PhD Thesis
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Item Nutrient management in cassava (Manihot esculenta Crantz) variety Vellayani Hraswa for southern laterites (Agro ecological unit 8)(Department of Agronomy, College of Agriculture ,Vellayani, 2024-06-01) Aparna, R A.Phosphorus transformation in acid sulphate rice soils of Kerala Acid sulphate soils are lowland soils situated below the mean sea level along the coastal tracts of Kottayam, Alappuzha, Thrissur and Malappuram districts of Kerala, spread in two agro-ecological units namely Kuttanad (AEU 4) and Kole lands (AEU 6). These soils are characterised by high levels of organic matter, low pH and toxicity of iron (Fe) and aluminium (Al) with wide variability in available phosphorus (P) content. Acid sulphate soils generally contain substantial quantities of Fe sulphide minerals or the oxidation reaction products of these sulphidic minerals and the protonated/non-protonated surfaces of Al/Fe hydroxides and oxides, resulting in P sorption and formation of the complexes, thus decreasing P availability in soil. However, the recent fertility evaluations across the state showed high available P status due to solubilization of the accumulated applied P. To develop an economically viable phosphorus nutrient management strategy, a pioneer study on P transformations in acid sulphate soils is highly required. The study aimed to understand seasonal variation of nutrients and transformations of phosphorus in acid sulphate soils. The investigation was conducted at Radiotracer laboratory, College of Agriculture, Vellanikkara, with four experiments viz., collection and characterization of soil samples from the acid sulphate soils of Kerala in two seasons, fractionation of phosphorus, adsorption study and an incubation study. In the first experiment, 125 representative soil samples from Kuttanad (AEU 4) (15 each from Upper Kuttanad, Lower Kuttanad, Vechur Kari, Purakkad Kari and Kayal lands) and Kole lands (25 each from Thrissur and Ponnani Kole) in pre-monsoon (April) and post-monsoon (November) were collected and characterised. The experiments on the fractionation and adsorption of phosphorus were done in thirty-five samples ie., five each from the seven selected locations with varying available P status. Phosphorus fractionation was carried out to quantify different fractions of phosphorus and their contribution to the available pool. The inorganic P fractions includes saloid bound P, Fe-P, Al-P, reductant soluble P and Ca-P. Adsorption study was carried out to work out the quantity/ intensity (Q/I) relationship of phosphorus and the pattern of adsorption in acid sulphate soils. Finally, an incubation experiment of 90 days duration was conducted to understand the effect of phosphatic fertilisers, lime and farmyard manure at different levels in low and high available P soils collected from Kuttanad and Kole lands. The treatment details of the incubation study were three levels of phosphatic fertilisers (as SSP - 0, 35 and 70 kg ha-1), two levels of lime (as CaO - without lime and lime as per POP recommendations) and two levels of farmyard manure (0 t ha-1 and 5 t ha-1). The observations were made on 30th, 60th and 90th days of incubation. Seasonal characterisation of soil samples during the two seasons revealed that among the collected samples, 50 per cent was sandy clay loam and 40 per cent was sandy loam in texture. The acidity characterisation of soil samples reaffirmed the extreme acidity condition of acid sulphate soils with 40 per cent of samples coming under extremely acidic class and 20 per cent under very strongly acidic. Among the collected soil samples, 37.60 per cent was low in available P, 23.20 per cent and 39.20 per cent under medium and high P respectively. The soil sample from Vechur Kari region showed the highest value of organic carbon (11.46 %). The available micronutrients viz., Fe and Mn showed very high concentrations. Among the acidity fractions, potential acidity was dominant followed by pH-dependent acidity in both seasons. Seasonal variation in electrochemical properties like pH and EC was noticed between two seasons. Ultra acidic soil reaction with high electrical conductivity was noticed during pre-monsoon period which reaffirm the salt water intrusion in these locations. Oxidation of pyrite mineral resulted in high amount of available sulphur as well as potential acidity during pre-monsoon. Reduced condition prevailing in the post monsoon resulted in high concentration of available iron. The fractionation study of phosphorus indicated that the per cent distribution of different phosphorus fractions followed the order, Fe- P > organic P > reductant soluble P > calcium P > aluminium P > saloid bound P. The contribution of dominant fraction (Fe-P) to the available P is mainly through saloid bound P. The phosphorus fixing capacity was significantly and positively correlated with clay, organic matter content, and negatively correlated with the available P. In the adsorption study, high buffer power indicated the ability of acid sulphate soils to replenish the depleted available P. Freundlich adsorption isotherm was found to be the best to explain P adsorption followed by Langmuir and Temkin adsorption isotherms. The Freundlich adsorption constant, KF was found to be correlated with organic matter which confirmed the fixation of phosphorus by organic matter in acid sulphate soils. In most of the soils, Langmuir adsorption constant (KL) increased with rise in temperature, indicates chemisorption behaviour of P adsorption. The incubation study affirmed that in soils with low available P, the addition of SSP at doses of 70 kg ha-1 and 35 kg ha-1 along with lime and FYM showed a significant increase in pH. In these soils, the addition of SSP (70 kg ha-1) along with lime and FYM registered the highest available P of 51.63 and 73.33 kg ha-1 respectively in Kuttanad and Kole soils at 60th day of incubation. In the same treatment, Fe bound P fraction was found to be highest with a decreasing trend towards 60th day of incubation, which increased after that. In the case of soils with high available P, the treatment combination with the addition of the highest dose of SSP (70 kg ha-1) along with lime and FYM showed the highest pH with an increasing trend towards 60th day. On the contrary to low P soils, in high P soils, the addition of SSP at 35 kg ha-1 along with lime and FYM registered the highest available P of 309.44 and 126.94 kg ha-1 respectively in Kuttanad and Kole at 30th day of incubation followed by a reduction towards 60th day of incubation. Phosphorus, a widely varying nutrient in acid sulphate soils is prone to high adsorption and fixation in soil depending upon the type of clay, organic matter content and amount of oxides and hydroxides of Fe and Al. There was no significant seasonal variation of P in soil samples from AEU 4 and AEU 6. In acid sulphate soils, the most dominant fraction, Fe-P contributed to available P mainly through saloid bound P, which is the water-soluble and loosely bound P fraction. The reduction of available P with the increase in P fixing capacity necessitates its estimation at least for the grouping of soils for the efficient management of phosphorus. In soils with high available P, addition of lower dose of SSP (35 kg ha-1) along with organic manure (FYM @ 5 t ha- 1) and lime (POP recommendations) is sufficient to enhance the P availability. Where as, in soils with low available P, addition of higher dose of SSP (70 kg ha-1) along with organic manure (FYM @ 5 t ha-1) and lime (POP recommendations) enhanced the P availability than its sole application. In this regard, field experiments in acid sulphate soils have to be conducted to confirm the results of incubation study in rice under natural system and more investigation is needed to know the interaction between organic matter and organic P fraction. As the organic matter plays the dual function in the environment- as a link and as a bottleneck for phosphorus availability, detailed study should be undertaken to know the complex formed by P fixation and its degree of crystallinity for developing better P management strategies in acid sulphate soils.Item Crop-weather-nutrient relations in cassava under drought stress(Department of Agronomy, College of Horticulture, Vellanikkara, 2020) Sreelakshmi, K; Meera Menon, VItem Yield maximization in cassava (Manihot esculenta Crantz) though Hunter`s systematic approach in fertilizer use(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 2003) Susan John, K; Venugopal, V KItem Soil test crop response studies in cassava in laterite soils of Kerala(Department of Agronomy, College of Agriculture, Vellayani, 1997) Kumari Swadija, O; Sreedharan, CItem Managerial efficiency of cassava farmers(Department Of Agricultural Extension, College Of Agriculture, Vellayani, 1991) Asnantharaman, M; Thyagarajan Nair, GThe study aimed at analyzing the managerial efficiency of cassava farmers. It was conducted in four districts namely, Thiruvananthapuram (low productivity), and Pathanamthitta (high productivity) in Kerala State and Kanyakumari (low productivity) and Selem (high productivity) in Tamil Nadu state. The first three districts were considered as non- industrial district and Selem district was considered as industrial district also. A total of 240 cassava farmers were selected, 60 from each district following stratified random sampling. The managerial efficiency was measured with the help of a scale consisting of 30 items developed for the study. The data on the managerial efficiency of farmers and on the fifteen socio- psychological and situational factors of the farmers were collected using an interview schedule. The components of managerial efficiency identified empirically were ‘planning’, ‘labour management’, ‘information management’, ‘financial management’ ‘production management (variety)’, ‘production management (practices)’ and ‘marketing management’. The managerial efficiency of cassava farmers as the whole was somewhat better as little more than half of the farmers had high managerial efficiency. While the farmers exhibited high efficiency in the managerial components namely, ‘planning’, ‘labour management’, ‘financial management’ and marketing management’, they were not efficient in the components of ‘Information management’, ‘production management (variety)’ and ‘production management (practices)’. The farmers of industrial district were found to have significantly higher efficiency in the overall managerial efficiency as well as in the managerial components viz., ‘planning’, ‘information management’, ‘financial management’, ‘production management (variety)’, and ‘production management (practices)’ when compared to farmers of non- industrial district. The component- wise performance of farmers on the whole was in the order of ‘labour management’, ‘marketing management’, ‘planning’, ‘financial management’, ‘production management (practices)’, ‘information management’, and ‘production management (variety)’. While farmers of industrial district relatively performed well in ‘production management (variety)’, ‘production management (practices)’ and ‘planning’ when compared to other components, non-industrial district farmers performance was good at ‘labour management’, ‘marketing management’ and ‘financial management’. The managerial components namely, ‘planning’, ‘information management’ and ‘financial management’ were found to be relatively more important than other components with regard to their contribution towards the profit from cassava cultivation. The socio-psychological and situational factors namely, closeness with agricultural support system, market perception, achievement motivation, economic motivation, attitude towards scientific management in crop enterprise, knowledge on scientific management in crop enterprise, cultivated holding, cassava area and irrigation potential were found to be significantly contributing to the managerial efficiency. The major managerial constraints faced by the farmers were lack of awareness, knowledge, conviction, timely information and planting materials; limited resources, uncertainty and shortage of labourers.Item Partial substitution of muriate of potash by common salt for cassava (Manihot esculenta crantz) in oxisols of Kerala(Department of Soil Science & Agricultural Chemistry, College of Agriculture, Vellayani, 1995) Sudharmai Devi, C R; Padmaja, PField experiments were carried out in the College of Agriculture, Vellayani during 1991 to 1994 to study the possibility and extent of substitution of K of Muriate of Potash with the Na of common salt in Cassava variety M4 used as the test crop. Substitution of K was tried at 4 levels viz. 25, 50, 75 and 100 per cent of the recommended dose. Muriate of potash, replaced by wood ash and a combination of KHCO3 and NaHCO3 (eliminating chlorine source) also were included in the experiment. Plant growth characteristics like plant height and number of leaves did not vary significantly as a result of substitution. The maximum LAI was observed in the case of 50% K as MOP + 50% Na as CS treatment at all the growth stages. An increase in chlorophyll content was observed with NaCl substitution. In the early growth stages there was no significant variation in the production of roots, but at the later stages there was significant difference in this aspect. The root volume at 2 MAP varied significantly between treatments. In general, there was an increase in total weight of plant with NaCI substitution upto 50% and thereafter a decrease with higher levels of substitution, at all growth stages. Significant treatment difference could be observed in tuber yield in both the years of the experiment. T3 (50% MOP +50% CS) registered the highest tuber yield and T5 the lowest. The bulking rate and Utilisation Index also differed significantly among treatments. The cooking quality of the tubers from T3 was as good as that of T1. Significant differences could be observed in total sugars, reducing sugars and sucrose content of fresh tubers under different treatments. With increasing levels of substitution, the content of total sugars increased. Sucrose content was found to increase with Na application upto 75% substitution of K by Na. Significant variation was observed in the crude protein, total amino acid and free amino acid content of tubers. Hydrocyanic acid, total phenols and crude fibre also differed significantly between treatments. The keeping quality studies revealed that tubers from T3 could be stored fresh up to 35th day in moist soil, whereas tubers from T1 could be stored only upto 12th day, without deterioration. Enzyme studies revealed significant difference in the activity of starch synthesising enzymes, but NRA at 6 MAP was not affected by different treatments. The uptake of N was highest in T1 and P and K in T3. Na uptake by T1 which received no Na was generally higher than other treatments receiving Na. Ca and Mg uptake also differed significantly between treatments. Changes in soil organic carbon, available P, available K and available Mg were statistically significant between treatments but that of Ca was significant only from 4 MAP onwards. Yield of tubers was positively and significantly correlated to the uptake of N, P, K, Na, Ca and Mg. Yield at harvest was positively and significantly correlated to the root weight and root volume and also to the bulking rate at 2 MAP. Path coefficient Analysis revealed that the maximum direct effect on yield was contributed by the drymatter of roots at 2 MAP. From the results, it can be concluded that in soils having low to medium status of K, the K of MOP can be substituted up to 50% by Na of commonsalt in cassava without affecting the quality and quantity of tubers.Item Biochemical and molecular studies on post-harvest physiological deterioration of cassava (Manihot esculenta crantz)(Department of plant physiology, College of agriculture,Vellayani, 2015) Saravanan, R; Roy StephenItem Identification of graft transmissible resistant factors and development of si RNA mediated resistance in cassava against cassava mosaic geminivirus(Department of Plant Pathology, College of Agriculture, Vellayani, 2017) Asha B Nair; Umamaheswaran, KItem 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 Characterization of Bemisia tabaci (Gennadius) (hemiptera: aleyrodidae), for genetic variability, endosymbionts and vector-virus interactions in cassava(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 2018) Harish, E R; Mani ChellappanCassava is one of the important tuber crops cultivated all over the World. Cassava Mosaic Disease (CMD) is the most important limiting factor in its production. Silverleaf whitefly, Bemisia tabaci (Gennadius) is the vector responsible for the transmission of Cassava mosaic virus in cassava, which causes CMD. Genetic variation among the members of B. tabaci, makes them very difficult to manage. Endosymbionts present in the whitefly system could be a factor responsible for making them a successful sucking pest. There are various kinds of interactions existing between whitefly and the CMV. Studying these interactions precisely will help to understand the behavioural and physiological variations in whiteflies. In this background the present study, “Characterization of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), for genetic variability, endosymbionts and vector-virus interactions in cassava” was proposed and carried out at the Department of Agricultural Entomology, College of Horticulture, Vellanikkara, during Mrch 2014 to April 2016, with the objectives to analyse the genetic variability in cassava whitefly, characterization of its endosymbionts and elucidation of cassava whitefly - cassava mosaic virus interactions. Various life stages of B. tabaci were collected from different cassava growing agro ecological zones of Kerala and reared in laboratory as well as in polyhouse at optimum conditions. Genetic variability study was conducted with 10 selected ISSR primers which had shown polymorphism in their banding pattern; with amplicon size ranged between 200bp to 2900bp. Phylogenetic analysis using NTsys software revealed the presence of two major clusters with Sultan Bathery population as out group. Similarity matrix had shown up to 49 per cent variation between the samples. Polymerase chain reaction using mitochondrial cytochrome oxidase1 primers, C1-J2195 and L2-N-3014 had given amplicon of 850bp. Nucleotide sequences had shown variation up to 16.5 per cent and dendrogram generated out of the sequences using MEGA-6 (Neighbor Joining Method) gave two clusters and one out group. Sequence similarity check using reference sequences from NCBI data base indicated the presence of two biotypes, AsiaI and AsiaII5 in cassava plants of Kerala. Morphometric studies were conducted to assess the variations in different pupal and adult characters of thirteen whitefly populations. Significant variations were found in pupal length and pupal width of the biotypes. Pupal length varied between 0.746 mm to 0.668 mm and pupal width varied between 0.539 mm to 0.468 mm in female pupa. Out of 14 characters of pupa studied, variations in length and width were found to be significant. Among seven characters of adults studied, variations in wing, antennal length, body length and width were significant. AsiaI biotype was found to have lesser body length, but more width compared to AsiaII5. AsiaII5 was found to be an important biotype of B. tabaci infesting cassava in 12 out of the 13 locations surveyed. Endosymbiont characterization from whitefly using Next Generation Sequencing (NGS) - Illumina platform revealed the variations in microbiota. At phylum level, Proteobacteria was found at 87.57 per cent in whitefly populations collected from plains. The populations from high ranges contained Firmicutes at 82.67 per cent. Arsenophonus, an ‘indirect helper’ for virus spread by protecting viral coat protein from degradation in insect system with their GroEL chaperones were found at 24. 69 per cent in B. tabaci populations collected from plains. Behavioural and life cycle variation study of B. tabaci using six cassava genotypes had shown that virus infection in B. tabaci altered the dispersal and settling. Speed of movement observed to be maximum at 16.25 cm/s in non- virulent female whiteflies on the genotype CMR-9. Life cycle of virulent and non-virulent whiteflies was found to vary between 19.57 days to 30.77 days. A thorough understanding of genetic variations, endosymbiont diversity and behavioural response to virus could help the researchers in planning proper management strategies for B. tabaci. In future, information generated of such kinds could also help the researchers and policy makers to foresee and manage any possible outbreak of the pest and avoid any havoc caused by them.