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20221
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Subject: Genetics and Plant Breeding × End date: 2022 × Start date: 2022 × 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.