so mac lon al variation

7/31/2019 So Mac Lon Al Variation

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TOPIC : SOMACLONAL VARIATION

Presented By:Submitted To:

Dr. Harsh KumarUniversity Professor

R.A.U., Pusa

Homa ManzarM.Sc. (Agri. Biotech)

1st Semester



INTRODUCTION

Regeneration of plants from callus produced during T.C.

show considerable variations. These are called samaclonalvariation.

The term S.C.V. given by Larkin & scowcroft in 1981.

They are stable variations which develop spontaneously inculture.

Some of the useful variations have been incorporated inplant breeding programs.

eg. :- Developed Fusarium wilt resistant plants of Carnation lilium & Robinia Pseudoacacia , Rhizoctonia root rot resistantplants of strawberry & cauliflower, rust resistance & hightemp. tolerance in wheat etc.

The stability of useful characters in subsequent generations

are also important.Plant cells, tissues & somatic embryos developed fromvarious ex plant, sources for S.C.V.

Explants are generally taken from any tissues namelyleaves, internodes, ovaries, roots & inflorescence.



ORIGIN & MECHANISMS OF SOMACLONALVARIABILITY

Origin :-

S.C.V. can be two sorts –

1. Genetic variability (i.e. heritable)Caused by mutations and other changes in DNA. Ie. Changein ploidy & structural changes in nuclear DNA.

2. Epigenetic variability (i.e. nonheritalde)

Caused by temporary phenotypic changes i.e. phenotypicchange seen in plant produced through T.C. is rejuvination.Rejuvination causes changes in morphology such as earlyflowering & enhanced adventitious root formation.

MechanismVariation in sormaclones occur due to following reasons

1. The pre-existing genetic variation in the explants tissue.

2. The spontaneous mutations.3. Intracellular mutagenic agents produced during invitro growth.

4. Numerical & structural changes in chromosomes duringinvitro growth.



FACTORS THAT CONTRIBUTE TO S.C.Vs are Physiological,

Genetic &

Biochemical1. Physiological cause of variation

Prolonged exposure to explanted tissue to powerfulauxin such as 2,4 D or 2, 4, 5 T often results in variationamong the regeneratnts

2. Genetic cause of variation

Chromosomal mutation (deletion, duplication, inversion,translocation) are the source of genetic variation whichare expressed by someclones,

Lee & Philips (1988) have described the possiblemechanisms of these chromosomal changes

eg.:- In maize (Zea mays) & In broad beans (Vicia faba).

3. Biochemical cause of variation Biochemical variations also include alteration in carbon

metabolism leading to lack of photosynthetic ability(albinos in cereals such as rice) starch biosynthesiscarotenoid pathway, nitrogen metabolism & antibioticresistance.



APPLICATION

S.C.V. is one of the aspects of T.C. technology &is widely recommended for crop improvementespecially of desired traits for the salt, drought,temp & disease tolerance.

The method refers to heritable change thataccumulates in the callus from the somaticexplants & express in the progeny of invitroregenerantes obtained from callus.

S.C.VS are used to uncover new variant retaining

all the favourable characters along with anadditional useful trait.

eg.:- resistance to disease or heraldries.



ADVANTAGES

The major likely benefit of S.C.V. is in plantimprovement.

Creation of genetic variability

Resistance to disease pathotoxins,herbicides & tolerance to environmental &chemical stress as well as for increasedproduction of sec. metabolites . Micro

propagation can be carried out throughoutthe year independent of the season.

so mac lon al variation

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