1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)
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Item Population structure analysis in stylo [Stylosanthes sp.] using SSR markers(Department of Plant Biotechnology, College of Agriculture , Vellayani, 2022-10-27) Fathima Zahra ,P M; Gayathri, GStylosanthes is a dominant pasture legume growing in tropical and subtropical regions of India and is extensively applied as forage and cover crop in agricultural systems. The fundamental concern with Stylosanthes is the restricted number of superior varieties. The genus Stylosanthes under the family Fabaceae comprises approximately 50 spp. distributed worldwide in the tropics among which S. scabra, S. seabrana, S. hamata and S. guianensis are predominant. The current study entitled “Population structure analysis in Stylo [Stylosanthes sp.] using SSR markers” was undertaken at College of Agriculture, Vellayani, Thiruvananthapuram to assess the genetic variability among Stylosanthes accessions using SSR markers and to construct the population structure of Stylosanthes genotypes thereby delimiting these species. In this study, 19 accessions of Stylosanthes which belong to the genotypes S. scabra, S. seabrana, S. hamata and S. guianensis were collected from IGFRI, Jhansi, Kerala Livestock Development Board and centres under AICRP on Forage Crops and Utilisation. The 19 accessions were characterized using fifty seven molecular markers and correlated with the available phenotypic data. The purity and concentration of DNA ranged from 1.63 to 1.96 and 525 ng/µl to 3024 ng/µl respectively, indicates that a good quality DNA obtained from the Stylosanthes species. Forty nine markers showed amplification and produced a total of 120 alleles among the 19 Stylosanthes accessions. Forty one showed polymorphic bands and they produced a total of 101 polymorphic alleles. The highest number of alleles was produced by gSsb-16 (6 alleles) and the polymorphism information content (PIC) for these markers revealed that gSsb-11, eSgu-29 and eScap-24 (0.48) have the highest PIC followed by gSsb-16 (0.477). S. hamata (T5) and S. seabrana (T18) showed more than one allelic band in a maximum number while S. seabrana Phule Kranti (T9) showed only one allelic band with the entire set of polymorphic markers A Bayesian model population structure study of these 19 Stylosanthes accessions using STRUCTURE v2.3.4 showed the existence of three gene pools (number of sub-population, k = 3). Also, the dendrogram generated using NTSYSpc v2.02e, based on 41 markers distinctively demarcated Stylosanthes accessions into five clusters indicating its vast genetic diversity in the 91 population. A maximum genetic similarity of 85.37% was shown by two pairs of accessions namely S. scabra ILCA140 (T1) with S. seabrana (T19) and S. scabra Fitzroy (T7) with S. seabrana (T13). A minimum genetic similarity of 48.78% was shown by S. guianensis CIAT (T10) with S. hamata (T11). Variance components analysis of seven phenotypic characteristics showed that the values of PCV and GCV was higher for leaf breadth, green fodder yield per plot and dry fodder yield per plot; high heritability coupled with high genetic advance was noted for green fodder yield per plot and dry fodder yield per plot. Cluster analysis based on phenotypic data divided the 19 Stylosanthes accessions into five clusters. The highest similarity was observed in S. scabra DRSS4-RRR94197 (T4) with S. seabrana (T14) at a similarity coefficient of 0.71. In the study, S. scabra with S. seabrana showed the highest genetic similarity within the genotypes in terms of molecular and phenotypic cluster analysis and the grouping was performed irrespective of the origin of genotypes. A better performance in phenotypic traits and molecular analysis was noticed in S. guianensis Reyan (T8) and S. guianensis CIAT (T10) showing their suitability in fodder improvement programmes of Stylosanthes species. Overall, the level of genetic variability and 76.9 per cent average polymorphism indicated by the primers in the current study suggests that SSR markers can be utilized for fodder improvement and genetic resource management and utilization. For proper validation of the results obtained, cytological studies of the Stylosanthes accessions, increasing the number of accessions in the different species and evaluation of more SSR markers need to be done.Item Genetic diversity analysis of indigenous rice varieties in Kerala using molecular markers(Department of Plant Pathology, College of Agriculture, Vellayani, 2019) Ajith, M K; Jayalekshmy, V GThe present study entitled “Genetic diversity analysis of indigenous rice varieties in Kerala using molecular markers “was carried out in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, Thiruvananthapuram during 2017-2018. The study was conducted with the objective to analyze the genetic diversity of traditional rice varieties in four agro climatic zones of Kerala using RAPD and SSR markers. Five varieties were collected from the each agro climatic zones viz., hill areas of Wayanad, rice growing tract of Palakkad, saline soils of Pokkali and Kuttanad soils. The DNA was isolated and RAPD analysis with 10 Operon primers and SSR analysis was done with ten RM primers. In the RAPD analysis the ten operon primers produced 88 amplicons with an average polymorphism 82%. Resolving power OPC-07 (15.4) had the highest value but its Polymorphism Information Content and Effective Multiplication Ratio (EMR) were considerably low. Considering all the three parameters together primer OPF-06 is found to be the best RAPD primer with considerably high polymorphism information content, resolving power and effective multiplication ratio. The dendrogram constructed based on the RAPD scoring showed that varieties Pokkali and VTL-2 had maximum similarity. These two were from Pokkali rice tract. PTB 12 from Pattambi was found to be unique and it clustered with others only at 30% similarity.The clustering of the genotypes did not show any correlation with the geographic origin. ABL 12 and VTL- 2 showed 70 % similarity but those two were from Wayanad Hills and Pokkali tract respectively. Vellakuttadan from Moncombu clustered with PTB 2 from pattambi at 72% a similarity. Kochuvith and Vellakuttadan from Moncombu clustered at 67 %. All the SSR markers produced two alleles except RM 210 and RM 204 which produced four alleles and one allele respectively. All the alleles of all the markers were polymorphic except that of primer RM204. The polymorphism information content of the SSR primers used in the study ranged from 0 to 0.88. In this study the highest PIC value of 0.88 was reported by RM 210 followed by RM 567 (0.85). The resolving power and EMR was also highest for RM 210. The dendrogram constructed based on the SSR markers could give a clustering of genotypes more correlated with the geographic origin. Genotypes Kochuvithu and Vellakuttadan showed 100 % similarity both where from Kuttanad. But Karavalakochuvith, T.virippu, and PTB 2 also showed 100% similarity but these three were from Moncompu, Pokkali and Palakkad respectively. At around 90 % similarity AMB 14, AMB 22 from Wayanad, Pokkali andVTL-2 from Pokkali, PTB 13 and PTB 8 from Palakkad clustered showing more correlation to the Geographic origin. SSR markers being sequence specific and flanking the repeat sequence which has more role in evolution, are more reliable in predicting the Genetic diversity based on origin. Since both of them could not give a clear-cut clustering based on geographic origin an analysis using both the markers together was done. This gave a better picture of the clustering as it involved more number of variables. But here also the varieties from Wayanad A1 to A5 were scattered in different clusters. Only A 14 and A15 (AMB 14 and AMB 5) clustered at 60 percentage similarity. The accessions from moncompu (A6-A10) clustered at around 50 % similarity. In the accession from Pokkali tract (A11-A15) only T.virippu to VTL-2 clustered at 78 % similarity. Accession from central zone Pattambi (A16-A20) was scattered into different clusters. PTB 12 was unique from other accessions. This molecular diversity analysis of the traditional rice genotypes from four different agro climatic zones could find that the maximum similarity was 78% and that too only between two accessions. The diversity among the genotypes was 64% as all the genotypes clustered at 36% similarity. The clustering of the genotypes did not show any correlation with the geographic origin. Exchange of varieties between the farmers and some amount of natural crossing would have led to the mixture of populations of rice genotypes in different agro climatic zones.Item Development of cytoplasmic male sterile line in an identified rice variety of Kerala through marker assisted back crossing(Department of Plant Breeding & Genetics, College of Agriculture, Vellayani, 2019) Tejashree Shivaputra Lachyan; Jayalekshmy, V GItem Characterisation of pumpkin (Cucurbita moschata duch.) varieties through morphological and molecular markers(Department of Seed Science and Technology, College of Horticulture, Vellanikkara, 2019) Agina Gopan; Rose Mary FranciesPumpkin (Cucurbita moschata Duch.), a crop of Central Mexican origin belonging to the family Cucurbitaceae, is popularly cultivated and valued in Kerala as a vegetable. The tender, large and often round immature fruits of pumpkin with a thick, smooth to slightly ribbed skin, which is mostly deep yellow to orange in colour, is an integral part of the Kerala cuisine. Despite its popularity in the state, few high yielding varieties are in cultivation. To ensure increased production, availability of high quality seeds of improved varieties or hybrids has to be guaranteed. Pumpkin being a cross pollinated crop, occurrence of cross contamination during its seed programme cannot be overruled. Hence, ensuring the purity and identity of seeds of the variety before sale becomes inevitable. Considering the importance of varietal identification in maintaining the genuineness and quality of seeds in seed production programmes, the present investigation envisaged to characterise six pumpkin varieties in the seed chain using morphological and molecular markers, and to generate fingerprints or molecular ID’s of the six varieties using selected polymorphic Inter-simple sequence repeats (ISSR) and Simple sequence repeats (SSR) markers. Characterisation of pumpkin varieties based on 28 quantitative and 16 qualitative traits was done using DUS and NBPGR descriptors. Qualitative vegetative traits like tendril characteristics (presence or absence of tendril, nature of coiling and branching) and leaf shape were not useful for grouping the varieties. Similarly, among the qualitative fruit characteristics, waxiness of mature fruit skin also proved insufficient to distinguish the varieties. Fruit shape was round flat in varieties Ambili, Suvarna and CO-2, while it was elongate/oblong in Saras, club shaped in CO-1 and flattish round in Arka Chandan. Based on qualitative traits, variety Arka Chandan could be clearly distinguished from the other varieties based on poor early growth vigour, moderately incised leaf blade margin, absence of silver patches on leaf blade, flattish round fruit shape, light green immature fruits and dark orange fruit flesh colour. In addition, the seeds of the Arka Chandan had a characteristic marking on the dorso-ventral surfaces unlike other varieties. Quantitative traits proved to be more useful than the qualitative traits for effective identification and categorisation of varieties. Results revealed that among the quantitative traits studied, leaf dimensions (blade length and width) and length of petiole could not be employed for distinguishing the six varieties. Variety Ambili flowered the earliest (49.25 days) and also possessed highly pubescent leaves, while variety Arka Chandan was late flowering (68.00 days). Peduncle length, fruit length and most of the seed dimensions (seed count per fruit, 100 seed weight, width and thickness of seed) was the least in this variety. In general, the size of seeds in varieties CO-1 and CO-2 was higher than those of others. Cluster analysis grouped Arka Chandan (Cluster V) and varieties CO-1 and CO-2 (Cluster IV) the farthest with an inter-cluster distance of 212.25. Principal component (PC) analysis indicated that trait components in PC1 registered an Eigen value of 16.79 and the traits in PC1 contributed 58 per cent to the variability among the varieties, emphasising their utility in identification of varieties. Among the 33 ISSR markers, 28 exhibited polymorphism. The total number of amplicons detected by an individual primer ranged from 4 in UBC-818 to 18 in UBC-847. High polymorphic information content (PIC) value was observed in UBC-809, whereas, low PIC was recorded in UBC-818. The six varieties grouped into four clusters based on ISSR binary data. Out of 20 SSR markers used for genotyping, only five showed polymorphism. The highest Jaccard’s similarity value (1.00) was observed between Saras and Suvarna. The most dissimilar varieties were Saras and Arka Chandan, and Suvarna and Arka Chandan, with a similarity coefficient of 0.12 each. The clustering algorithm grouped the varieties into four clusters. The polymorphic SSRs could be efficiently utilised for distinguishing Arka Chandan and therefore can prove useful for testing the genetic purity of this variety. Unique bands producing ISSR markers were used to generate variety specific DNA fingerprints. No single primer per se proved useful in distinguishing all six pumpkin varieties. However, ISSR primer UBC-822 could distinguish four out of six varieties studied. It produced unique amplicons of size 473 bp, 552 bp, 1403 bp and 517 bp, respectively in Ambili, Saras, CO-1 and Arka Chandan, proving its utility in testing for genuiness and purity of seed lot. In general, it can be concluded that the correlation that existed between morphological and molecular assessments was of medium magnitude. The absence of high consensus between the assessments should not be considered a limitation of these tools to characterize and quantify variability. It only indicates that both morphological and molecular characterisation is important and play a complementary role in providing a better understanding and differentiation of the pumpkin varieties.Item Marker assisted selection for heat tolerance in rice (Oryza sativa L.)(Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, 2019) Silpa, V; Sindhumole, PRice is highly susceptible to heat stress, particularly during the reproductive and ripening stages. In the major rice growing tracts of Kerala viz., at Palakkad, Kole and Kuttanad, the temperature tends to rise up to 40 ºC or more during the second/third crop. Consequently, high temperature induced sterility has become a serious problem. To tackle this, high yielding varieties coupled with heat stress need to be developed. As most of the prevalent high yielding rice varieties in Kerala including Uma are highly susceptible to heat stress. It is therefore, essential to impart heat tolerance to such varieties which are cultivated to a very large extent. Marker assisted selection (MAS) has been identified as a dependable, reproducible and time saving strategy to confirm the presence of desirable gene and to quicken the breeding cycle. A study conducted for the identification of SSR markers linked to the genes for heat tolerance in rice through bulked segregant analysis approach using F3 population of the cross Uma x N22 revealed that microsatellite marker, RM5749 was tightly linked to spikelet fertility trait under heat stress. The F4 population (59 nos.) raised from seven F3 lines that were found tolerant to heat stress comprised the base population for the present study. They were characterised morphologically and heat tolerance was scored under natural heat stress in the field conditions based on IRRI spikelet fertility classification. In the 26 F4 lines that registered more than 75 per cent spikelet fertility, foreground selection was done using RM5749. All the 26 F4 plants registered an amplicon corresponding to the heat tolerant parent N22. Background selection of these 26 lines was done using 35 markers found polymorphic between the parents Uma and N22. Seventy five F5 plants were evaluated for morphological characters. Among these, nine F5 plants (Plant nos.16.1.4, 16.1.5, 16.1.6, 31.2.3, 31.2.4, 31.2.5, 31.5.1, 31.6.6, and 31.6.9) with high spikelet fertility (60-70 %) were selected and genotyped using RM5749. These lines were further genotyped using the 35 polymorphic background markers. All the nine F5 plants recorded 54-64 % similarity to Uma genome. The highest spikelet fertility percentage was observed in plant no.16.1.5 (70.78 %) while the highest recovery of the parental genome of Uma was found in plant no. 31.2.5 (64.28 %). Backcrossing of the seven selected heat tolerant lines of F4 (lines 12, 13, 15, 16, 31, 41, and 45) with Uma as male parent resulted in production of BC1F1 seeds. However, the seedlings raised from these seeds did not survive under field conditions. The results obtained thus indicated that the nine lines selected in the present study are to be evaluated in further generations morphologically inorder to isolate genotypes with tolerance to heat stress.Item Characterization of selected curcuma species germplasm using morphological and molecular markers(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2018) Bimal Thomas; Asha, K ICurcuma L., a perennial rhizomatous herb, is gaining global importance as a source of starch besides its medicinal property and use as a spice. Characterization of germplasm is very essential in crop plants and it is the basis for selection of accessions for use in crop improvement programmes. This research work was an attempt to characterize the fifteen selected accessions in eight species of Curcuma collected from different parts of India and maintained in the field gene bank of ICAR-CTCRI using morphological and molecular markers. Two accessions in each of C. amada, C. angustifolia, C. aromatica, C. decipiens, C. malabarica, C. raktakanta, C. zedoaria and one of C. longa were selected. These 15 accessions were morphologically characterized using 13 qualitative and 15 quantitative traits and a wide variability was observed. Dendrogram based on the morphological characters grouped the genotypes into four clusters. PCC analysis revealed that the accessions of the same species have shown more than 83% similarity except C. angustifolia. C. raktakanta accessions have shown a highest intra-specific similarity of 94%. C. decipiens accessions were found to be the highly variable from the most commonly exploited species C. longa while C. aromatica has shown highest similarity. PCA showed that the characters such as leaf midrib colour, rhizome flesh colour, leaf texture and aroma of rhizome have contributed mostly to the variability. Molecular characterization was done using 10 ISSR and 7 SSR markers. The total percentage polymorphism obtained by ISSR characterization was 94.31 while it was 91.11 percentage in the SSRs. C. angustifolia-1 was found to be highly variable from C. angustifolia-2 suggested the occurrence of intraspecific variability. The intra-specific similarity among C. raktakanta accessions were found to be highest than all other accession pairs. Clustering based on ISSR markers grouped the genotypes into five clusters while SSRs into six clusters. Mantel’s test showed a positive correlation between the morphological and molecular data. The results of the present study indicated that the morphological as well as the molecular tools were found to be very effective in the characterization of germplasm of Curcuma species for the developement of core collections and for further use in the crop improvement programmes.Item Genome wide marker assay for the recovery of recurrent parent genome in rice (oryza sativa)(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2018) Bhagyalekshmi, R; Jayalekshmy, VGBacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major constraint in major rice growing areas of the world particularly in Asia. The disease is prelevant in the kharif season and it results in a greater yield loss. Since there is no valid chemical control measure, exploiting host plant resistance is an efficient way to tackle this problem. Approximately 40 genes conferring resistance to BB were identified. Pyramiding of these genes into the background of susceptible parent with good agronomical traits is the best strategy that can be adopted to develop plant varieties durable resistance to BB. So the present study entitled “Genome wide marker assay for the recovery of recurrent parent genome in rice (Oryza sativa)” was undertaken in College of Agriculture, Vellayani, Thiruvananthapuram to estimate the reconstitution of genome of Aiswarya (RP) rice variety in the BC2F1 plants pyramided with genes for resistance to Bacterial leaf blight through molecular markers covering the entire genome of Aiswarya. DNA markers closely linked to the BB resistance genes,viz.,xa13 pro (xa13gene), pTA248 (Xa21gene), RMWR7.1 (Xa33gene) were used for validation of the marker polymorphism in the donors for the genes. Improved Samba Mahsuri with xa13 and Xa21, Samba Mahsuri with Xa33, were taken as donors and Aiswarya was chosen as the recipient parent. The validation of gene specific markers confirmed the absence of the genes in the recurrent parent used in the study. And these markers were further used for foreground selection in BC2F1 plants. Also, the donor and recurrent parents used in the study were screened with 320 SSR primers in order to find the markers specific to the recurrent parent. In this screening out of 320 markers used, 44 were found to be polymorphic and these polymorphic markers were used in the background selection. Foreground selection was performed initially in all the 149 BC2F1 plants to identify the presence of these genes. In the foreground selection, a total of 149 plants were screened and 79 plants were found to have xa13 gene and 38 plants confirmed the presence of Xa21 gene while none of the screened plants showed the presence of Xa33 gene. 23 plants were found to possess two gene combinations of xa13+Xa21 and these plants were subjected to background selection to estimate the percentage introgression of the recurrent parent genome. Background screening of the plants identified with two gene combination using the 44 markers specific to recurrent parent revealed the number of markers showing homozygosity and heterozygosity with the recurrent parent. With this information percentage recovery of RPG was calculated and found that among 23 plants, the maximum recovery found was 84.09% and a total of 5 lines were showing more than 80% recovery of recurrent parent genome. The present study could identify BC2F1 plants identified with xa13 and Xa21 with genome recovery of more than 80% and further screening can be done in the BC2F2 generation to develop Essentially Derived Variety.Item Association mapping for cassava mosaic disease (cmd) resistance in cassava using SSR marker(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2017) Aparna, T K; Mohan, CThe present study” Association mapping for Cassava Mosaic Disease (CMD) resistance in cassava using SSR marker” Was conducted to identify the marker which are closely associated with CMD resistance in cassava. 30 CMD resistant and 25 CMD susceptible cassava varieties were analyzed with 2n selected SSR primers. Genomic DNA isolated from the leaves and PCR amplification was done with SSR primers. PCR products were separated by PAGE. Polymorphic bands were used to assign loci for each primer and score as presence (1) or absence (0) of bands. RMEI primer showed double banding pattern in 700bp size for all the resistant accessions. But in case of susceptible accessions only single bands were observed. TASSEL and STRUCTURE software were used ro analyses the data obtained from the PAGE.. Cladogram was constructed using genotypic data. Different clusters were formed. Clusters clearly distinguished CMD resistant and CMD susceptible varieties of cassava. CMD resistant varieties sub divided into three sub clusters. Dissimilarity matrix constructed by the software used for the diversity study of collected cassava accessions. Two markers were associated with CMD resistance was identified by the software. SSR36 are the two markers associated with CMD resistance. Result showed that there are eight sub populations in the cassava population used. Based upon the output obtained from Evanno’s method a bar diagram was constructed. Which shows the distribution of genotypes in different sub populations.Item Introgression of mosaic resistance in popular short duration cassava varieties of Kerala through marker assisted selection(Deparment of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2018) Darshan, S; Arya, KThe present study entitled “Introgression of mosaic disease resistance in to popular short duration cassava varieties of Kerala through marker assisted breeding”was conducted in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, Kerala Agricultural University and Division of Crop Improvement, ICAR- Central Tuber Crops research Institute, Sreekariyam, Thiruvananthapuram, Kerala during the period 2014 - 2017 with the core objective of introgression of cassava mosaic disease (CMD) resistance to short duration varieties of cassava through marker assisted selection (MAS) and to study the inheritance of early bulking nature. The research work was carried out as four experiments. In the first experiment, Five early bulking high yielding lines viz, Sree Jaya, Sree Vijaya, Vellayani Hraswa, CI 889 and 9S 75 and three testers viz, CR 54A3, IMS2-5 and CI 273 with resistance to cassava mosaic disease were selected and planted in a pollination block and crossed in Line x Tester (LxT) design to produce hybrid seeds of 15 F1 combinations. Experiment II was conducted in two parts. Screening of F1 seedlings for CMD resistance and early bulking nature was carried out in the first part of experiment II, where hybrids along with the parents were evaluated. Analysis of variance revealed significant differences among the genotypes for all the traits studied. All the agronomic traits were recorded and inheritance of early bulking and its correlation with other traits were studied. The CMD incidence expressed significant and negative correlation with tuber yield per plant where as significant and positive correlation for all other traits with tuber yield per plant was observed among the F1’s. As a part of experiment II (b), seedlings without the CMD visual symptoms were subjected to multiplex PCR and the results revealed that among the parents Sree Jaya, Sree Vijaya, Vellayani Hraswa expressed presence of Srilankan Cassava mosaic Virus (SLCMV) and Vellayani Hraswa expressed the presence of both SLCMV and Indian Cassava mosaic Virus (ICMV). Among the crosses, Sree Jaya x CR54 A3 (L1x T1), Sree Jaya x IMS2-5 (L1xT2), Vellayani Hraswa x IMS2-5 (L3xT2), CI 889 x CI 273 (L4xT3) expressed the presence of SLCMV. Real time PCR (qPCR) assay for seedlings identified CI 889 (L4), 9S 75(L5), CR 54A3 (T1), IMS2-5 (T2) and CI 273(T3) among the parents and Sree Jaya x CR54 A3 (L1x T1), Sree Jaya x IMS2-5 (L1xT2), Sree Jaya x CI 273(L1x T3) and 9S 75 x CR54 A3 (L5x T1), 9S 75 x IMS2-5 (L5xT2) and 9S 75 x CI 273 (L5x T3) among the crosses as highly resistant, based on viral load present in the DNA sample. Based on the previous report ten CMD resistance linked markers were screened through BSA and five of which SSRY 28, SSRY 44 SSRY 40, SSRY 106 and SSRY 235 were selected. Among the CMD linked SSR markers studied, the maximum polymorphism was elucidated by SSRY 28, SSRY 44 and followed by SSRY 235. SSRY 28 is a strongly linked marker to CMD2 which is a dominant gene conferring resistance among the clones of combinations (L1xT1, L2xT2, L3xT1 and L3xT3) three of five markers revealed alleles associated with CMD2 gene In the third experiment to evaluate the early bulking clones, field was laid out in randomized block design (RBD) with three replications consisting of CMD resistant clones along with parental clones using miniset technique. Analysis of variance revealed significant differences among the genotypes for all the traits. Measurement of heterosis was carried out considering parent Vellayani Hraswa (L3) as check and results revealed that standard heterosis was positive and significant in the combinations Sree Jaya x CR 54A3 (L1xT1) and Sree Jaya x CI 273 (L1xT3) for all the yield contributing traits. The crosses Sree Jaya x CR54 A3 (L1x T1) and Sree Jaya x CI 273 (L1xT3) exhibited negative standard heterosis for CMD. Combining ability analysis showed significant gca, sca variances and gca, sca effects for all the traits. Moreover gca/sca variance ratio indicated preponderance of dominance / non-additive gene action for the inheritance of all traits. Among the lines, Sree Jaya (L1) exhibited positive and significant gcaeffect for tuber yield and yield contributing traits. Among the testers, IMS2-5 (T2) exhibited negative and significant gca effect for CMD. Among the crosses Sree Jaya x CR54 A3 (L1x T1) exhibited positive and significant scaeffect for girth of tuber and stem girth, 9S 75 x CI 273 (L5xT3) exhibited positive and significant scaeffect for tuber yield per plant, CI 889 x CR 54A3 (L4xT1) exhibited negative and significant scaeffect for CMD. In the last experiment, through bulk segregants analysis using 5 SSR markers linked to early bulking in cassava were selected out of 9 SSR markers selected. Among 5 SSR markers of CMD and early bulking nature two SSR markers (SSRY 28 and SSRY 106) associated with resistance to CMD and One SSR marker, ESTs (SSRY) 292 associated to early bulking nature has been identified. Among the crosses, clones from Sree Jaya x CR54 A3 (L1xT1), Sree Jaya x CI 273 (L1x T3) and 9S 75 x CR 54A3 (L5xT1) are being confirmed with CMD resistance as well as early bulking nature.Item Molecular characterization of rice genotypes having Variability in heat tolerance(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2017) Neethu V Mohan; Beena, RThe study entitled “Molecular characterization of rice genotypes having variability in heat tolerance” was conducted at the Department of Plant Physiology, College of Agriculture, Vellayani, Thiruvananthapuram. Rice (O. sativa) is very sensitive to high temperature especially at the reproductive and grain filling stage which leads to higher spikelet sterility and ultimately yield losses. The present investigation was, therefore, carried out with the objective to study the variation in rice genotypes for heat tolerance using microsatellite markers. In the present study, a set of 50 SSR primers were employed to assess the genetic diversity among the 10 genotypes. Out of 50 markers, 11 markers showed polymorphism, the marker RM6100 was found as a functional marker associated with heat tolerance in rice, and is functional for further crop breeding programmes. A dendrogram was generated with the aim of analyzing the relationships between the 10 genotypes tested. The genetic similarity index ranged from 0.1 to 0.833. The lowest value 0.1was obtained between PTB7 and CR Dhan202 while highest similarity value (0.833) calculated was between the PTB7 and CR Dhan204 genotypes. However, the genetic diversity analysis with SSR markers will contribute to maximize the selection of diverse parents in the future rice breeding program or development of heat tolerant cultivars.