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  • Author or Editor: Stephen L. Sinden x
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Cultured leaf explants obtained from 36 accessions of the wild tomato species, Lycopersicon hirsutum Humb. and Bonpl., were evaluated for morphogenic capacity in response to three cytokinins (zeatin, BA, and kinetin) in combination with IAA. Media containing 0.1 μm IAA plus 4.6 or 9.2 μm zeatin were optimal for shoot induction. Cotyledon explants were superior to true leaf explants for obtaining shoot formation. Morphogenic responses of L. hirsutum f. typicum and L. hirsutum f. glabratum were clearly accession-dependent and ranged from exceptional with numerous shoots produced to recalcitrant with no shoots produced. The high morphogenetic capacity of leaf explants from L. hirsutum f. typicum accession 128644 was also evident in protoplast-derived calli that readily regenerated shoots. Chemical names used (E)-2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin), N-(phenylmethyl) -1H-purin-6-amine (BA), N- (2-furanylmethyl) -1H- purin-6-amine (kinetin), 1H- indole-3-acetic acid (IAA).

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For the yellow-flesh fresh market, potato clones with intense yellow-flesh and uniform size are desired. Twenty-five yellow-flesh clones were evaluated for individual tuber weight and tuber yellowness as measured by a reflectance colorimeter in replicated field trials in Presque Isle, Maine, in 1991. There were significant differences among clones for yellowness. Cluster analysis was used to group the clones by mean tuber weight in grams (MTWT) and variance of the mean tuber weight (VMTWT). Four clusters were identified. `Yukon Gold' was in a cluster by itself: MTWT=90 and VMTWT=86. Four clones formed a second cluster. The averages of these four clones were: MTWT=33 and VMTWT=3. MTWT was too small in the second cluster for these four clones to warrant further evaluation. Three clones formed a third cluster. The averages of these three clones were: MTWT=78 and VMTWT=43. The remaining 17 clones formed the fourth cluster. The averages of these 17 clones were: MTWT=54 and VMTWT= 11. The more intense yellow-flesh clones in the third or fourth clusters should undergo further evaluation for their fresh market potential.

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Abstract

Certain plant species have been propagated clonally over long periods of time using classical techniques. Variants occasionally appear, but usually in relatively low frequencies (31). Thus, “carbon copies” of the parent plant might have been expected when tissue explants and single cells were first isolated and regenerated into plants by cell-culture techniques. Most regenerated plants are, in fact, apparent exact copies of the parent plant (40, 41). However, some culture systems now available for commercial propagation and research purposes appear to produce cell cultures and regenerated plants with considerable phenotypic variability.

Open Access

Use of wild species for in vitro sweetpotato improvement has been limited, in part, by the lack of suitable regeneration systems for these species. Shoot regeneration in 4 closely related species, I. batatas, I. cordatotriloba, I. trifida and I. triloba, were evaluated. Callus was initiated using methods described by Otani and Shimada (1988). Calli were transferred to regeneration media containing 17.75 uM BAP and 0, 1, 10 and 100 uM PCIB. Organogenesis was enhanced by the presence of PCIB. With I. cordatotriloba calli grown on media with 10 uM PCIB, a 2-fold increase in the percentage of calli exhibiting shoot regeneration was observed as compared to calli grown on media with BAP alone. A significant increase in the average number of shoots per callus was also observed. The other species examined appeared to be less sensitive than I. cordatotriloba to the PCIB treatments.

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Leaf callus of Ipomoea cordatotriloba was initiated by culturing explants on Linsmaier and Skoog medium containing 3 g yeast extract/liter, 18.9 μm ABA, 2.3 μm 2,4-D, and 0.15 m sucrose. Calluses were transferred to Murashige and Skoog media containing 17.8 μm BA and 0, 1, 10, or 100 μm PCIB. The number of shoots from calluses grown on medium containing 10 μm PCIB increased significantly, and the percentage of calluses exhibiting shoot regeneration almost doubled compared to calluses grown on regeneration medium without PCIB. Protoplasts isolated from stem and petiole tissues of in vitro-grown plants were cultured in Kao and Michayluk 8p medium to the callus stage. Calluses (4-6 mm) were transferred to the callus induction and regeneration media used to regenerate leaf-explant callus. Of the protoplast-derived calluses cultured on media containing 10 or 100 μm PCIB, ≈13% and 18%, respectively, regenerated shoots after 2 months; none regenerated on the medium without PCIB. Chemical names used: abscisic acid (ABA); 2,4-dichlorophenoxyacetic acid (2,4-D); N6-benzyladenine (BA); α -p-chlorophenoxyisobutyric acid (PCIB).

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The use of wild Ipomoea species in sweetpotato improvement may be facilitated by the use of in vitro techniques such as somatic hybridization. Plant regeneration from callus cultures is essential to the successful application of these in vitro techniques. This is the first report of plant regeneration of I. cordatotriloba from protoplast derived calli. Protoplasts isolated from petiole and stem tissues of in vitro grown I. cordatotriloba were initially cultured on KM8p media. All calli cultured regenerated roots after 1 month on regeneration media. Approximately 13% and 19%, respectively, of the calli cultured regenerated shoots after 2 months on media containing 10 and 100 uM parachlorophenoxy isobutyric acid (PCIB). Regenerated shoots developed into whole plants when transferred to MS media without hormones. The regenerated plants closely resembled the parent's morphology.

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Incorporation of genes from wild species has been a major contributor to tomato improvement in recent years. Solanum ochranthum, a woody non-tuber bearing species, is a potential source of resistance against tomato diseases and insect pests but is genetically isolated from tomato. Somatic hybridization methods were developed to facilitate the use of S. ochranthum for tomato germplasm improvement. Leaf mesophyll protoplasts of S. ochranthum and a Lycopersicon esculentum hybrid were chemically fused with polyethylene glycol. The protoplasts were initially cultured in Shepard's CL, a MS based medium, containing 1 mg·1-1 NAA, 0.5 mg·1-1 BAP and 0.5 mg·1-1 2,4-D. Hybrid regenerants and regenerants of the L. esculentum parent were recovered; S. ochranthum did not regenerate. Hybridity was established by morphological characters, peroxidase isozyme and RAPD markers. Use of these somatic hybrids for tomato improvement was evaluated.

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Solanum ochranthum, a woody non-tuber bearing species, may possess genes for insect and disease resistance which could be useful in solanaceous crop improvement. Methods for tissue and protoplast culture of S. ochranthum were developed as part of an ongoing project to improve tomato and potato using wild relatives and in vitro techniques such as somatic hybridization. For protoplast experiments, axenic shoot tip cuttings were propagated on medium containing MS salts, Staba vitamins, 100 mg·l-1 casein, 3% sucrose and 0.6% activated charcoal (OM) or medium containing MS salts and vitamins, 100 mg·l-1 casein and 2% sucrose (TPM). Plants grown on OM were significantly taller, had higher root dry weight and gave protoplasts with higher average plating efficiency than plants grown on TPM. Leaf protoplasts from 5 week old plants cultured in medium with high Ca2+ and myoinositol generally had higher percent viability and plating efficiency than protoplasts grown in a modified Kao and Michayluk 8p medium.

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