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|Authors:||BOMMESH, J. C|
|Title:||GENETIC STUDIES OF DOWNY MILDEW RESISTANCE IN INDIAN SLICING CUCUMBER (Cucumis sativus L.)|
|Abstract:||Cucumber (Cucumis sativus L.) is one of the most important Cucurbitaceous vegetable crop grown extensively in tropical and sub-tropical parts of the world. However, cucumber production is limited by the most devastating disease downy mildew. The present work was started with the objectives to identify the resistance source for downy mildew disease in cucumber and to study the inheritance of downy mildew resistance along with yield traits. Biochemical and molecular analysis were also under taken to develop DNA marker for resistance. The experiments were conducted at the experimental farm of Division of Vegetable Crops, ICAR-IIHR, Hessaraghatta, Bengaluru, Karnataka, during 2015-2018. In screening experiment forty-one cucumber genotypes were screened under natural condition and also under artificial epiphytic condition using detached leaf assay method. Based on the screening of genotypes under field conditions, sporulation of pathogen, progress of disease, detached leaf assay and non-linear statistical analysis it was observed that none of genotypes were immune to downy mildew but genotypes IIHR -438 and African horned cucumber were resistant to downy mildew disease. Ten genotypes recorded susceptibility PDI and rest of the genotypes recorded highly susceptibility with PDI of > 60. The six generation populations of two cross combinations were planted in randomized block design with three replications. Result indicates that resistance in both crosses was controlled by two pairs of dominant and recessive interacting genes (inhibitory recessive epistasis). In generation mean analysis the epistatic interaction was greater importance than main effects in Swarna Agethi x IIHR-438 cross whereas, dominance x dominance epistasis effect was higher and duplicate epistasis was prevailing in IIHR-431x IIHR-433 cross. The estimates of gene effects of yield traits through analysis of six generations revealed that the magnitude and direction of the gene effects varied in crosses. In Swarna Agethi x IIHR-433 cross showed preponderance of both additive and dominance effects for number of fruits per plant and epistatic interactions were observed for yield per plant. However, scaling test was non-significant for fruit length, diameter and weight. In 133 IIHR-431 x IIHR-433 cross fruit length, average fruit weight and yield per plant showed duplicate type of interaction and it hampered the selection at early generation. Epistatic interactions were observed for node to first flower, number of fruits per plant, fruit diameter. Total phenols and enzymatic activity of peroxidase, polyphenol oxidase and super oxide dismutase were higher in both resistant parents (IIHR-438 and IIHR-433) compared to susceptible (Swarna Agethi and IIHR-431) parental lines from 0 DPI (days to post inoculation) to 16 DPI. A total of 143 SSR primers were employed to identify polymorphic primers using 225 F2 populations of Swarna Agethi x IIHR-438 through BSA, SSR 3-5 and SSR 4-13 are co-segregated with disease reaction in BSA. The ‘dm’ genes were tagged with SSR 3-5 and SSR 4-13 markers loci with distance of 16.6 cM in linkage group 3 and 18.1 cM in linkage group 4, respectively. The backcross breeding along with markerassisted selection (MAS) can be employed for early selection of downy mildew resistance gene in cucumber and its introgression to develop a resistant variety or hybrid. Keywords : Cucumber, Genetics, Resistance, Downy mildew and Mapping|
|Theme:||GENETIC STUDIES OF DOWNY MILDEW RESISTANCE IN INDIAN SLICING CUCUMBER (Cucumis sativus L.)|
|Research Problem:||GENETIC STUDIES OF DOWNY MILDEW RESISTANCE IN INDIAN SLICING CUCUMBER (Cucumis sativus L.)M. Pitchaimuthu|
|Appears in Collections:||Theses|
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