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Theses

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2014 - 201912020 - 20221
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Subject: Genetics and Plant Breeding × Start date: 2013 × Type: Thesis × Thesis Type: Ph.D ×
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    ThesisItemOpen Access
    GENETIC ASSESSMENT FOR WEED SUPPRESSIVE ABILITY AND VESICULAR ARBUSCULAR MYCORRHIZA (VAM) ASSOCIATION OF RICE (Oryza sativa L.) CULTIVARS IN ORGANIC CULTURE CONDITION
    (2022) Roy, Swapan Deb; Borgohain, Rupam
    Rice cultivation in direct seeded condition encounter a lot weed pressure as compared to wet condition leading to considerable yield loss. Organic direct seeded rice face two major constraints in the early growth stage viz. profound weed competition and poor soil nutrient availability due to non-application of inorganic fertilizers. This makes the situation challenging because of lower production. Development of a weed suppressive variety coupled with higher Vesicular Arbuscular Mycorrhiza (VAM) colonization in the root might be a wholesome approach to mitigate the overall weed problem, water scarcity and poor nutritional status of direct seeded organic production system. An effort was made in the present investigation to study the genetic variability with respect to weed suppressive ability and VAM colonization rate among 50 rice genotypes grown by the farmers in the north eastern India. The genotypes comprised of Jhum, Ahu and Sali cultivars (including joha, bora and bao rice). Attempt was also made to elucidate the inter relationships among different morphological traits contributing to weed suppressive ability and VAM colonization. Path coefficient analysis was used to study the direct and indirect effects of different morphological characters on weed suppressive ability and VAM colonization. Half diallel analysis was carried out to study the gene effects of the two characters and identification of parental genotypes having good combining ability and suitable cross combinations. To assess the weed suppressive ability and VAM response, experiments were carried out in the field condition (in Weedy and weed-free environments) and pots (in VAM inoculated soil and control environments) respectively. The yield loss of the genotypes due to weed infestation ranged from 15.08% (cultivar Inglongkiri) to 73.03% (cultivar Jhummalati). The decline in harvest index due to weed pressure was also observed in some genotypes though there was no coherence in harvest index decline and loss in yield. Marked variation was observed in root zone VAM colonization (measured as % of root colonization) among the genotypes which ranged from 53.5% in Garumalati to 10.5% in Rongadoria. The effect of VAM on the growth of rice genotypes was found to be positive and was reflected by the increased values of some quantitative characters. Among the plant characters positively affected by the VAM, root volume (increased by 8.55%) was the maximum followed by grain yield (7.88%) and straw yield (7.55%) whereas there was no effect of VAM on days to 50% flowering, and days to maturity of the cultivars. The weed suppressive ability of the genotypes (WSA) as measured in term of weed competitive index (WCI) was found to be affected positively by seedling growth rate (r=0.71), seedling vigour index (r=0.71), flag leaf area (r=0.67), number of leaves per panicle (r=0.70), number of effective tiller per plant (r=0.71), harvest index (r=0.74), Grain per panicle (r=0.44) and specific leaf area (r=0.36). Plant characters that were found to have positive correlation with VAM response were number of leaves/panicle (r=0.41), specific leaf area (r=0.31) and grain per panicle (r=0.34). VAM response was however negatively correlated with days for maturity (r=- 0.48), leaf area index (r=-0.35) and root dry weight (r=-0.53). The plant characters having a direct effect on WSA were found to be straw weight (1.13), harvest index (1.31), specific leaf area (0.20), seedling growth rate (0.17), days for maturity (0.31). VAM response had direct effect from number of leaves/plant (0.81), grain number/panicle (1.12), grain yield (0.43) and root volume (0.64) but was affected negatively by seedling growth rate (-0.48), root weight (-0.77) and days for maturity (- 0.01).Based on the response of the cultivars on WAS and VAM response 7 parent cultivars were selected and crossed by half diallele mating design to obtain 21 different F1s. The genotypes along with their parents were evaluated for assessment of their combining ability and nature of gene action contributing to characters WSA and VAM response. Four parents, Inglongkiri (3.49), Adhuma (1.88), Maiborok (1.34) and Rongadoria (1.34) had positive GCA effect for WCI but three parents Garumalati (- 1.16), Jhummalati (-0.76), and Begunagutia (-1.58) showed significant negative GCA effect. Out of the 21 crosses seven crossed genotypes had significant positive effect on WCI and nine crosses had shown negative but significant effect for WCI while, rest five crosses had no significant SCA effect. The genotypes Garumalati (2.80), Inglongkiri (11.83) and Maiborok (4.71) showed significant positive effect for VAM response, while the remaining four parents had showed significant negative GCA effect for root colonization. The SCA effect was positively significant for seven crosses, negatively significant for four crosses and ten crosses showed no significant SCA effect for root mycorrhization. For most of the traits studied including WCI and VAM root colonization, higher magnitude of SCA variance was found compared to GCA variance i.e. GCA/SCA variance ratio was less than unity indicating the predominance dominance variance and non additive gene action. Genotypes Inglongkiri, Garumalati, Maiborok Adhuma and crosses Garumalati X Adhuma, Inglongkiri X Maiborok, Adhuma X Inglongkiri were found to be most promising for future breeding programs for Weed Suppressive ability and VAM responsiveness.
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    ThesisItemOpen Access
    STUDIES ON COMBINING ABILITY AND GENETIC DIVERSITY OF PARENTAL LINES FOR EXPLOITATION OF HETEROSIS IN RICE (ORYZA SATIVA L
    (2014) Borah, Pulin
    The present investigation was conducted at Assam Agricultural University, Jorhat with three broad objectives - (i) to identify potential maintainer and restorer lines from local and improved germplasm, (ii) to study the genetic diversity of CMS, maintainer and restorer lines and (iii) to assess combining ability of CMS and restorer lines. Out of 79 lines evaluated, 22 restorers identified were for 1A, 13 for 3A, 3 for 4A and 10 for 5A based on pollen and spikelet fertility, whereas 3, 2 and 1 maintainers were obtained for IR68888A, IR79156A and IR80555A respectively. Morpho-physiological characterization of the genotypes revealed 6 characters as monomorphic, 12 as dimorphic and 32 as polymorphic. PCV and GCV were high for chaffs per panicle, grains per panicle, grain yield per plant, flag leaf area, culm length, days to first and 50% flowering. Narrow difference between PCV and GCV estimates suggested effective selection for these traits. High heritability coupled with high genetic advance was recorded for days to first flowering, days to 50% flowering, days to maturity, culm length, grains per panicle, flag leaf length, flag leaf breadth and flag leaf area. D² statistics grouped the genotypes into 9 clusters with the highest inter-cluster distance between clusters II-III and IV-IX. The most important characters contributing towards divergence were days to first flowering (40.91%) followed by culm length (17.88%), grains per panicle (9.9%) and panicle length (7.88%). At molecular level, 76 alleles were detected using 15 SSR markers with an average of 5.07 per marker. The Jaccard’s coefficient of similarity ranged from 0.758 to 0.111with an average of 0.385 suggesting diverse nature of the genotypes. The Mantel matrix correspondence test indicated that clusters produced based on morphological and SSR markers were not conserved. The line x tester analysis revealed preponderance of non-additive gene effects suggesting heterosis breeding as a suitable approach for yield improvement. Among the lines, 4A was the best general combiner for earliness, dwarfness and effective tillers per plant and 1A for grains per panicle. A good number of cross combinations had significant SCA effects in desirable directions. The degree of mid/better parent and standard heterosis varied with crosses and characters. Two for panicle length, 16 for effective tillers, one for grains per panicle, 44 for 1000-grain weight and one for biological yield exhibited significant heterobeltiosis as well as standard heterosis. The most productive 14 hybrids recorded 10.12% to 56.46% standard heterosis over Ranjit and could be chosen for evaluation in preliminary yield trials.