls. Pure seed shall include a) intact seed units (commonly found as dispersal units i.e. achenes and similar fruits, schizocarp, florets etc)as defined for each genus or species; b)pieces of seed units larger than, one half their original size.
From the above main principles certain exceptions are made for particular genera or species as follows:
i.seed units of families Leguminaceae, cruciferae, cupressaceae, Pinaceae and Taxodiaceae with the seed coat entirely removed shall be regarded as inert matter. Separated cotyledons of legumanaceae are regarded as inert matter, irrespective of whether or not the radicle plumule axis and/or more than half of the tests may be attached.
ii. In certain genera of family gramineae.
a) A minimum size of caryopsis is required i.e. in Lolium, Festuca and Elytrigia repens a floret with a caryopsis one third rachilla is regarded as pure seed, but a caryopsis less than 1/3.
 The length of palea is regarded as inert matter.
b)The presence of caryopsis in spikelets and florets is not always obligatory.
c)The separation of pure seed and inert matter is done by uniform blowing procedure.
This   method   is   obligatory for   Poa protensis and Dactylis glomerata.
d)Multiple   seed unit  is  (MSU)  are left  intact  in  the  pure  seed fraction e.g. Doctylis  and Festuca.
e)Attached  sterile florets  are not removed, but left  attached and included  in the pure seed fraction e.g. Arrhenatherium, Avena, Chloris, Dactylis, Festuca, Holens, Poa, Sorghum and Triticum spelta.
f)For certain genera appendages are left  on the seed but reported if  found  to  the  extent of  1%  or  more, the percentage of  such material  must be  shown  on  Analysis certificate  (example  -paddy).

Other  Crop  Seed

Other crop seed shall include seed units of any plant species other than of pure seed grown as crops. Multiple structures, capsules, pods are opened and the seeds are taken out and the non-seed material is placed in the inert matter.

 Weed Seeds

 Seeds bulblets or tuber of plants recognized by laws, official regulations or by general usage shall be considered as weed seeds.

Inert matter
Inert matter shall include seed units and all other matter and structures not defined as pure seed excluding other crop seed and weed seeds.

General Principles
As per ISTA Rules the working sample is separated into three components i.e. pure seeds, other seed, and inert matter. The percentage of each part is determined by weight. All species of seed and each kind of inert matter present shall be identified as far as possible and if required for reporting, its percentage by weight shall be determined.

Equipments

Aids such as transmitted light, sieves and blowers may be used in separating the component parts of the working sample. The blower to be used for the uniform blowing method for species of family Gramineae.
Other equipments required are:
1.Dividers

a) Soiltype
b) Boerner(work on gravitational force)
c) Gamete(work on centrifugal force and electrically operated)

2.Balance:
Electric or electronic balance are better due to their accuracy and  quickness

3. Blowers

4.Diaphnoscope using reflected light are used to separate inert matter such as empty florets of grasses.

5.Sieves.

6.Sample pans, dishes, forceps, spatula and hand lens

7.seed herbarium 0f crop and ,weed seed

Procedure

1.Obtaining Working   sample

           Since the size of  the working  sample is minute  as compared with  the size of the  seed lot  to  which  it  represent, it  is  therefore,  very  essential that the  working sample should be obtained  in  accordance with  the procedures. The working sample shall be either a weight estimated to  contain atleast 2,500 seed units  or not less than weight indicated i.e. 40 g for Oryza sativa.

          Boerner or soil type seed divider should be used to homogenize the submitted sample before reducing it  to  the size of  working  sample.  The following  guidelines

need to be followed:

i.Check the cleanliness of the divider and the container.

ii.Pour the  entire  contents of  the  submitted  sample into  the  hopper of  the divider.

iii.Allow the content of the submitted sample to pass through the main body of the divider.   In case of 'Soil type'  seed divider this can be accomplished by  tilting   the  hopper  over  the  body  of  the  divider  while   in  case of 'Boerner'   divider,  by  opening the  gate-valve situated  at the base of  the hopper.

iv.     Recombine the contents of  both  sample receiving  pans and again pass it through the divider.

v.Repeat this  process  twice   in  order to homogenize   the submitted   sample.

vi.Divide   the  submitted   sample.

vii.Set aside the  contents  of one container.

viii.Divide   the  contents  of  the  other  container   subsequently  till   the  weight of

working    sample  is obtained.

 

2.Separation

a)Clean  the  work  board,  sample  and purity  dishes before  starting  the  separation

b)Examine the  working sample  to  determine   the  use  of  particular aid  such  as blower   or  sieves  for making   separation.

c)After preliminary separation with the help of sieves or blower, place and spread the retained or heavier  portion   (A)  on the purity   work  board.

d) With the help of spatula or forcep, draw working sample into thin line and examine each particle individually. The criteria   used being   the   external appearance (shape, size, color,   gloss, surface texture) and/on  appearance  in transmitter   light.

e)Separate  out  impurities   such  as other  crop  seeds, weed seeds  and  inert  matter and place  the  impurities separately  in  purity   dishes,  leaving   only  the pure  seed on the  purity  board.

f)Seed  enclosed   in   fruits  other  than   those  indicated in  pure   seed  should be separated  and the  detached  empty  fruit/appendages   classed as inert  matter.

g)Collect the pure  seed in the sample pan.

h) Put the lighter portion (B) of the work board and examine under magnification for further separating into the requisite classes (other  crop seed, weed seed and inert matter).

i)After separation, identify   the  other  crop  seed, weed  seed and record  their names on the  analysis card. The kind of inert matter present in the sample should also be identified and recorded.

j)Weight each component, pure  seed, other  crop  seed, weed  seed and  inert matter in grams to the number of decimal places shown below:

 

SL.No.

Wt. of working Sample (g)

No of decimal place required

Example

1.

Less than 1

4

.9025

2.

1 to 9.990

3

9.025

3.

10 to 99.99

2

90.25

4.

100 to 999.99

1

902.5

5.

1000 or more

0

1025

 

k)Calculate the percentage by weight  of  each component to  one decimal place only, basing  the  percentage  on  the   sum  of   the  weight   of   all   the four components.If   any component  is  less than  0.05%  record  it  as  'Trace'.Component of 0.05% to 0.1% are reported as 0',1%.

 

3. Reporting  Results

The  results  of   purity   test  be  given  to  one  decimal  place  only  and  the percentage of all component must be total 100.If the result for a component is nil,this must be shown as 0.0% in the appropriate space of the report form.The report    should also include the kind of inert matter and the Latin names of the crop seed and weed seed found in the sample.

-Definition of Pure Seed

GRAMINEAE

Oryza(Paddy)              .

-Spikelet, with glumes,lemma and palea enclosing a caryopsis including the awn irrespective of its size.
-Floret,with  or  without lemmas,with lemma and palea enclosing a caryopsis including the awn irrespective of its size.
-Caryopsis 

-Piece of caryopsis larger than one-half the original size.

N.B.  Seeds with awns longer than length of floret are reported according

Rule3.7

Hordeum    (Barley)
-Floret,with lemma and palea enclosing a caryopsis with or without awn or with or without rachis segment irrespective of their length.
-Piece of floret containing a caryopsis larger than one-half the original size.,     .8

-Caryopsis 
-Piece of caryopsis larger than one-half the original size.

N.B.  Florets with awn or rachis segment longer than length of floret are reported according to Rule3.7   

Avena (Oat)

-Spikelet with lemma and palea enclosing a caryopsis, with or without awn plus attached sterile floret.

-Floret with lemma and palea enclosing a caryopsis,with or without awn.

-Caryopsis

-Piece of caryopsis larger than one-half the original size.

Triticum, Zea,Secale (Wheat,Maize,Triticale)

-Caryopsis
-Piece of caryopsis larger than one-half the original size.

Panicum (Sawa

-Spikelet,with glumes,lemma  and  palea  enclosing  a  caryopsis,  plus attached sterile lemma.

-Floret with lemma and palea enclosing a caryopsis.

-Caryopsis

-Piece of caryopsis larger than one one-half the original size.    t

-No need to check the presence of caryopsis.

Pennisetum (Pearlmillet)

-Fascicle of 1-5  spikelets(spikelets   with   glumes,  lemma   and  palea

enclosing a  caryopsis,  plus  attached sterile  lemma)  with   involucre of bristles.

-Floret with lemma and palea enclosing a caryopsis.

-Caryopsis.

-Piece of caryopsis larger than one-half the original size.

Sorghum(Jowar)

-Spikelet, with glumes, lemma and palea enclosing a caryopsis with or without hyaline palea or lemmas,rachis segments padicle(s),awn(s),attached sterile or fertile floret(s).

-Floret,with lemma and palea ,with or without awn.8

-Caryopsis.

-Piece of caryopsis larger than  one-half the original size.
Leguminaceae(Gram, Pea, Mung,Urd, Bean,Cluster bean,Soybean,Lupins,
Crotolaria(Sunhemp),Medicago,Arachis,Trifolium)

-Piece of seed larger than one-half the original size with testa.

-Seeds and pieces of seed without testa is regarded as inert matter.
-Separated cotyledons are regarded as inert matter irrespective of whether or not the radicle-plumule axis or more than half of the testa may be attached.

Cruciferae(Radish,Mustard,Cabbage and Cauliflower)
-As given in Leguminaceae

Solanaceae(Chillies,Brinjal,Tomato,Tobacco)

-Seed with or without testa.

-Piece of seed larger than one-half the original size with or without testa.

Linaceae(Linum)
As giving in Solananceae

Liliaceae(Onion,Garlic)

-As above 

Amaranthaceae (Arnaranthus)

-As above

Cucurbitaceae (Watermelon, Longmelon, Muskmelon,  Cucumber, Pumpkin,  Squash,

Bottle  guard)

-As    above

Pedaliaceae(Sesamum)

-As    above       

Umbelliferae (Carum, Coriander, Cumin, Carrot, Fennel)

-Schizocarp is a dry fruit which separates into two or more units

(mericarps) at maturity.

-Piece of mericarp larger than one-half the original size unless it is obvious that no seed is present.

-Seed with the pericarp partially  or entirely removed.

-Piece of  seed larger  than  one-half  the  original   size,  with  the  pericarp partially  or entirely removed.

N.B.  Fruits with  pieces of pedicel longer than the length of schizocarp/mericarp are reported according to Rule 3 7
Malvaceae (Cotton)

-Seed with or without testa (testa with  or without  fuzz).

-Piece of seed larger than one-half the origina1 size with or without testa. Compositeae(Sunflower,  lettuce, chicory)

-Achene, with   or  without  beak,  or  with   or  without  pappus, unless  it  is

obvious that no seed is present.

-Piece of achene larger than one-half the original size, unless it is obvious that no seed is present.

-Seed with the pericarp/testa partially or entirely removed.

-Piece of seed larger than one-half the original size, with the pericarp/testa partially or entirely removed.

Euphorbiaceae (Ricinus)

-Seed with or without testa,with or without caruncle.

Chenopodiaceae(Spinach,Beet,Sugarbeet,Red beet).

-Cluster, or piece of cluster, with or without stalk unless it is obvious that no seed is present.

-Seed, with pericarp/testa partially or entirely removed.

-Piece of seed larger than one-half the original size with the pericarp/testa partially or entirely removed.

-Seeds with pieces of  stalk protruding more than the width of  cluster are reported according to Rule 3.7. When a particular kind of inert matter,species of other seed, multiple seed unit (MSU) or seeds with appendages attached is  found to  the extent of  1% 'of  more, the percentage of  such material must be shown on the analysis certificate.

-In certain genera seeds/fruits may have various appendages(awns/stalks etc.)attached. Such appendages shall be left attached to the seeds,but the content of seeds with appendages longer than the greatest dimensions must be reported on the certificate.