Vigour Test PDF

EXERCISE – 6 STUDY OF VIGOUR TESTS IN CROPS  WHAT IS SEED VIGOUR? Sum total of those properties of seed which determine the activity (i.e. rapid and uniform production of healthy seedlings) and potential level of performance of seed lots of acceptable germination in a wide range...

EXERCISE – 6 STUDY OF VIGOUR TESTS IN CROPS  WHAT IS SEED VIGOUR? Sum total of those properties of seed which determine the activity (i.e. rapid and uniform production of healthy seedlings) and potential level of performance of seed lots of acceptable germination in a wide range of field conditions is called seed vigour: OBJECTIVES: To determine seed vigour of a given sample WHY IS VIGOUR TESTING IMPORTANT? Vigour testing is an important component of seed testing because it’s more sensitive test than germination, and because loss of vigour may be noted much earlier than loss of germination.  WHAT CAUSES VIGOUR LOSS? Vigour loss is due mainly to seed deterioration and aging, which starts as soon as the seed becomes physiologically mature. It’s imperative, therefore, that seed be handled carefully to prevent accelerated reduction in performance through physical damage to cell membranes. This is particularly true of large seeds, such as pulses and legumes, where seed damage is the primary cause of deterioration. Other associated detrimental factors include: Enzyme activity in immature and dormant seeds; Respiration during harvest and storage; Impaired protein and the use of protein and RNA synthesis during periods of low temperature stress; Genetic damage; Accumulation of toxic metabolites.  The biological basis of the seed vigor concept It has been established that the conditions of seed development, maturation, storage and aging influence seed vigor. Seeds developed under moisture stress, nutrient deficiency, extreme temperatures, etc. often result in light, shriveled seed or collectively called poor-vigor seed. Preharvest environment of high humidity and warm temperatures can also cause loss in seed viability and vigor. Seed mechanical damage, whether induced by harvesting or conditioning equipment, as well as improper storage conditions are among the factors that adversely affect seed vigor. In addition, genetic factors such as hard-seededness, resistance to diseases, and seed chemical composition influence the expression of seed vigor.  Methods of measuring seed vigor A. Physical test B. Stress Test C. Electric D. Biochemical E. Seedling conductivity Test : Vigor test Tetrazolium Classification (TZ test) Test (SVCT) 1. Seed size 1. Cold test - - - 2. Seed Density 2. Accelerated - - - (cm3) aging test 3. Physical 3. Brick gravel - - - soundness test 4. Paper piercing - - - test 5. Compact soil - - - test 6. Pathogen - - - infested soil test 7. Low or high pH - - - test  (A) PHYSICAL TEST: 1. Seed size: One hundred seeds drawn randomly and weighed in gram. The seed lot with high seed weight is considered as vigorous. 2. Seed Density (cm3): Kerosene oil is placed in a graduated measuring cylinder and initial level is measured. Weighed sample is poured in this measuring cylinder and the level of kerosene is again measured. The difference between initial level of kerosene and after placement of seed shows the density of the seed. The seed lot with higher density is considered as vigorous. 3. Physical soundness: Seed lot containing shriveled seeds, undersized, undeveloped, discolored and insect damaged seeds are considered as weak.  (B) STRESS TEST 1. Cold Test (CT) When can the cold test be used? 1. Select cultivars with the best ability to perform under cold wet soils for early spring planting. 2. Provide basis for adjusting planting rates for individual seed lots. 3. Evaluate the effects of adverse storage conditions, mechanical damage, drying injuries or other causes on seed germination in cold wet soils. The cold test simulates early spring field conditions by germinating the seeds in wet soils (»70% water holding capacity) and incubating them at 5-10°C/41- 51°F for a specified period. At the end of the cold period, the test is transferred to a favorable temperature for germination (e.g., 25°C / 77°F in case of sweet corn). The percentage of normal seedlings is considered as an indication of seed vigor. Vigorous seeds germinate better under cold environments.  2. Accelerated Aging Test (AAT) The principle of this test is to stress seeds with high temperatures of (40- 45°C/130-139°F) and near 100% relative humidity (RH) for varying lengths of time, depending on the kind of seeds, after which a germination test is made. High vigor seeds are expected to tolerate high temperatures and humidity and retain their capability to produce normal seedlings in the germination test. When can the AAT test be used? 1.Can be used to determine the seed vigor of many crops. 2.Useful in predicting the potential storability of a seed lot.  3. Brick gravel test: Seeds are placed at a depth of 3.00 cm in the tightly packed crushed brick granules of 2-3 mm in size. As the seedlings emerge, the brick granules place a stress on the emergence of elongating seedlings and impede the emergence of weak and mechanically injured seedling Table: Observation of brick gravel test: Lot No. Number of First count Germination Speed of seed sown (%) germination 1. 2. 3. 4. Paper piercing test: Seeds are planted on 1.25 cm of moist sand. It is covered with specially selected dry filter paper. This filter paper is again covered with 3.00 cm of moist sand. This is kept at 20-25°C for the days required for final count. The seedlings which are able to penetrate the paper are considered vigorous.  5. Compact soil test: Seeds are planted in soil at optimum condition in a tray. It is covered with uniform compact layer of the same soil. The seed lot with maximum percentage of emergence under this condition is considered as vigorous. 6. Pathogen infested soil test: Seeds are planted in soil mainly infested with species of Pythium, Fusariam or Rhizopus and other fungi and kept at 10°C for 7 days followed by 3 days at 30°C up to the day of final count. The lot showing maximum germination percentage is considered as vigorous. 7. Low or high pH test: Seeds are planted in soil with low or high p I and kept in optimum temperature in an incubator for germination up to ten day of final count. Lot with high germination percentage is considered as vigorous.  (C) Electric Conductivity This test Test measures the integrity of cell membranes, which is correlated with seed vigor. It is well established that this test is useful for garden beans and peas. It has been also reported that the conductivity test results are significantly correlated with field emergence for corn, and soybean. As seeds lose vigor, nutrients exude from their membranes, and so low quality seeds leak electrolytes such as amino acids, organic acids while high quality seeds contains their nutrients within well structured membranes. Therefore, seeds with higher conductivity measurement are indication of low quality seeds as vice versa. (D)Biochemical test: 1. Tetrazolium (TZ) test  (E) Seedling Vigor Classification Test (SVCT) This vigor test is an expansion of the standard germination test (SGT). The normal seedlings obtained from the SGT results are further classified into ‘strong’ and ‘weak’ categories. This test has been used for corn, garden beans, soybean, cotton, peanuts and other crops. THE PRINCIPLE OF THE TEST Seedlings have four significant morphological sites for evaluating vigor: 1.Root system. 2.Hypocotyl (the embryonic axis between cotyledons and root). 3.Cotyledons (storage tissue of reserve food for seedling development). 4.Epicotyl (the embryonic axis above the cotyledons). In this test, seedlings are classified as ‘strong’ if the above four areas are well developed and free from defects, which is indication of satisfactory performance over a wide range of field conditions. On the other hand, normal seedlings with some deficiencies such as missing part of the root, one cotyledon missing, hypocotyl with breaks, lesions, necrosis, twisting, or curling are classified as ‘weak’.  FUTURE ROLE OF SEED VIGOUR TESTING: Seed vigour is an important component of seed quality and satisfactory levels are necessary in addition to traditional quality criteria of moisture, purity, germina­tion and seed health to obtain optimum plant stand and high production of crops. As agricultural and horticultural techniques become progressively more sophisti­cated, the need for high vigour seeds will increase and testing standards, similar to those recognized for germination will be required. The technology of seed vigour testing has not been perfected so far, so much so that there is not a single universally accepted seed vigour test method. Research is needed to further refine the current seed vigour test methods and to develop new methods which are related to field/storage conditions.  ASSIGNMENTS: 1. What is seed vigor? Write the objective of seed vigour test. 2. Describe physical test of seed vigor in detail. 3. List out the various stress tests for testing seed vigor. Describe in brief the ‘Accelerated ageing test’. 4. Write short note on following: a. Brick gravel test. b. Paper piercing test. c. Cold test. d. Electric Conductivity Test e. Compact soil test. 5. Describe in brief the ‘Tetrazolium test’. THANK YOU