REGULATION OF BUD GROWTH IN KENTUCKY BLUEGRASS (POA PRATENSIS L.) AS INFLUENCED BY TEMPERATURE, ETHYLENE AND KINETIN By David E. Aldous A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1978 ABSTRACT REGULATION OF BUD GROWTH IN KENTUCKY BLUEGRASS (POA PRATENSIS L.) AS INFLUENCED BY TEMPERATURE, ETHYLENE AND KINETIN. BY David Ernest Aldous High midsummer temperatures inhibit bud growth in many cool season grasses. Experiments were conducted, both under field conditions and controlled environments (growth chambers), on the regulation of bud growth in Kentucky bluegrass (Poa pratensis L.) cv. Merion and Nugget. Bud growth was schematically illustrated by stages: 1) initiation of bud activity to first primordial leaf; 2) second primordial leaf to leaf unfold, and; 3) ligule formation to leaf emergence above the subtending leaf sheath. The increase in the number of active buds (bud activity) never ceased but was reduced when the grasses were grown at 33C. Temperatures of 22C were found to significantly increase bud length in both cultivars compared to 330. The change in temperature influenced the number of active buds in Merion to a much greater extent than in Nugget. The number of active buds at the stem base and nodes were also reduced by supraoptimal temperatures compared to cooler temperatures in both cultivars. To evaluate the effect of ethylene concentration on bud activity, David Ernest Aldous ethylene was introduced for 24 hr in two temperature treatments of 22 and 33C. Following the treatment, the grasses were grown for 10 days at either temperature. Results showed that only a 24 hr exposure at 33C was needed to inhibit bud activity. Inhibition was extended when both cultivars were subsequently exposed to 10 days of supraoptimal temperatures. Significant increases in the number of active buds at 22/22C were evident when comparing treatments of 10 and 100 ul/L ethylene in Nugget and l and 10 ul/L ethylene in Merion with respective controls. Both cultivars exhibited lowered numbers of active buds when both the initial exposure and postinitial temperatures were 330, irre- spective of ethylene concentration. The number of active buds increased when cultivars exposed to 33C were returned to cooler temperatures. When the grasses were placed under hypobaric ventilation to reduce ethylene and other gases to subnormal levels, the number of active buds were reduced at 22C. Bud activity returned to normal when ethylene was reintroduced. Under higher temperatures the number of active buds could not be restored by the reintroduction of ethylene. Ethylene production, measured at 5C increments from 150 to 400, peaked at 27C in Merion and 34C in Nugget. High ethylene levels were considered a contributing factor in bud activity inhibition at high temperatures. Kinetin was applied as a foliar spray to both cultivars grown at 22 and 330 to evaluate its effect on bud activity and ethylene product- ion. Ethylene and kinetin, when applied alone, significantly increased the number of active buds at 22C. When the cultivars were grown at David Ernest Aldous 33C, neither ethylene, kinetin nor their combination had a significant effect on bud activity. Results from hypobaric conditions suggest that bud activity may be influenced by kinetin stimulated ethylene. Kinetin was found to enhance bud activity in Nugget grown at 22C apparently through stimulation of ethylene. Inhibition of bud activity resulted from increased ethylene production generated endogenously or by kinetin application at 33C. Rates of Ethephon (2-chloroethylphosphonic acid), less than 1000 ul/L applied as drenches, were ineffective in increasing shoot numbers under summer field conditions. Monthly nitrogen drenches of 0.48 kg N/lOOmZ, were more effective in improving shoot density and quality in both cultivars compared to combinations of nitrogen and Ethephon. ACKNOWLEDGMENTS The author wishes to express his sincere appreciation and gratitude to his major professor, Dr. J. E. Kaufmann for his guidance and constructive criticism in the preparation of this dissertation. Appreciation is expressed to Dr. D. R. Dilley, Dr. D. Penner and Dr. P. E. Rieke for serving as guidance committee members and for their helpful discussions and suggestions during my graduate program. Thanks are also extended to Mr. W. J. Eaton for his technical assist- ance and expertise in the field. To the ones very special to me, my wife Kaye and children Matthew and Janine, my thanks for their understanding, patience and support throughout the course of study. To the Department of Crop and Soil Sciences, Michigan State University, grateful acknowledgement is made for the assistantship during the period the study was undertaken. ii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . LIST OF FIGURES O O O O O O O O O O O O O O O 0 INTRODUCTION 0 C O O O O O O O C O O O O O O O 0 CHAPTER 1: TEMPERATURE INFLUENCES 0N BUD MORPHOGENESIS IN KENTUCKY BLUEGRASS Abstract . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . Materials and Methods . . . . . . . . . . . . . Results and Discussion . . . . . . . . . . . . . Literature Cited 0 O O O O O I O O O O O O O O 0 CHAPTER 2: HYPOBARIC AND TEMPERATURE EFFECTS ON BUD GROWTH ETHYLENE PRODUCTION IN KENTUCKY BLUEGRASS Abstract . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . Materials and Methods . . . . . . . . . . . . . Results and Discussion . . . . . . . . . . . . . Literature Cited . . . . . . . . . . . . . . ... CHAPTER 3: REGULATION OF BUD GROWTH IN KENTUCKY EFFECT OF KINETIN AND TEMPERATURE ON PRODUCTION Abstract . . . . . . . . . . . . . . . iii BLUEGRASS. ETHYLENE Page vii 20 22 23 25 27 39 42 Introduction . . Materials and Methods Results and Discussion . Literature Cited . 43 44 48 55 CHAPTER 4: INFLUENCE OF ETHYLENE, KINETIN AND NITROGEN DRENCHES ON SHOOT DENSITY IN KENTUCKY BLUEGRASS UNDER SUMMER FIELD CONDITIONS Abstract . . . . . Introduction . . Materials and Methods Results . . . . . Discussion . . . Literature Cited . CONCLUSIONS . . LIST OF REFERENCES iv 57 58 60 61 71 77 80 82 LIST OF TABLES Table Page CHAPTER 1 1. Schematic presentation of the influence of temperature on bud growth in Merion and Nugget Kentucky bluegrass . . . . . . . . ll 2. Effect of sampling date, temperature and position on bud length of Merion Kentucky bluegrass expressed as the percent of total bud numbers at each position . . . . . . . . l4 3. Effect of sampling date, temperature and position on bud length of Nugget Kentucky bluegrass expressed as the percent of total bud numbers at each position . . . . . . . . 15 4. Influence of time and temperature on length of subtending leaf in Merion and Nugget Kentucky bluegrass . . . . . . . . . 16 CHAPTER 2 I. Effect of ethylene and temperature on bud activity in Merion and Nugget Kentucky bluegrass . . . . . . . . . . . . . 28 2. Effect of temperature and gas mixture on rhizome/tiller ratio in Merion and Nugget Kentucky bluegrass . . . . . . . . 34 3. Effect of ethylene concentration and temperature exposure on the number of active buds in Merion Kentucky bluegrass . . 35 4. Effect of ethylene concentration and temperature exposure on the number of active buds in Nugget Kentucky bluegrass . . 36 CHAPTER 3 1. Effect of temperature on the number of active buds in Merion and Nugget Kentucky bluegrass as influenced by ethylene and Kinetin concentration . . . . . . . . . . . . . . . . . . . . 49 2. Effect of kinetin concentration on the number of active buds in Nugget Kentucky bluegrass as influenced by temperature . . 52 3. Effect of kinetin and temperature on Kentucky bluegrass bud activity in response to hypobaric ventilation with or without supplemental ethylene . . . . . . . . . . . . . . . . . . . . 53 Table CHAPTER 4 Effect of turfgrass Ethephon concentration and nitrogen level on quality rating and shoot density in Merion Kentucky bluegrass during the months June to September Effect of turfgrass Ethephon concentration and nitrogen level on quality rating and shoot density in Nugget Kentucky bluegrass during the months June to September Effect of Ethephon and kinetin concentration on turfgrass shoot density and quality in Merion Kentucky bluegrass during the months June to September . . . . . . . . . Effect of Ethephon and kinetin concentration on turfgrass shoot density and quality in Nugget Kentucky bluegrass during the months of June to September . . . . . . . Effect of turfgrass bluegrass Effect of turfgrass bluegrass Ethephon and silver nitrate concentration on shoot density and quality in Merion Kentucky during the months June to September . . . . Ethephon and silver nitrate concentration on shoot density and quality in Nugget Kentucky during the months June to September . . . . vi Page 62 64 66 67 68 70 Figure 2.1 2.2 2.3 LIST OF FIGURES Page CHAPTER 1 Schematic presentation of tiller bud growth and development in Kentucky bluegrass . . . . . . . . . . . . . . . . . . . . 8 Photomicrograph illustrating bud swell, Stage I of initiation of bud activity to first primordial leaf in Merion bluegrass x 25 O O O O O O O O . O O O O O O O O O O O O O O O O C O O 10 Photomicrograph illustrating second primordial leaf, Stage II of second primordial leaf to leaf unfold in Merion bluegrass x 25 O O O O O O O O C O O I O O O O O O O O I O O C O O O O 10 Section through Merion bluegrass tiller bud illustrating the dome shaped growing point overarched by leaf primordia x 1000 O C O O O O O O O O O O O O O O O O O O O O O O O O 0 Effect of temperature and time on bud length in Merion and Nugget bluegrass O O O I O O O O O O I O O O O I O O O O O 0 13 Effect of temperature and time on the s/t ratio (tiller bud length/length of subtending leaf) in Merion and Nugget blue- grass 0 O O O O O O O I O O O O O O O O O I O O O O O O O O O 17 CHAPTER 2 Method of gas sampling from turfgrass under conditions of controlled temperature . . . . . . . . . . . . . . . . . . . 30 Effect of temperature on ethylene production in Nugget and merion bluegrass O O O O I O O O O O O O O O O O O O O O O O 32 CHAPTER 3 Method for ethylene detection of turfgrass sample . . . . . . 46 Effect of kinetin concentration and time on ethylene product- ion in Nugget bluegrass grown at optimal (22C) and supraoptimal (33C) temperatures . . . . . . . . . . . . . . . . . . . . . 50 vii Figure Page CHAPTER 4 1. Daily minimum and maximum temperatures from May to September 1977, recorded at the Crop and Soil Science Barns, Michigan State University, 300m trial area . . . . . . . . . . . . . . 74 viii INTRODUCTION Bud activity in many cool season turfgrasses in inhibited by supraoptimal temperatures, or those temperatures higher than the optimum for growth. Although the potential buds are present, their inhibition results in poor shoot density and lowered turfgrass quality. Lack of shoot density is also compounded by excessive wear during the summer period. The fact that repression or inhibition of bud activity occurs in grasses suggests control of bud growth by endogenous growth regula— tors, particularly at an early stage of bud development. Recent theories on bud develoPment in cool season grasses have credited Indole-3-acetic acid (IAA) with a major role, but its mode of action is still not clear. Recent research has implicated ethylene, which can be induced by auxin, in the improvement of tillering and stem elongation in Kentucky blue- grass. Ethephon (2-chloroethylphosphonic acid), which breaks down to ethylene, has also been reported to induce both tiller and rhizome bud activity in other graminaceous plants. These studies suggest that bud activity in Kentucky bluegrass may be controlled by ethylene levels. Cytokinins have also been credited with the release of lateral buds from apical dominance, tiller bud elongation and leaf recovery from supraoptimal temperatures. It was proposed that application of a foliarly applied kinetin would increase bud activity when grown under supraoptimal temperatures. The objective of the dissertation was to evaluate the influence of endogenous and exogenous ethylene levels and kinetin on bud activity in Kentucky bluegrass when grown under optimal (22C) and supraoptimal (33C) temperatures. Lack of information on tiller bud activity of Kentucky bluegrass necessitated a preliminary study to document bud development by illustration,and to evaluate the influence of temperature on morphogenesis. The technique of hypobaric ventilation, which reduced endogenous ethylene and other gases to subnormal levels, was used to determine the influence of ethylene on bud activity. CHAPTER 1 TEMPERATURE INFLUENCES ON BUD MORPHOGENESIS IN KENTUCKY BLUEGRASS Abstract Poa pratensis L. cv. Merion and Nugget were studied to evaluate the influence of temperature on bud morphogenesis. Turfgrass buds were schematically illustrated by stages for description: 1) initiation of bud activity to first primordial leaf; 2) second primordial leaf to leaf unfold and; 3) ligule formation to leaf emergence above the sub- tending leaf sheath. The increase in the number of active buds (bud activity) never ceased but was reduced when the grasses were grown at 33C. Temperatures of 220 were found to significantly increase bud length in both cultivars compared to 33C. The change in temperature influenced the number of active buds in Merion to a much greater extent than in Nugget. The number of active buds at the stem base and nodes were also reduced by supraoptimal temperatures compared to cooler temperatures in both cultivars. The establishment of s/t ratio, which ~ is the ratio of the tiller bud length to subtending leaf, suggests a direct relationship between tiller bud growth and maturation of the subtending leaf sheath. Introduction An important component of turfgrass quality is density or the number of shoots per unit area. In cool season grasses, two types of buds contribute to shoot density, those developing into rhizomes, or into intra or extravaginal tillers (3, 4). Buds can also be found in the axils of scale leaves on rhizomes (13). Reviews on tillering have largely centered on the effect of envir- onmental factors on shoot and inflorescence morphology (2, 5, 6, 8) or on tiller number after emerging above the subtending leaf sheath (9, 11). Little is known about the growth of tillers before they become visible externally. In 1975, Williams apd co-workers examined the growth and form of the wheat tiller bud and its response to two levels of light intensity and nitrogen supply grown at 20/150 day night temperatures. They found that axillary buds never cease growing from initiation but may vary in their rate of development. Tiller buds develop both in the axils of the coleoptile and the first one or two foliage leaves in graminaceous seeds (8). Following seed germination, the bud is organized from intercalary meristematic tissue at the base of the phytomer, or grass shoot unit (5, 12). These buds have an outer skin, the dermatogen, and an inner hypodermis, both of which are derived from the main shoot. Deeper tissues such as the subhypodermis and core are derived from subhypodermal tissue of the main axis (17). These buds are initiated at the same rate as the leaf primordia and arise in acropetal succession from the base upwards (9). The developed bud can often be recognized by the time the leaf primor- dium has arched over the stem apex (6). Buds are dormant in the sense that its potentially active subapical meristem is arrested; hence, little internode elongation occurs. Bud break and shoot elongation are the result of leaf elongation and subapical meristematic activity (14). The objective of this study was to illustrate the bud growth and development of Kentucky bluegrass and to evaluate the influence of temperature on the stages of morphogenesis. Materials and Methods Plugs of Kentucky bluegrass cv. Merion and Nugget were taken from the field and broken into tillers having the same leaf number. Follow- ing preliminary observations, the axillary bud of the fourth leaf from the top was selected for description. This was also in agreement with previous work (10, IS) in that tiller expansion is limited only to sites in the axils of mature leaves. Seven tillers were equally spaced and planted near the circumference of 200ml stryofoam cups containing a soil admendmentl and acclimated in the greenhouse for 10 days. Prior to the temperature treatment, the fourth leaf was identified by a felt pencil mark. The cups were then transferred to two growth chambers which were maintained at 22 or 33C. Both chambers were set on a 16 hr 1Turface., wyandotte Chemicals of Canada, Scarborough, Ontario. ' photoperiod with a photosynthetic radiation rate of 30 wmz. Every second day at 1300 hr, until the tiller was expose, twenty-eight plants were harvested and wrapped in moist towelling. Harvesting was in accordance to a predetermined randomized plan. The buds were separated carefully from their stem under a stereoscope with bud length being determined with an occular micrometer. Measurement of bud length was from their tip to the point of disappearance of the buttress bulge (19). Both length of the tiller bud and its subtending leaf were expressed in mm. Bud growth in Kentucky bluegrass was described in three separate stages, each being subcatagorized into A, B, and C to provide greater description (Figure l). The designation of stages and subcatagories was determined by the number of buds having the highest common descrip4 tion on any particular harvest day. Photomicrographs were also taken to provide detail of the stages in bud development. In another study, plants were grown under similar environmental conditions as previously described, the position and length of buds were recorded as to their location on the stem base and nodes. Data was taken every 5th day with nonactive buds classed as those less than 1.0 mm in length and elongated buds as those exceeding 1.0 mm in length. Values stated in the tables or shown in figures are the mean of four replications repeated twice with the mean separation carried out using Duncan's Multiple Range Test. Results and Discussion A schematic presentation of bud growth and development was gener- ated and described by stages which were as follows: State I. Initiation of bud activity to first primoridal leaf State II. Second primordial leaf to leaf unfold; State III. Ligule formation to leaf emergence (Figure 1) Prior to their increase in length, the buds initiated a basal swelling (Figure 2-1) which occurred within two days from earliest observation. This was represented by Stage I(b) in Figure 1. Elonga- tion followed, in which up to three leaf primordia were developed . (Figure 2-2). This was designated as the conclusion of Stage II(c). These morphological events occurred within 6.days in Merion, but were delayed to the tenth day in Nugget (Table l). A basipetal unfolding of the leaf followed demarcation of the ligule region, which occurred with- in the enclosed leaf sheath. Ligule formation in Merion, as represented by Stage III(a) in Figure l, was present on the eighth day when the leaf was approximately 1.2 to 1.8 cm in length. By the tenth day the leaf blade protruded above the subtending leaf in Merion Kentucky blue- grass. Bud development followed similar pattern in both cultivars. Bud morphogenesis in Nugget Kentucky bluegrass did not proceed past Stage II(a) over the ten day study. Table 1 shows that leaf emergence (Stage III(b)) was attained by Merion in ten days, irrespective of temperature. Bud length in Nugget Kentucky bluegrass was not influenced Ligule formation Stage m leaf. to ‘ loaf unfold to leaf emergence Stage II primordial in! Stage 1 activity to first ‘ o Initiation oibud Second primordial Figure 1. Schematic presentation of tiller bud growth and development in Kentucky bluegrass. Figure 2.1. Photomicrograph illustrating bud swell, Stage 1 from initiation of bud activity to first primordial leaf in Merion bluegrass X 25. Figure 2.2. Photomicrograph illustrating second primordial leaf, Stage 11 from second primordial leaf to leaf unfold in Merion bluegrass X 25. Figure 2.3. Section through Merion bluegrass tiller bud illustrating the dome shaped growing point overarched by leaf primordia X 1000. 10 Figure 2.3 11 Table 1. Schematic presentation of the influence of temperature on bud growth in Merion and Nugget Kentucky bluegrass. CULTIVAR TEMPERATURE DAYS FROM TEMPERATURE TREATMENT (C°) 2 4 6 8 10 NUgget 22 bud IIIIICI third.II.II>IIIIIIII-III-I-III-I-I leaf initiate break unfold Merion 22 bUd gang... leaf .IIIIII>II..-II 118L118 III-Illeaf initiate unfold formation emergence Nugget 33 bUd III-Illsecond IIII>IIIIII.IOIIIIIIIIIOICDIthj-rd initiate break ' break Merion 33 bUdOIIIIIII third-IIIII>IIIIIIIIligUIeIIIIII leaf , ' initiate break formation emergence l ‘ . . Mean of twenty-eight observations 12 by temperature and was always significantly less than Merion (Figure 3). Supraoptimal temperatures slowed bud elongation after the sixth day in Merion bluegrass. Elongation did occur in Nugget at both tempera— tures but at a much reduced rate. The significance of temperature on bud elongation is shown in Tables 2 and 3. The first sampling of Merion Kentucky bluegrass at 22C revealed that a large percentage of buds had not elongated further than 10 mm, a major portion of which had not exceeded 1 mm. Bud expansion had occurred at the stem base and the first nodal region at this temperature. Shifts were detected 15 days after the temperature treatment as indicated by the large percentage of buds in the higher bud length categories. This indicates that buds were elongating into potential tillers and that growth was not inhibited. New bud develop- ment was evident in the 0-10 mm range at the termination of the study. Growing temperature of 33C reduced bud length and the rate of new tiller development. Bud elongation did not occur in Nugget Kentucky bluegrass, irrespective of temperature, over the study period. At the lower growing temperature, a small shift occurred at the stem base on the last three sampling dates, but buds at nodes above this did not elongate. The (s/t) ratio, which is the ratio of the tiller bud length to the length of the subtending leaf (Table 4) was established and presented in Figure 4. The ratio suggests that between the second and fourth day after the temperature treatment, leaf elongation LENGTH OF BUD [mm] Figure 3. 13 DAYS AFTER TREATMENT Effect of temperature and time on bud length in Merion and Nugget bluegrass. Means within days having the same letter are not significantly different at the 5% confidence level (Duncan's Multiple Range Test). 14 Table 2. Effect of sampling date, temperature and position on bud length of Merion Kentucky bluegrass expressed as the percent of total bud numbers at each position. TREATMENT BUD LENGTH (mm) Sampling Temperature Position of 0-1 l—lO 11-20 21-30 30+ Date (C) bud* Percent of Buds 9/9 22 Stem base 11 37 32 16 4 lst node 33 44 12 - 11 2nd node 17 83 - — - 3rd node 83 17 - - - 4th node 100 - - — - 33 Stem Base 43 36 14 - 7 lst node 28 28 - 16 28 2nd node 33 50 - - 17 3rd node 33 33 33 - - 4th node - 100 - - - 9/14 22 Stem base 33 25 - 33 9 lst node 33 67 - - - 2nd node 80 20 - - - 3rd node 33 33 33 - - 4th node 33 - 66 - - 33 Stem base 42 33 25 - - lst node 67 33 - - - 2nd node 100 - - - - 3rd node 100 - - - - 4th node 100 - - - - 9/19 22 Stem base - 20 30 30 20 lst node - 40 40 20 - 2nd node - 60 - 20 20 3rd node - 80 - 20 - 4th node 20 60 - - 20 33 Stem base 50 25 8 l7 - lst node 40 60 - - - 2nd node 80 - 20 - - 3rd node 100 - - — - 4th node 100 - - - - 9/24 22 Stem base - 42 l7 17 24 lst node - 83 - - 17 2nd node 33 67 - - - 3rd node 80 20 - - - 4th node 100 - - - - 33 Stem base 90 10 - - - lst node 100 - - — - 2nd node 100 - - - - 3rd node 100 - - - - 4th node 100 - - - - * The lst, 2nd, 3rd and 4th node of the phytomer unit commencing above the stem base 15 Table 3. Effect of sampling date, temperature and position on bud length of Nugget Kentucky bluegrass expressed as the percent of total bud numbers at each position. TREATMENT BUD LENGTH (mm) Sampling Temperature Position of 0-1 1-10 11-20 21-30 30+ Date (C) bud* Percent of buds 9/9 22 Stem base 100 - - - - lst node 100 - - ‘ ‘ 2nd node 100 - - - ’ 3rd node 100 - - - ’ 33 Stem base 100 - - - ’ lst node 100 - - ' ‘ 2nd node 100 - - - ' 3rd node 100 - - - ' 9/14 22 Stem base 83 17 - ‘ ' lst node 100 - - ' ' 2nd node 80 20 - ‘ ‘ 3rd node 100 - - - ‘ 33 Stem base 80 20 - - ' lst node 83 17 - - ' 2nd node 80 20 - - ‘ 3rd node 100 - - - ‘ 9/19 22 Stem base 80 20 - ' ’ lst node 100 - - ' - 2nd node 100 - - - ' 3rd node 100 - - - - 33 Stem base 100 - - r ‘ lst node 100 - - - ' 2nd node 100 - r - ’ 3rd node 100 - - - - 9/24 22 Stem base 60 20 - 20 - lst node 100 - - - - 2nd node 100 - - - ' 3rd node 100 - - - . ‘ 33 Stem base 100 - - - ‘ lst node 100 - - r “ 2nd node 100 - - r ' 3rd node 100 - - - ‘ * The lst, 2nd and 3rd node of the phytomer unit commencing above the stem base 16 Table 4. Influence of time and temperature on length of subtending leaf in Merion and Nugget bluegrass TIME TEMPERATURE LENGTH OF SUBTENDING LEAF (mm)1 (DAYS) (C°) MERION NUGGET 2 22 53.0 b 62.0 d 33 62.5 ab 62.2 d 4 22 74.1 a 63.8 cd 33 68.2 a 76.0 ab 6 22 74.3 a 69.6 bcd 33 75.3 a 71.7 bc 8 22 73.5 a 72.9 b 33 73.5 a 80.4 a 10 22 70.4 a 72.1 b 33 68.1 a 84.3 a 1Mean values followed by the same letter within cultivars are not significantly different at the 52 confidence level (Duncan's Multiple Range Test). 17 hzu2hoH Nm one um ucouommww hHuEMUHMHowam uoo mum nouuoa mama on» up oo3oaaom mqasaoo canoes mamozH oooa%nuo and o~.o + m 6a.H mm An.H N8 NmH.o\No an.am ~.o A 8m.H , w mH.H Noo Nmfi.o\~o Nmm.ma ~.o «6 wo.~ use 86.H mamasnum ans 4m.H +.AH< H m mm.a mm 4m.H ufi< H mm ocoamnuo and o~.o + a am.~ mm mm.H N8 Mma.o\mo Nmm.aa ~.o s ~6.H m w8.H Noo NmH.o\ o Now.aa ~.o u mm.~ a 4w.H mcmHAEum aaa 4m.H + ““4 H 8 H4.N we AA.H Afi< H on mcoahsuo and 05.0 + n ~6.~ n m6.m moo NmH.o\No nmm.mm ~.o m Hm.H u 4H.m oo NmH.o\~o Nmm.ma N.o m oo.m 6 6H.s maoHAEEm aqa sm.a +.AH< H on ~6.N n mu.m ufi< H «N Asumv A.uw umwwoz oowuoz unsung: mow ouammoum ououmuogaoa Husmad pom moan ucoauuouy o>wuom mo nonaoz .mmmuwooap uowwsz vow aofluoz EH moan o>wuum mo sweeps osu so ousuuuodaou can ocoahnuo mo uoomwm .H «Home 30 FREERIE‘IEGULNNII GENE! IEHUGEUHTD: llflflil IAMHTNND C Figure 1. . . ... .. .... . ... .. .... . .. . . .. . . , .... ... m .... ... ' 0... II. t . . ‘ I ‘i ‘ \ . o Method of gas sampling from turfgrass under conditions of controlled temperature. 31 demonstrates bud activity inhibition at both 30 and 350 temperatures. This is shown by the lack of significance in the number of active buds between the air control and where ethylene was supplemented at 1 atm. Therefore, possible interrelationships between ethylene and another hormone(s) is hypothesized when Kentucky bluegrass is grown under supraoptimal temperatures. If ethylene alone was suspected as the bud dormancy releasing agent, the number of active buds per plant under supraoptimal temperatures should be similar to those at the optimum temperature of 22C. This was not the case in this study. Ethylene Production. Ethylene production in both cultivars was influenced by temperature as illustrated in Figure 2. The rate of ethylene production differed between the two grasses with Merion showing peak production at 27C and Nugget at 34C. The decline in peak ethylene production was sharper in Nugget than for Merion Kentucky bluegrass. Under the higher temperatures the increase in ethylene production may be considered as one of a number of changes contributing to bud inhibition. Rhizome/Tiller Ratio. In Kentucky bluegrass, tillers develop from axillary buds and rhizomes from nodal buds (25). Tillering is most frequent in spring and fall and is favored by temperatures slightly lower than the optimum for growth (2, 12). A major portion of rhizome bud initiation and elongation occurs during summer (29) and is favored by long days (24). The change in the r/t ratio 32 F '3 0'3“: g“; 3 s? z: N' N. x g g ‘2’ S5 i2 .53 1'- . 9 6 83': -- >- >"- a I I z o. .- :2 8 5. 05 .§ 8 - a 6 (”10,6 snow") Housman mamas Figure 2. Effect of temperature on ethylene production in Merion and Nugget bluegrass. 33 of the air treatments at 22 and 35C favors rhizome growth in Merion Kentucky bluegrass (Table 2). The addition of supplemental ethylene to Merion, irrespective of temperature, also shows strong rhizome development. Stimulation of stem elongation with ethylene generating chemicals have been previously demonstrated in Kentucky bluegrass (14, 27). Nugget maintained a high r/t ratio irrespective of ethylene or temperature treatment. According to Beard (4), Nugget also has exhibited a superior sod strength in summer plantings compared to Merion. In addition, the summer rooting performance of Merion was poor, suggestive of a lower r/t compared to Nugget. Length of Temperature Exposure. Merion Kentucky bluegrass, grown under optimum conditions of 220/22C, had a significant increase in the number of active buds per plant at 10 and 100 ul/L ethylene treatment (Table 3). Nugget gave a similar response at the l to 10 ul/L ethylene level (Table 4). The number of active buds was not significantly altered by 10 days of supraoptimal temperatures following the 24 hr. exposure at 22C. Both cultivars had fewer active buds when both the exposure temperature and the post initial temperatures were 33C compared to treatments of 22C/ZZC. This agrees with the earlier study which suggests that high levels of ethylene in the tissue may contribute to bud inhibition at supraoptimal temperatures. Twenty-four hours were sufficient to reduce the number of active buds at the 33C exposure temperature, as bud activity did improve when the cultivars were 34 .ude owdmm oadfiuaaz m.ooooon hp hufiafinmnoua mo Ho>oa Nm as» on ucouomwfio hauomofimaowam uoo ouo nouuoa oamm can an voSoHHom moaoaoo canoes ammo: H m Nam m Em 83.366 E: 34 + :2 m h.mH m m.n Ham mm m 9% . em m.m 23266 E3 and + .52 m n.HN on 5.6 uw< on a 92 nu ma 883.286 ER and + A: m m.mH a m.H .uH< NN $8 powwoz soaps: ouauxflz mow ououmuodaoa wNu\uv owuuu van uoHHHH auscuaam .mmouwooan uowwoz woo sowuoz oa oaumu won uoHHfiu\oaoNfisu so assuage wow wow ououuuoeaou mo uoommm .N wanna 35 Table 3. Effect of ethylene concentration and temperature exposure ' on the number of active buds in Merion Kentucky bluegrass. Treatment Number of active budsperplant1 Ethylene 2 Concentration 22/22 22/33 33/22 33/33 (pl/L) 0 1.31 c 0.15 f 0.28 ef 0.81 d l 1.56 bc 0.28 def 1.31 c 0.81 d 10 1.79 b 0.51 def 1.54 be 0.62 def 100 2.21 a 0.13 f 2.54 a 0.64 de 1000 0.59 def 0.17 f 1.59 be 0.48 def 1 Mean values followed by the same letter are not significantly different at the 52 confidence level (Duncan's Multiple Range Test) 2 22/22: 22C for 24 hr undergoing ethylene exposure, followed by 3 22C growing temperature for 10 days. 36 Table 4. Effect of ethylene concentration and temperature exposure on the number of active buds in Nugget Kentucky bluegrass. Number of active budsperplant1 Treatment Ethylene 2 Concentration 22/22 22/33 33/22 33/33 (pl/L) 0 0.60 de 0.27 ghi 0.25 hi 0.36 fgh l 1.46 b 0.21 hi 0.55 def 0.37 fgh 10 1.81 a 0.33 fghi 0.76 c 0.63 de 100 1.02 c 0.24 hi 0.98 c 0.28 ghi 1000 0.61 de 0.12 i 0.30 ghi 0.50 efg 1 Mean values followed by the same letter are not significantly different at the 52 confidence level (Duncan's Multiple Range Test) 2 22/22: 22C for 24 hr undergoing ethylene exposure, followed by a 22C growing temperature for 10 days. 37 subsequently transferred to a favorable temperature of 22C (Tables 3 and 4). The effectiveness of temperature exposure on the number of active buds was found to be significant for both cultivars. At 330/330, both Merion and Nugget lacked significance in response to ethylene concen- tration. When the cultivars were grown at 220/220 a significant increase in the number of buds exhibiting activity was observed between 10 and 100 ul/L in Merion and l and 10 ul/L in Nugget. Under similar post initial conditions, but different exposure temperatures, a single day at 33C significantly reduced the number of active buds per plant. The effect of ethylene on bud activity was still measurable at the cooler post growing temperature. A single day at 220, followed by a 330 post growing temperature, did not significantly increase bud breaks in Merion Kentucky bluegrass. These results indicate that 24 hr. at an exposure temperature of 330 can induce bud inhibition. Inhibition was extended when the grasses were kept at supraoptimal temperatures for 10 days. The number of active buds were increased when cultivars exposed to 330 were returned to cooler temperatures of 220. The knowledge that ethylene production is influenced by temperature, and can be translocated rapidly (17, 34) suggests that high ethylene levels produced at supraoptimal temperatures may inhibit bud activity. Such inhibition may also be influenced by the marked diurnal variation in endogeneous ethylene recently reported (16). 38 The results of this study support the auxin concept of apical dominance as it has been shown that auxin-induced ethylene production could account for the inhibitory action of applied IAA (8). This concept fits well into recent tillering research (33) in that high summer temperatures, favored the accumulation of endogenous auxin in the stem bases of tall fescue, which appeared to be related to inhibi- tion of tiller initiation. Therefore, endogenous auxin concentrations may, in fact, determine ethylene concentrations which could act as the intermediate initiating molecules in bud break. 10. 11. 12. 39 Literature Cited Akhavein, A. A. 1976. Effects of Ethrel and selected environ— mental factors on growth of quackgrass and field bindweed. Ph.D. Thesis, Oregon State University. Alberda, T. 1965. The influence of temperature, light intensity and nitrate concentration on dry matter production and chemical composition of Lolium perenne L. Plant and Soil 8: 199-230. Anonymous. 1969. Ethrel. Technical service data sheet H-96. Amchem Products, Inc. Ambler Pa. 64 pp. Beard, J. B. 1972 Comparative sod strengths and transplant sod rooting of Kentucky bluegrass cultivars and blends. 42nd Annual Michigan Turfgrass Conference Proceedings 1: 123-127. Beard, J. B. 1973. Turfgrass—science and culture. Prentice-Hill, Inc. Englewoods Cliffs, NJ. 658 pp. Buellner, M. R., R. D. Ensign, A. A. Boe. 1976. Plant growth regulators effects on flowering of Poa pratensis L. under field conditions. Agron. J. 68: 410-413. Burg, S. P., E. A. Burg. 1965. Gas exchange in fruits. Physiol. Plant 18: 870-884. Burg, S. P., E. A. Burg. 1968. Ethylene formation in pea seedling; its relation to the inhibition of bud growth caused by indole- 3-acetic acid. Plant Physiol. 43: 1069-1074. Burg, S. P. 1973. Ethylene in plant growth. Proc. Nat. Acad. Sci. Byers, R. E., L. R. Baker, H. M. Sell, R. C. Herner and D. R. Dilley. 1972. Ethylene: a natural regulator of sex expression of Cucumis melo L. Proc. Nat. Acad. Sci. USA. 69(3): 717-720. Darrow, R. A. 1939. Effects of soil temperature, pH and nitrogen nutrition on the development of Poa pratensis. Bot. Gaz. 101: 109-127. Duff, D. T., J. B. Beard. 1974. Supraoptimal temperature effects upon.Agrostis palustris. Part 1. Influence or shoot growth and density, leaf blade, width and length, succulence and chlorophyll content. Physiol.Plant.32: 14-17. 13. 14. 15. l6. 17. 18. 19. 20. 21. 22. 23. 24. 25. 40 Harrison, 0. M. 1934. Responses of Kentucky bluegrass to, variations in temperature, light, cutting and fertilization. Plant Physiol. 9: 83-106. Heng, D. A., D. B. White. 1969. Investigations into the activity of Ethrel (2-chloroethy1 phosphoric acid) in the growth of Poa pratensis. Agron. Absts. p. 54. Jewiss, D. R. 1972. Tillering in grasses - its significance and control. J. Br. Grassld. Sco. 27: 65. Kapuya, J. A., M. A. Hall. 1977. Diurnal variations in endogen- ous ethylene levels in plants. New Phytol. 79: 233-237. Kwong, F. Y., H. B. Lagerstedt. 1977. Translocation of Ethephon in beans and peas. J. Am. Soc. Hort. Sci. 102(4): 437-440. Langer, R. H. M. 1963. Tillering in herbage grasses. Herb. Absts. 33(3): 141-148. Laude, H. M. 1971. Effect of temperature on morphogenesis in plant morphogenesis as the basis for scientific management of range resources. ARS-USDA Misc. Pub. No. 1271. pp. 25-33. Leopold, A. 0. 1949. The control of tillering in grasses by auxin. Am. J. Bot. 26: 437-440. Lindsay, K. E., M. L. Peterson. 1962. High temperature suppression of flowering in Poa pratensis L. Crop Sci. Lopez, R. R., A. 0. Matches, J. D. Baldridge. 1967. Vegetative development and organic reserve of tall'fescue under conditions of accumulated growth. Crop Sci. 7: 409-412. Mitchell, K. J. 1955. Growth of pasture species. 11. Perennial ryegrass (Lolium perenne), cocksfoot (Dactylis glomerata) and paspalum (Paspalum dilatatum). NZ J. Sc. Tech. 27: 8-26. Moser, L. E., R. R. Anderson, R. W. Miller. 1968. Rhizome and tiller development of Kentucky bluegrass (Poa pratensis L.) as influenced by photoperiod, cold treatment and variety. Agron. J. 60: 632-635. Musgrave, R. B. 1940. Life history studies of Poa pratensis L. Ph.D. thesis. University of Illinois. 26. 27. 28. 29. 30. 31. 32. 33. 34. 41 Poovaiah, B. W., A. C. Leopold. 1973. Effects of ethephon on growth of grasses. Crop Sci. 13: 755-758. Peterson, M. L, W. E. Loomis. 1949. Effects of photo period and temperature on growth and flowering of Kentucky blue- grass. Plant Physiol. 24: 31-43. Russell, D. W. 1960. Studies on the factors influencing inhibition of lateral buds and branches. M. Agric. Sc. Thesis. University of Canterbury, New Zealand. Sachs, R. M. 1973. Growth of the grass plant - its response to change. Proc. of California golf course superintendents Institute. Uni. of California Extension Davis. pp. 83-87. Van Andel, O. M. 1973. Morphogenetic effects on vegetative plants of Poa pratensis L. of 6-Azauracil, (2-0hloroethyl)- phosphonic acid, and (2-Chloroethy1) trimethyl ammonium chloride and their interaction with gibberellic acid. J. of Exp. Bot. 27(8): 245-257. Watschke, T. L., R. E. Schmidt, R. E. Blaser.' 1970. Responses of some Kentucky bluegrasses to high temperature and nitrogen fertility. Crop Sci. 10: 372-376. Williams, R. F., R. H. M. Langer. 1975. Growth and development of the wheat tiller. II. The dynamics of tiller growth. Aust. J. Bot. 23: 745-59. Yeh, R. Y., A. 0. Matches, R. L. Larson. 1976. Endogenous growth regulators and summer tillering of Tall fescue. Crop Sci. 16: 409-413. Zimmerman, P. W., A. E. Hitchcock, W. Crocker. 1931. The move- ment of gases in and through plants. Contrib. Boyce Thompson CHAPTER 3 REGULATION OF BUD GROWTH IN KENTUCKY BLUEGRASS. EFFECT OF KINETIN AND TEMPERATURE ON ETHYLENE PRODUCTION. Abstract Kinetin was applied as a foliar spray to Poa pratensis L. cv. Merion and Nugget to evaluate its effect on bud growth and ethylene production grown at optimal (220) and supraoptimal (33C) temperatures. Ethylene and kinetin, when applied alone, both significantly increased the number of active buds at 220. When both cultivars were grown at 33C, neither ethylene, kinetin nor their combinations had a signif- icant effect on the number of active buds compared to their controls. Studies using hypobaric ventilation conditions, which reduced ethylene and other gases to subnormal levels, suggested that bud growth may be influenced by kinetin stimulated ethylene production. Kinetin was found to enhance the number of active buds in Nugget Kentucky bluegrass grown at 220, apparently through stimulation of ethylene. Increased ethylene production, generated endogenously or by kinetin application, resulted in a decrease in the number of active buds grown under supraoptimal temperatures. 42 43 Introduction Both tiller bud and shoot growth of cool season grasses are often inhibited by supraoptimal temperatures, or those temperatures higher than the optima for growth. Under these high summer temperatures, tiller bud growth is inhibited (7) although buds are present (15). Often turfgrass quality deteriorates because of excessive wear and loss of density. Although the control of lateral bud development has been recently reviewed (19), relatively little research has been done on regulation aspects of bud growth in Kentucky bluegrass under supraoptimal tempera- tures. Auxin inhibition of bud development was first proposed in 1949 (14) and revised to include theories of indirect inhibitor production as reported for perennial ryegrass (Lolium perenne) (20) and tall fescue (Festuca arundinacea) (23). Ethylene inhibits growth by reducing cell division and elongation (5). Recently, the ethylene generating compound Ethephon (2-chloro- ethylphosphonic acid) was found to increase tillering (3, 22) promote stem length and reduce growth of leaf blades (18) of Kentucky blue- grass. Ethylene has also been shown to trigger bud activity in Kentucky bluegrass grown at optimal temperatures (1). However, an interrelationship between ethylene and other hormones is hypothesized under supraoptimal temperatures. Under these conditions ethylene is considered as one of several factors contributing to bud inhibition. 44 Cytokinins have been shown to release lateral buds from apical dominance and auxin inhibition (19), to improve tiller bud elongation (10, 11) and assist leaf tissue recovery from supraoptimal temperatures (9). V This investigation was designed to evaluate the effect of foliarly applied kinetin on ethylene production and bud growth in Kentucky bluegrass grown at optimal (220) and supraoptimal (330) temperatures. A second study was initiated to evaluate a possible kinetin/ethylene interaction on bud growth using the method of hypobaric ventilation which reduced ethylene concentration to subnormal levels. Materials and Methods Effect of Kinetin and Ethylene. Plugs of Poa pratensis L. cv. Merion and Nugget were broken into tillers having the same leaf number. Senescent leaves were removed resulting in a plant with six leaves. The tillers were planted near the circumference of 200 ml styrofoam cups containing a soil admendment (Wyandotte Turface Soil Admendment, wyandotte Chemicals of Canada, Scarorough, Ontario). Following 10 days of acclimation in a greenhouse, the plants were placed into sealed desiccators at temperatures of either 22 or 330 and exposed to either 0 or 10 ul/L ethylene for 24 hrs. They were then grown in chambers having the same temperatures. The chambers were maintained at a 16 hr. 2 photoperiod and at a photosynthetic radiation rate of 30 Wm . A kinetin solution (23 uM of 6-furfurylaminopurine) was atomized on to leaves 45 daily to drip point. Equal volumes of distilled water were applied to the control treatments. Buds were counted after 10 days and expressed as the number of active buds per plants (Table l). Ethylene Production. Plugs of the same cultivars were taken from the field and categorized as previously described. Forty tillers were planted in styrofoam cups containing Turface soil amendment and acclimated in a greenhouse for 10 days. One cup was then placed in an inverted 1000 ml glass jar fitted with a closure as illustrated in Figure 1. Each jar and contents represented a treatment which was replicated three times. Inserted in each lid were three ports, a gas inlet leading from a filter and flow regulator, a gas outlet for vent- ilation and a serum stopper for gas sampling. One milliliter gas samples were taken every 24 hrs. Ethylene production was measured with a Varian aerograph model 1700 gas chromatograph equipped with a 2 mm by 1mm activated alumina column and a flame ionization detector. The carrier gas was nitrogen at 600. Following each gas sampling the plants received a spray application of either 5, 14 or 23 pH kinetin (6-furfurylaminopurine) (Sigma Chemical 00;, St. Louis, MO) applied to the drip point. Control plants were sprayed with equal volumes of distilled water. anch jar and contents was then ventilated with air at 500 mllmin. for 5 minutes. This procedure was repeated daily over the duration of the study. Approximately 10 pMoles of ethylene 46 Air inlet 1 Figure 1. Method for ethylene detection of turfgrass sample. 47 accumulated over the 24 hr period at both temperatures in glass jars without plant tissue, and such production was attributed to the rubber seals. The cultivar Nugget was selected for this study because it was shown to generate more ethylene than Merion (l) and therefore thought to be more definitive in demonstrating bud regulation when using the hypobaric technique. This grass has also shown improved heat toler- ance when grown under supraoptimal temperatures (2). Ethylene production was expressed as nMOIes gm"1 hr"1 (Figure 2) and buds as the number of active buds after 6 days (Table 2). Environ- mental conditions during the investigation were temperatures of 22 or 32:_20, photoperiod of 16 hr and a photosynthetic radiation rate of 30 2 WE as measured within the jar. Effect of Ethylene Evacuation. Turfgrass plants were acclimated as described in the first study. The hypobaric technique, used to reduce endogenous ethylene to subnormal levels by evacuation at 0.2 atm, has been previously described (4, 6, 16). Three replications of cups containing each cultivar were placed into holes made in a stage located within 10 L desiccators. Desiccators were maintained for 10 days under the conditions outlined in Table 3. Dilute ethylene concentrations were premixed in compressed gas cylinders (21) and the composition verified by gas chromatography. The desiccators were opened daily at 1300 hrs. to apply an aerosol spray of 23 uM kinetin or distilled water 48 to the respective grass treatments. Values stated in the tables or shown in figures are the mean of ' three replications repeated twice with the mean separation carried out according to Duncan's Multiple Range Test. Results and Discussion Effect of Kinetin and Ethylene. At the 220 growing temperature, both ethylene and kinetin applied alone, significantly increased the number of active buds per plant in Merion Kentucky bluegrass (Table 1). When kinetin was applied following an ethylene treatment, bud activity was not significantly increased over the control. Neither separate nor combined applications of ethylene or kinetin treatments had a significant effect on the number of active buds of either cultivar when grown at 330. As kinetin is known to increase lateral bud out- growth (10, 11), it was speculated the material would improve bud growth in Kentucky bluegrass, especially when grown under supraoptimal temperatures. The results of the first study suggested that ethylene, either exogenously applied or influenced by kinetin may inhibit bud growth at such temperatures. The effect of temperature and kinetin level on ethylene production was substantiated by later studies. Ethylene Production. At 220 kinetin stimulated ethylene production for the first 3 days compared to the distilled water control (Figure 2). Kinetin applications have been previously reported to increase ethylene production in sorghum (Sorghum vulgare) (8, l7) and mung bean Table 1. Effect of temperature on the number of active buds in Merion and Nugget bluegrass as influenced by ethylene and kinetin concentration. TREATMENTS CULTIVAR Temperature Ethylene Kinetin Number of actiye buds (C) (ill/L) (uM) per plant Merion Nugget 22 0 0 0.38 c 0.14 c 23 1.65 a 0.71 a 10 0 0.72 b 0.29 be 23 0.48 c 0.27 bc 33 0 0 0.48 c 0.24 bc 23 0.40 c 0.39 b 10 0 0.47 c 0.32 bc 23 0.41 c 0.23 bc 1Mean values followed by the same letter within cultivars are not significantly different at the 5% confidence level (Duncan's Multiple Range Test). 50 330 KINETIN CONCENTRATION 6‘ uM O 5 . 5 14 ___ I 2. 4. ETHYLENE PRODUCTION [nMoles g.hr."] Figure 2. Effect of kinetin concentration and time on ethylene production in Nugget bluegrass grown at optimal (22 C) and supraoptimal (33 C) temperatures. 51 (Phaseolus aureus) hypocotyls (12, 13). The data in Table 2 shows that kinetin may enhance bud growth in Nugget bluegrass by stimulating ethylene production. When grown at 220, foliarly applied kinetin was shown to significantly stimulate plants to produce more ethylene than the control (Figure 2), which in turn induced additional bud activity. At 330 kinetin increased ethylene production above the control. Under these supraoptimal temperatures high endogenous ethylene production inhibited bud growth in Nugget Kentucky bluegrass as shown by the lower number of active buds (Table 2). Inhibition of bud growth at supraoptimal temperatures may be due to the three fold increase in ethylene production either produced by turfgrass tissue or influenced by kinetin application. However, as kinetin activity is lower under supraoptimal temperatures (9), kinetin appears secondary to temperature. Effect of Ethylene Evacuation. Foliarly applied kinetin increased the number of active buds in both cultivars at 220 compared to the control (Table 3). Hypobaric conditions, which enhanced diffusion of ethylene and other gases from turfgrass tissue were significantly lower compared to their control. At 330 only Nugget bluegrass showed a decline in the number of active buds compared to the control following kinetin application. The decline in the number of active buds also occurred at both temperatures when similar treatments were under hypobaric conditions (Table 3). Similarly, plants not receiving the kinetin application showed an increase in the number of active buds compared 52 Table 2. Effect of kinetin concentration on the number of active buds in Nugget bluegrass as influenced by temperature. Kinetin Number of active buds per plant1 (M) 220 330 0 0.41 a 0.19 a 5 0.77 b 0.38 a 14 0.76 b 0.31 a 23 0.86 b 0.32 a 1Mean values followed by the same letter within temperatures are not significantly different at the 5% confidence level (Duncan's Multiple Range Test). 53 83.366 .5: H N8 836 + N38 «6 5.. N6 N .Aumoa owomm madfiuaoz m.omooonv Ho>oH ouoovwmooo nm was an uoouommao maucoofim«owwm uoo mum mousuouodawu wowsouw uo>auaao awnuwa nouuoa mama onu an vosoaaom moaao> com: A u «H.o on om.o no ma.o A mm.a : : : = : ofiuoofim u mH.o u mm.o a os.o e em.a mamHAEUo mafia = = = Houuaou a om.o n mo.a a No.H a om.~ : : : owuoofix m oc.o . o 05.0 o no.H u mH.H Noofiuoafiuoo> oaumnodmn made Houuooo p 5~.o m m5.H no m5.H m Nm.N Azamuv owuoowm m oq.o o om.o o om.H n wo.a Houuoou 0mm UNN 0mm UNN Hamwopz onmmz HZMZH¢MMH .oooamnuo Houooaoadmau uoonuas no :uHB coaumawuoo> ofiumnodhn ou uncommon EH huH>Huoo van mmmuwooan axoouooM so unnumuomaou can afiuoofix mo uoomwm .m wanna 54 to their counterparts under hypobaric ventilation. In the presence of kinetin, ethylene had no effect on the number of active buds in either cultivar when grown at 22 or 330 under hypobaric ventilation. These conditions suggest that bud activity may be influenced by kinetin stimulated ethylene production. Such ethylene production promoted bud growth in Kentucky bluegrass under optimal temperatures. Previous research has implicated high rates of ethylene production in bud inhibition (1). Under supraoptimal temperatures such inhibition may result from increased ethylene production, either produced endogenously or induced by kinetin application. 10. 11. 55 Literature Cited Aldous, D. E., D. R. Dilley, J. E. Kaufmann. 1977. Ethylene as an agent in bud growth of Kentucky bluegrass (Poa pratensis L.). Hortscience 12(4): 384. Aldous, D.E., J. E. Kaufmann. 1978. The role of root temper- ature on growth and carbohydrate levels in two Kentucky bluegrass cultivars grown at supraoptimal temperatures. (accepted by Agronomy J.). Buellner, M. R., R. D. Ensign, A. A. Boe. 1976. Plant growth regulator effects on flowering of Poa pratensis L. under field conditions. Agron J. 68: 410-413. Burg, S. P., E. A. Burg. 1965. Gas exchange in fruits. Physiol. Plant 18: 870-884. Burg, S. P. 1973. Ethylene in plant growth. Proc. Nat. Acad. Sci. 70(2): 591-597. Byers, R. E., L. R. Baker, H. M. Sell, R. C. Herner, D. R. Dilley. 1972. Ethylene: a natural regulator of sex expression of Cucumis melo L. Proc. Nat. Acad. Sci. U.S.A. 69(3): 717-720. Darrow, R. A. 1933. Effects of soil temperature, pH and nitrogen nutrition on the development of Poa pratensis. Bot. Gaz. 101: 109-127. Franklin, 0. D. 1976. Characterization of auxin-induced ethylene synthesis in four maturity genotypes of sorghum. M.S. Thesis Texas A & M University. Gur, A., B. Bravdo, Y. Muzrahi. 1972. Physiological responses of apple trees to supraoptimal root temperatures. Physiol. Plant 27: 130-139. Johnson, G. F. S., B. Jefcoat. 1977. Effects of some growth regulators on tiller bud elongation in cereals. New Phytol. 79: 239-243. Langer, R. H. M., R. 0. Prasad, H. M. Laude. 1973. Effects of kinetin on tiller bud elongation in wheat (Triticum aestivum L.). Ann. Bot. (Lond) 27: 565-571. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 56 Lau, 0., K. Yung. 1974. Synergistic effect of kinetin on IAA- induced ehtylene production. Plant and Cell Physiol. 15: 29-35. Lau, 0. S. F. Yang. 1976. Stimulation of ethylene production in the mung bean hypocotyls by cupric ion, calcium ion, and kinetin. Plant Physiol. 57: 88-92. Leopold, A. C. 1949. The control of tillering in grasses by auxin. Am. J. Bot. 26: 437-440. Lopez, R. R., A. 0. Matches, J. D. Baldridge. 1967. Vegetative development and organic reserves of tall fescue under field conditions of accumulated growth. Crop Sci. 7: 409-412. Mayak, S., D. R. Dilley. 1976. Regulation of senescence in carnation (Dianthus caryophyllus). Effects of abscisic acid and carbon dioxide on ethylene production. Plant Physiol. 58: 663-665. Owens, L. D., M. Lieberman, A. Kunishi. 1971. Inhibition of ethylene production by rhizobitoxine. Plant Physiol. 48: 1-4. Pooviah, B. W., A. 0. Leopold. 1973. Effects of ethephon on growth of grasses. Crop Sci. 13(6): 755-758. Rubenstein, B., M. A. Nagao. 1976. Lateral bud outgrowth and its control by the apex. The Bot. Rev. 42(1): 83-108. Russell, D. W. 1960. Studies on the factors influencing inhibition of lateral buds and branches. Thesis for M. Agr. Sc. Uni. NZ (Lincoln College) Saltveit, M. E., D. R. Dilley. 1977. Simple procedure for preparing dilute concentrations of ethylene in air or oxygen in high pressure cylinders. Hortscience 12(3): 252-253. Van Andel, O. M. 1973. Morphogenetic effects on vegetative plants of Poa pratensis L. of 6-azauracil, (2-chloroethy1)- Phosphonic acid, and (2-chloroethy1) trimethyl ammonium chloride and their interaction with gibberellic acid. J. Exp. Bot. 27(8): 245-257. Yeh, R. Y., A. 0. Matches, R. L. Larson. 1976. Endogenous growth regulators and summer tillering of tall fescue. Crop Sci. 16: 409-413. Chapter 4 INFLUENCE OF ETHYLENE, KINETIN AND NITROGEN DRENCHES ON SHOOT DENSITY IN KENTUCKY BLUEGRASS UNDER SUMMER FIELD CONDITIONS Abstract Ethephon (2-chloroethy1phosphonic acid), kinetin (6-furfury1amino- purine), silver nitrate, and ammonium nitrate drenches were applied to Poa pratensis L. cv. Merion and Nugget to evaluate their effects on shoot density and turfgrass quality under summer field conditions. Rates of Ethephon less than 1000 ul/L did not increase shoot density in either cultivar. Monthly nitrogen drenches of 0.48 kg N/lOOm2 increased both shoot density and quality in both cultivars compared to combinations of nitrogen and Ethephon. No strong trend developed to support field applications of silver nitrate for suppression of ethylene synthesis and/or action to enhance tiller bud numbers. Kinetin drenches increased turfgrass quality, as measured by greenness and density, in Nugget only under supraoptimal temperatures in July but the effect could not be sustained through the season. 57 58 Introduction Both shoot growth (10) and tiller bud initiation (8) are inhibited by temperatures higher than the optimum for growth. Stress on turfgrass is increased due to excessive wear resulting in a decline in shoot density (tillers per unit area). According to a recent review (20) of research on lateral bud development, relatively little field work has been attempted on bud activity under summer field conditions. Lateral buds are present but fail to become active and elongate into tillers (15). It has been suggested that growth regulators influence the tillering rate, parti- cularly at bud initiation (12). Recent theories on bud development in cool season grasses have credited IAA with a major role (14), with revised theories including indirect inhibitor production (21, 29). Recently, ethylene generating chemicals have increased tillering (6, 24), promoted stem elongation and shortened the leaf blade in Kentucky bluegrass (l9). Ethylene has also been reported to affect bud growth of Kentucky bluegrass under optimum growing temperatures (1). Nitrogen applications are also known to improve tillering (13, 28). One of the main effects of nitrogen is to extend the duration of tillering. Withholding nitrogen causes plants to stop producing new tillers at an early date (25). Both the limitation on soil mois- ture and soil nitrogen influenced grass growth in midsummer (3). As high rates frequently injure plants and reduce stand density (16), 59 only low nitrogen rates are practical during summer. Turf grown under low nitrogen levels has been found to be more tolerant to high tempera- tures (18, 27). watschke and co-workers (1970) suggest that the inher- ent ability of certain bluegrasses to absorb lower amounts of nitrate- nitrogen under high temperatures, may influence growth and rooting ability. The decline in shoot growth is predisposed by an increase in root maturation and death (5) brought on by the high summer temperatures. Cytokinins, thought to be of root origin, can extend regulatory control over the metabolism of aerial parts (4). Cytokinins have also been shown to release lateral buds from apical dominance and also inhibition by auxin (20). In addition cytokinins are known to improve root growth (23) and tiller bud elongation (12) in graminaceous plants as well as assisting in recovery of plant tissue from supraoptimal temperatures (11). Recently Ag (1), applied as AgNO3, effectively blocked the ability of exogenously applied ethylene to elicit responses in the etiolated pea, cotton and orchid (7). This material has also found to inhibit both ethylene synthesis and action in postclimacteric apple and banana tissue (22). Since endogenous ethylene levels influence changes in shoot density (1) silver nitrate treatments could also alter turfgrass shoot density via inhibition of ethylene action. The objective of this field study was to compare the influence of Ethephon, kinetin and nitrogen alone and in combination on shoot density 60 and turfgrass quality in Kentucky bluegrass. Materials and Methods Studies were carried out on a 111 m2 block of Merion and an equal size block of Nugget at the M.S.U. turfgrass research plots. Ethephon rates of 0, 10, 100 and 1000 ul/L were applied alone and in combination with either of two rates of ammonium nitrate (0.30 and 0.48 kg N/100m2), two rates of silver nitrate (10 and 100 ul/L) and a single rate of 5 ul/L kinetin. All treatments were applied as drenches to 1.67 m2 plots at approximately monthly intervals from May to September. Dates of both evaluation and treatment applications were 5/29, 6/22, 7/20 and 8/22 for Nugget Kentucky bluegrass and 5/23, 6/13, 7/14 and 8/16 for Merion Kentucky bluegrass. The silver nitrate was sprayed late in the after- noon to avoid photodecomposition. Application was with a hand held sprayer pressurized with 002 at 2.0 atmospheres. This was followed by 2 cm of irrigation. The cultivars were mowed to 4 cm two times per week and regularly irrigated. One month after application, 3 by 10 cm diameter plugs were removed per treatment with a cup cutter and the shoots counted. Data, expressed as shoots per dmz, was used as a measure of the bud activity, influenced by the different treatments. Ratings were also taken on turfgrass quality, (l=high; 9=low) throughout the study. Each value stated in the tables or shown in figures are the mean" of a single study comprising three replications, with mean separation 61 by Duncan's Multiple Range Test. Results Ethylene and Nitrogen combinations. An interaction between nitrogen and ethylene levels occurred in shoot numbers of Merion Kentucky bluegrass recorded for June (Table 1). At 0 nitrogen, ethylene application stimulated shoot density while at 0.48 nitrogen, ethylene levels reduced shoot density. High nitrogen levels stimulated Merion shoot density at 0 ethylene, but had no effect on reduced shoot density if ethylene was applied. In the July rating, no differences occurred among treatments. The densities of Merion Kentucky bluegrass, increased by ethylene and nitrogen in June, were reduced significantly to the levels of the check by the July rating. A significant increase in Merion shoot density occurred when comparing August and September with June and July. This increase appeared to occur independent of treatments. At the highest nitrogen rate, ethylene applications resulted in a lower density of Merion Kentucky bluegrass in August and September similar to the response found in June. Reverse shifts in shoot density of Merion bluegrass in June and September, irrespec- tive of ethephon or nitrogen rate, may be under the influence of day- length. In the June rating, applications of nitrogen significantly improved turfgrass quality compared to 0 nitrogen. However, continued applications did not result in improved quality over the 0 nitrogen treatment at the July, August and September rating. While higher .AumoH owcmm vanguanz m.amod:av Ho>oa ooaowfimcoo Nm can on udouommwo aHuomoHMHomHm uoc mum 5onaoo woo wowuou zuHHmov awzufis Houuoa mama onu an oozoaaom mooHo> amoza 62 mo m.4 Hno o.4 enH «.4 eno HmH Hnn m4H ono mmH OOOH mo m.4 mm 4.4 “no m.m «no omH eno ««H ono smH oOH «6 «.4 enm «.4 fine m.m «no omH one mmH mnp O4H OH one «.4 mo m.4 Hnw m.m 6 «AH one m4H ono «4H . o ooeaoooom Hne m.m HH H.m Ho 5.4 one m«H mnp omH wnn H4H OOOH HH «.m we m.4 mo «.4 on; m4H one mmH ono moH OOH o m.4 Hnw m.m Hno o.4 eno ««H eno OHH mno 44H oH Hnw m.m H w.« Hne m.m no moH one HmH ene HHH o omomoo no “.4 one 4.4 one o.o H no HE «« HnH om oo0H so m.o oo «.m oo «.m He ca H no HnH om COH oo n.m one m.4 one o.o Ha OH Ha 6H He H« OH one m.o o o.“ no «.6 He HH HnH 4m Ha «H o AHoe Hno m.m Hno m.m Ho «.4 HnH on He AH Hno «HH oOOH Hnw n.m HH «.m we m.4 HnH Hm HnH am an: 4OH oOH HH «.m Hne m.m mo «.4 HnH om HnH Hm HnH we OH H m.« Hne m.m Hno o.4 Hnm HHH HnH Ha H no o ones m4.o om.o o m4.o om.o. Ho AH\Hao onaaeazmozoo Anoo685NEOOH\z wee Hm>mH zmuomeHz zomommam maze: HsoHnm mewHenHv ozHeoH cowouuao can ooauouuoouooo condonum mo uoommm .H manna 63 turfgrass quality ratings were found for 1000 ul/L Ethephon compared to 0, 10 and 100 ul/L at all fertility levels in June, this reduction in quality could not be documented statistically. Furthermore, Ethephon concentration had no effect on turfgrass quality at the July, August, and September rating in Merion Kentucky bluegrass. Turfgrass quality was significantly less at the July rating compared to June, August and September. This reduction and subsequent increase in quality appeared to occur independent of the treatments. Nugget Kentucky bluegrass exhibited a significant increase in shoot density in June and August when Ethephon was applied at 1000 ul/L compared to their controls (Table 2). Density remained high in September. Significantly high densities were demonstrated in July and August at 100 ul/L Ethephon resulted in increased shoot density in all months. However, the shoot density on the plots receiving 0.48 kg N/100m2 was significantly higher than its control only in June and July. In the absence of both Ethephon and nitrogen, the quality of Nugget Kentucky bluegrass decreased progressively from June to September (Table 2). Ethephon concentration did not significantly effect rating. A significantly lower rating was recorded in August and September compared to June and July, irrespective of Ethephon concentration. Both nitrogen rates, when applied alone, produced a better rating when compared to the control in June and July. Only higher nitrogen rates were successful in maintaining better quality turf in August and .Amoe owcmm oHdHuHaz m.:moaonv Ho>oH ooaoonooo Nm onu um uooHoMMHo HHuooonHome uoa mum Ho>oH cowouuHo com onuou zuHHmso aHnuHa HouuoH meow osu 5n oosoHHom moon> cooza 64 Hno «.4 Hno «.4 oe «.O one ««« Hno 4H« one ««« OOOH eno «.4 ono H.H one O.O o 4H« eo wH« one «OH OOH Hne o.m Hno H.4 eo m.e Hno 4H« one ««« one «oH OH Hno O.m o «.« one 0.0 oe e«« Hno HH« mno OH« O ooeaoooom Hno H.4 eno «.4 oe «.O eno HH« ono HH« one H«« OOOH eno «.4 ono H.H one O.e onH OOH Hno HO« eno OH« OOH Hne O.H Hno H.4 eo H.O ano 40« one «OH one HO« OH Hno «.m o H.« one O.O onH OOH oo HOH HnH OoH O ooeoeo Hno H.H eno O.4 Hno «.4 ano HO« onH OOH o HHH OOOH Hno «.4 mno O.H Hno H.4 one HO« Hno OO« eno HH« OOH Hno O.4 Hno 4.4 HH H.m eno OH« one «wH o H«H OH Hne o.H Hne O.H eno «.4 eno OH« one HoH one 4mH O HHeo eno H.4 eno o.4 Hno «.4 eno HH« eno HH« o O4« OOOH Hno «.4 Hno H.4 Hno 4.4 one HHH onH OOH onH HOH OOH H H.H Hno H.4 Hno H.4 one HO« one ««« wno OH« OH H «.H H «.H Hno O.4 ono oH« one «O« one 4OH O ooze e4.0 O«.O O o4.O OH.O HO XHH\H1O ZOHaeeHzoOZOO «moaoa\«aOOH\z woo HHOHH szOmHHz ZOmomon eHzOz AEOHnO mewHenHO ozHeom HHHHoH sowouuHo coo EOHuouucoocoo oosdofim mo uooumu .N oHoma 65 September. However, both fertilizer rates did interact with Ethephon concentration during these months to produce significantly better ratings than their controls. Ethylene and Kinetin Combinations. Table 3 shows that Merion bluegrass density was not influenced by either kinetin or kinetin/ ethephon drenches throughout the study. A significant increase in shoot density occurred between July and August which was independent of these treatments. Generally, Ethephon and kinetin combinations did not alter turfgrass quality ratings in Merion Kentucky bluegrass. An exception was in August where Ethephon at 1000 ul/L plus kinetin resulted in a significantly higher quality rating. Combinations of Ethephon and kinetin on Nugget Kentucky bluegrass did not increase shoot density either within or between months (Table 4). Shoot density did decline when the higher Ethephon rates were combined with kinetin, a trend also observed in Merion Kentucky bluegrass. Ethylene and Silver Nitrate Combinations. Ethephon rates of 100 and 1000 ul/L, either applied alone or in association with 100 ul/L silver nitrate, significantly increased the shoot density of Merion Kentucky bluegrass in June (Table 5). However, when the same Ethephon levels were combined with 100 ul/L silver nitrate, density was signifi- cantly depressed. The shoot density of Merion was not influenced by Ethephon/silver nitrate combinations in July. In August, both rates of silver nitrate when combined with 100 and 1000 ul/L Ethephon significantly increase shoot density compared to the control and the 66 .AumoH owaom onHuaaz m.ooo:=nv Ho>oH ooooonaoo Nm onu um oooooOOHo hHuoooHMchHm uo: mum muHmaoc pom wcHumu OuHHmoo oHnuH3 Houuoa mama on» he oosoHHom moon> amoza ono O.4 mno «.4 eo OOH o OOH OOOH ono O.4 OO O.O ono O«H o OOH OOH ono O.4 O 0.0 eno «O eo O4H OH O 0.0 mm 0.0 o «OH o «OH O ooeaooOoO o «.O ono «.4 eo H4H eo H4H OOOH one «.O mno O.4 ono O«H o OOH OOH ono O.4 mno O.4 eo O4H eo 44H OH o «.O O 0.0 o OOH ono OOH O ooeoeo o 0.0 eo O.O eno OO eno OO OOOH one «.O ono «.O e «O eno OO OOH one «.O eo O.O e OO eno H« OH o «.O o «.O eno OO enO «« O OHOO Hno O.4 ono «.4 mno OO one «HH OOOH OO O.O Ono O.4 eO OO ono 4OH OOH O «.O mno O.4 eno «O eno OO OH O 0.0 wno O.4 eno «O eo OO O ooze O O O HO OH\H:O ZOHHOOOszzOO Azuco8\a\anv ooHumuucooooo :HuocHM zommmmam maze: AaoHnO HewHenHO ozHHOO OHHHHOO. O«ao\oooonO OHHOsz .uooaoudom ou mosh onuooa onu onuoo mmouwoaHo hxoaucox EOHuoz 6H huHHmad mmmuwmuou vow OuHmooo uoonm do :oHumuuoooooo dHuoaHx vow condonum mo uommmm .m manna 67 .Aumoa owamm oHdHuH52 m.ono:=av Ho>oH moaoonooo nm on» um uooquMHv OHuGOOHwHome uod mun OuHmcoo can onuou huHHoau :HnuHa nouuoa 08mm onu mo ooonHow mooHo> one: H o «.O o «.O One OOH eo O«« OOOH oe «.O eo O.O One «O« One «OH OOH o «.O o 0.0 ono OH« one OOH OH o «.O eo O.O ono ««H ono OH« O HoeaooOoO o «.O o «.O one «OH ono 4«« OOOH oe O.O eo O.O one 4O« ono OH« OOH o «.O o 0.0 one OOH one 4O« OH o 0.0 eo 0.0 One HOH One OOH O oOOOo< oo O.4 Ono «.4 One «O« O OOH OOOH oo O.O ono O.4 ono O«H ono HH« .OOH .ono O.4 OO 0.0 One OOH Ono 4«H OH Ono 0.0 oo «.4 One OOH One 4OH O OHOO ono O.4 Ono «.4 mo OOH o OO« OOOH OO 0.0 ono 4.4 Ono O«H One OOH OOH O «.O Ono H.4 Ono O«H ono OH« OH ono O.4 Ono O.4 ono «H« one 4OH O ooze O O O HO HHHHeHn ZOHHOOOzOOzOO AeoooaHHHHaO OOHooooeooooo oHooaHO zOOOOOHO mazoz HOOHnO meOHenHO OZHOOO OHHHoH ouoovaooo Nn osu um unoHoMMHo OHucmoHMHome uoo mum muHmaoo mom moHuou huHHmao aHnuH3 nouuoH 08mm onu ho uosoHHom mooam> duo: 68 H OH «.O Hne O.4 HH «.4 Hno «4H o OOH ene OOH OOOH eO O.4 Ono O.4 aH O.O one «O eo O«H One OOH OOH enH O.4 8 HH «.4 a 0.0 Hne HOH Hno «4H HnO O4H OH He «.4 an O.4 aH O.O One OOH one ««H one «OH O ooeaooeoO HH «.4 5H 0.0 He «.4 ono «OH one 4OH Hno H4H OOOH He O.4 a O.O enH O.4 one OOH one 4OH one OOH OOH H O.O Ono O.4 , He O.4 one OOH Hno OOH Hno 44H OH 5H O.O aH O.O a 0.0 enH O«H anH OOH one OOH O oeeOe< oo 0.0 e O.O one 0.0 >no «« one 4O >no OO OOOH one O.O e «.O oo «.O >no O« >no «O >ne OO OOH one «.O oo «.O one O.O >o H« >e «O >e H« OH o O.O o O.O o «.O ono OO >no 4« >no «« O OHOO eo O.O one «.O He «.4 >no OO ono OOH one «HH OOOH oo O.O Oo 4.O Ono O.4 >ne O« one «OH one 4OH OOH one «.O o O.O enH O.4 enH HHH >n4 «O eno OO OH .o «.O one 0.0 He O.4 one OOH >no 4O > OO O ooze OOH OH O OOH OH HO HH\H:O ZOHHOOHZOOZOO Aeooee\H\HeO eeHoooooooeeo OOOOO zOOOOOOO eozoz AseHnO HeOHenHO ozHooe OHHHOOO H«ao«eoeeeOO OOHOZOO .uooamudom Ou moon nausea onu wcHuao mmmuwooan Oxoouoox oOHumz cH OuHHosv mmmuwwu5u use OuHmooo uoonm do aoHuouuoooooo ououuH: uo>HHm woo condonum mo uoomwm .m oHan 69 density counts of June and July. This interaction also occurred at 100 ul/L Ethephon when combined with the 100 ul/L silver nitrate rate. The addition of silver nitrate to Merion Kentucky bluegrass, either applied alone or with Ethephon, caused a significant decline in the quality rating in June. In July, quality dropped which could not be explained by silver nitrate or Ethephon treatment. Turfgrass shoot density was increased significantly in June when Nugget Kentucky bluegrass was drenched with Ethephon applications of 1000 ul/L alone or combined with 10 ul/L silver nitrate (Table 6). I This trend was also significant in July. Density did not vary greatly in August and September due to any Ethephon or silver nitrate treat- ments. A decline in density however, was observed when 10 ul/L was combined with 10 ul/L silver nitrate when compared to the controls. The quality rating changed little in June, although quality was poorer when Ethephon was combined with 100 ul/L silver nitrate compared to the controls. Quality fell significantly in August and September when compared to the June and July ratings, apparently independently of Ethrel or silver nitrate concentration. A significant improvment in quality, compared to the control, was observed when 10 ul/L Ethephon was combined with 10 ul/L silver nitrate in August and September. However, this was reversed at the higher silver nitrate level. 7O .Aumoa owamm oHdHuHSZ m.oooooav Ho>oH moooonaoo Nm onu um oeooooooo OHuEOOHmHomHm uoo mum OuHmooo woo onumn OuHHmao cHsuHs Houuoa oamw oSu he oosoHHom mooHo> aomza ono «.O oo O.O one «.O One «H« one O«« one O«« OOOH oe 0.0 oe O.O. one O.O One OH« One OH« HnO «OH OOH e O.« Oo «.O e O.O Ono «OH anH 4OH Hno OOH OH one «.O ono 0.0 one O.O ene OO« One «H« one OH« O ooeaooeoO ono «.O ono «.O one «.O Hno OOH One «H« one 4«« OOOH oe O.O oe 0.0 one 0.0 aH OOH Hno OOH One OH« OOH Oo «.O oo 0.0 e O.O Ono OOH a O4H ene 4O« OH ono O.O ono O.O one O.O Hne OOH Hno OOH eno OOH O oeeOoe Hne O.4 HnH H.4 HnH «.4 Hno HOH ee OO« ane OOH OOOH He 0.0 One 4.4 Hne O.4 Hno OOH anH OOH One HH« OOH He «.4 a O.O a 0.0 Hno «OH HnO 4OH ane O«H . OH H 0.0 HnH H.4 He «.4 HnO «OH one 4«H Hno 4OH O OHOO eO O.4 He 0.0 HnH «.4 one OO« ee «O« e OO« OOOH Hne O.4 Hne O.4 one 4.4 Hno OOH Hno 4OH Hno OOH OOH Hne O.4 one 4.4 HnH H.4 ane O«H one ««« one OH« OH He «.4 a «.O HnH O.4 one O«H one OH« Hno 4OH O oeee OOH OH O OOH OH HO HH\HOO n zOHonOZOOZOO Heooea\o\HeO oeooeoooooeeo Oozwm, zomommom mozoz HaeHnO memoenHO ozHOOO OOHHHHm odd condonum mo uoomom .@ oHomH 71 Discussion Under hypobaric conditions, ethylene has been shown to be the agent to stimulate bud break in Kentucky bluegrass when grown at 220 (1). However, under supraoptimal temperatures of 330, the increase in endogenous ethylene is considered a contributing factor in bud inhibi- tion. Both an increase in tillering and stem length have been reported using rates of Ethephon ranging from 1.4 to 8.6 kg a.i.lha (l6). Ethephon sprays at rates of 0.5 to 2.2 kg a.i.lha have generally stimulated tillering in Kentucky bluegrass, tall fescue and annual ryegrass (2). However, the present price of $12.2/L (9) which repre- sents $211.1/kg active, prevents the widespread usage on extensive turfgrass areas. It was speculated that monthly Ethephon drenches at low concentrations during summer would increase bud activity by supplementing endogenous ethylene. The stimulation of tillering would be of significant value over summer in cool season grasses. Field results showed that only in June for Merion Kentucky bluegrass and July and August for Nugget was there a significant improvement in shoot density. Ethephon rates of less than 1000 ul/L were not considered practical in promoting bud activity. Generally, quality was not increased following Ethephon application and research indicated that it may increase Dollar spot (Sclerotinia homeocarpa) activity in Nugget Kentucky bluegrass. Summer nitrogen application should be practiced judiciously, as 72 shoot growth is often minimal. The use of light frequent applications of readily available nitrogen fertilizer are often preferred to heavy infrequent applications (26). The use of light (0.30 and 0.48 kg N/ 100m2) and frequent (monthly) rates applied in combination were expected to improve the longevity of tillering by providing nutrition to the new buds. In Merion Kentucky bluegrass, neither 1000 ul/L Ethephon nor 0.48 kg N/100m2, applied alone, provided an increased June density. The latter treatment also offered an improvement in quality over the Ethephon treatment. This trend was also apparent in Nugget. In July, neither the application of Ethephon or nitrogen produced any dramatic differences in density or quality. Therefore the decision to either forego nitrogen application in July or apply it at the lower rate will rest on the proposed use of the turf. In Nugget Kentucky bluegrass the higher nitrogen rates were considered desirable to obtain higher density, but quality was not altered, when nitrogen was applied in July. In August and September there was a significant increase in the shoot density of Merion but not Nugget Kentucky bluegrass compared to earlier months. The 0.48 kg N/lOOm2 applied alone, continued to be the best drench to increase density in Merion and Nugget Kentucky bluegrass over the months of August and September. 'The results showed that the higher nitrogen rate should be used in these months as it gave both 73 a higher quality, a greater density, and reduced Dollar spot activity. However, a combination of drenches incorporating nitrogen with 10 ul/L Ethephon was also found to reduce disease activity. Ethephon applica- tions, applied alone to Nugget should be avoided during August and September as quality is reduced and Dollar spot activity increased. Little information is available on the effects of kinetin drenches on shoot density and quality of Kentucky bluegrass. Earlier work with cytokinins has shown this material to release lateral buds from dormancy (20) promote tiller bud elongation (12) and to prevent loss of leaf chlorophyll content (11). Kinetin drenches could not be recommended for Merion Kentucky bluegrass as little effect was observed in shoot density or quality over the study. Both density and quality were improved in August and September, compared to the July figures, but this was independent of any kinetin Ethephon combination. The addition of kinetin did not alter the quality differences between June and July and those of August and September as found in Table 2. In Nugget Kentucky bluegrass, a kinetin drench, applied on its own, was shown to improve quality in July, the month having both the highest average maximum and minimum temperatures (Figure l), but the effect could not be sustained by succeeding monthly applications. A Silver nitrate drench was included in the field study to evaluate its effect on ethylene produced by turf. Silver nitrate was found to be a potent anti-ethylene agent in several plant processes under a 74 .mmum mvsum man Scum Boom .mufimum>aob mumum omwanuaz .mcumm mocofium Hwom can mono onu um coxmu mumv muaumnomaos .nemfi .umoawuamm ou hm: scum monoumuomaou aaafixma cam Esafiawa mafimn .H ouamfim cantata» 5:03 . hi , . 35.. .3! Q: as. «38.1888 «.2. QN— OO« 3:95 NE em. «.3 :1 2.... no. new .5. .3. «.9 no... .6... .95. .553: .. 1 x, .oau .£1= ans: a§=o.oaxcullllll \, .3 "mum; 75 contolled environment (7). It was speculated that a silver nitrate drench would prevent ethylene action and/or synthesis to give a lowered bud activity. Reductions in shoot density was apparent in June when 100 ul/L silver nitrate was applied in combination with 100 and 1000 ul/L in Ethephon to Merion. This was also observed in September when 10 and 100 ul/L silver nitrate were combined with 10 ul/L Ethephon and compared to their controls. However, in the case of July no differences were observed in the cultivar. In other cases the higher silver nitrate rate, combined with 100 and 1000 ul/L Ethephon in August, indicated a significant increase in density when compared to its control. Similar interactions occurred for Nugget Kentucky bluegrass. No strong trend developed supporting the above concept when silver nitrate was applied under field conditions. The influence of field temperature should not be underestimated in this study. Although all drenches were applied over a 6 hour period, with the silver nitrate treatments applied in late evening, subsequent field temperatures were found to have a large influence on shoot density and quality. The daily maximum and minimum temperatures from May to September are presented in Figure 1, allowing examination of previous months application and the subsequent climatic pattern. The May applications were followed by a month in which the average tempera- ture was 17.7. The June temperatures were optimum for tiller bud growth (5) and significant improvements were found in density and quality due to Ethephon and nitrogen drenches. In Merion Kentucky 76 bluegrass, all drenches applied in June generally maintained the status quo but the high July temperatures did adversely effect quality. The significant increase in shoot density of Merion in August was more apparent than in Nugget Kentucky bluegrass. This improvement in density may be influenced by the cooler growing temperatures, as it was independent of treatment. It can also be speculated that the growth of buds in June were inhibited by the supraoptimal July temperatures and were only fully expressed in the cooler fall months. 10. 11. 12. 77 Literature Cited Aldous, D. E., D. R. Dilley and J. E. Kaufmann. 1977. Ethylene as an agent in bud growth of Kentucky bluegrass (Poa pratensis L.) Hortscience 12(4): 384. Anonymous. 1969. Ethrel Technical service data sheet H-96. Amchem Products, Inc. Ambler, Pa. 64 pp. Anslow, R. C., 1965. Grass growth in midsummer. Br. Gland. Soc. J, 20(1): 19-26. Atkin, R. K., G. E. Barton and D. K. Robinson, 1973. Effect of root-growing temperature on growth substances in xylem exudate of Zea mays. J. of Exp. Bot. 27(79): 475-87. Beard J. B., 1963. Turfgrass-science and culture. Prentice-Hall Inc., Englewood Cliffs, N. J. 658 pp. Buellner, M. R., R. D. Ensign and A. A. Boe, 1976. Plant growth regulator effects on flowering of Poa pratensis L. under field conditions. Agron. J. 68: 410-413. Beyer, E. M., 1976. A potent inhibitor of ethylene action in plants. Plant Physiol. 58: 268-271. Darrow, R. A., 1939. Effect of soil temperature, pH and nitrogen nutrition on the development of Poa pratensis L. Bot Gaz. 101: 109-127. de Wilde, R. C., 1977. Private communication. Duff, D. T. and J. B. Beard, 1974. Supraoptimal temperature effects upon Agrostis palustris. Part 1. Influence of shoot growth and density, leaf blade width and length, succelence and chlorophyll content. Physiol. Plant 32(1): 14-17. Gur, A., B. Bravado and Y. Mizrahi, 1972. Physiological responses of apple tress to supraoptimal root temperature. Physiol. _Plant. 27: 130-138. Langer, R. H. M., P. C. Prasad and H. M. Laude, 1973. Effects of kinetin on tiller bud elongation in wheat (Triticum aestivum L.). Ann. Bot. (Lond) 37: 565-571. l3. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 78 Laude, H. M., 1972. External factors affecting tiller development In: The biology and utilization of grasses. (Ed.) V. B. Youngner and C. M. McKell. Chapter 11, pp. 146-154. Leopold, A. C., 1949. The control of tillering in grasses by auxin. Am. J. Bot. 26: 437-440. Lopez, R. R., A. G. Matches and J. D. Baldridge, 1967. Vegetative development and organic reserves of tall fescue under field conditions of accumulated growth. Crop Sci. 7: 490-412. McAfee, J. A., 1973. Use of ethephon (2-chloroethy1phosphonic acid) as an inhibitor of plant height for Kentucky bluegrass, Poa pratensis (L.). Ph.D. Thesis, Purdue University, 60 pp. McKee, W. H., R. H. Brown and R. E. Blazer, 1967. Effect of clipping and nitrogen fertilization on yield and stands of tall fescue. Crop Sci. 7: 567-570. Pellet, H. M. and E. C. Roberts, 1963. Effects of mineral nutrition on high temperatures induced growth retardation of Kentucky bluegrass. Agron. J. 5: 473-476. Poovaiah, B. W. and A. C. Leopold, 1973. Effects of Ethephon on growth of grasses. Crop Sci. 31: 755-758. Rubinstein, B. and M. A. Nagas, 1976. Lateral bud outgrowth and its control by the apex. The Bot. Rev. 42(1): 84-109. Russell, D. W., 1960. Studies on the factors influencing inhibition of lateral buds and branches. Thesis M. Agr. Sc. N.S. (Lincoln College). Saltveit, M. E., K. J. Bradford and D. R. Dilley, 1977. Silver, Ag(I), inhibits ethylene synthesis and action in ripening fruits. Plant Physiol. 59(6): 45. .Splittstoesser, W. E. and H. J. Hopen, 1970. Root growth inhibition by siduron and its relief by kinetin. Physiol. Plant. 23(5): 964-970. Van Andel, O. M., 1973. Morphogenetic effects on vegetative plants of Poa pratensis L. of 6—azauracil, (2-chloroethy1)-phosphoric acid, and (2-chloroethy1) trimethyl ammonium chloride and their interaction with gibberellic acid. J. Exp. Bot. 27(8): 245-257. 25. 26. 27. 28. 29. 79 Vose, P. B., 1960. The physiology of the vegetative grass plant. Waddington, D. V., J. M. Duich, and E. L. Moberg, 1969. Lawn fertilizer test. Pennsylvania Agricult. Exp. Stn. Prog. 296. pp 0 1-580 Watschke, T. L., R. E. Schmidt and R. E. Blazer, 1970. Responses of some Kentucky bluegrasses to high temperature and nitrogen fertility. Crop Sci. 10: 372-376. Williams, R. F., B. C. Sharman and R. H. M. Langer, 1975. Growth and development of the wheat tiller. I. Growth and form of the tiller bud. Aust J. Bot. 23: 715-743. Yeh, R. Y., A. G. Matches and R. L. Larson, 1976. Endogenous growth regulators and summer tillering of tall fescue. Crop Sci. 16: 490-413. 1. CONCLUSIONS Bud growth was described and illustrated by stages, 1) initiation of bud activity to first primordial leaf; 2) second primordial leaf to leaf unfold and, 3) ligule formation to leaf emergence above the subtending leaf sheath. Bud growth in Nugget Kentucky bluegrass compared to Merion was less sensitive to inhibition at high temperature. In both culti- vars the increase in the number of active buds (bud activity) never ceased but was reduced at supraoptimal temperatures. Temperatures of 220 were found to significantly increase bud length. The number of buds at the stem base and nodes were reduced by supraoptimal temperatures compared to cooler temperatures in both cultivars. Hypobaric ventilation studies at 220 showed that endogenous ethy- lene levels reduced the number of active buds. Bud activity was returned to normal when ethylene was reintroduced. Under supra- optimal temperatures bud activity could not be restored by reintroduction of ethylene. High ethylene production was found to be a contributing factor in bud inhibition at 33C. Natural ethylene production, measured at SC increments from 15 to 40C peaked at 27C, in Merion Kentucky bluegrass and 34C in Nugget. In another study, temperatures of 22C generated increased ethylene production upon application of kinetin, compared to the distilled water control. At supraoptimal temperatures a three-fold increase in ethylene production was generated by the turfgrass tissue both 80 81 with and without kinetin application. Foliar applied kinetin was found to increase the number of active buds through stimulation of ethylene production when grown at 22C. Hypobaric studies revealed that under supraoptimal temperatures, inhibition of bud activity resulted from increased ethylene product- ion generated endogenously or by kinetin application. A twenty-four hour exposure at 33C inhibited bud activity of Merion and Nugget Kentucky bluegrass. The number of active buds increased when cultivars, exposed to 33C, were returned to cooler temperatures of 22C. Ethephon rates less than 1000 ul/L, applied as drenches, were ineffective in improving shoot numbers under summer field conditions. Monthly nitrogen drenches of 0.40 kg N/lOOm2 were more effective in improving shoot density and quality in both cultivars compared to combinations of nitrogen and ethephon. No strong trend developed to support field applications of silver nitrate for suppressing ethylene synthesis and/or action. 10. ll. 12. 13. List of References Aldous, D. E., D. R. Dilley and J. E. Kaufmann. 1977. Ethylene as an agent in bud growth of Kentucky bluegrass (Poa pratensis L.) Hortscience 12(4): 384. Aldous, D. E. and J. E. Kaufmann. 1978. The role of root temper- ature on growth and carbohydrate levels in two Kentucky bluegrass cultivars grown at supraoptimal temperatures. (accepted by Agronomy J.) Anonymous. 1969. Ethrel Technical service data sheet H-96. Amchem Products, Inc. Ambler Pa. 64 pp. Arber, A. 1934. The gramineae - a study of cereal, bamboo, and grass. Cambridge Uni. Pres, Land. and New York. Anslow, R. C. 1965. Grass growth in midsummer. Br. Grassld. Soc. J. 20(1): 19-26. Artschwager, E. 1925. Anatomy of the vegetative organs of sugar cane. J. Agr. Res. 30: 197-221. Atkin, R. K., G. E. Barton and D. K. Robinson. 1973. Effect of root growing temperature on growth substances in xylem exudate of Zea mays. J. of Exp. Bot. 27(79): 475-487. Beard, J. B. 1972. Comparative sod strengths and transplant sod rooting of Kentucky bluegrass cultivars and blends. 42nd Annual Mich. turfgrass conf. proc. 1: 123-127. Beard, J. B. 1973. Turfgrass-science and culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. 658 pp. Beyer, E. M. 1976. A potent inhibitor of ethylene action in plants. Plant Physiol. 58: 268-271. Buellner, M. R., R. D. Ensign and A. A. Boe. 1976. Plant growth regulator effects on flowering of Poa pratensis L. under field conditions. Agron. J. 68: 410-413. Burg, S. P. and E. A. Burg. 1965. Gas exchange in fruits. Physiol. Plant. 18: 870-884. Burg, S. P. 1973. Ethylene in plant growth. Proc. Nat. Acad. Sci. 70(2): 491-597. 82 14. 15. l6. 17. 18. 19. 20. 21. 22. 23. 24. 25. 83 Byers, R. E., L. R. Baker, H. M. Sell, R. C. Herner and D. R. Dilley. 1972. Ethylene: a natural regulartor of sex expression of Cucumis melo L. Proc. Nat. Acad. Sci. U.S.A. 69(3): 717-720. Darrow, R. A. 1939. Effect of soil temperature, pH and nitrogen nutrition on the development of Poa pratensis L. Bot Gaz. 101: 109-127. Duff, D. T. and J. B. Beard. 1974. Supraoptimal temperature effects upon Agrostis palustris. Part 1. Influence of shoot growth and density, leaf blade width and length, succu- lence and chlorophyll content. Physiol. Plant. 32(1): 14-17. de Wilde, R. C. 1977. Private communication. Evans, M. W. 1940. Developmental morphology of the growing point of the shoot and the inflorescence in grasses. J. Agr. Res. 61(7): 481. Gur, A., B. Bravado and Y. Mizrahi. 1972. Physiological responses of apple trees to supraoptimal root temperature. Physiol. Plant. 27: 130-138. - Harrison, C. M. 1934. Responses of Kentucky bluegrass to varia- tions in temperature, light, cutting and fertilization. Plant Physiol. 9: 83-106. Jewiss, 0. R. 1972. Tillering in grasses - its significance and control. J. Br. Grassld. Soc. 27: 65-81. Johnson, G. F. S. and B. Jefcoat. 1977. Effects of some growth regulators on tiller bud elongation in cereals. New Phytol. 79: 239-243. Kapuya, J. A. and M. A. Hall. 1977. Diurnal variations in endo- genous ethylene levels in plants. New Phytol. 79: 233-237. Kwong, F. Y. and H. B. Lagerstedt. 1977. Translocation of ethephon in beans and peas. J. Am. Soc. Hort. Sci. 102(4): 437-440. Langer, R. H. M. 1959. Growth and nutrition of timothy (Pheleum pratense). V. growth and flowering at different levels of nitrogen. Ann. Appl. biol. 47: 740-751. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 84 Langer, R. H. M. 1963. Tillering in herbage grasses. Herb. Abst. Vol. 33(3): 141-148. Langer, R. H. M. 1972. How grasses grow. Edward Arnold Ltd., Lond. 60 pp. Langer, R. H. M., P. C. Prasad and H. M. Laude. 1973. Effects of kinetin on tiller bud elongation in wheat (Triticum aestivum L. ). Ann. Bot. (Lond. ) 37: 565- 571. Lau, 0. and K. Yung. 1974. Synergistic effect of kinetin on IAA-induced ethylene production. Plant and Cell Physiol. 15: 29-35. Lau, 0. and S. F. Yang. 1976. Stimulation of ethylene production in the mung bean hypocotyls by cupric ion, calcium ion, and kinetin. Plant. Physiol. 57: 88-92. Laude, H. H. and B. A. Chaugule. 1953. Effect of stage of seed- ling development upon heat tolerance in bromegrass. J. Range Management 6: 320-325. Laude, H. H. 1964. Plant responses to high temperature. Am. Soc. of Agron. Special Pubs. 5 pp. 15-31. Laude, H. M. 1972. External factors affecting tiller development. In: The biology and utilization of grasses. (Ed.) V. B. Youngner and C. M. McKell. Chapter 11, pp. 146-154. Leopold, A. C. 1949. The control of tillering in grasses by auxin. Am. J. Bot. 26: 437-440. Lindsay, K. E. and M. L. Peterson. 1962. High temperature suppression of flowering in Poa pratensis L. Crop Sci. 2: 71-74. Lopez, R. R., A. G. Matches and J. D. Baldridge. 1967. Vegetative development and organic reserves of tall fescue under field conditions of accumulated growth. Crop Sci. 7: 490-412. Marinucci, M. and V. Rivera. 1954. D031 termiche inductenti paralisi vegetativa in Lupinus albus. (Thermic dises inducing suspension of growth in Lupinus albus) (English summary). Annali di Botanica. 24: 42-45. Mayak, S. and D. R. Dilley. 1976. Regulation of senescence in carnation (Dianthus caryophyllus). Effects of abscisic acid and carbon dioxide on ethylene production. Plant Physiol. 58: 663-665. 39.. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 85 McAfee, J. A. 1973. Use of ethephon (2-chloroethy1phosphonic acid) as an inhibitor of plant height for Kentucky bluegrass, Poa pratensis L. Ph.D. Thesis, Purdue Univeristy, 60 pp. McKee, W. H., R. H. Brown and R. E. Blazer. 1967. Effect of clipping and nitrogen fertilization on yield and stands of tall fescue. Crop Sci. 7: 567-570. Milthorpe, F. L. and J. D. Ivins. (eds) 1966. The growth of cereals and grasses. Butterworth, Lond. Mitchell, K. J. 1953. Influence of light and temperature on the growth of ryegrass (Lolium spp.). 1. pattern of vegeta- tive development. Physiol. Plant. 6: 21-46. Mitchell, K. J. 1956. Growth of pasture species under controlled environment. 1. growth at various levels of constant temper- Musgrave, R. B. 1940. Life history studies of Poa pratensis L. Ph.D. Thesis. Uni. of Illinois. Owens, L. D., M. Lieberman and A. Kunishi. 1971. Inhibition of ethylene production by rhizobitoxine. Plant Physiol. 48:1-4. Pellet, H. M. and E. C. Roberts. 1963. Effects of mineral nutri- tion on high temperatures induced growth retardation of Kentucky bluegrass. Agron. J. 5: 473-476. Poovaiah, B. W. and A. C. Leopold. 1973. Effects of ethephon on growth of grasses. Crop Sci. 13(6): 755-758. Romberger, J. A. 1963. Meristems, growth and development in woody plants. Tec. Bull. 1293, 214 pp. Rubenstein, B. and M. A. Nagao. 1976. Lateral bud outgrowth and its control by the apex. The Bot. Rev. 42(1): 83-108. Russell, D. W. 1960. Studies on the factors influencing inhibi- tion of lateral buds and branches. Thesis for M. Agr. Sc., Uni. N.Z. (Lincoln College). Ryle, G. J. A. 1964. A comparison of leaf and tiller growth in seven perennial grasses as influenced by nitrogen and tempera- ture. J. Br. Grassld. Soc. 19: 281-290. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 86 Saltveit, M. E., K. J. Bradford and D. R. Dilley. 1977. Silver, Ag(I), inhibits ethylene synthesis and action in ripening fruits. Plant Physiol. 59(6): 45. Saltveit, M. E. and D. R. Dilley. 1977. Simple procedure for preparing dilute concentrations of ethylene in air or oxygen in high pressure cylinders. Hortscience 12(3): 252-253. Sharman, B. C. 1942. Developmental anatomy of the shoot of Zea mays L. Ann. Bot. (Lond) (N.S.) 6: 245-282. Sharman B. C. 1945. Leaf and bud initiation in the graminaceae. Bot. Gaz. March. pp. 269—289. Soper, K. and K. J. Mitchell. 1956. The developmental anatomy of perennial ryegrass (Lolium perenne). N.Z.J. Sci. Tec., Splittstoesser, W. E. and H. J. Hopen. 1970. Root growth inhibi- tion by siduron and its relief by kinetin. Physiol. Plant. 23(5): 964-970. Suge, H. 1972. Mesocotyl elongation in japonica rice: Effect of high temperature pretreatment and ethylene. Plant and Cell Physiology 13: 410-415. Van Andel, 0. M. 1973. Morphogenetic effects on vegetative plants of Poa pratensis L. of 6-azauracil, (2-chloroethy1)-phosphoric ' acid, and (2-chloroethy1) trimethyl ammonium chloride and their interaction with gibberellic acid. J. Exp. Bot. 27(8): 245-257. Vose, P. B. 1960. The physiology of the vegetative grass plant. Rep. Welsh P1. Breed. Sta. 1959. 17-18. waddington, D. V., J. M. Duich, and E. L. Moberg. 1969. Lawn fertilizer test. Pennsylvania Agricult. Exp. Stn. Prog. 2960 pp. 1-580 Watschke, T. L., R. E. Schmidt and R. E. Blazer. 1970. Responses of some Kentucky bluegrasses to high temperature and nitrogen fertility. Crop Sci. 10: 372-376. Williams, R. F., B. C. Sharman and R. H. M. Langer. 1975. Growth and development of the wheat tiller. I. Growth and form of the tiller bud. Aust. J. Bot. 23: 715-743.