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ThesisItem Open Access Identification of molecular markers and quantitative trait loci(QTLs)associated with drought tolerant and plant production traits in rice(Oryza sativa L.)using association genetic analysis(Department Of Plant physiology, College Of Agriculture, Vellayani, 2020) Nithya, N; KAU; Beena, RThe present investigation entitled “Identification of molecular markers and Quantitative Trait Loci (QTLs) associated with drought tolerant and plant production traits in rice (Oryza sativa L.) using association genetic analysis” was conducted at Department of Plant Physiology, College of Agriculture, Vellayani and RARS, Pattambi during 2016-18 . The objective of the study was to identify molecular markers, Quantitative trait loci (QTLs) associated with drought tolerance and plant production traits in rice under drought condition. The extend of variation for water stress indicators for morpho-physiological and plant production traits were assessed by evaluating 81 rice genotypes collected from RARS, Pattambi and NRRI, Cuttack under water stress and irrigated conditions in the open field. Each genotype was raised in four rows of 2m length and was exposed to water stress at panicle initiation stage for a period of 25 consecutive days by withdrawing irrigation along with irrigated control and replicated twice. The morpho- physiological, and plant production traits were recorded after imposing water stress. Significant variation was observed for these traits under water stress condition. Genotyping of 81 rice genotypes were done using 100 SSR primers. Quality and quantity of DNA was checked. Amplification pattern of 100 primers were scored as per standard procedure. Population structure was calculated using the software “STRUCTURE” with genotypic score value. The molecular markers/ QTLs linked to drought tolerance and plant production traits were identified using the software, TASSEL 5. The result of the study revealed that morphological parameters such as the plant height at flowering was observed to be highest in PTB1 and lowest in ASD-16 under water stress condition in both experiments. The number of tillers were maximum for PTB7 (10.5 plant-1) and minimum for Kuttithekkan under water stress condition in both experiments. Delayed days to 50% flowering (7 days) was observed for the genotypes under water stress in two experiments compared to irrigated control. Physiological parameters such as Relative Water Content (RWC) decreased where as leaf temperature increased significantly in most of the genotypes under water stress condition. Highest leaf rolling (score – 7.78) was observed in Prathyasha in both experiment I (7.78) and experiment II (7.84). But the genotypes PTB55 (1.78) & PTB 29 (1.11) showed least leaf rolling symptoms in both experiment I and II respectively. Among the genotypes, the RWC was recorded to be highest in PTB15 (78.72%) while the lowest was recorded in Prathyasha (57.34%) under water stress condition in experiment I and in experiment II maximum relative water content was observed in PTB27 (72.98%) and minimum in ADT37 (50.25%). Membrane stability index was highest in PTB29 in experiment I (94.36 %) and in PTB27 in the experiment II (92.24%). Maximum leaf temperature was observed in PTB1 and minimum in Prathyasha under water stress condition in both experiments. Among the genotypes, chlorophyll stability index was recorded to be highest in PTB27 (95.59%) while the lowest in Pandichempan (80.36%) in experiment I, and in experiment II maximum was recorded in variety PTB7 (92.85%) and minimum in Pandichempan (75.52 %). The grain yield per plant under water stress condition was positively correlated with parameters such as tiller numbers, days to 50% flowering, relative water content, membrane stability index, chlorophyll stability index , spikelet fertility percentage and 1000 grain weight where as negatively correlated with leaf temperature, leaf rolling score, leaf drying score and percentage relative yield reduction. Under water stress the first principal component showed 41.77% variation, while second component exhibited 16.57% variation. Among the 14 morpho-physiological and plant production traits, relative water content, cell membrane stability index and chlorophyll stability index contributed towards maximum diversity. Under irrigated control condition the first principal component revealed 48.9 % variation, while the second component showed 16.57% variation. Among the 8 morpho-physiological and plant production traits studied, the relative water content and spikelet fertility percentage contributed towards maximum diversity. Clustering by Ward method was done to establish a relationship among the 81 rice genotypes. Similar types of genotypes were clustered together based on the phenotypic data. All the genotypes were clustered mainly into 5 clusters under water stress as well as irrigated control condition. Genotyping of eighty one rice genotypes were done using 100 SSR markers. Among them, 40 primers which demonstrated polymorphism among the genotypes were used to classify the genomic regions (QTLs) associated with drought tolerance and plant production traits through association genetic analysis. The marker trait association for all the traits under water stress and irrigated control condition were calculated using GLM and MLM model of TASSEL5 software. A total of 136 marker trait associations were observed while performing GLM analysis and MLM analysis resulted in 48 marker trait association based on the P and r2values in water stress as well as irrigated control condition. LD was distributed unequally on each chromosome and more concentrated on chromosomes 1 and 7. LD analysis in the whole population showed that there were significant LD pairs (P<0.05). A total of 52 LD pairs were observed under water stress and irrigated control conditions and out of these, there were 46 inter chromosomal LD pairs and 6 intra chromosomal LD pairs. The markers RM3825, RM455, RM490, RM259 and RM1026 showed significant associations with many phenotypic traits in water stress as well as irrigated control conditions. The Q-Q (Quantile-Quantile) plot also confirmed the association of these markers with phenotypic traits. In summary, there was significant variation for morpho-physiological and plant production traits among rice genotypes under water stress condition. Genotypes having higher relative water content, cell membrane stability index and chlorophyll stability index were found to be tolerant to drought. In the present study, the genotypes viz PTB28, PTB29, PTB30, PTB15, PTB7, PTB55, N-22 and Chomala identified as drought tolerant can be used in breeding programmes to improve drought tolerance in rice. From this study, 29 significant (P<0.05) marker trait associations were detected using mixed linear model (MLM). The identified most significant markers and their corresponding QTLs are, RM455 (Chromosome7) was linked to tiller number, leaf temperature, relative water content, yield per plant and spikelet fertility percentage. RM490 (Chromosome1) was associated with leaf temperature and chlorophyll stability index. Marker RM259 (Chromosome1) was associated with leaf temperature, chlorophyll stability index, leaf drying score, yield per plant and spikelet fertility percentage. RM1026 (Chromosome 9) was associated with leaf rolling score and drying score. Among them, RM 490 and RM259 showed co-location of QTLs for leaf temperature and chlorophyll stability index and RM259 & RM1026 showed co-location of QTLs for leaf drying score.ThesisItem Open Access Mitigating the phytotoxic effect of ALS inhibiting herbicides in rice (Oryza sativa L.)(College of Horticulture, Vellanikkara, 2016) Nithya, N; KAU; Girija, TThe study on “Mitigating the phytotoxic effect of ALS inhibiting herbicides in rice (Oryza sativa L.).” was conducted during 2015-2016 at Agricultural research station, Mannuthy, with the prime objective of mitigating the growth inhibition due to the application of post emergent ALS (Aceto Lactate Synthase) inhibitors, bispyribac sodium azimsulfuron and to improve the productivity of rice. The experiment was laid out in RBD with three replications and there were eleven treatments comprising of two Aceto Lactate Synthase inhibitors viz., bispyribac sodium (30 g ai/ha) , azimsulfiiron (35g ai/ha) and five mitigating treatments viz., Urea spray (0.1%), Micronutrient spray (1 gm each of zinc sulphate and borax, 0.01 gm of molybdic acid/litre), NAA spray (100ppm), Tank mix and water spray (1000 ml) with hand weeded as control. Herbicides were sprayed on 15 DAS whereas mitigating treatments were sprayed on 35 DAS. Observations on morphological, physiological, biochemical, yield and yield attributes of rice were recorded. Morphological characters were studied at 15 days interval and biochemical estimations were done 7 days after herbicide application and at the time of flowering. Mitigation treatments resulted in a 10- 13 % increase in height and 4-8 % improvement in tiller number of rice plant at harvest compared to plants in the hand weeded plot. Effect of mitigating treatments on growth attributes viz., relative growth rate, crop growth rate , net assimilation rate, and leaf area index indicated that at the final stages of growth there was no significant difference between the treatments. However during the critical stages of growth i.e.,45-75 DAS significant variation was observed. Among the mitigation treatments, bispyribac sodium followed by tank mix applied plots had higher values as compared to the other treatments whereas azimsulfuron applied plots had the lowest value for these parameters. The biochemical parameters such as nitrate reductase enzyme activity and total soluble protein content showed an initial decline when estimated one week after application of herbicide. At the time of flowering, recovery was higher in the plants where foliar spray of mitigating treatments were given as compared to water spray. Tank mix applied plots recorded more value for the above biochemical parameters in both bispyribac sodium and azimsulfuron applied plots. Proline content and catalase enzyme activity showed increase with herbicide application when compared to hand weeded control indicating that application of these chemicals may be imparting stress to the plant, however by flowering time in most of the treatments there was recovery. The physiological parameters such as chlorophyll content, and IAA content showed decline but there was no significant variation in photosynthetic rate and stomatal conductance between treatments when estimated one week after herbicide application. In the case of chlorophyll content the recovery of the plant was comparatively less as compared to all other chemical constituents. Treatments in azimsufuron applied plots showed maximum reduction in these constituents. In the present study, among the ALS inhibiting herbicides azimsulfuron contributed to higher inhibition in growth and yield of rice when compared with bispyribac sodium. Mitigating treatments contributed to 20 to 24 % increase in grain yield and 20 to 27 % increase in straw yield of rice. Tank mix applied plots recorded highest grain yield and urea applied plots recorded highest straw yield.
