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|Authors:||SHETE, BALU JAGANNATH|
|Title:||INTERSPECIFIC HYBRIDIZATION IN LYCOPERSICON SPECIES|
|Publisher:||Mahatma Phule Krishi Vidyapeeth, Rahuri-413 722.|
|Abstract:||The major objective of interspecific hybridization is to incorporate resistance for biotic and abiotic stresses from wild taxa to cultivated type. Major crop improvement in tomato (L. esculentum) has been achieved for transfer of economic attributes from wild Lycopersicon species to commercial tomato cultivars, especially for disease resistance through interspecific hybridization. Eventhough wealth of nine species is available in genus Lycopersicon certain crossing barriers are observed for interspecific hybridization. In genus Lycoperesicon, 'peruvianum complex" contained two species viz., L. peruvianum and L. chilense which distantly related with tomato (L. esculentum) and showed severe barriers for interspecific hybridization. But, "peruvianum complex" is the most important reservoir as a source of resistance for biotic and abiotic stresses. Considering best source of resistance for biotic and abiotic stresses and its limited application in tomato breeding; L. peruvianum species was utilized in present investigation for tomato interspecific hybridization programme; which was carried out at MPKV, Rahuri during 2000-2003. The study involved two tomato cultivars (viz., cv. Dhanashree and 85-1) were reciprocally crossed with six accessions of L. peruvianum. For development of in vitro interspecific F1 hybrids, immature seeds from various eight fruit growth stages starting from 10 days after pollination with five days interval upto 49 DAP were cultured on 26 MS based media with various levels of cytokinins (BAP) and auxins (NAA). The ex-vitro F, plants grown under field conditions were used for morphological and biochemical studies for hybridity confirmation. The interspecific F1 hybrids were also screened against biotic and abiotic stresses. Furthermore, plant regeneration studies were undertaken using 2 explants (leaf and cotyledon) of 3 genotypes (two tomato cultivars viz., Dhanashree and Bhagyashree and L. peruvianum accession EC 106294) on 20 culture media. In L. esculentum x L. peruvianum hybridization, an unilateral compatibility was observed with use of tomato cultivar as a maternal parent and L. peruvianum as a pollen parent and 46 to 57.28% crossing index was recorded. Still decisive mechanism of post-zygotic sterility was observed for hybrid seed development; as immature seeds were observed at fruit ripening during interspecific hybridization. Among eight fruit stages studied, the fruit growth stage of 30 to 34 DAP was found optimum which gave 0.77% seed germination for culture of immature seeds particularly in crosses involved tomato cv. Dhanashree as a maternal parent whereas for crosses involved tomato cv. 85-1 as a maternal parent, fruit growth stage of 25 to 29 DAP was optimal and gave 0.38% seed germination. Thus, fruit growth stage was an important parameter in culture of immature seed of tomato interspecific hybrids and it was based on involvement of tomato cv. as a maternal parent. The best culture medium was MS based medium without supplement of plant growth regulators for culture of immature seed of L. esculentum x L. peruvianum (1.46% seed germination). An interspecific cross of tomato cv. Dhanashree with L. peruvianum accessions EC 106294 or EC 252 showed lower crossing barrier and recorded the highest seed germination (0.43%). However, L. peruvianum accessions EC 34479 and EC 492 proved as recalcitrant pollen parents for seed germination. Overall, 0.18%o seed germination i.e. recovery of in vitro interspecific F1 hybrids was obtained. In morphological characterization of interspecific F1 hybrids, the most distinguishing feature was self-sterility (i.e. fruit set without mature seeds) while overall other morphological traits were dominated by wild pollen parent, L. peruvianum. Similarly, the hybridity of these F1, hybrids were easily confirmed by protein electrophoretic analysis as hybrid specific and intermediate bands were amplified. While screening interspecific F1, hybrids against biotic and abiotic stresses, considerable lower pest incidence and complete disease resistance was observed under natural field conditions. Especially resistance was recorded against viral diseases like TSWV and TLCV. For evaluating plant regeneration in genus Lycopersicon, 100 per cent shoot regeneration was recorded by leaf segment of 14 day old in vitro plants of all three genotypes (tomato cv. Dahanshree, Bhagyashree and L. peruvianum accession EC 106294) in 3 culture media containing MS salt supplemented with 1 mg l-1 NAA and 1.5-5.0 mg l"1 BAP. The root induction was seen on MS media devoid of hormones.|
|Appears in Collections:||Thesis|
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