Theses and Dissertations

Issuing Body

Mississippi State University


Harkess, Richard L.

Committee Member

Baldwin, Brian S.

Committee Member

Bi, Guihong

Committee Member

Denny, Geoffrey

Committee Member

Collins, Pamela

Date of Degree


Original embargo terms

MSU Only Indefinitely

Document Type

Dissertation - Campus Access Only



Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


Red firespike (Odontonema strictum) is an ornamental shrub with potential for use as a flowering potted plant due to its dark green foliage and attractive red flower spikes. Studies were conducted to evaluate the effect of photoperiod and plant growth retardants on firespike growth and flower initiation and development. Firespike is reported to be a short day plant. To determine the critical photoperiod requirements to initiate flowering, plants were placed in short days (SD) for 0, 8, 16, 24, or 32 days before being returned to long days (LD). Meristems were sampled 0 or 8 days after return to LD for histological examination. Plants receiving only 8 SD showed early floral initiation; however, plants receiving 16 or more SD reached anthesis earlier than plants grown under fewer SD. To evaluate the effects of light intensity and temperature on flowering and growth characteristics of firespike, two experiments were conducted. Plants were grown under LD or SD, 0%, 45% or 65% shade and temperatures of 15, 25 or 35°C. Plants grown under 45% shade and LD and 65% shade and SD had greatest and least height, respectively. The first open flower was observed after 92 days under no shade while 45% shade in both LD and SD resulted in more inflorescences. To evaluate effectiveness of various plant growth regulators on firespike height control, foliar and drench applications of uniconazole, flurprimidol, daminozide, and paclobutrazol were examined in two experiments. The results showed flurprimidol and paclobutrazol drenches at 0.24 and 0.35 mg a.i./pot could be used to control the growth of red firespike more effectively than other PGRs. However, growth index decreased up to 88% and 84% when paclobutrazol and flurprimidol were applied at 0.59 and 0.71 mg a.i./pot, respectively. The morphological and physiological characteristics of firespike treated with paclobutrazol and flurprimidol under drought stress were studied. Drought stress delayed days to flowering and number of replications flowering. Application of paclobutrazol and flurprimidol enhanced drought resistance of red firespike reducing adverse effects of water stress during the experiment.