Masters Theses

Date of Award

5-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Robert N. Trigiano

Committee Members

Dr. Stephen Garton, Dr. Mark T. Windham

Abstract

Selection of superior individuals followed by clonal vegetative propagation is a very important strategy for plant improvement. Cloning via tissue culture can produce a population of an identical genotype without limits. A single specimen tree of Cladrastis kentukea and five different Cornus kousa cultivars were selected for tissue culture studies. These trees exhibited superior performance in horticultural trials, including disease resistance and drought tolerance, which are highly important to the green industry.

Axillary buds from a single C. kentukea tree were initially cultured on either Woody Plant Medium (WPM) or Murashige and Skoog (MS) containing 0, 1, 2, or 4 μM 6–benzylaminopurine (BA). Cultures were transferred to fresh medium every four weeks. Elongated shoots were harvested after thirty-nine weeks and transferred to half-strength MS medium supplemented with following concentrations of IBA: 0, 3, 30, 100, and 300 μM for three days then returned to half-strength MS without growth regulators. Explants exposed to 300 μM of IBA produced significantly more roots (75%) compared to explants exposed to other treatments. Fifty- four and forty- six percent of the microshoots rooted when exposed to 100 and 30 μM IBA, respectively. Only 4% of the microshoots rooted when exposed to 3 μM IBA and none of the microshoots in the control treatment (0 IBA) rooted. Although 300 μM treatment yielded the most rooted plantlets, there was significantly higher terminal meristem abortion compared to other treatments. There were no statistical differences between the numbers of roots and total root length among all treatments. Additionally, all microshoots that rooted had lenticels, suggesting that presence of lenticel cambial activity can possibly predict rooting abilities of selected microshoots. Rooted microshoots were gradually acclimatized to non-sterile environment.

Axillary and apical buds from five Cornus kousa cultivars (‘Little Beauty’, ‘Samaritan’, ‘Heart Throb’, ‘Rosabella’ and ‘Christian Prince’) were initially established on either WPM or one-half Woody Plant Medium/Broad Leaved Tree Medium (BW), amended with the following concentrations of 6–benzylaminopurine (BA): 0, 2, 4, and 8 μM. After explants were transferred at four-week intervals for 28 weeks beginning in April, only microshoots of ‘Samaritan’, ‘Heart Throb’, and ‘Rosabella’, were harvested from proliferating cultures and placed on rooting media. ‘Little Beauty’ and ‘Christian Prince’ did not perform well in multiplication phase of tissue culture and were excluded from further studies. Rooting media contained WPM or BW supplemented with either 1- naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA), or indole-3-acetic acid (IAA) at the following concentrations: 0, 0.5, 1.5, 4.5, and 13.5 μM. Six weeks following rooting experiment, preliminary data was collected and results indicated a total of nine plants rooted on both WPM and BW media supplemented with IBA, 17 plants rooted on media supplemented with NAA, and 14 plants rooted plants supplemented with IAA. NAA and IAA appeared to be better for root production on C. kousa cultivars microshoots than IBA. Moreover, both WPM and BW media supported rooting of C. kousa microshoots. However, WPM appears to support more root production compared to BW. A greater number of ’Samaritan’ and ‘Heart Throb’ microshoots rooted on WPM amended with a wide range of NAA concentrations, whereas more ‘Rosabella’ microshoots rooted on BW medium amended with various concentrations of IAA. Since ‘Rosabella’ and ‘Heart Throb’ are very closely related and should have rooted with similar treatments, further research is needed to confirm this finding. Additionally, microshoots placed on either basal media supplemented with NAA produced significant amount of callus compared to microshoots exposed to other growth regulator treatments. The highest mean number of roots per rooted microshoot was recorded on ‘Samaritan’ when exposed to various NAA concentrations. In conclusion, the most and best rooting occurred with IBA treatments at lower concentrations, 0.5 and 1.5 μM, whereas NAA and IAA treatments were inconclusive.

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