Cytokinins tolerance and in vitro selection for dwarfism in apple (Malus x domestica Borkh.)
Sarwar, Mushtaq
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https://hdl.handle.net/2142/20474
Description
Title
Cytokinins tolerance and in vitro selection for dwarfism in apple (Malus x domestica Borkh.)
Author(s)
Sarwar, Mushtaq
Issue Date
1996
Doctoral Committee Chair(s)
Skirvin, Robert M.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Plant Culture
Biology, Plant Physiology
Language
eng
Abstract
A reliable in vitro shoot regeneration system was developed for leaf segments of six apple (Malus Xdomestica Borkh) cultivars ('Wijcik', 'McIntosh', 'Macspur', 'Regal Gala' and 'M 26') grown in vitro using modified Murashige and Skoog (MS) medium supplemented with N-phenyl-N$\sp\prime$ 1,2,3,-Thidiazuron (TDZ). TDZ was found superior to benzylaminopurine (BAP) in promoting adventitious shoot formation. The optimum levels of TDZ ranged from 2 to 4 $\mu$M whereas, the optimum levels of BAP occurred between 4 to 12 $\mu$M depending on cultivar. Naphthaleneaceticid (NAA) was not necessary for adventitious shoot formation. In general, 3 to 4 weeks of dark incubation increased regenerate capacity of apple cultivars. The optimum levels of sucrose for regeneration were between 20 to 40 grams. Overall, no significant interaction was found between TDZ and dark period and between TDZ and sucrose to affect shoot regeneration. In most of the cultivars large leaves regenerated better than small ones. More adventitious shoots were obtained by plating the leaf segments on the medium with their abaxial surface uppermost. Regenerative capacity decreased as the number of times the a single shoot had been subcultured increased. Most of the adventitious shoots originated from cut edge of leaf segments, therefore the leaf mid segment was the most productive.
The adventitious shoots obtained from our regeneration experiments were transferred to modified MS medium with different concentrations of various cytokinins (BAP, Kinetin, TDZ, and 2iP). These shoots were observed for their growth and proliferation.
Selected adventitious shoots of each cultivar were incubated for up to 12 days in darkness on half strength MS rooting media supplemented various levels of sucrose (0 t 50 grams) and either indolebutyric acid (IBA) or (NAA). The response of NAA was poor. In most cultivars the optimum range of dark incubation was 6 to 10 days and optimum range of sucrose was 20 to 40 grams. No rooting occurred without sucrose. Although 'M 26' rooted without dark incubation, the other cultivars required darkness for rooting.
In vitro rooted plants were transferred to soil in a greenhouse. After seven months growth under greenhouse conditions, regenerants were evaluated for plant height and internode length. Plants selected at the higher BAP levels were found to have reduced height and shorter distance between nodes than those selected at lower BAP levels.
Greenhouse-grown regenerants were later transferred to University of Illinois farms. After one years growth in the field, they were evaluated for their growth characteristics (plant height, internode distance, number of nodes per 30 cm of uppermost shoot and leaf area). Regenerants exhibited continuous differences among those selected at both the higher and lower levels of BAP. However, the differences were not as pronounced as they were in the greenhouse. In general, plants selected at higher levels of BAP were smaller, had short distance between nodes, more number of nodes per 30 cm of uppermost shoots and larger leaf area than those selected at lower levels of BAP.
We concluded that tissue culture can be used to select dwarf apple trees. However, at this stage we are not sure whether the selected plants will remain dwarf after 6 to 7 years, when they should begin to bear fruit. These field-grown plants are to be observed regularly in the field for their growth and fruiting characteristics.
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