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W. Msikita, H.T. Wilkinson and J.C. Silva Dias

Tronchuda (Brassica oleracea var. tronchuda Bailey syn. costata) regenerants with resistance to Xanthomonas campestris pathovar campestris Pammel (Dawson) were produced by culturing epicotyl segments of 3-week-old seedlings on Murashige and Skoog medium supplemented with 2 mg BAP and NAA at 0.1 mg·liter–1. Cultures were placed in darkness (1, 2, or 3 weeks) or in a 16-hour·day–1 light regime. Seedlings of all four cultivars were more susceptible (mean disease severity rating of 3.8 to 4.0; where 1 = trace and 4 = more than 2 cm2 diseased leaf tissue) than the respective regenerants. There were significant differences in disease severity of regenerants among and within the four cultivars. Dark incubation of cultured explants generated plants with higher disease resistance than evident with control plants. One week of dark incubation resulted in increased resistance in regenerants of `Penca de Chaves', `Portuguesa', and `Vilinda' (2.1, 2.3, and 2.7 mean disease severity, respectively), whereas 2 weeks of dark incubation increased resistance in regenerants of `Ana Maria' and `Vilinda' (2.1 and 2.7 mean disease severity, respectively). The genotype×plant treatment interaction was significant. Chemical names used: 6-benzylaminopurine (BAP); a-naphthaleneacetic acid (NAA).

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Dirk R. Vuylsteke and Rodomiro Ortiz

In vitro-propagated plants of plantain (Musa spp., AAB group) did not manifest consistently superior horticultural performance compared to conventional propagules. Tissue culture plants grew vigorously and taller than sucker-propagated plants, but higher yield was not obtained, probably because of severe disease and suboptimal husbandry input. Phenotypic variation was higher in tissue culture plants, although this increase was not always statistically significant. There were no other detrimental effects of in vitro propagation on field performance. Botanical seed set rates for the two types of propagules were similar. The advantages of tissue-culture-derived plants as improved planting material would be most relevant for establishing field nurseries for further clean, conventional propagation of newly bred or selected genotypes.

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Maciej Ladyzynski, Aleksandra Korzeniewska and Stefan Malepszy

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Ken McPheeters and Robert M. Skirvin

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Ritika Gupta, S. Banerjee, G.R. Mallavarapu, S. Sharma, S.P.S. Khanuja, A.K. Shasany and Sushil Kumar

An efficient protocol has been established for generating somaclones in the Indian rose-scented geranium Pelargonium graveolens cv. Bipuli, which yields Reunion Island-type essential oil. Murashige and Skoog's (MS) medium supplemented with 4.5 mg·L-1 BA and 1.0 mg·L-1 NAA was found optimal for induction of callus from leaf explants. Callus regenerated shoots when transferred to MS medium with 2.5 mg·L-1 BA and 0.1 mg·L-1 NAA. The regeneration percentage as well as number of shoots per cm2 of callus was greatly improved by addition of ADS at a concentration of 3.0 mg·L-1. Regenerated shoots rooted within 20 days following transfer to half-strength MS medium with 0.1 mg·L-1 NAA. Plantlets were acclimatized under glasshouse conditions with 80% to 85% survival. Randomly selected 30 individual calliclones were subjected to field trial with wild-type parent in randomized block design, replicated three times with 90% survival for two successive years. Characterization of these calliclones for essential oil yield and quality traits demonstrated induction of variability in all the characteristics examined in negative and positive directions in comparison with the wild-type parent. This screening led to the identification of somaclone B22, which out-yielded the wild-type parent as well as the rest of the somaclones. The quality of the essential oil of B22 was similar to that of the parent. Chemical names used: N 6-benzyladenine (BA); naphthalene acetic acid (NAA); adenine di-sulphate (ADS).

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Wagner A. Vendrame, Gary D. Kochert, Darrell Sparks and Hazel Y. Wetzstein

Field evaluations were conducted of pecan [Carya illinoinensis (Wangenh.) C. Koch] trees regenerated via somatic embryogenesis to assess if the trees maintained clonal fidelity and exhibited true-to-type characteristics. Phenotypic and molecular comparisons were made of trees from two different tissue culture lines after 4 years in the field. Factors evaluated included shoot growth, leaf morphology, and susceptibility to fungal scab [Cladosporium caryigenum (Ellis & Langl.) Gottwald] and southern pecan leaf phylloxera (Phylloxera russellae Stoetzel). Genetic fidelity was examined using amplified fragment length polymorphism (AFLP) analysis. Statistically significant differences were observed between the culture lines in phenotypic leaf characteristics (i.e., specific leaf weight and leaf length-to-width ratio), number of shoots per 1-year-old branch, and in the frequency of scab lesions on leaves. No between-line differences were observed in trunk caliper, average and total shoot growth, shoot length per cross-sectional area, or presence of phylloxera galls. AFLP analysis readily detected differences between culture lines. Cluster analysis generally grouped trees together that were regenerated from the same line. Trees within a culture line usually exhibited similar leaf characteristics, but not shoot growth or tree height. A few trees exhibited more extreme leaf characteristics and differed from each other. However, they were statistically similar to most of the other trees in the population evaluated. AFLP data revealed that some trees exhibited greater divergence and less similarity than other trees from the same line. The nature and significance of such variation at this time are not related to any detectable phenotypic differences.

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Carol A. Bobisud, Susan P. Martin and Terry T. Sekioka

`Healani' tomato (Lycopersicon esculentum Mill.) somaclones were tested in a bacterial wilt (Pseudomonas solanacearum E.F. Smith) infected field. Survival percentages of selected somaclonal lines were from 40% to 100%, while the original `Healani' had a survival rate of 0% and resistant `Kewalo' had 30%. Eighteen bacterial wilt resistant somaclonal lines were selected and tested for retention of horticultural characters in a noninfected field. `Healani' significantly outyielded all tested somaclonal lines in total fruit weight and total number of fruit per plant. `Healani' had greater fruit diameter than seven of the lines, greater width of the outer wall of the fruit pericarp than seventeen of the lines, and fewer locules in the fruit than seven of the lines.

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Hamidou F. Sakhanokho, Anthony L. Witcher, Cecil T. Pounders and James M. Spiers

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Kelly M. Oates, Thomas G. Ranney and Darren H. Touchell

cotton allopolyploids ( Adams and Wendel., 2005 ). Stochastic changes in gene expression may explain the variability observed in allopolyploid hybrids of R. subtomentosa × hirta . It is also possible somaclonal variation may have been induced in

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Xiaoming Wang, Jianjun Chen, Yongxin Li, Qiying Nie and Junbin Li

formulation. To minimize the potential of somaclonal variation, only those calluses that were initially induced from leaf explants 4 weeks after culture were used for adventitious shoot induction. Shoot induction. The calluses were cut into 1-cm 3 pieces