PhD Thesis
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Item Pyramiding bacterial leaf blight resistance genes into popular rice varieties of Kerala through marker assisted selection(Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2017) Ramaling Hundekar; Jayalekshmy, V GItem Identification of molecular markers linked to iron toxicity tolerance through bulk segregant analysis (BSA) in rice (Oryza sativa L.)(Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, 2016) Amaranatha Reddy, M; Rose Mary FranciesGlobally rice is the most important food crop, serving as staple food for more than half of the world’s population. As in other parts of the country, rice is the major food crop grown in Kerala too. The total annual production of rice is however insufficient to meet the total demand in the state. Iron toxicity prevalent in the rice growing tracts of the state, further compounds the problem of low rice production. Although, several attempts to ameliorate the iron toxic soil conditions are being made, the best way to combat this stress and increase rice production in the affected soils is to develop varieties tolerant to iron toxicity. The present investigation on 'Identification of molecular markers linked to iron toxicity tolerance through bulk segregant analysis (BSA) in rice (Oryza sativa L.)’ was conducted at College of Horticulture, Kerala Agricultural University (KAU), Vellanikkara, Thrissur during 2013 to 2015 year. The study involved screening of thirty rice genotypes for response to iron at toxic levels, hybridization between the most tolerant and susceptible genotype, production of F2 generation of this cross, parental polymorphism study using molecular markers and Bulk Segregant Analysis (BSA). The thirty rice genotypes were selected on the basis of their response to iron stress under KSCSTE project: ‘Donor identification for tolerance to iron toxicity in rice (Oryza sativa L.)’. Further screening of the thirty genotypes (Confirmation test 1 and 2) as per the method advocated by Shimizu et al. (2005) to confirm their tolerance or susceptibility to iron toxicity revealed existence of high significant differences among the genotypes with respect to leaf bronzing and biomass produced under varying concentrations of iron (0 ppm, 600ppm and 800ppm of Fe). Considering that at higher concentrations of Fe, a lower leaf bronzing and reduction in biomass, is a valid criterion for identifying genotypes tolerant to Fe stress, twelve genotypes viz., Cul-8709, Cul-210-29, AM-10-7, Cul-90-03, PM-709, ASD-16, ASD-18, Abhaya, IR-1552, T(N)-1, IR-36 and Cul-3 213 were found to be highly susceptible to iron stress while genotypes Cul-8723, Tulasi, Cul-18716, Kargi and IVT-33 were identified as the most tolerant ones. Selfing of F1s obtained on hybridizing the genotype (Tulasi) and genotype (CUL-8709) which were found respectively to be most tolerant and most susceptible to iron stress was done, to produce F2 population for the conduct of bulk sergegant analysis (BSA). Phenotyping of F2 plants under iron at toxic levels indicated presence of wide variability for shoot length, root length, total number of roots, number of fresh roots, shoot weight, root weight and visual scoring for iron-toxicity symptoms. The measures of skewness and kurtosis for various traits revealed a large quantitative variability. All the above traits except iron content in root of F2 lines exhibited a positive platykurtic distribution pointing to presence of gene interaction in trait expression. Measures of skewness and kurtosis also indicated occurrence of transgressive segregation in the F2 population. Leaf bronzing the typical symptom of Fe toxicity, showed a strong negative correlation with shoot length, root length, total number of roots, number of fresh roots, shoot weight and root weight. The results indicated that leaf bronzing is associated with growth reduction due to Fe2+ toxicity in this F2 population. Parental polymorphism (Tulasi and CUL-8709) survey using 338 Rice Microsatellites (RM) markers revealed 37 RM markers polymorphic between the two. These 37 polymorphic rice microsatellites markers (SSR markers) were found to be distributed over all 12 linkage groups of rice varying between one in case on Chromosome 7 to five each on Chromosome 2, 9 and 10. Bulk segregant analysis indicated that out of the 37 microsatellite markers that were polymorphic between parents seven viz., RM 263, RM 107, RM 12292, RM 24616, RM 24664, RM 13619 showed clear co-segregation with the susceptible parent and susceptible bulk, and resistant parent and resistant bulk. Probability of all seven putative markers was highly significant (P < 0.001) indicating strong association of these markers to the genomic region governing Leaf Bronzing Index which is a valid indicator of tolerance to iron toxicity. Through single marker analysis, three probable quantitative trait loci (QTL’s) of Leaf Bronzing Index were identified, each on 214 chromosome 1, 2 and 9. The QTL on chromosome 1 was located between 42.8 Mb and 43.2 Mb and associated with markers RM 12255 and RM 12292. The QTL for LBI was found to be associated with RM 13619 and RM 263 markers and placed between 24.9 Mb and 25.9 Mb on chromosome 2 while on chromosome 9, it was a located between 19.3 Mb and 20.1 Mb and linked to marker RM 107, RM 24616 and RM 24664.Item Genetic analysis of brown planthopper resistance in rice(Department of Plant Breeding, College of Agriculture, Vellayani, 1988) Rema Bai N; Gopinathan Nair, VThe Brown planthopper (BPH), Nilaparvata lugens (Stal), has become a serious threat to rice production throughout Asia. Very extensive losses have occurred in India, Indonesia, and the Phylippines. The most severe outbreak in India occurred in Kerala during 1973-74 in ‘Kole’ lands of Trichur district and ‘Kuttanad’ area of Kottayam and Alleppey districts. Although insecticides provide effective control, this approach is expensive and creates problems of environmental pollution. Resistant varieties can provide protection and insurance against this insect pest at no extra cost and with no danger from chemical residues. Very little work has been done in Kerala to identify sources of resistance to the local biotype of BPH and on the genetic basis of BPH resistance. The major objectives of the present investigation were to identify sources of resistance to BPH and to conduct genetic analysis and understand the mode of inheritance of BPH resistance. One hundred and nine rice types were studied for their reaction to BPH through the bulk seedling test at the seedling stage and tiller test and honeydew experiment at the tillering stage. Out of them 41 were found to be resistant, 22 moderately resistant, 13 moderately susceptible and 33 highly susceptible. In the tiller test, 31 out of the 41 resistant varieties were resistant, nine moderately resistant and one moderately susceptible. The thirty one types found resistant under tiller test were subjected to honeydew experiment, out of which 30 were found to be resistant and one was moderately resistant. 2 The inheritance of resistance was studied in eight types selected from among the 30 types proved to be resistant in all the three tests. They were crossed with the susceptible variety TN1 and the F1, F2 and F3 generations were studied by bulk seedling test, tiller test and honeydew experiment. F1 seedlings were also screened by bulk seedling test, tiller test and honeydew experiment. The F2 progenies were screened by the bulk seedling test and tiller test. The F3 seedlings were screened by bulk seedling test only. The F2 and F3 progenies were scored separately as resistant and susceptible types and the observed segregation ratios were tested against the expected by applying the test of goodness of fit. The F1s of all the eight crosses were resistant indicating that resistance in each of the eight types was governed by dominant gene. The F2 populations of all the eight crosses segregated in the ratio of 3 resistant : 1 susceptible indicating that a single dominant gene governed resistance in each of the eight resistant types. F3 breeding behaviour of the nine F2 resistant plants from each of the eight crosses confirmed the monogenic control of resistance over susceptibility. Two dominant genes Bph1 and Bph3 were identified at IRRI (Bph1 in variety Mudgo and Bph3 in RatuHeenati). In the present study, Mudgo containing Bph1 and RatuHeenati with Bph3 gene were not resistant. Hence it is assumed that the dominant resistant gene identified in the present study is neither Bph1 nor Bph3. 3 Diallele crosses were made between six resistant types selected based on diverse origin. The F1 and F2 progenies of the 15 combinations were studied to get information on the allelie relationship between the resistance genes. The F1 progenies of all the crosses were resistant and the F2 progenies were homogeneous for resistance. This lead to the conclusion that all the six types have the same dominant gene for resistance. All the six resistant types were isogenic and hence all of them are expected to carry a dominant gene for BPH resistance other than Bph1 and Bph3. The present study has thus made available several types resistant to the local biotype of BPH and also enabled the location of a new dominant gene conferring resistance to this biotype. These results and the materials made available can form the basis for a more effective breeding approach for BPH resistance in this region.Item Fruit component and seedling progeny analysis of komadan coconut types(Department of Plant Breeding, College of Agriculture, Vellayani, 1992) Manju, P; Gopimony, RThe present study was undertaken with a view to unravel the genetic status of a coconut type, Komadan, popular in the Central Travancore region of Kerala, in relation to its origin by comparing its three generations with WCT and NCD through fruit component and seedling progeny analysis. The study revealed that the Komadan types showed significant superiority for majority of the mother palm characters especially number of bunches and spadices and number of nuts per palm per year. Number of nuts per palm per year and number of female flowers per bunch had high heritability combined with moderate to high genetic advance indicating the predominance of additive genes. Among the Komadan palms, 33 per cent were of self pollinating nature thereby occupying a position in between WCT and NCD regarding pollination system. All the Komadan palms had nuts of different shades of brown while 70 per cent of WCT palm had nuts of green shade and NCD palms had varying shades of green, olive and brown nuts indicating the distinction of Komadan as a separate group. Komadan types were superior to WCT in all seednut characters except polar diameter of nut, oil content, thickness of husk and husk/nut ratio. It behaved as a distinct type regarding thickness of meat. One or the other of the Komadan generations was found to be on par with NCD for majority of the seednut characters. Komadan types occupied an area midway between NCD and WCT based on Niu kafa-Niu vai Introgression hypothesis with a clear progression through generations towards better weight of unhusked nut. Inbreeding depression was noticed in WCT and NCD as indicated by significant reduction in embryo and kernel weight in selfed nuts compared to open pollinated nuts. In Komadan there was no inbreeding depression indicating a high degree of homozygosity. The seednuts of Komadan types showed early germination compared to WCT and NCD. Regarding seedling characters, Komadan behaved as a distinct type for total leaf area over both WCT and NCD. Number of seedlings with split leaves was also more in Komadan. This type was superior to WCT for seedling vigour index also. Estimation of prepotency based on recovery of quality seedlings showed that 40 to 60 per cent of Komadan palms were prepotent where as the same in WCT and NCD were only about 20 per cent. Analysis of petiole colour of seedlings showed that 71 to 82 per cent of seedlings among the three Komadan generations showed moderates brown colour (bronze) ; 97 per cent of WCT seedlings had different shades of green and wider variations in petiole colour were noticed in NCD seedlings. It can be concluded that the Komadan type maintained its genetic identity over generations with respect to economically important characters viz. Kernel, copra, and oil content and also in the recovery of quality seedlings which inturn reflects its prepotent nature. The collection and maintenance of typical komadan germplasm through inter se crossing and development of isolated seed gardens for large scale production of komadan seedlings are suggested as future line of work.