Gowda, M V CSheshagiri, R2019-09-042019-09-042000No. of references 168http://krishikosh.egranth.ac.in/handle/1/5810126420"An investigation into tljc nature and utility of mutational organ 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 rtinner (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 tiunover 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 demethylating agent also induced such sub specific and botanical changes indicating a role for methylation in the botanical differentiation of the CTop. 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 variabiUty. The analysis of variance and principal component analysis revealed abundant morphological variability, which was comparable to the natiu^ 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 F1 and F2 plants was observed in the crosses between mutants belongmg 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 pattems, wliich 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. 7Tie 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 germplasm line in tliree way crosses was found to be a potential approach to improve resistance and productivity, simultaneously."ennullThesis