1. INFLUENCE OF CULTIVAR AND ROOTING HORMONE CONCENTRAION ON
SHOOT GROWTH AND ROOT MASS OF BASIL (OSIMUM BASILICUM)
BY
STEPHANIE PETRAKOS
Submitted to the Honors Program for the graduation requirement of
SUMMA CUM LAUDE HONORS
UNIVERSITY OF FLORIDA
College of Liberal Arts and Sciences
MAY 2016
________________________________
Student Signature: Stephanie Petrakos
Contact: spetrakos@ufl.edu
________________________________
Thesis Advisor Signature: Dr. Brian J. Pearson
Contact: bpearson@ufl.edu
________________________________
Co-Thesis Advisor Signature: Dr. Jeremy Lichstein
Contact: jlichstein@ufl.edu
________________________________
Departmental Honors Coordinator Signature: Dr. Leslie Paul Thiele
Contact: thiele@ufl.edu
Stephanie Petrakos

2. 2
Abstract
Basil (Ocimum basilicum) is a popular aromatic herb cultivated primarily for its culinary
attributes. Recent increased demand for this crop has prompted a need for an improvement in
production technique aimed at enhancing yield and improving production efficiency. The aim of
this study is to measure and record growth of three popular basil cultivars during propagation
and identify optimal root hormone concentration for these cultivars. A secondary objective of
this work is to identify cultivars with enhanced root:shoot ratios that may be produced under
reduced irrigation regimes and possess enhanced drought tolerance. Three basil cultivars (Mrs.
Burns Lemon, Red Rubin, and Aroma 2) were chosen for the study and seventy-two cuttings
from each cultivar were taken and treated with 0%, 0.1%, 0.3%, and 0.8% indole-3-butyric acid
rooting hormone. Two weeks after vegetative clones were propagated, plant height was recorded
and root mass was measured. Mrs. Burns Lemon was significantly taller than Aroma 2 cultivars.
However, the root mass of Aroma 2 was greater than Mrs. Burns Lemon and Red Rubin. Greater
root:shoot ratios associated with Aroma 2 suggests lower irrigation needs during production and
enhanced drought tolerance for this cultivar. Root mass was similar amongst plants treated with
0%, 0.1%, and 0.3% indole-3-butyric acid. Results from this work aid in the development of
sustainable or reduced-input production strategies with specific aim at reductions in reliance on
synthetic plant hormone and irrigation use.

3. 3
Introduction
Basil (Ocimum basilicum) is a popular, aromatic herb prized for its superior flavors and
aromas. Essential oils extracted from its fresh leaves and flowers are used as additives in
pharmaceutical, household, cosmetic, and culinary products (Loughrin and Kasperbauer, 2003).
In addition to these uses, basil is also cultivated for its neutraceutical properties. Basil can be
used as a stomachic, antihelminthic, antipyretic, diaphoretic, expectorant, carminative, stimulant,
and pectoral (Sahoo et. al, 1997). Despite the diverse applications of basil and its essential oils,
basil is an important culinary herb, marketed fresh, frozen, or dried. (Jayasinghe et. al, 2003).
Basil is often dried post-harvest rather than sold fresh (wet) to aid in storage and transport
(Bekhradi et al., 2014). However, recent interest in fresh, localized food products, has increased
demand for wet, recently harvested basil. In order to satisfy increased demand for fresh basil,
production methods which maximize production need to be established.
Although traditional basil production practices are well established, producers have
recently investigated new methods to reduce plant production time and meet consumptive
demands (Purcino et al., 2012). Despite traditional soil-based cultivation from seed, soilless basil
production utilizing clonal propagules within protected greenhouse environments has grown in
popularity. Advantages of greenhouse production include precise control of environmental
conditions, nutrient availability, and irrigation. However, high precision production requires
proper selection of cultivar and propagation technique to maximize production and efficiency.
Research focusing on the development of appropriate and efficient production practices are
needed to establish effective and sustainable production of this crop (Bekhradi et al., 2014).
Sustainable utilization of water is critical to commercial plant production and long term
protection of natural resources. In 2010, mean total water usage in the United States was 355

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billion gallons per day. Of that volume, total irrigation withdrawals were 115,000 million gallons
per day, or 61% of total freshwater withdrawals (Maupin, et al., 2014). Besides thermoelectric
power, irrigation remained the largest single use of freshwater resources (Maupin, et al., 2014).
Research examining plant water use and drought tolerance is necessary to assist in the selection
of plant species which would help allow for reduction in consumption of freshwater for irrigation
purposes. Further, related research has observed reduced irrigation can result in higher quality
basil crop. Water stress has been shown to increase the content of phenolic acids and antioxidant
properties in green and purple varieties of sweet basil (Luna, et al., 2015). Thus, reduced
irrigation may improve plant quality while simultaneously reducing reliance on natural
resources.
Disease management is an important component in plant production. Downy mildew, a
relatively new and destructive disease in basil, was first discovered in Florida in the fall of 2007
(Wyenandt, et al., 2010). The disease is believed to have originated from Uganda (McGrath,
2015) and since its introduction into the US has been reported in commercial basil production
facilities in California and the Midwest. The first symptoms of downy mildew are yellowing in
the leaves, at first making downy mildew overlooked as a nutrient deficiency. As the disease
develops, dark, gray-purple sporangia forms on the abaxial surface of the leaves, eventually
making its way to the adaxial side of the leaves (Wyenandt, et al., 2010). This sporangia prevents
photosynthesis in the leaves, stunts plant growth, and destroys the essential oils that the basil
leaves produce, making the basil plant unviable. There is no specific treatment or cure for downy
mildew, but preventing wet, moist environments for the mildew to grow and selecting a cultivar
less susceptible to downy mildew is crucial to maximizing the prevention of the disease. Ocimum
basilicum is more susceptible to the disease than basil varieties of a different species such as

5. 5
Ocimum citriodorum and Ocimum americanum (McGrath, 2015). However, purple or red
varieties of Ocimum basilicum such as Red Rubin and lemon varieties of Ocimum basilicum such
as Mrs. Burns Lemon are less susceptible to downy mildew. The Aroma 2 variety of basil, most
similar in aroma and taste to the popular Genovese basil, has also shown a resistance to downy
mildew that is nearly equal to that of Mrs. Burns Lemon and Red Rubin (Wyenandt, et al., 2010).
Due to their high disease resistance, these three cultivars of basil were chosen for this study.
Materials and Methods
Seed propagation. Seeds of three basil cultivars (Mrs. Burns Lemon, Red Rubin, and Aroma 2)
were purchased (Johnny’s Selected Seeds in Winslow, MA) and propagated from seed on June
17, 2014. Seeds of each cultivar were germinated in a 72 cell pack tray (n=216) containing
Fafard Growing Mix 2 (SunGro, Agawam, MA) soilless substrate in a greenhouse located in
Apopka, FL. The experiment was conducted over a duration of eight weeks starting on June 17,
2014, and concluding on August 8, 2014. Data was recorded over a six week period, starting on
June 17, 2014. Each tray received irrigated mist every 5 minutes for a duration of 15 seconds. On
June 24, one week after the seeds were planted, plant height was recorded for Mrs. Burns Lemon
and Aroma 2 varieties. Slow germination rate for Red Rubin precluded measurement of plant
height until three weeks after transplant (WAT) on June 2, 2014. Trays were irrigated for a
duration of 4 weeks with the mist irrigation system prior to container production. Fertilizer (50
ppm N) was applied through capillary tray absorption 3 weeks after transplant. After reaching a
height of 30 cm, 8 basil plugs were removed from their trays and transplanted into 7.5 L
containers (8 basil plugs per container). Each container was irrigated twice daily utilizing a low-
volume drip emitter. Plant height measurements were collected weekly beginning post-transplant

6. 6
and terminated 6 WAT. Throughout this production period, electrical conductivity was collected
(data not shown) to ensure adequate substrate nutrient availability.
Vegetative clonal propagation. On July 27, 2016, 6 WAT, seventy-two cuttings from the three
basil cultivars were taken and treated with 0%, 0.1%, 0.3%, and 0.8% indole-3-butyric acid
(IBA) (Hormodin, OHP, Inc., Mainland, PA) rooting hormone. After application of the rooting
hormone, cuttings were transplanted into a 72 cell pack tray containing Fafard Growing Mix 2
(SunGro, Agawam, MA) soilless substrate. Cuttings were placed within the greenhouse and
irrigated every 5 minutes for a duration of 15 seconds using a mist irrigation system. Plant height
measurements were collected weekly for a duration of 2 weeks at which time the clonal
propagules were ready for transplant. Plants were destructively harvested and dried in an oven at
65 °C until a constant dry weight was obtained to quantify root mass and shoot mass.
Statistical analysis. Plants cultivated for this experiment were arranged utilizing a completely
randomized design. Plant height, root, and shoot mass data were analyzed using the PROC GLM
procedure in SAS with mean separation by Duncan’s multiple range test. Statistical tests were
considered to be significant if P<0.05.
Results and Discussion
Seed propagation. Beginning 2 WAT, mean height of Mrs. Burns Lemon and Aroma 2 were
approximately 2.14 and 1.07 cm, respectively (Figure 1). Three WAT Red Rubin varieties were
large enough to measure and had a mean height of 1.27 cm. Beginning 3 WAT, rapid growth was
observed. High growth rates between 3 and 6 WAT are likely a result of nutrient application.
Beginning 4 WAT, Mrs. Burns Lemon had greater plant height than either Aroma 2 or Red
Rubin (Figure 1). Beginning 5 WAT, Aroma 2 and Red Rubin displayed rapid growth. Aroma 2
had an average height of 9.2 cm with the largest Aroma 2 plant being 17.5 cm tall. Red Rubin

7. 7
had an average height of 4.75 cm with the largest Red Rubin plant being 13.8 cm tall. Mrs. Burns
Lemon had an average height of 24.38 cm with the tallest being 32.7 cm (Figure 1). Rubin
remained the most compact cultivar with mean height of 9.5 cm at termination of the experiment
(6 WAT).
At termination of the experiment (6 WAT), downy mildew was present on all three
cultivars, making them unviable and ineffective for further experimentation. However, the
quantity of downy mildew and severity of the outbreak varied dependent upon cultivar. Downy
mildew was most virulent on Aroma 2 cultivars where it infected approximately 60% of plant
leaves. Disease incidence was less severe for Red Rubin and Mrs. Burns Lemon with leaf
infection of approximately 25% and 40%, respectively. These observations imply that significant
variability of disease resistance exists amongst basil cultivars. Further research is warranted to
identify and potentially breed resistance amongst popular, susceptible varieties.
Amongst the cultivars tested, greatest plant growth was observed for Mrs. Burns Lemon.
As expected, Mrs. Burns Lemon possessed the highest mean leaf count with 8 leaves on each
stem and an average height of 8 cm (Table 1). Aroma 2 had an average of at least 6 leaves on
each stem and an average height of 4 cm whereas Red Rubin had an average of at least 6 leaves
on stem and an average height of 4 cm. Greater leaf count in Mrs. Burns Lemon may be
significant to the culinary market given its application in food preparation and production.
Vegetative clonal propagation. Plant height was not influenced by hormone application.
Over the duration of the experiment, the height of Mrs. Burns Lemon was approximately 2-fold
greater and significantly different than Aroma 2 despite higher mean variability. Red Rubin had
similar plant height to both Mrs. Burns Lemon and Aroma 2 in the three weeks prior to the

8. 8
application of fertilizer in week four. Although plant height of Mrs. Burns Lemon was greatest, it
had similar root mass to Red Rubin and significantly less root mass than Aroma 2 (Figure 2).
This suggests Aroma 2 may possess greater root:shoot ratios and greater drought tolerance when
compared to Mrs. Burns Lemon and Red Rubin cultivars. This may be beneficial when
considering selection of cultivar for transplant and establishment in the landscape. Dry root mass
amongst all three cultivars was highest when propagated using 0.3% IBA, but similar to those
treated with 0% and 0.1% (Figure 3). Root mass was lowest when treated with 0.8% IBA and
was approximately 2-fold less than propagates treated with 0.3% IBA (Figure 3). Increased root
mass as a result of IBA application was similar to findings reported by Sahoo et al. (1997). In
contrast to Sahoo et al., (1997); however, we observed deleterious effects when IBA
concentrations exceeded 0.3% (Figure 3).
Conclusion
Plant growth utilizing conventional seed germination techniques was acceptable and
similar to expectations for related ornamental and edible crops produced under a protected
greenhouse system. Although not the main focus of this thesis, information collected and
presented within this manuscript is beneficial and of value to commercial production of this
unique crop. Overall, high growth rates observed for Mrs. Burns Lemon and Aroma 2 varieties
suggest these varieties possess the greatest commercial production potential.
Although there is currently no cure for downy mildew, there are measures that can be
taken in commercial production to prevent downy mildew from occurring and to control the
severity of a downy mildew outbreak. It is increasingly common for the Ocimum basilicum
species to be marketed as resistant to downy mildew. However, additional research efforts are
needed to scientifically quantify levels of resistance and to aid in identification of cultivars that

9. 9
may be utilized for plant breeding to confer resistance to popular, susceptible cultivars.
Currently, it is recommended that commercial cultivators of Ocimum basilicum select cultivars
crossed with disease resistant varieties of basil, such as Ocimum citriodorum or Ocimum
americanum. If a pure Ocimum basilicum cultivar must be selected for production, it is
recommended that Red Rubin or Mrs. Burns Lemon be selected based upon our experimental
observations. In order to avoid an outbreak, maintenance of a warm, dry environment and the
avoidance of moisture on the basil leaves are vital.
Overall, Mrs. Burns Lemon did not possess significantly greater root mass than Aroma 2
or Red Rubin cultivars, despite greater plant height. Even though Aroma 2 had a shorter average
height than Mrs. Burns Lemon, the greater root mass of Aroma 2 indicates that Aroma 2 may
have a greater root:shoot ratio and a greater drought tolerance when compared to Mrs. Burns
Lemon and Red Rubin cultivars. A greater root:shoot ratio and its associated effect on a drought
tolerance may be beneficial when considering selection of cultivar for cultivation within a
greenhouse or transplant and establishment in the landscape given less water would be required
to cultivate healthy, high quality plants. This would likely have significant impact on
improvements in water conservation. Therefore, out of all three basil cultivars, Aroma 2 would
most likely be the most sustainable in terms of water utilization.
In regards to root hormone concentration influence on the growth of basil root mass, root
mass is generally increased following the application of 0.1% and 0.3%IBA. However, the root
mass of hormone treated propagates was not significantly higher than the root mass of untreated
propagates. In order to avoid deleterious effects to root development in these three basil
cultivars, it is not recommended to apply a root hormone concentration that is greater than 0.3%
IBA. Despite positive correlations between IBA application and root development in related

10. 10
research, our findings suggests root hormones are not significantly advantageous to commercial
production of basil. Additionally, our findings suggests that basil cultivar, not concentration of
root hormone, is of importance for root development. The natural tendency for increased, healthy
root development, or lack thereof, is what makes a particular basil cultivar sustainable or not
sustainable in the physical environment.

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References
Bekhradi, F., Luna, M., Delshad, M., Jordan, M., Sotomayor, J., Martínez-Conesa, C., & Gil, M.
(2015). Effect of deficit irrigation on the postharvest quality of different genotypes of
basil including purple and green Iranian cultivars and a Genovese variety. Postharvest
Biology and Technology, 100, 127-135. Retrieved June 10, 2015, from Web of Science.
Jayasinghe, Chamila, Naohiro Gotoh, Tomoko Aoki, and Shun Wada. "Phenolics Composition
and Antioxidant Activity of Sweet Basil ( Ocimum Basilicum L.)." J. Agric. Food
Chem. Journal of Agricultural and Food Chemistry 51.15 (2003): 4442-449. Web. 11
June 2015.
Loughrin, J., & Kasperbauer, M. (2003). Aroma Content of Fresh Basil (Ocimum basilicum L.)
Leaves Is Affected by Light Reflected from Colored Mulches. Journal of Agricultural
Food Chemistry, 2272-2276. Retrieved July 12, 2015, from Web of Science.
Luna, María C., Farzaneh Bekhradi, Federico Ferreres, María J. Jordán, Mojtaba Delshad, and
María I. Gil. "Effect of Water Stress and Storage Time on Anthocyanins and Other
Phenolics of Different Genotypes of Fresh Sweet Basil." J. Agric. Food Chem. Journal
of Agricultural and Food Chemistry 63.42 (2015): 9223-231. Web.
Maupin, Molly A., Joan Kenny, Susan S. Hutson, John K. Lovelace, Nancy L. Barber, and
Kristin S. Linsey. "Estimated Use of Water in the United States in 2010." USGS (2014):
25. Web.
McGrath, M. (2015). Expect and Prepare for Downy Mildew in Basil. Department of Plant
Pathology and Plant-Microbe Biology, Cornell University, 1-6. Retrieved June 10, 2015,
from http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html
Purcino, M., Machado, M., & Biasi, L. (2012). Effect of Leaves on the Rooting of Cuttings of
Clove basil (Ocimum gratissimum L.) and anis (Ocimum selloi Benth). Revista De

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Ciências Agroveterinárias, 11(2), 93-98. Retrieved June 10, 2015, from CabDirect.
Sahoo, Y., Pattnaik, S., & Chand, P. (1997). In vitro Clonal Propagation of an Aromatic
Medicinal Herb Ocimum basilicum L. (Sweet Basil)by Axillary Shoot Proliferation. In
Vitro Cellular &amp; Developmental Biology. Plant, 293-296. Retrieved July 12, 2015,
from Jstor.
Wyenandt, C., Simon, J., McGrath, M., & Ward, D. (2010). Susceptibility of Basil Cultivars and
Breeding Lines to Downy Mildew. HortScience, 45(9), 1416-1419. Retrieved June 10,
2015, from Web of Science.

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Appendix
Figure 1. Mean height of three basil (Ocimum basilicum) cultivars (n=72) from June 22, 2014
(Week 1) through July 27, 2014 (Week 6).
0
5
10
15
20
25
30
35
40
Week 1 Week 2 Week 3 Week 4 Week 5 Week 6
Height(cm)
Weeks After Transplant
Height of Basil Cultivars
Red Rubin Mrs. Burns Lemon Aroma 2

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Figure 2. Dry root mass of three basil (Ocimum basilicum) cultivars (n=24) two weeks after
transplant planted into Fafard Growing Mix 2 soilless substrate. Error bars represent the standard
error of the mean.
b
b
a
0
0.5
1
1.5
2
2.5
3
Mrs. Burns Lemon Red Rubin Aroma 2
Dryrootmass(mg)
Cultivar

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Figure 3. Dry root mass of basil (Ocimum basilicum) (n=18) two weeks after transplant into
Fafard Growing Mix 2 soilless substrate propagated with 0%, 0.1%, 0.3%, and 0.8 indole-3-
butyric acid (IBA) rooting hormone treatments. Error bars represent the standard error of the
mean.
ab ab
a
b
0
0.5
1
1.5
2
2.5
3
0% 0.1% 0.3% 0.8%
Dryrootmass(mg)
Indole-3-butyric acid concentration

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Table 1. Height and leaf count of three basil (Ocimum basilicum) cultivars (Mrs. Burns Lemon,
Aroma 2, and Red Rubin) four weeks after transplantz
.
Cultivar Height (cm) Leaf count
Mrs. Burns Lemon 8 8
Aroma 2 4 6
Red Rubin 4 6
z
Means of 72 plants per cultivar.