PG Thesis
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Item Identification of the population genetic structure of Carcharhinus longimanus (oceanic white tip shark or brown Milbert's shark) using mitochondrial DNA markers(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2019) Sreelekshmi, S; Sandhya SukumaranEven though sharks are the largest fishes in the world with their size varying size and behaviour, they were over exploited and most of them were at the fear of extinction. Among these Carcharhinus longimanus, an epipelagic bottomless shark considered as at the point of extinction were IUCN Red list points out this shark as a “vulnerable” species at global level. In order to implement the management measures for these species which require the information regarding its population in interoceanic regions. Population genetics can be characterized as the study of how hereditary variance is dispersed among the species and population on a very basic level (Hansen, 2003). Assessment of genetic makeup and variability of fish stock is important for scientific management of fishery, conservation and rejuvenation of endangered species. Mitochondrial DNA (mtDNA), which in general possess a five to ten times greater variability than single copy nuclear genes hence, served as a powerful tool for elucidating population structures studies. Among the 150 specimens of C. longimanus sequenced, we obtained sequences ranging from 720 base pairs were obtained 12 polymorphic sites yielding 13 haplotypes. Genetic differentiation among the populations of C. longimanus from Indian Ocean was revealed as a non-significant statistical analysis. Vital insights were gained from this study indicating lack of significant substructuring and its capability to migrate across large expanses of Open Ocean. The capability to migrate may provide it with some buffering against habitat loss and climate change, but excessive fishing is a danger to its populations. Globally sharks are in danger due to their inherent vulnerabilities like long gestation time and reduced number of offsprings coupled with over fishing. Our study also corroborated the findings of shark decline, as decline in genetic diversity is an indicator of decrease in resilience capacity. The present study calls for restrictions on its fishery so that populations will get sufficient time to replenish and consequently their resilience is ensured in the face of changing oceans.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 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 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 Genetic diversity analysis of sweet potato (ipomoea batatas (L.) lam.) germplasm using morphological and ISSR markers(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2018) Sabarinath, V B; Shirly Raichal AnilCharacterization of crop germplasm based on determination of amount and distribution of crop genetic diversity is necessary for proper utilization andconservation. This could be achieved through both morphological and molecular tools. This study entitled “Genetic diversity analysis of sweet potato (Ipomoea batatas (L.) Lam.) germplasm using morphological and ISSR markers” was carried out in the Division of Crop Improvement, ICAR-Central Tuber Crops Research Institute, Sreekariyam, Thiruvananthapuram during 2017-2018 with an objective to identify genetic diversity in the sweet potato germplasm based on morphological and molecular markers. ICAR-CTCRI is the National Active germplasm site (NAGS) of tropical tuber crops which maintains 1400 accessions of sweet potato at Sreekariyam and its regional Centre at Bhubaneswar. 54 accessions of sweet potato including 52 accessions from eastern states of India and two wild species I. triloba and I. aquatica were selected from this collection. The study consisted of two parts -morphological and molecular characterization. Morphological analysis was performed by using eighteen sweet potato descriptors as provided by IPGRI (CIP et al., 1991). The recorded data was analyzed statistically by various tools such as PCA and cluster dendrogram using Multivariate statistical package (MVSP 3.22). The dendrogram separated into the accessions into two principal clusters and one outlier at a Euclidean distance of 1.2. The PCA analysis revealed predominant vine colour, leaf lobes type as the major variables that contributed to the clustering of the sweet potato accessions. Molecular analysis was performed using ISSR markers. The genomic DNA was isolated from young leaves using Dellaporta et al. (1983) method. 11 ISSR primers were used for screening of fifty four accessions. After the final PCR using selected primers, the product was resolved in 2% agarose and polymorphic bands were obtained. Primers showed 89.8% polymorphism and the number of bands ranged from 5 to 16 with a mean value of 7.3 polymorphic bands per primer. A total 63 of 80 polymorphic bands were obtained. The data analysed using NTSYS PC 2.02 program generated a dendrogram, which grouped the accessions based on Jaccard‟s similarity coefficient which separated the fifty four accessions into three principal clusters. The first principal cluster comprised of 37 accessions which were grouped into many subclusters and there was lot of intra-clusteral variation. The second principal cluster consisted of 15 accessions and this principal cluster comprised of two accessions with 89% similarity which were also found similar in morphological characterization. The third principal cluster comprised of the two wild species, Ipomoea troloba and Ipomoea aquatica. The similarity between the different accessions ranged between 37-89%. The accessions S1574 and S1576 were 89% similar. The least similar accessions were S1408 and S1572, S1527 and S1572 (37%). A high diversity of 63% existed within the selected accessions.Mantel‟s test also showed significant correlation (r = 0.0985; p = 0.0003) between the molecular and morphological distance matrices. The hexaploid nature of the crop, self-incompatibility, along with the out crossing nature together might have contributed to the high variation observed among the accessions.Item Identification of duplicates in the germplasm of sweet potato (Ipomoea batatas (L.) Lam.) using morphological and molecular markers(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2017) Babitha Babu; Shirly Raichal AnilThe study entitled “Identification of duplicates in the germplasm of sweet potato (Ipomoea batatas (L.) Lam.) using morphological and molecular markers” was carried out at the Division of Crop Improvement, ICAR-Central Tuber Crops Research Institute, Sreekariyam, Thiruvananthapuram during 2016-2017. The objective of the study was to identify duplicates in the sweet potato germplasm based on morphological and molecular markers. Identification and elimination of these common redundant materials will enhance the germplasm viability. Fifty accessions were selected for the study. The study was divided into two phases - morphological and molecular analysis. Morphological analysis was performed by using twenty descriptors as provided by IPGRI (CIP et. al., 1991). The recorded data were analyzed statistically by various tools such as PCA and cluster dendrogram. Cluster dendrogram identified three sets of morphological duplicates and the accessions were separated into six principal clusters and two outliers at a Euclidean distance of 1. The PCA analysis revealed predominant vine colour and secondary vine colour, abaxial vein pigmentation and petiole pigmentation as the major factors that contributed to the clustering of the sweet potato accessions. After morphological analysis, molecular analysis was performed. The genomic DNA was isolated using CTAB method which gave good quality DNA. 11 ISSR primers were used for screening of fifty accessions. After the final PCR using selected primers, the product was resolved in 2% agarose and polymorphic bands were obtained. All the primers showed 100% polymorphism and the number of bands ranged from 9 to 18 with a mean value of 14.7 bands per primer. Using the molecular scoring data, UPGMA clustering was done and the whole fifty accessions were divided mainly into two principal clusters and one outlier. The first principal cluster comprised of 40 accessions which were grouped into many subclusters and there was lot of intraclusteral variation. The second principal cluster consisted of 9 accessions and this principal cluster comprised of two true duplicates which were also found similar in morphological characterization. The outlier was different from all the other accessions and may be due to the peculiar leaf shape which is not seen in other accessions selected in the study. SD-29 was different from all the remaining accessions by a similarity coefficient of 0.61.The similarity between the different accessions ranged between 52-100%. The duplicates S-236 and S-256 were 100% similar. The least similar accessions were SD-39 and S-298 (52%). Thus it can be inferred that a 48% variability or diversity existed within the selected accessions which can be considered as a moderate diversity. The hexaploid nature of the crop, self incompatibility, along with the out crossing nature together might have contributed to the high variation observed among the accessions. Only two duplicates were identified. In future more specific markers may be used for core collection development and to eliminate duplicates.Item Characterization and validation of microsatelite markers for resistance to vascular streak dieback disease in cocoa (Theobroma cacao L.)(Centre for Plant Biotechnolgy and Molecular Biology, College of Horticulture, Vellanikkara, 2016) Waghmare Sandesh Tulshiram; Deepu MathewCocoa is the third important plantation crop next to coffee and tea. The global production and consumption of cocoa is 27.00 lakh MT. Among the fungal diseases, Vascular Streak Dieback (VSD) caused by Ceratobasidium theobromae is the main constraint in cocoa growing countries, causing heavy losses in mature trees as well as seedlings. The VSD disease cannot be effectively controlled by chemicals and hence breeding for the development of resistant varieties is the best strategy to tackle the disease. In order to confirm the transfer of a desired gene into the offspring, conventional breeding methods rely on the field screening which will be highly influenced by the environmental factors. Marker assisted selection is an alternate where the tightly linked molecular markers will be employed to confirm the presence of the gene of interest in the selected plants. Five ISSR and one SSR markers linked to VSD resistance were identified at Kerala Agricultural University (Chandrakant, 2014). The present study was undertaken with the objective of validating the identified SSR and ISSR markers and to characterize the ISSR markers to identify the corresponding SSR markers. For validation and characterization, twenty VSD resistant hybrids and four susceptible clones were used. For molecular analyses, good quality genomic DNA was isolated from twenty four genotypes and ISSR markers UBC 811, UBC 815, UBC 826, UBC 857, UBC 866 and SSR marker mTcCIR 42 were screened. ISSR analysis had shown that all the primers are capable to differentiate resistant and susceptible genotypes. The SSR assay has also differentiated the resistant and susceptible genotypes. The distinct markers generated in resistant genotypes using UBC 811, UBC 826 and UBC 857 were eluted, cloned to pGEMT vector and sequenced. The nucleotide sequences were annotated using BLAST, ORF finder and SSR finder. The BLASTn of UBC811A and UBC811D nucleotide sequence have shown that this resistance locus lie in the chromosome V of Theobroma cacao genome. BLASTn of UBC826A, UBC826B and UBC857 has positioned these loci in chromosome III. ORF1 and ORF3 in UBC811D are shown to code for aflatoxin biosynthesis regulatory protein and NAD(P)H dehydrogenase quinine, respectively. ORF1 in UBC826B and ORF5 in UBC857-2 code for potassium transporter 27 (0sHAK-27) and structural polyprotein precursor of VP2, capsid protein VP2, respectively. All these proteins are identified to have definite roles in defence pathways. The frequency and distribution of SSR motifs, dimmers to decamers, in these ISSR markers and the corresponding primers were identified. The reported ISSR and SSR markers were validated and found to be successful in differentiating resistant and susceptible genotypes of cocoa; thereby these markers can be used in marker assisted breeding for VSD resistance.Item Genetic diversity analysis of phytophthora colocasiae using SSR markers(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2017) Akshara George; Jeeva, M LItem Development of scar marker for authentication of gender in kodampuli (Garcinia gummi-gutta var.gummigutta)(Centre for Plant Biotechnology and Molecular Biology, College of Horticulture, Vellanikkara, 2010) Shelke Sunil Marotarao; Rajendran, P CThe diabetes and cardiovascular disease are the two serious obesity related life-style diseases, spreading at alarming rate throughout the world, especially in thickly populated third world countries in which India occupies the prime position. The fleshy fruit rind of Kodampuli (Garcinia gummi-gutta) is the richest natural source of anti-obesity metabolite hydroxyl citric acid (HCA). Which inhibit the conversion of carbohydrate to fats without affecting Kreb’s cycle through an enzyme ATP citrate lyase. Since Kodampuli is a polygamodioecious tree, it takes 8 to 12 years to identify the female trees. No significant reports are available for sex determination in Kodampuli on the basis of physiological, biochemical or molecular characters. Sex identification, lack of orthotropic shoots for grafting, prolonged seed dormancy, poor seed germination and lack of awareness of its pharmaceutical significance are hindering the extensive cultivation of this backyard companion crop in Kerala and other coastal regions of country. In the present study, an attempt was made to develop simple PCR based technique which can use for gender diagnostic in this plant. DNA samples were extracted from field grown 15 to 20 years old 25 male and 25 female trees and were bulked to 5 samples each by sex type. Earlier reported RAPD primers viz. Kit C1, Kit C8 and Kit C9 were screened but no significant polymorphism was observed. So a total of random 46 decamer primers were tested and six primers were selected for further analysis. On rescreening of the six selected primes viz. RN 5, RN 9, RN 10, RY 5, RY 18 and OPAH 12 only OPAH 12 reproduce male specific band in bulked and individual samples. Random amplified polymorphic DNA (RAPD) fragments were generated in the both bulks in order to identify markers that were polymorphic between male and female plants. A 550 base-pair (bp) male-specific DNA fragment generated with the OPAH-12 primer was identified. The polymorphic male specific band produced by OPAH 12 primer was eluted and cloned in pGEM-T vector, and transformed into E. coli JM 109 cells. Cloned cells were subjected to blue-white screening and transformed one was sent for sequencing The sequence obtained after vector screening was subjected to nucleotide blast search and ORF finder. It does not reveal any significant levels of homology and reading frame. Two pairs of SCAR primer were designed on the basis of sequence. These SCAR primers were checked for male and female samples but no polymorphic band was observed. The future line of work can be to screen the male and female genotypes with more number of primers to obtain larger base pair polymorphic band. That can used to convert this dominant marker to co-dominant one like SCAR marker. SCAR marker would be successfully employed in breeding experiments for Marker Assisted Selection.Item Male sterility and its utilization for crop improvement in ridge gourd Luffa acutangula (L.)Roxb.(Department of Olericulture, College of horticulture, Vellanikkara, 2009) Vijeeth C Hegade; Predeepkumar, TThe present investigation on male sterility and its utilization for crop improvement in ridge gourd is undertaken with the objective of investigating the stability of male sterility in ridge gourd Luffa acutangula (L.) Roxb. and expression of male sterility on combinations with different pollen parents of diverse groups. Micropropagation was effective in maintaining the male sterile line. Standardized protocol was followed for in vitro maintenance of male sterile line. In vitro regenerated plants exhibited stable male sterility all round the flowering season. Pollen fertility found to be zero in all the male sterile plants. Cytological analysis of pollen mother cells revealed normal meiosis in form of tetrad formation and pollen degradation found to be in post meiotic stage. Fourteen ridge gourd genotypes were collected from different parts of the country and evaluated for variability with respect fourteen traits. The genotypes exhibited significant variability for the characters studied. Genotypes were grouped into five clusters based on Mahalanobis’s D2 statistics. Five pollen parents from diverse groups were selected for hybridization with the male sterile female parent. Heterosis values were estimated over mid, better and standard parents. Out of five hybrids, four were male sterile and one was partially fertile. Inheritance of male sterility and restoration of fertility is a complex mechanism and the available information on male sterility is not sufficient to explain this unique mechanism. Available result points towards the presence of partial dominant gene action in controlling male sterility. The pattern of inheritance of male sterility and restoration of fertility can only be explained by studying the F2 and back cross generations and the three way cross involving male sterile hybrids and the pollen parent which restores the fertility.