Stolon Nodes Research Articles

H2O2 promotes trimming-induced tillering by regulating energy supply and redox status in bermudagrass.

Tillering/branching pattern plays a significant role in determining the structure and diversity of grass, and trimming has been found to induce tillering in turfgrass. Recently, it has been reported that hydrogen peroxide (H2O2) regulates axillary bud development. However, the role of H2O2 in trimming-induced tillering in bermudagrass, a kind of turfgrass, remains unclear. Our study unveils the significant impact of trimming on promoting the sprouting and growth of tiller buds in stolon nodes, along with an increase in the number of tillers in the main stem. This effect is accompanied by spatial-temporal changes in cytokinin and sucrose content, as well as relevant gene expression in axillary buds. In addition, the partial trimming of new-born tillers results in an increase in sucrose and starch reserves in their leaves, which can be attributed to the enhanced photosynthesis capacity. Importantly, trimming promotes a rapid H2O2 burst in the leaves of new-born tillers and axillary stolon buds. Furthermore, exogenous application of H2O2 significantly increases the number of tillers after trimming by affecting the expression of cytokinin-related genes, bolstering photosynthesis potential, energy reserves and antioxidant enzyme activity. Taken together, these results indicate that both endogenous production and exogenous addition of H2O2 enhance the inductive effects of trimming on the tillering process in bermudagrass, thus helping boost energy supply and maintain the redox state in newly formed tillers.

Auxin mediated elevated CO2-induced stolon growth and soluble sugar accumulation in creeping bentgrass

Stolon is crucial for competitive ability, stresses tolerance, as well as carbohydrate and nutrition storage in plants. In our previous study, stolon growth as well as the content of both indole-3-acetic acid (IAA) and carbohydrates (glucose, sucrose, and fructose) in stolon nodes and internodes were found to be increased due to elevated CO2 in stoloniferous creeping bentgrass. The objectives of this study were to determine the roles of auxin and the underlying mechanism of auxin in regulating elevated CO2-induced improvement on stolon growth and carbohydrate accumulation in stolon nodes and internodes of creeping bentgrass. Plants were treated with foliar applications of auxin (1-naphthalene acetic acid, NAA) and auxin transport inhibitor (2,3,5-triiodobenzoic acid, TIBA) at different concentrations to observe their effects on stolon growth. Hence, 10 mg⋅L−1 NAA and 100 mg⋅L−1 TIBA were selected as optimal concentrations to foliarly spray plants grown under either ambient CO2 (400 µmol⋅mol−1) or elevated CO2 (800 µmol⋅mol−1). Under water control and NAA treatments, stolon growth (stolon internode number, total stolon length, and stolon biomass) and contents of carbohydrate (glucose, sucrose, and fructose) were significantly increased by elevated CO2, but no positive effects were found in TIBA treatments in stolon nodes and internodes of creeping bentgrass. The results confirmed that IAA mediated elevated CO2-enhancement in stolon growth and carbohydrates accumulation in stolon nodes and internodes. The increase in IAA level was mainly associated with genes involved in auxin synthesis and transport in stolon nodes and internodes of creeping bentgrass. Our results would provide new insights for the rapid growth of stoloniferous plants under the scenario of continuous rise of the atmosphere CO2 concentration.

Reallocation of Soluble Sugars and IAA Regulation in Association with Enhanced Stolon Growth by Elevated CO2 in Creeping Bentgrass.

Extensive stolon development and growth are superior traits for rapid establishment as well as post-stress regeneration in stoloniferous grass species. Despite the importance of those stoloniferous traits, the regulation mechanisms of stolon growth and development are largely unknown. The objectives of this research were to elucidate the effects of the reallocation of soluble sugars for energy reserves and endogenous hormone levels for cell differentiation and regeneration in regulating stolon growth of a perennial turfgrass species, creeping bentgrass (Agrostis stolonifera L.). Plants were grown in growth chambers with two CO2 concentrations: ambient CO2 concentration (400 ± 10 µmol mol−1) and elevated CO2 concentration (800 ± 10 µmol mol−1). Elevated CO2 enhanced stolon growth through increasing stolon internode number and internode length in creeping bentgrass, as manifested by the longer total stolon length and greater shoot biomass. The content of glucose, sucrose, and fructose as well as endogenous IAA were accumulated in stolon nodes and internodes but not in leaves or roots under elevated CO2 concentration. These results illustrated that the production and reallocation of soluble sugars to stolons as well as the increased level of IAA in stolon nodes and internodes could contribute to the enhancement of stolon growth under elevated CO2 in creeping bentgrass.

Responses to elevated carbon dioxide for postdrought recovery of turfgrass species differing in growth characteristics

AbstractElevated CO2 concentration affects plant responses to drought, but its effects on poststress recovery for perennial grass species with different growth habits are unclear. The objective was to determine how stoloniferous and bunch‐type grass species may exhibit differential responses to elevated CO2 concentration during drought stress and postdrought recovery upon rewatering due to different growth characteristics. Stoloniferous creeping bentgrass (Agrostis stolonifera L.) ‘Penncross’ and bunch‐type tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] ‘Sitka’ were grown at ambient CO2 (400 μl L−1) or elevated CO2 concentration (800 μl L−1) repeated in four growth chambers for 28 d, subsequently subjected to either irrigation (control) or drought stress (irrigation completely withheld) for 28 d, and then rewatered for 18 d. During drought stress, both species exposed to elevated CO2 maintained higher turf quality, leaf water content, and membrane stability than plants at ambient CO2. Elevated CO2 caused significant increases in the viability of stolon–node meristematic tissues in creeping bentgrass under drought stress and rapid regeneration of daughter plants during rewatering, as shown by increased shoot biomass and percent turfgrass cover. Elevated CO2 had no significant effects on the viability of crowns with meristematic tissues in tall fescue during drought nor shoot biomass or percent turfgrass cover during rewatering. The stoloniferous grass species was more responsive to elevated CO2 compared to bunch‐type species for poststress recovery, as creeping bentgrass rapidly regrew and recovered from drought damages. Such information is of great importance for making appropriate turfgrass selections and breeding improvements in growth habits in areas with prolonged drought and the anticipated rising CO2 levels.

Regenerative capacity and response to pre‐emergent herbicides by stolon fragments of triquetrous murdannia (Murdannia triquetra) in rice

AbstractTriquetrous murdannia is an annual stoloniferous weed commonly found in wheat‐rice rotation fields in China. Disturbance after wheat harvesting can fragment stolons of triquetrous murdannia, and the regeneration of these fragments may contribute to the spread of this weed. In this study, the regenerate capacity and response to pre‐emergence (PRE) herbicides of stolon fragment of triquetrous murdannia were evaluated in a screenhouse. The experiment consisted of two types of single node fragments (2‐cm stolon node and five‐leaf stolon tips) placed under different floating, flooding and burial depth conditions. Results indicated that floating depth did not influence the survival of the two types of fragments but significantly decreased their growth (stolon length, number of branches, and biomass). The stolon nodes were more sensitive to flooding than stolon tips; no stolon node survived at a flooding depth of 6 cm. The highest survival was observed for fragments placed on the soil surface, and no fragments buried to a depth of 2 cm survived. PRE application of benzobicyclon, butachlor, metazosulfuron, and triafamone significantly decreased the branching and biomass of the stolon nodes; however, only triafamone and metazosulfuron significantly inhibited the regeneration of the stolon tips. These results suggest that stolon fragments with one node are likely to promote vegetative reproduction in triquetrous murdannia, and thus, disturbance may contribute to the spread of this weed. Tillage to bury fragments below their maximum regeneration depth and application of an effective PRE herbicide could serve as important tools for managing triquetrous murdannia.

Unusual developmental morphology and anatomy of vegetative organs in Utricularia dichotoma\u2014leaf, shoot and root dynamics

The terrestrial carnivorous species Utricularia dichotoma is known for a great phenotypic plasticity and unusual vegetative organs. Our investigation on 22 sources/populations revealed that after initiation of a leaf and two bladders on a stolon, a bud was formed in the proximal axil of the leaf, developing into a rosette with up to seven organs. The first two primordia of the bud grew into almost every possible combination of organs, but often into two anchor stolons. The patterns were generally not population specific. The interchangeability of organs increased with increasing rank in the succession of organs on stolon nodes. A high potential of switching developmental programs may be successful in a fluctuating environment. In this respect, we were able to show that bladders developed from anchor stolons experimentally when raising the water table. Anatomical structures were simple, lacunate and largely homogenous throughout all organs. They showed similarities with many hydrophytes, reflecting the plant’s adaptation to (temporarily) submerged conditions. The principal component analysis was used in the context of dynamic morphology to illustrate correlations between organ types in the morphospace of U. dichotoma, revealing an organ specific patchwork of developmental processes for typical leaves and shoots, and less pronounced for a typical root. The concept and methods we applied may prove beneficial for future studies on the evolution of Lentibulariaceae, and on developmental morphology and genetics of unusual structures in plants.

Transgenic creeping bentgrass plants expressing a Picea wilsonii dehydrin gene (PicW) demonstrate improved freezing tolerance.

Agrostis stolonifera L. 'Penn A-4' is a common creeping bentgrass species that is widely used in urban landscaping and golf courses. To prolong the green stage of this grass, a dehydrin gene PicW isolated from Wilson's spruce (Picea wilsonii) was transformed into plants of 'Penn A-4' cultivar via a straightforward stolon node infection system. A putative transgenic plant was obtained and its tolerance to low-temperature stress was evaluated. When the transgenic line was subjected to a freezing (- 5°C) treatment, it showed better viability and more robust physiology than wild type, as evidenced by higher soluble sugar and proline contents, and lower relative electrical conductivity and malondialdehyde content. The transgenic line also showed tolerance to a chilling treatment (5°C), although its performance was not significantly different from that of wild-type plants. Overall, the research here clearly revealed the explicit role of PicW in increasing freezing tolerance of grass at the whole-plant level, and demonstrated that the straightforward stolon node transformation method could be well used to genetically modify turfgrass. The obtained transgenic line might be as genetic resource for breeding program and practiced to grow in cold temperate zones.

Sodium Chloride Transport in the Stolons of Zoysia matrella in a Heterogeneous Saline Environment

Zoysia matrella Merr. can tolerate salt. However, nothing is known about NaCl transport in the stolon between ramets. We examined how much NaCl is transported to other ramets via the stolons to enhance understanding of the salt tolerance mechanisms from the perspective of physiological integration. In this study, interconnected clonal stolon ramets were grown in three separate pots (basal [BR], intermediate [IR], and apical ramets [AR]), such that the stolons were not touching the soil (SNTS). The study was conducted in two experimental plots: (A) all ramets were irrigated with tap water (control), and (B) IR was irrigated with NaCl solution, while BR and AR were irrigated with tap water (NaCl application in IR). For the IR irrigated with NaCl solution, the leaves, stolons, and roots had higher Na+ and Cl− concentrations than those of the ramets irrigated with tap water. In comparisons of BR and AR, there were no significant differences in the Na+ or Cl− contents of each part of the ramet, compared with plants irrigated with tap water. In the SNTS irrigated with NaCl solution, the leaves and stolons contained more Na+ and Cl− than those irrigated with tap water. From these results, it was found that until a stolon node touches the ground and develops roots, Na+ and Cl− are transported through the stolon. However, for interconnected ramets under heterogeneous saline conditions, there are two hypotheses: NaCl might be diluted with water in BR and AR, or NaCl is not transported from IR to either BR or AR after ramets are established.

들잔디 재배지에 발생한 총생 증상 및 형태적 특성

Yellow tuft symptoms of a dense cluster on zoysiagrass (Zoysia japonica Steud.) occurred extensively at cultivated fields of zoysiagrass sods in Jangsung. The dense cluster of zoysiagrass showed significant morphological changes such as the tufts of shortening of internodes. The disease symptom was spread on a large scale throughout stolon nodes with multiple short leaves and it thrives in broom-like shaped clusters, exhibiting light green or yellow color on their leaves. The dense cluster of zoysiagrass had approximately 5.8 times more leaves on each node of its stolon then healthy zoysiagrass. Also, these zoysiagrass had poorly developed root and stolon caused by the tufts of a dense cluster of shoots. The dense cluster of zoysiagrass were collected for the putative causal agent incubation and upon close observation, it was found that the sporangia took the shape of a lemon, each sporangium was pointed at the end of its axis and was measured to be 60~96×42~51 μm. These findings were analogous to the mycological characteristics of sporangia formed by the pathogen Sclerophthora macrospora. The symptoms of yellow tuft were prevalent in spring and autumn. Therefore, this study aims to present fundamental data in relation to yellow tuft on zoysiagrass in Korea.

Effects of node position on regeneration of stolon fragments in congeneric invasive and native Alternanthera species in China

AbstractVegetative regeneration plays an important role in the adaptation of clonal plants in frequently disturbed habitats, but few studies have compared vegetative regeneration capacity of invasive clonal plants with that of their native congeners. Vegetative regeneration capacity from shoot nodes can also be affected by the position of the nodes, but this appears little studied. We conducted a greenhouse experiment with Alternanthera philoxeroides, a highly invasive species in China, and its native congener A. sessilis to test the difference in vegetative regeneration capacity of stolon nodes at five different positions (i.e. 3rd, 4th, 5th, 6th and 7th node starting from the apex of the stolon). At the end of the experiment, we counted and harvested all regenerated plants and determined their biomass and allocation. Both species could successfully regenerate from stolon fragments and node position significantly affected regeneration rate and subsequent growth. However, the vegetative regeneration capacity of A. philoxeroides was not higher than that of A. sessilis. These results suggest that vegetative regeneration from stolon fragments may not be a trait that can explain the invasiveness of A. philoxeroides.

포장생육 잔디 포복경을 이용한 잔디 형질전환에 있어서 살균방법의 영향

Zoysiagrass (Zoysia japonica Steud.) is an important forage and turfgrass that spreads by stolons and rhizomes. Zoysiagrass stolon can be used directly for Agrobacterium-mediated genetic transformation by exploiting the potential of direct shoot formation. However, surface sterilization of field-grown stolons is difficult and remains to be explored. We developed an effective surface sterilization and culture method using the stolon explant for infection with Agrobacterium tumefaciens. Among various treatments, sequential disinfection in 30% bleach for 15 min followed by 0.1% mercuric chloride for 25 min resulted in the highest number of clean stolons. The efficacy of mercuric chloride was increased under vacuum conditions by incubating at 800 mbar for 5 min. The inclusion of 2.5 mg/l amphotericin B further prevents fungal growth in in vitro cultures. This protocol would speed up the development of transgenic plants by utilizing field-grown stolon nodes.

Differentiation rule of Amomum villosum Lour floral bud

Objective To study the differentiation rule of Amomum villosum Lour floral bud.Methods The stolon network of Amomum villosum Lour was classified into a few grades,The stolon length was measured.The stolon node and floral bud numbers were calculated.Results Flowers distributed from 6th to 10th nodes of stolon,but mainly on the 7th,8th,and 9th nodes.The 7th node was the most favorable position for flower differentiation.There were differences among the three breeds in floral bud numbers,node numbers and the ratio.Conclusions The node number within a grade of stolon network is a breed characteristic.The ratio is an indicator for the extent of floral bud differentiation and clear the differentiation rule of Amomum villosum Lour. Key words: Amomum villosum Lour; Stolon; Floral bud; Differentiation

Transgenic zoysiagrass (Zoysia japonica) plants obtained by Agrobacterium-mediated transformation

Zoysiagrass (Zoysia japonica Steud.) is an important turfgrass that spreads by stolons and rhizomes. By exploring the potential of direct shoot formation from stolons, we developed a straightforward and efficient transformation protocol without callus induction and propagation. Sterilized stolon nodes were infected and co-cultivated with Agrobacterium tumefaciens harboring pCAMBIA vectors. Hygromycin phosphotransferase gene (hph) was used as the selectable marker and hygromycin was used as the selection agent. Both green and albino shoots were directly regenerated from the infected stolon nodes 4-5 weeks after hygromycin selection. Greenhouse-grown plants were obtained 10-12 weeks after Agrobacterium-mediated transformation. Based on the number of transgenic plants obtained and the number of stolon nodes infected, a transformation frequency of 6.8% was achieved. Stable integration of the transgenes in the plant genome was demonstrated by PCR and Southern blot hybridization analyses. Expression of the transgenes was confirmed by RT-PCR analysis and GUS staining. The new transformation system opens up new opportunities for the functional characterization of genes and promoters and the development of novel germplasm in zoysiagrass.

Influence of Late‐Season Iron, Nitrogen, and Seaweed Extract on Fall Color Retention and Cold Tolerance of Four Bermudagrass Cultivars

Late‐season fertilization of bermudagrasses (Cynodon spp. L.C. Rich.) in the transition zone of the United States has traditionally been not recommended. This study was conducted to determine whether late‐season fertilization could extend the duration of turfgrass color retention and visual quality without negatively impacting cold tolerance. Field plots of ‘Midiron’ and ‘Tifway’ bermudagrasses (C. dactylon × C. transvaalensis Burtt Davy), as well as ‘Princess‐77’ and ‘Riviera’ bermudagrasses [C. dactylon (L.) Pers. var. dactylon] received applications of seaweed extract (SWE) (0.54 kg ha−1), N (49 kg ha−1), and Fe (1 kg ha−1) every 3 wk during the fall of 2001 and 2002. Visual turfgrass assessment showed that cultivar color ratings decreased as the fall progressed, with Princess‐77 having greatest color retention in November of both years. Nitrogen was the only treatment to increase turfgrass color ratings relative to the control at the end of each growing season. Stolon samples removed from acclimated plants were artificially frozen to determine freezing tolerance. Midiron displayed the best freezing tolerance followed by Riviera, Tifway, and Princess‐77. Chemical treatments did not have a significant effect on shoot regrowth from stolon nodes after freezing. In both years Midiron and Riviera displayed the quickest and greatest amount of spring greenup followed by Tifway and then Princess‐77. Cold tolerance indicators proline and linolenic acid were highest in Midiron, followed by Riviera, Tifway, and Princess‐77. Nitrogen, SWE, and Fe did not generally have an effect on linolenic acid and no consistent effects of these chemical treatments were noted on proline concentration. The results of this study indicate that judicious N applications during the fall can promote color retention and do not have a negative effect on bermudagrass cold tolerance.

Rapid and efficient production of transgenic bermudagrass and creeping bentgrass bypassing the callus formation phase.

Callus culture has been an inevitable step in genetic transformation of monocotyledonous (monocot) species. The induction and maintenance of embryogenic calluses is time-consuming, laborious and also requires experience. A straightforward and callus-free transformation procedure was developed and demonstrated for two monocot species, bermudagrass (Cynodon spp.) and creeping bentgrass (Agrostis stolonifera). Stolon nodes were infected and co-cultivated with Agrobacterium tumefaciens harboring pCAMBIA or pTOK233 binary vectors. Green shoots were directly produced from infected stolon nodes 4-5 weeks after hygromycin selection. Without callus formation and with minimum tissue culture, this procedure allowed us to obtain well-rooted transgenic plantlets in only 7 weeks and greenhouse-grown plants in only 9 weeks. The established plants were screened by PCR; the transgenic nature of the plants was demonstrated by Southern hybridisation analysis. Expression of the transgenes was confirmed by northern hybridisation analysis and GUS staining. Based on the number of transgenic plants obtained and the number of stolon nodes inoculated, transformation frequencies of 4.8%-6.1% and 6.3%-11.3% were achieved for bermudagrass and creeping bentgrass, respectively. The rapid and efficient production of transgenic plants without callus induction is a significant improvement for genetic transformation of monocot species.

The White Clover enod40 Gene Family. Expression Patterns of Two Types of Genes Indicate a Role in Vascular Function

Enod40 is one of the genes associated with legume nodule development and has a putative role in general plant organogenesis. We have isolated a small enod40 gene family from white clover (Trifolium repens), with three genes designated Trenod40-1, Trenod40-2, and Trenod40-3, all containing the conserved enod40 regions I and II. Trenod40-1 and Trenod40-2 share over 90% homology in the transcribed regions and high levels of similarity in their upstream regulatory sequences. Trenod40-1 and Trenod40-2 are similar to the enod40 genes of legumes forming indeterminate nodules (group II) and are predominantly expressed in nodules. Trenod40-3 shares only 32.8% identity with Trenod40-1 and Trenod40-2 within the transcribed region. Trenod40-3 is similar to the enod40 genes of legumes with determinate nodules (group I) and is not predominantly expressed in nodules. To our knowledge, this is the first report of both group I- and group II-type enod40 genes being expressed in a single legume species. In situ hybridization studies revealed that Trenod40 genes were highly expressed in non-symbiotic tissues, particularly in stolon nodes during nodal root and lateral shoot development. High levels of Trenod40 transcripts were also present in the vascular bundles of mature plant organs, mainly at sites of intensive lateral transport, suggesting a role in vascular tissue function. The expression pattern of Trenod40 genes was analyzed further using Trenod40 promoter-gus fusions in transgenic white clover and tobacco (Nicotiana tabacum), indicating that white clover and tobacco share the regulatory mechanisms for Trenod40-1/2 promoters and some aspects of Trenod40-3 regulation.

Growth potential of buds of two contrasting cultivars of white clover during winter and early spring

In order to compare the growth potential of buds of two contrasting cultivars of white clover (Trifolium repens L.) (cv. AberHerald and Grasslands Huia) during the winter–early spring period, we adapted a method to assess the potential for activity of shoot buds and root primordia. The growth potential was evaluated following the excision of individual stolon nodes sampled in the field, from experimental plots located in the eastern part of France. Two populations of nodes were sampled: (i) the youngest node emerged from the apical bud (node 1), (ii) the third node behind the apex (node 3). The excised nodes were placed in controlled conditions and the outgrowth of axillary buds and roots was recorded every day for a week. The study demonstrated a seasonal influence on the potential for activity of axillary buds and root primordia, particularly for buds at node 3. The proportion of potentially active shoot and root buds was less than 50% at the end of March, and then increased from end of March to reach 80% in April. The data indicated a genetic variation in potential for outgrowth during winter. AberHerald had a higher percentage of potentially active buds than Huia during winter, irrespective of the node position. Moreover AberHerald buds had faster rates of outgrowth than Huia buds. Differences between cultivars in winter survival and potential for growth in spring were linked to identified cultivars' differences in developmental characteristics of buds.

Growth of White Clover Ecotypes, Cultivars, and Germplasms in the Southeastern USA

ABSTRACTNaturalized populations, or ecotypes, of white clover (Trifolium repens L.) are found in many southeastern U.S. pastures, often persisting despite adverse environmental and cultural conditions. Our objective was to compare the growth, morphology, and vegetative persistence of white clover ecotypes (small‐ to medium‐leaf) with selected cultivars (large‐leaf) and improved germplasm under grazing in four southeastern states. Seed or stolons of white clover ecotypes were collected primarily from grazed pastures in spring 1994 in Louisiana, Mississippi, Alabama, and Georgia, and increased by intercrossing. Plots of seven ecotype collections, ‘Osceola’, ‘Regal’, ‘Louisiana S‐1’, ‘Grasslands Huia’, ‘Grasslands Prestige’, Brown Loam Synthetic No. 2 germplasm, and Southern Regional Virus Resistant germplasm were established in October 1995 in each state. Plots were stocked continuously with cattle (Bos taurus) (5‐cm stubble) from January 1996 to January 1998. Stolon length and axillary bud viability, and number of stolon apices, rooted nodes, and seedlings were measured every 3 mo. Stolon length of the ecotypes usually exceeded that of the cultivars and germplasm at all locations, particularly in the winter and spring. By the end of the experiment, the ecotypes also exhibited greater stolon branching than the cultivars and germplasm (1580 vs. 320 branches m−2). Superior vegetative growth of the ecotypes was attributed to a greater proportion of the stolon nodes being both branched and rooted, particularly during the summer. White clover ecotypes represent a valuable source of germplasm to incorporate into breeding programs or to develop directly into more persistent cultivars.

Evidence For Root Contraction In White Clover (Trifolium repens L.)

White clover (Trifolium repens L.) stolons become buried in the field. It was observed that this also occurred in the greenhouse where the accepted mechanisms of burial, treading by livestock and earthworm casting, did not occur. It was also observed that the crown of seedling T. repens plants become closely appressed to the soil. Experiments showed that, regardless of variety of T. repens or depth of planting, all seedling hypocotyls first lift the cotyledons clear of the soil, then ‘ contract’ towards the soil until the cotyledons are in contact with or below the soil surface. Auxanometers were used to measure the rate and extent of this contraction and were also attached to stolon nodes in experiments which showed that stolons move downwards relative to the soil surface and that the speed and extent of this duration varied with soil type. A further experiment showed that only rooted nodes show this behaviour. The force exerted by the contraction of nodal roots was estimated experimentally as 0.21 N g-1fresh root. A mechanism for the root contraction, based on examination of root anatomy of seedling tap-roots and nodal roots, is suggested. These experiments provide evidence for root contraction in T. repens which may lead to stolon burial. The importance of this to T. repens as a pasture species and as a means of further improving T. repens varieties is discussed.

Seasonal Variation in Morphology of Continuously Stocked White Clover

Efforts to improve persistence of white clover (Trifolium repens L.) in the southeast USA would benefit from knowledge of annual growth patterns and associated periods of environmental stress. Our objective was to determine seasonal changes in morphological traits that contribute to plant growth and persistence among adapted cultivars and germplasm. ‘Louisiana S‐l’, ‘Osceola’, Brown Loam Synthetic No. 2 germplasm, and Southern Regional Virus Resistant germplasm were sown in common bermudagrass [Cynodon dactylon (L.) Pers.] pastures in September 1993 at Mississippi State and Newton, MS, and continuously stocked with cattle to maintain a 5‐ to 10‐cm sward height. Stolon length, viability of axillary buds, and seedling numbers were measured monthly for the next 2 to 3 yr. Stolon length of all entries increased to a maximum by June before declining to a minimum in October. Peak stolon production in the first, second, and third year after seeding at Mississippi State was 42, 123, and 59 m m−2, respectively. There were no monthly differences among the four entries for proportion of stolon nodes having elongated, viable, or nonviable axillary buds at either location. The proportion of nodes with elongated buds increased from 10 to 20% in October to 45% in March before declining during the spring. An increase in elongated buds during early summer preceded the fall decline. Number of volunteer seedlings ranged from 10 to 1870 m−2 during the year, but any positive influence on stand persistence was not apparent. The cyclical trends for axillary bud viability indicate continued potential for vegetative persistence, particularly in the winter and spring, but the longterm decline in stolon length of all entries suggests that selection for different characters was not associated with improved persistence.