DR. K. SWARAJYA LAKSHMICHANNAPURAPU SAI RATNA SHARAVANI2022-02-042022-02-042019-11-07https://krishikosh.egranth.ac.in/handle/1/58101817141. To determine the lethal dose of the physical mutagen gamma rays in tuberose cv “Hyderabad Single” 2. To study genetic variability in mutant population 3. Molecular characterization of desirable mutants using molecular markersTuberose (Polianthes tuberosa L.) is a vegetatively propagated crop used as loose flowers, cut flowers and also as raw material for the extraction of the highly valued natural flower oil. Genetic improvement of tuberose is hampered by meager genetic variability, self incompatibility, seed sterility and these factors impair the conventional improvement programme. Mutation breeding is one of the best options for supersizing the genetic base and enhancing the crop diversity. Hence the present experiment entitled “Studies on mutagenic effects of gamma irradiation in tuberose (Polianthes tuberosa L.)” was carried at Floriculture block, College of Horticulture, Anantharajupeta, Y.S.R. Kadapa District, Andhra Pradesh during 2017-19 with the objective to estimate the lethal dose of physical mutagen, gamma rays, to evaluate the growth, yield and qualitative traits of tuberose cv. ‘Hyderabad Single’, subjected to gamma irradiation at LD50 (20 Gy) and to conduct molecular analysis of desirable mutants obtained from mutant population with RAPD and ISSR markers. The bulbs of tuberose cv. ‘Hyderabad Single’ were treated with different doses of gamma rays viz., 5 Gy, 10 Gy, 15 Gy, 20 Gy, 25 Gy and 30Gy at BARC, Mumbai. Untreated bulbs were used as control and the experiment was laid out in a CRD. The sprouting percentage decreased with gradual increase in dose of irradiation. The plant height was maximum in 5 Gy (44.8 cm), as the gamma irradiation dose increased all vegetative (survival per cent, plant height, plant spread, leaf area, width of leaves, number of shoots per clump), floral (spike length, rachis length, number of florets per spike, weight of floret, number of spikes per plant and flower yield), bulb (number of bulbs per clump, weight of bulbs, average diameter of bulbs, average length of bulbs and circumference of clump) and biochemical characters (SPAD chlorophyll content) recorded a gradual decline. The irradiation doses higher than 20 Gy recorded no flowering through out the period of study. Leaf variegation was observed for plants treated with 15, 20 and 25 Gy. The LD50 value was assessed based on mortality percentage and the probit analysis revealed that the LD50 value was 20 Gy. Subsequently, a total of 500 bulbs were treated with LD50 (20 Gy) value at BARC, Mumbai. The results indicated that, the growth, yield and quality parameters of some irradiated plants at LD50 value (20 Gy) showed superiority over control. Out of 265 mutants, 88 mutants were superior to control with regards to days to sprouting, 35 mutants were superior to control with regards to plant height, 35 mutants were found superior for leaf length, 21 mutants were found superior interms of leaf width, four mutants were found superior for number of shoots per clump, two mutants showed variegated leaves (M185 and M243) and 34 mutants with respect to number of primary branches. Among 265 mutants 69 mutants showed flowering. Among the floral components the mutants exhibited a superiority in the characters viz., early spike emergence (3 mutants), days to first floret opening (2 mutants), spike length (11 mutants), rachis length (6 mutants), number of florets (8 mutants), weight of floret (2 mutants), length of floret (23 mutants), perianth tube diameter (29 mutants), number of spikes per plant (1 mutant) and flower yield per plant (3 mutants) compared to control. Among 265 mutants, 5 mutants showed more number of bulbs per clump and weight of bulbs per clump, 45 mutants recorded maximum average diameter of bulb, 14 mutants recorded maximum average length of clump and four mutants recored maximum circumference of clump. Seventeen mutants were recorded superior for SPAD chlorophyll content and 180 mutants recorded superior for per cent disease index of Alternaria leaf spot compared to control. Wide spectrum of variation was observed in M1V1 generation for leaf colour. M185 had showed yellowish green (151C) at centre and green (137 A) at perifery, while, M243 showed green (138B) at centre with yellowish green (151C) at perifery. All the mutant population including control bore white colour flowers. There was a positive correlation among majority of the significant estimates, for flower yield per plant. Maximum positive correlation was recorded for number of florets per spike with flower yield, while minimum positive correlation was recorded for circumference of clump with flower yield per plant. Among the 113 significant correlations, 99 showed a positive trend, this correlation suggests that the improvement of those individual traits would simultaneously improve other pair wise traits due to correlated response. Traits which are significant with the flower yield per plant will also be useful in selection of desirable plants from the mutant population. From the mutant population molecular analysis was conducted for seven mutant plants, M2 (mutant plant showing compact floret arrangement and more number of florets), M 185 and M243 (Chlorophyll mutants), M308 (Dwarf statured mutant) M349, M395, M398 (branched inflorescence mutant) with 25 RAPD and 29 ISSR primers, which enabled to know the diversity among mutants and control. Maximum PIC, He, Ho, EMR and Rp registered with the RAPD and ISSR primers prompts insight of molecular complexity involved. Mutant population showing novelity, superiority in quality and yield were selected for progressing them to the next generation. The mutants M2, M50, M63, M83, M120, M185, M212, M243, M308, M319, M336, M337, M349, M395, M398, M436, M490 showed superiority in yield and quality traits. Hence, these mutant plants have been selected for progressing to M2 generationEnglishThesis