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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-I', `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.sup-.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.sup.-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 long-term decline in stolon length of all entries suggests that selection for different characters was not associated with improved persistence., White clover persistence is dependent on vegetive proliferation of stolons in New Zealand (Chapman, 1987) and in the United Kingdom (Turkington et al., 1979), two countries with temperate climates recognized [...]

Natural reseeding of subterranean clover (Trifolium subteranneum L.) grown with a warm-season gram in the southern USA depends on the proper softening rate of bard seed. Three experiments were each conducted over 2 yr to determine (t) the rate of seed softening, (ii) the cause of reduction in seed softening over time, and 0h) the effect of dipping management on seed softening. In all experiments, subterranean clover hard seed were placed in dacron limp and buried 1 cm deep in field plots. In Exp. 1, bags were placed in bermudagrass [(Cynodon dactylon (L.) Pers.] sod and in bare ground in July and sampled over the summer and fail. In Exp. 2, bags were placed *in sod and bare ground and replaced with separate samples at intervals of 28 d throughout the summer and &I. In Exp. 3, begs were buried in bare ground or sod that was clipped monthly to 7.5 an or biweekly to 2 cm starting in August, September, or October. Hard seed softened more rapidly in bare ground than in sod, reaching a minimum of 15.6 and 49.0%, respectively. The softening of hard seed over 28-d intervals decreased from 75.5 and 67.1% in July to 92.6 and 93.2% in November for sod and bare ground, respectively. Fag clipping management had no effect on bard seed softening rate of subterranean clover, reaching a minimum of 64.0% bard seed averaged over all sod clipping treatments compared to 47.0% hard seed for bare ground. Results indicated that subterranean clover reseeding ability should be evaluated under the same environment as the clover is used., Subterranean clover, a cool-season annual legume can be sown into warm-season grasses to provide additional high quality forage during the winter when the grass is dormant (Fairbrother et al., 1992). [...]

Winter hardiness of 'Bigbee' berseem clover (Trifolium alexandrinum L.) was reported to differ between plants grown from certified seed and breeder seed. Winter growth form also differed, with plants from breeder seed forming a rosette and plants from certified seed elongating. To determine if growth form differences were due to a change in vernalization response, imbibed seeds of Bigbee certified and breeder seed and certified 'Multicut' were vernalized at 2 [degrees] C for 0 to 6 wk in weekly increments. Seeds from all treatments were simultaneously germinated and grown in a greenhouse under 18-h daylength. Days to flowering, node at first flower, and the number of nodes below 5 cm at flowering were recorded. Replicated experiments were conducted with germination dates of 17 Aug. 1992 and 25 Feb. 1993. The regression of days to flowering and node at first flower on vernalization period was significant for Bigbee certified and breeder seed. Response slopes of Bigbee plants grown from certified and breeder seed differed from each other for all variables. As vernalization period decreased, plants from Bigbee breeder seed flowered later and at a higher node than plants from Bigbee certified seed. Vernalization had no effect on days to flowering or node at first flower for Multicut. Variation in vernalization response between Bigbee breeder seed and certified seed indicated that a change occurred during the production of certified seed. Multicut and Bigbee certified seed may have less winter grazing tolerance than Bigbee breeder seed since there were fewer nodes near the soil line to support regrowth.

Cyanogenesis, the production of hydrocyanic acid, is a trait in white clover (Trifolium repens L.) controlled by alleles at two unlinked loci, Ac and Li. The objectives of this study were (i) to determine the proportion of cyanogenic plants in the accessions of the U.S. white clover germplasm collection, (ii) to determine how representative the core subset was of the entire collection for cyanogenesis, and (iii) to determine the relationship of cyanogenesis, in accessions collected in situ, to collection site and climate. Twenty plants from each of 548 white clover accessions were grown in the greenhouse from 1991 to 1993. Two to three leaves per plant were harvested and the presence or absence of hydrocyanic acid was determined by the picric acid test. The U.S. germplasm collection was predominantly acyanogenic with a third of the plants evaluated being cyanogenic. Accessions with the most cyanogenic plants were collected in Morocco, Spain, Portugal, France, and Turkey while the least cyanogenic plants were collected in China, Romania, Russia, Kazakhstan, Croatia, Bosnia-Herzegovina, and Slovenia. Accessions collected in Morocco, Portugal, and Spain had the greatest intensity of cyanogenic reaction. Geographic stratification with random sampling was an effective method of developing a core subset, as the white clover core subset was representative of the entire collection for total cyanogenesis and distribution of cyanogenic plants. Cyanogenic frequency was greater in accessions collected at low altitudes and at sites with high winter temperatures, lower summer precipitation, greater spring cloudiness (% sunshine), and less snow cover. Latitude of collection was not associated with cyanogenic frequency in white clover.

Forage digestibility is influenced by plant cell wall composition. We compared changes in cell wall composition of the herbage and plant fractions of four clovers differing in life cycle and growth habit and examined the relationship between digestibility and cell wall composition in these plant fractions. Primary spring growth of berseem (Trifolium alexandrinum L.), red (T. pratense L.), subterranean (T. subterraneum L.), and white (T. repens L.) clover was harvested in each of 2 yr beginning in late March and thereafter every 10 d (eight harvests total). Cell wall, hemicellulose, cellulose, and lignin concentration were determined for leaf, petiole, stem, and reproductive fractions and herbage at each harvest. Herbage cell wall concentration of berseem, red, and white clover increased 3.1, 2.4, and 0.8 g [kg.sup.-1] [d.sup.-1], respectively. Maximum herbage cell wall concentrations of annual berseem and subterranean clover herbage were greater than those of perennial red and white clover (500 and 497 vs. 425 and 280 g [kg.sup.-1], respectively). With the exception of subterranean clover, leaf cell wall concentration of all clovers ranged from [is approximately equal to] 200 to 300 g [kg.sup.-1]. Trends for stem cell wall and hemicellulose concentration of erect-growing berseem and red clover were similar, while petiole cell wall and hemicellulose trends were similar for annual berseem and subterranean clover. Herbage and plant fraction cell wall concentration were negatively correlated with digestibility due primarily to the inverse relationship between digestibility and cell wall-lignin concentration. The minor differences in leaf cell wall concentration during primary spring growth indicate minimal differences exist among these clovers in relation to their value to grazing ruminants.

An impermeable seedcoat or hardseededness is the most important germination regulation mechanism in subterranean clover (Trifolium subterraneum L.). Hardseededness breakdown rate has been evaluated by exposing hard seed to fluctuating temperature (60/15 [degrees] C) for 6 mo. Our objective was to compare four methods for evaluating breakdown rates of hardseededness from four subterranean clover cultivars and to determine if the Weibull model accurately described the loss of hardseededness with time. The Weibull model accurately described the loss of hardseededness with time of 24 legume genotypes with diverse softening rates from data reported in the literature. Hard seed from greenhouse-grown plants of |Nungarin', |Meteora', |Trikkala', and |Mount Barker' were tested for hardseededness breakdown rate in 1988 and 1989. Hardseededness breakdown rate was determined by using diurnal fluctuating temperature methods of 60/15 [degrees] C in Australia or 47/25 [degrees] C in the USA and constant temperature method of 50 or 60 [degrees] C followed by 7 d of 60/15 [degrees] C fluctuating temperature. The Weibull model accurately described the loss of hardseededness with time of all treatments ([S.sub.y.x] = 4.35). Meteora was the slowest to soften followed by Nungarin, Mt. Barker, and Trikkala. The U.S. temperature treatment softened seed the slowest followed by Australia's, 50 and 60 [degrees] C. All temperature methods ranked cultivars in the same order for hardseededness breakdown rate. Variation among cultivar softening rate was measured in 112 fewer days by the constant temperature methods compared to the fluctuating temperature methods.

Forage quality of clover (Trifolium spp.) may be influenced by changes in nutrient concentration of morphological fraction as a function of growth habit or life cycle. We compared the dry matter (DM) accumulation trends of four clovers differing in growth habit and life cycle, and determined the influence of plant fraction nutritive value on total forage quality. Primary spring growth of berseem (T. alexandrinum L.), red (T. pratense L.), subterranean (T. subterraneum L.), and white (T. repens L.) clovers was harvested in each of 2 yr beginning in late March, and thereafter every 10 d (eight harvests total). Digestible dry matter (DDM) and crude protein (CP) concentration were determined for leaf, petiole, stem, and reproductive fractions, and total forage of each species at each harvest. Total DM accumulation of berseem and red clover increased linearly to a maximum of 547 and 407 g DM m to the -2, respectively, by Day 61, while that of subterranean and white clover increased nonlinearly to a maximum of 336 and 219 g DM m to the -2, respectively, by Day 51. Days to maximum accumulation of stem DM in erect species and petiole DM in prostrate species corresponded with maximum total DM accumulation in the respective species. Leaf-to-stem weight ratio ranged from 0.27 to 1.42 for berseem clover and from 1.10 to 3.04 for white clover, although quadratic trends for leaf DM accumulation for the two species were similar. Mean DDM of berseem and red clover forage declined 2.0 g kg to the -1 d to the -1. Based on trends for dry matter accumulation and nutrient concentration of the leaf fraction, subterranean and white clover merit consideration equal to berseem berseem and red clover as pasture legumes.

B1, B2, B3, and B4 berseem clover (Trifolium alexandrinum L.) germplasms, (Reg. no. GP192 to 195, PI 606771 to 606774), were released in 1998 by the USDA-ARS and the Mississippi [...]

Bean yellow mosaic virus-resistant berseem (BYMVRB) clover (Trifolium alexandrinum L.) germplasm (Reg. no. GP196, PI 606775), was released in 1998 by the USDA-ARS and the Mississippi Agricultural and Forestry Experiment [...]