AN ANALYSIS OF MUTATIONAL ORIGIN OF GENETIC DIVERSITY IN GROUNDNUT (Arachis hypogaea L.)
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Date
2001-08-07
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK BANGALORE
Abstract
An investigation into the nature and utility of mutational origin of genetic diversity in
groundnut {Arachis hypogaea L.) was carried out during 1995-1999. The material consisted of the
mutants derived from Dharwad early runner (DER).
The mutagenic treatment of DER with gamma-rays and ethyl methane sulphonate (EMS)
generated high frequency of mutants representing all four botanical types of groundnut Viz.. Spanish
bunch (SB), Valencia (VL), Virginia bunch (VB) and Virginia runner (VR). A detailed analysis of the
breeding behaviour of these mutants revealed several unusual features such as, homozygous mutations,
multiple character mutations, germinal reversions, segregation distortions, non-random mutations etc.
The non-Mendelian turnover mechanisms such as transpositions, retropositions, DNA methylation,
gene conversion, unequal crossing overs etc., were invoked as possible causes of mutations.
Treatment of DER with 5-Azacytidine, a donethylating agent also induced such sub specific and
botanical changes indicating a role for methylation in the botanical differentiation of the crop. The
mutagens EMS, gamma rays and 5-Azacytidine might have triggered the non-Mendelian turnover
mechanisms.
Selected DER mutants representing four botanical types were assessed for morphological,
cytological and biochemical variability. The analysis of variance and principal component analysis
revealed abundant morphological variability, which was comparable to the natural variation existing in
the crop. The karyotypic analysis did not showed any significant variation among the mutants except
the number and location of asymmetric chromosomes and secondary constrictions. A very low
sterility in parents but high pollen sterility in F| and F2 plants was observed in the crosses between
mutants belonging to different botanical groups. However, the meiotic analysis indicated normal
chromosome pairing except the appearance of a quadrivalent in both, the parents and hybrids. The
glutamate oxaloacetate transaminase (GOT) isozyme analysis showed three banding patterns, which
were specific to the botanical groups viz., SB, VL and VB/VR. Three polymorphic bands were
identified from the seed protein analysis (SDS-PAGE), which distinguished the mutants belonging to
two subspecies. Thus, the mutants representing different botanical types at morphological level might
be mere expression syndromes at molecular/physiological level.
The mutagenesis of DER has resulted in identification of several useful mutants resistant to
foliar diseases. Recurrent mutagenesis of selected resistant mutants with EMS and gamma-rays
revealed the mutagen and genotype specificity in their mutagenic response. The recurrent mutagenesis
was found to be a potential tool to improve for other characters, retaining resistance in these mutants.
The use of resistant mutants along with a resistant geimplasm line in three way crosses was found to be
a potential approach to improve resistance and productivity, simultaneously.
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