Seed quality testing of vegetable seeds at lab

Seed quality testing of vegetable seeds at lab

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  SEED QUALITY TESTING PreparedBy: Ganesh Lamsal HRT-01M-2018
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  CONTENT  Introduction  Importanceof quality seed  History and regional seed testing laboratory  Seed Sampling method  Purity test  Seed germination test  Seed Viability test  Seed vigour test  Moisture determination  Conclusion
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  INTRODUCTION  Seed: “Seedis a matured ovule having embryonic plant, food substance and protective cover or seeds or germ which can be used in sowing or planting to produce crops by reproducing in a sexual or asexual mode” (Seed Vision 2013-25).  Quality seed: Seed possessing quality factors like genetic purity, trueness to type with high degree of physical purity, uniformity, high germination potential, optimum moisture and vigor, freedom from diseases and pests and noxious weeds.
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  IMPORTANCE OF QUALITYSEED  Alone can increased productivity by 15-20% (Joshi, 2015)  Decreased the seed requirement rate  Can be stored for longer period of time.  Increased income
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  QUALITY SEED ATTRIBUTES Fourquality attributes 1)Physical Attributes 2) Physiological Attributes 3) Genetic Attributes 4) Seed Health Attributes
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  WHY SEED TESTING?  Seed testing is the cornerstone of all other seed technologies.  Provides essential information for determining the quality of seed.  Concern with parameters such as germination, physical purity and moisture content.  Means to regulate the use and maintenance of seeds.  Required to assess the seed quality attributes of the seed lots which have to be offered for sale.
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  History and RegionalSeed testing laboratories  In Nepal, 1st seed testing laboratory was established in 1962 under Agronomy Division of Department of Agriculture (DOA) then it got accredited to the International Seed Testing Association (ISTA) in 1964.  Currently 5 regional seed testing laboratories in Nepal (Source: Krishi Diary, 2073).  Regional seed testing laboratory at Jhumka, Hetauda, Bhairawa, Nepaljung, Sundarpur.
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  Seed sampling  Primarysample: small portion of seed drawn from different container of seed lot  Composite sample: primary samples combined together  Submitted sample: sample prepared for seed testing to be submitted to seed testing lab  Working sample: sample prepared from submitted sample for carrying specific seed test
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  Seed lot andits sizes Seed lot: huge quantity of seed combined together and bagged with lot number. Seed lot must be of same variety, same seed class, same quality standard, same moisture%, and no heterogeneity.
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  Sampling intensity
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  Sampling instruments Sleeve typetrier Nobble trier for jute bags
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  SAMPLING METHOD FORWORKING SAMPLE Sampling method is used to make homogenous sample and reduce the sample size without any bias. 1) MECHINICAL METHOD: a) Boerner divider  It consists of a hopper, a cone and series of baffles directing the seeds into 2 spouts. Disadvantage: difficult to check for cleanliness. Fig.1: Boerner divider
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  ……………sampling method………………….. b) Slotdivider  It is a sample divider built on the same principles as the Boerner divider.  Here the channels are arranged in a straight row.  It is suitable for large seeds and chaffy seeds. Figure 2. Slot divider
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  ………sampling method………………….. c) Centrifugalor Gamet divider  Seeds fall on a shallow rubber spinner which on rotation by an electric motor  Approx. equal quantities of seed will fall in each spout. Figure 3. Gamet divider
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  ……………sampling method…………. 2) Handhalving method  Whole submitted sample is spread over the large sheet of paper.  Divided into 4 equal portion and each portion is again divided into four quarters.  Out of 16 quarters, every alternate portion combined together.  Process repeated till required sample size is obtained.  Eg: carrot
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  ……………sampling method…………. 3) Spoonmethod  Practice for small seeded sample.  Seed lot to sample poured and spread uniformly over the tray.  With spatula on one and and spoon in another hand, pick the small portion of seed from random palces on the tray until required quantity of sample is obtained.  Eg. Onion, Brassica
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  SEED TESTING PRACTICE 1.Purity testing 2. Germination testing 3. Viability testing 4. Seed vigour testing 5. Moisture content
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  1. PURITY TEST It conforms to the prescribed physical quality standards.  The working sample is weighted and separated into its components on purity board and magnifying glass (diaphnoscope).  The ISTA purity values results are expressed as % of pure seeds, other crop seeds, weed seeds and inert materials.  the percentage in weight of all components are added up to get purity %.  Check the tolerance of calculation that is permitted.
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  Instrument used forDetermining Purity Figure 4. Purity Work Board Figure 5. Seed Blower  Blower is used to separate pure seed from inert material and other crop seed  purity work board helps for easier counting of pure seed , inert material and other crop seed percentage in the given sample.
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  2. SEED GERMINATIONTEST  Estimate the maximum number of seeds that will produce a normal seedling.  Germination tests shall be conducted with a pure seed fraction.  The test is conducted under favorable conditions of moisture, temperature, suitable substratum and light if necessary.  No pretreatment is given except for those recommended by ISTA.  Test carried out on 4 × 100 seeds as certification set out in replicates of 25, 50 or 100 seeds.  Reporting: normal seedlings out of 400 on test are counted and expressed in %
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  Methods used fordetermining seed germination.  Sand germination method  Petridish method  Roll towel method  Paper germination method
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  22 Figure 6: Sandgermination Figure 7: Petridish germination Figure 8: Roll towel method Figure 9: Seed germinated on paper
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  Germination test usingpaper
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  Between paper(BP)
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  Pleated paper (PP) Forseeds with multigerm eg, spinach, beet
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  Pre treatments forbreaking dormancy  Pre-chilling: 5-100 C for 3-7 days may be needed , eg brassica, onion  Pre-drying: 30-450 C for 3-7 days, eg: rice  Pre-washing: pre-soaked in water, eg: bean  0.2 % KNO3 : eg: tomato  GA: 200-1000ppm  Scarification: mechanical (piercing, rubbing)  Acid Scarification: H2SO4/HNO3
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  3. VIABILITY TEST Tetrazolium test :  It is done to determine seed viability, which may be expected to germinate.  Very rapid (<24 hr.) and useful also for dormant seeds.  Tetrazolium react with enzyme dehydrogenase which is present in the seed and indicate whether the seed is ‘living’ or ‘dead’. 2,3,5-triphenyl + Dehydrogenase Triphenyl formazan + HCl tetrazolium chloride (red and insoluble)
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  ……viability test ……………… Tetrazolium salt solution of 0.5 % is used for bisected seed or embryo and 1% solution for whole seed .  Dead seed remains colorless even after dipping in tetrazolium salt solution. Limitation:  too high values of vitality, no separation of abnormal.  does not detect the presence of pathogen or phytotoxic effect. Figure : Stained embryos after tetrazolium test
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  4. SEED VIGOURTEST o Vigour tests are not a replacement for germination tests, however they provide additional information. o It is the ability to germinate rapidly and to tolerate various environmental factors which may be negative. o Better vigour is correlated with field condition under unfavorable environment condition. o Method used to determine seed vigour: o 1) Hiltner/ Brick gravel test 2) Paper piercing test o 3) Accelerated aging test 4) Conductivity
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  ……………..seed vigour ………….. 1)Hiltner Test (Brick gravel test)  Under unfavourable conditions only high vigour seed can form good seedling  100 seeds are placed upon sand inside the box.  After placing seed, 2-3 mm layer of porous brick gravel is spread over the seeds.  The box is kept in the germinator at appropriate temperature.  Seedlings which have emerged through the brick gravel layer are counted.  Then % of emerged seedlings are used to compare seed vigour of different lots.  Eg. Bean
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  ……………..seed vigour ………….. 2)Paper piercing test  The seeds are placed on 1.5 cm moist sand in a tray or sand box.  Then covered with special filter paper, followed by 2 cm of moist sand.  After this, the sand boxes/trays are kept in a germinator at 20°C for 8 days.  After then taken out and seedlings emerging above the paper are counted. Figure: Seedlings at paper piercing test
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  ……………..seed vigour ………….. 3)Accelerated aging test  This test is conducted with the stress of high temp. and moisture.  The given weight of seeds is placed in a small box with a screen tray that suspends the seeds over a reservoir of water.  These boxes are then placed in an aging chamber at 40 to 43 °C for 72 hrs.  At the end of the period, the seeds are planted and tested for germination under the standard conditions. Figure: The accelerated aging test is conducted by placing seeds in a plastic box with a water reservoir and holding them at 40 ºC for 72 hours.
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  ……………..seed vigour ………….. 4)Conductivity test for pea  The electrical conductivity test has been widely tested in agriculture but has not been adopted as routine practice.  2-5 gm seeds are soaked in 100 ml water at 250 C for 10-12 hours  Deteriorated or dead seeds leak electrolytes more readily than high-vigor seeds.  This greater leakage causes the water to have a higher conductivity which can be measured with a conductivity meter. Figure: Electrical conductivity to determine seed vigour
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  5) Controlled deteriorationtest for brassica sps  First initial weight and MC is determined  Environment is adjusted to raise to 20%MC, weighting is done at intervals till the seeds attain desired weight of seeds at 20% MC.  Immediately this is paked in aluminium pouch and sealed, not allowing to equilibrate with ambient RH and kept at 720 C for 24 hours.  Now, packets are floated into water bath at 450 C for 24 hours and allow to cool for 5-10 minutes  After this, seeds undergo standard germination test on Whatman paper or filter paper  Count the seedlings germinated
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  5. Moisture test First tests conducted when seed sample is arrived at the seed lab.  The seeds will likely gain or lose moisture in exchange with the ambient air.  The standardized laboratory test : oven method (ISTA 1996).  It is expressed as a percentage of the weight of the original sample. Method of determination of seed moisture 1. Air oven method 2. Moisture meters
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  ………moisture determination……… 1) Airoven method :  Materials req.: Grinder, Container, Oven, Desiccator, Analytical balance  Grinding : For leguminous seeds, coarse grinding is recommended Fine seeds doesn’t need any grinding operation.  Pre drying : For which grinding is necessary and the moisture content is > 17%  Weight of the submitted sample o 10 g for species that have to be ground. o 5 g for all other species. o The sample should be submitted in polythene bag of 700 gauge.
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  Two types ofAir oven Method  high constant temperature(130±30 C for 1 or 2 hours): seeds with non-volatile materials eg; carrot, tomato, bean, cowpea, pea  grinding into 4 mm for legumes and 0.5-1 mm for cereals  Weight and put in oven at 130±30 C for 1 or 2 hours  Remove the dishes and note down the weights.
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   Low constanttemperature (103±20 C for 17 hours) , seeds with volatile materials eg; onion, cauliflower, BLM, radish  Griend into 4 mm for legumes and 0.5-1 mm for cereals  Weight and put in oven at 103±20 C for 17 hours  Remove dishes and note down weights
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  …………moisture determination…………. 2) Moisturemeter  The principle involved in these moisture meters is that wet grains are good conductors while dry grains are less conductors of electricity.  So, the MC is directly proportional to the electrical conductivity of the seed.  It consists of a compression unit to compress the sample to pre -determined thickness.  The test seed taken in a test cup and is compressed.  Then press the push type switch till the reading comes in the display. Figure: Moisture meter
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  Moisture meter
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  Calculation of moisturecontent  Formula for samples not requiring pre-drying  %MC=  Formula for samples requiring pre drying  %MC=S1+S2-  Where: S1=% MC at first stage of drying, S2= %MC at second stage of drying
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  CONCLUSION  Purity, moisture,viability, vigour and germination are the important seed quality testing parameters  SQCC is the body responsible for quality control of seed and 5 regional labs test the seed quality in Nepal.  Sampling is very crucial and sample should be prepared without bias.  Quality seed helps to increase productivity, decrease seed rate requirement, improves storage capacity and ultimately increases farmers income.