Friday, 23 January 2015

Induction of polyploidy to increase vegetative growth in Berseem

Livestock has major role in farming system and agriculture economy of many countries. Forages and fodders are main feeding components of livestock animals. Thus, they play a major role in the production of meat, milk and wool. Berseem or Egyptian clover (Triffolium alexandrin ‘m L) is very important winter legume grown for green fodder in many countries. It is originated from Egypt so it is so called Egyptian clover. For the first in Indo-Pak, it was introduced in Sindh in 1904. Then it was grown in Peshawar and other irrigated areas of Punjab. Berseem is cross-pollinated crop. Berseem has trifoliate leaves with hair present on them.
Polyploids organisms have more than two basic sets (x) of homologous chromosomes and the phenomenon is called polyploidy. Berseem has chromosome number 2n=2x=16. Polyploidy method is used to increases the vegetative growth of clover because our main output is large sized leaves for fodder purposes. Induction of polyploidy is natural or artificial. In case of berseem, autotetraploid (2n=4x=32) and autohexaploid (2n=6x=64) are present which increase the vegetative growth. Morphological and physiological changes occur in berseem genotypes. Polyploid berseem plants have larger inflorescence size and number per plants with larger size leaves.
Artificial polyploidy may has positive or negative affects but induced polyploidy method is used via different treatments of colchicine, X-rays, gamma rays and other different mutated material. Induced polyploidy is done under control conditions.Basic chromosome number of berseem is x=7 and x=8. Change in ploidy level of berseem has various chromosomal evolution mechanisms in which translocation, inversions, duplications and deletions are prominent. Pairing of chromosomes leads to interspecific hybrids between x=7 and x=8 with increase in vegetative growth. Trifolium pratense and Trifolium diffusum supports the mechanism of increase in vegetative growth.
Polyploidy has also been a major factor in species evolution in Trifolium. Studies of interspecific hybrids between the polyploid Egyptian clover and related diploid species show that several diploid annual and perennial species have chromosome relationships to Egyptian clover. Polyploid hybrids of berseem between (2n=58-60) are fertile with high vegetative growth.
Artificial induction of polyploidy is done by different mutagenic agents like colchicine, radiations and chemical agents. But the most effective treatment is colchicine application. Colchicine is applied on seedling, booting, floral parts etc. Different genotypes of berseem like, Helaly, Serw-1, Shaka-4, Gemmiza-1 and Fahl are treated with colchicine and get maximum positive results in India.Berseem has x=8 chromosomes which is best for polyploidy induction. Polyploidy induction in berseem is found useful to obtain new genotypes having higher vegetative growth as compared to diploids. Polyploid have bigger organ size than their parents. Several methods have been used for producing autopolyploids in legume forages.
Colchicine is extracted from the plant (Colchicum autumnale  L.) which  is  one  of  the  most  widely  used chemicals  for  polyploidy  induction in many crops. It blocks the spindle fibers formation and stops the mitosis at anaphase stage. So at this stage cell division does not take place and multiplication of chromosome occur and hence polyploid cells are formed. Polyploid cells are larger in size and thus they increase the volume of plants organs. For colchicine treatment 100 seeds of berseem clover are used.
 There are two different methods of colchicine treatment. (a)Seeds of berseem are soaked in colchicine solution (0.05%) for 2.5 hours. Before sowing these seeds are washed with distilled water. (b)In this method colchicine is applied in three different concentrations (0.1, 0.2, and 0.3%). In old seedling, apical meristems are used for colchicine treatments every 3 hours in the same day. Colchicine treatments are applied on every genotype of berseem clover and then pots are kept under greenhouse conditions. Numbers of surviving plants after full germination are counted. First cut is carried out after 60 days of sowing. Polyploidy induction in berseem is highly effective and gets maximum positive results. After plantation, a large difference is detected between different genotypes of berseem in field.
After treatment the first cut is made and all plants which are morphologically affected has thickened leaves and stunted growth habit which is potted up and retained. Polyploid plants had a larger inflorescence size.Colchicine treatment increases the number of tillers per plant, branches, sub-branches and number of inflorescence which leads to increase in forage yield. After colchicine application, various changes occur in leaflet size, shape and number.There is a huge difference between diploid and tetraploid species during cutting. In first two cuttings tetraploid were superior over diploid but in third cutting tetraploid came down and diploid were superior over tetraploid. The average green fodder yield of berseem is 4-6 cuttings varies from 100-125 tons/ha. After colchicine treatment this yield increases upto 150-170 tons/ha in the same period of cuttings.

Induction of polyploidy increases the vegetative growth like increases the leaf surface area, tillering, seed per plants, plant height etc. Polyploidy is induced by different methods. Colchicine is treated with seedlings and get benefits results to increase the surface area. Ploidy level of Egyptian clover is increases upto certain level to get maximum positive results colchicine treatment is done by different methods and get different results. Ourmain focus is to increase it vegetative growth not reproductive growth because vegetative growth increases the tonnage of green fodder. 

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