DEVELOPMENTAL ANATOMY OF THE STEM APEX OF THE BETTER TIMES ROSE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University by Richard Stadden Lindstrom, B. Sc,. ^ . M. Sc. The Ohio State University 1956 Approved by: Adviser Department of Horticultui and Forestry ACKNOWLEDGEMENT There are many to whom I owe acknowledgement for the completion of this dissertation. In particular, I wish to express sincere appreciation to Professor Alex Laurie for suggesting the problem and to Dr. L. C. Chadwick and to Dr. D. C. Kiplinger for making it possible to complete the work. I also wish to thank Dr. R. A. Popham, Botany Department, for his constant interest and guidance on the anatomical aspects of the problem. Appreciation is also extended to Roses Incorporated, whose fellowship I held for three years and to the Department of Horticulture of Michigan State University for the use of their laboratory and the many hours of freedom for investigation. P. G. Coleman's assistance with the microphotography and Dr. R. F. Stinson's suggestions are also appreciated. TABLE OF CONTENTS Page Introduction ............................. 1 Review of Literature ...... ......... 3 Materials and M e t h o d s ........... , 13 r Results ................................ , 19 Discussion . ......................... 43 Summary .......... ..................... 49 Bibliography ............................ 50 Autobiography .............. .......... • • • 52 iii LIST OF ILLUSTRATIONS Figures Page 1. A vegetative stem apex from a shoot that presumably would have been flowering (terminal)............................ 20 2. A vegetative stem apex from a shoot that presumably would have been blind (axillary)............. 21 3. The first evidence of reproduction in a presumably flower­ ing s h o o t ............................ 23 4. An early stage of sepal primordia ........................ 24 5. A later stage of development of sepal primordia ........ 25 6. An early stage of petal primordia which appeared 13 days after the cutback ' ’............... 26 7. A later stage of petal primordia formation ............ 27 8. An early stage of pistil primordia ...... 28 9. A later stage of pistil primordia development ........... 29 10. The first evidence of reproduction in a presumably blind s h o o t ....................................................... 31 11. An early stage of sepal primordia in a presumably blind s h o o t .......... 32 12. The first evidence of disintegration of tissue in a presumably blind shoot ................. 33 13. Further disintegration of the s e p a l s ............... 34 14. Complete abortion of the rose apex at petal primordia stage 35 15. Intermediate stage of disintegration at stamen primordia s t a g e ..................................... 36 16. Abscission layer formed in the stamen primordia stage . 37 17. Intermediate stage of disintegration at pistil primordia s t a g e ....................................................... 33 18. A very late stage in the disintegration of tissue at the pistil primordia stage .... 39 19. An aborting rose apex showing necrotic bands and cell disintegration .............................................. 40 20. The formed abscission layer of an aborting a p e x ......... 41 iv DEVELOPMENTAL ANATOMY OF THE STEM APEX OF THE BETTER TIMES ROSE INTRODUCTION Roses are the most important floricultural greenhouse crop in the United States. According to the Agriculture Census (1) the wholesale value of roses grown under glass in 1949 was $30,582,022.00 and for all cut flowers grown under glass was $93,478,944.00. A comparison of these values shows that roses constituted 32.7 per cent of the cut flower income for that year. The greenhouse rose is an ornamental decidious shrub with upright or climbing stems which are usually associated with spines. The rose is classified under the family name Rosaceae. Accurate information on parentage and origin of the present day hybrid varieties is lacking but it has been reported by Wildon (21) that some of the species which are parents of the modern hybrid teas are R. gallica, R. damascena, 3i* centifolia, r . Borionica, and R. odorata. Commercially the rose grower receives the greatest profit for his crop during the months of November through May. The midwestern growers have the most difficulty producing the crop during this season because of low prevailing light intensities. The grower becomes increasingly aware of the unproductiveness of "blind wood" (a shoot with an aborted - 1 - - 2 - flower bud), which reduces his potential crop and therefore profit. It would be advantageous if the cause could be found or the incidence of blind wood materially reduced, especially since some greenhouse rose varieties will produce shoots of which as many as 50 per cent will have aborted flower buds. The hybrid tea greenhouse rose Better Times was used in this anatomical study of the development of both blind and floi;ering shoots. REVIEW OF LITERATURE Blind wood has long been recognized by many investigators (11, 14, and 19) as an economic loss to the rose grower. One of the first reports on the formation of blind wood was presented in 1859 by an anonymous writer (3) working with the variety Isabella Gray who stated, "It produced thirty strong shoots each of which terminated with blind ends". Since that time, some of the theories which have been advanced to explain the causes of blind wood are as follows: 1) an inherited characteristic (7), 2) a growth expression dependent upon the vigor or the stock (11), 3) the result of a hormonal condition (13), 4) variations in light intensity and temperature (6), 5) light intensity and nutrition (23), factors other than light intensity and nutrition (8). Heredity: The first important work in blind shoots was done by Corbett (7). One of the questions he was trying to answer was, "Do cuttings tend to perpetuate the individual peculiarities of the parent branch from which they are taken?" After 5 years of research he concluded in 1902, "that the tendencies manifested in a branch are perpetuated from generation to generation in plants propagated by asexual processes". The basis for his theory was that rose plants propagated from flower­ ing shoots averaged 29.4 flowers per plant, while rose plants propaga- gated from blind shoots averaged 11.5 flowers per plant. - 3 - - 4 - Hubbell (12) was unable to substantiate the work of Corbett. He budded axillary buds from mature flowering shoots onto flowering and blind shoots and axillary buds taken from blind shoots onto flowering shoots. He found that buds from flowering and blind shoots budded on flowering wood produced high percentages of flower­ ing shoots. Whereas, axillary buds taken from flowering shoots and budded on blind shoots produced a high percentage of blind shoots. Hubbell concluded that the tendency for rose plants to produce blind- wood is not inherited but is a growth expression dependent upon the vigor of the stock. Therefore, according to Hubbell, the budding experiments indicated that the limitations of flower formation are based on the activity of the stock and not of the bud. Activity versus Carbohydrabe-Nitragen Relationship: In a pruning experiment by Hubbell (11) 97 per cent of the flowering shoots pruned back to the first, second, or third axillary bud from the tip remained flowering, while 97 per cent of the blind shoots pruned back in the same manner again became blind. He found that chemical analyses of blind shoots showed much greater percentages of non-colloidal nitrogen and insoluble carbohydrates than flowering wood; whereas flowering wood contained higher percentages of reducing sugars. In the spring of the year it became evident that there was an increase in the carbohydrate-nitrogen ratio. Since many blind shoots produced flowers in the spring, this caused a decrease in - 5 - blind shoots, and it was assumed that the increase in carbohydrate- nitrogen ratio brought about a condition xtfhich was favorable to flower formation, Hubbell (11) stated that the budding experiments combined with these pruning experiments indicated that blindness was not due to the impotency of the bud but was a result of the stock, In a review of Hubbell's (11) work on chemical analysis of blind versus flowering wood, Kamp (13) expressed the opinion that Hubbell had compared mature blind wood with immature flowering wood. Also it was pointed out that Hubbell had analyzed the entire shoot as a unit rather "than allowing for the possibility that gradients in composition existed within the length of the stem. Kamp (13) there­ fore, cut blind and flowering rose shoots into segments of varying lengths and compared them. In the chemical analysis he measured free reducing substances, total sugars, total nitrogen, and protein and non­ protein nitrogen of comparable stem length segments. He concluded that considering all these contradictory evidences, it was not possible to see any clearly defined relationship between the number of blind shoots and the chemical composition at least with respect to the fractions analyzed in his study. He also stated that blindness seems to be caused by a hormonal mechanism rather than by a nitrogen- carbohydrate relationship. - 6 - Karap (13) found upon examination of unshaded plants that regardless of variety, flowering shoots bore on the average more than twice the number of leaves as did blind shoots. Therefore, if blindness was attri­ buted to an insufficient number of leaves