Number Of Stolons Research Articles

Development of a breeding strategy for interspecific hybrids between Caucasian clover and white clover

A single 8× F1 hybrid between Caucasian clover (T. ambiguum) and white clover (T. repens) was backcrossed to seven white clover plants to generate fertile 6× BC1 families. To determine the most useful combination of desired traits of both parental species, and to develop a breeding strategy for this population, subsequent generations were produced in various ways. Self‐pollination and intercrossing among BC1F1 families produced F2, and later, F3 and F4 generations. Second, third and fourth backcrosses to white clover produced BC2, BC3 and BC4 generations. All generations were compared with the parental species in a single experiment grown in sand. Expression of the desired below‐ground traits of Caucasian clover was best in the BC1 generation. By contrast, the best expression of the desired above‐ground white clover traits was shown by the BC2F1 generation. However, the BC2F1 was pentaploid and did not stably transmit its desirable features to subsequent generations. On the other hand, advancement in the BC1 from F1 to F4 revealed significant positive variation in most of the important traits and suggested that selection would be successful. A breeding strategy was developed based on the genetically stable BC1 generation, advancing to BC1F6 by selecting for increases in shoot dry matter (DM), stolon numbers, stolon growth, improved nodal rooting radius, larger numbers of flowers and high fertility and seed‐set.

Produção de mudas de morangueiro em casa-de-vegetação utilizando recipientes suspensos

Este trabalho foi realizado com o objetivo de quantificar o potencial de propagação de dez cultivares de morangueiro em casa-de-vegetação, utilizando recipientes suspensos. Os tratamentos foram constituídos pelas cultivares Aromas, Bürkley, Camarosa, Campinas, Dover, Milsei-Tudla, Oso Grande, Santa Clara, Sweet Charlie e Vila Nova. Em casa-de-vegetação, plantas matrizes foram individualmente plantadas em sacolas plásticas de 5 L, contendo substrato à base de terra vegetal e esterco, e, posteriormente, alocadas em bancadas a 1,20 m de altura do solo. Os estolões foram conduzidos verticalmente, sendo a nutrição realizada exclusivamente pelas plantas matrizes. Os tratamentos foram dispostos em delineamento inteiramente ao acaso, com dez repetições de cada cultivar, representadas pelas matrizes iniciais. As características número de estolões, de mudas e de folhas por planta matriz e comprimento médio de raízes foram avaliadas 180 dias após o plantio. Considerando o conjunto de cultivares, foram produzidos, em média, 6,9 estolões por planta matriz, que produziram 27,4 mudas com 3,4 folhas desenvolvidas e raízes com 4,1 cm de comprimento. Verificou-se pronunciada variabilidade entre as cultivares para as características avaliadas. Os maiores números médios de estolões emitidos por matriz foram observados para as cultivares Dover (8,4), Camarosa (7,9), Milsei-Tudla (7,9), Sweet Charlie (7,6), Campinas (7,3) e Oso Grande (7,2). De maneira geral, o desempenho das cultivares quanto ao número de mudas produzidas por estolão apresentou resultado inversamente proporcional ao número de estolões produzidos. O maior número de mudas por estolão foi obtido com a cultivar Aromas (6,8), que diferiu significativamente das demais cultivares. Quanto ao número total de mudas, os melhores resultados foram obtidos com as cultivares Dover (34,0), Campinas (31,9), Oso Grande (30,9), Sweet Charlie (30,7), Milsei-Tudla (28,8), Vila Nova (28,0) e Aromas (27,2).

Respon Tanaman Pegagan (Centella asiatica L. Urban) Terhadap Pemberian Pupuk Alami di Bawah Naungan

The objectives of this experiment was to study the growth, yield and qualitative bioactive compounds of Indian pennyworth ( Centella asiatica L. Urban) under different shading levels and biofertilizers. Field experiment was conducted from February until May 2006 at Kuntum Nurseries Bogor. Split plot design was used in this experiment. The main plot was shading level: 55, 65 and 75%. The sub plot was biofertilizer types: Fertifort Super, Fertifort Fine and NPK Novelgro fertilizer. The result of this experiment showed that plants under the 65% shading level significantly showed better growth, biomass weight and qualitative bioactive compounds (tanin, flavonoid, steroid and triterpenoid) than those of 75% shading level. The 75% shading level was unsuitable because all plants were dead at 10 weeks after fertilizer application; the 55% shading level gave the best growth responses but 55 and 65% shading level gave no significant differences in biomass weight. Biofertilizer gave no significant differences in leaf and stolon numbers, biomass weight and physiological characteristics except NPK content in plant tissue. Significant difference occured only in N plant tissue content because of interaction with shading level. The different effect in qualitative bioactive compound showed that saponin was found in 55% shading level but not in 65% shading level. Key words: Shading, biofertilizer, qualitative bioactive compound, Centella asiatica .

HIERARCHICAL PLASTICITY OF CENTELLA ASIATICAIN RESPONSES TO MICROSITES WITH DIFFERENT HERBACEOUS COVERAGE OF FOREST EDGE AND ABANDONED GRASSLAND SLOPE

Aims In natural environments, resources of critical importance to plant growth are patchily distributed, even at a small spatial scale. The aims of this study are to address: 1) Centella asiatica exploitation of heterogeneous microsites in different habitats, 2) hierarchical effects of habitats and microsites with different herbaceous coverage on growth traits of C. asiatica, and 3) differences in hierarchical response patterns for large and small scales of heterogeneous habitats. Methods Microsites with low and high herbaceous coverage were selected in abandoned grassland slope and forest edge habitats. We measured morphological and physiological characteristics of C. asiatica in spring 2004 and 2005 at three levels: ramet population, clonal fragment and leaf. Environmental factors of different microsites were investigated again in September 2006. Important findings At the ramet population level, we observed no effect of habitat (forest edge vs. abandoned grassland slope). Root-shoot ratio of ramet population with low herbaceous coverage was significantly higher than that with high herbaceous coverage. At the level of clonal fragment, root dry weight, flower and fruit dry weight were significantly higher and internode length of primary and total stolons were shorter on abandoned grassland slope. Root-shoot ratio and number of primary stolons were significantly larger with low herbaceous coverage, but flower and fruit dry weight, internode length of secondary stolon and internode length of total stolon were lower. At the leaf level, lamina length, lamina width and lamina area were larger on abandoned grassland slope and with high herbaceous coverage. Plants with high herbaceous coverage had larger petiole length and specific petiole length. No significant effects of habitat and microsite on chlorophyll content were observed. These findings indicated that there were hierarchical effects of habitat and microsite on the growth traits of C. asiatica, and different hierarchical responses of C. asiatica to different habitats and microsites with different herbaceous coverage were observed. Plastic response to heterogeneous habitat is stronger at smaller scale than that at larger scale.

Potato minituber production using aeroponics: Effect of plant density and harvesting intervals

To optimize minituber production through aeroponics some horticultural management factors should be studied. Potato plantlets, cv Zorba, were grown aeroponically at two different plant densities (60 and 100 plants/m2). Plants showed an extended vegetative cycle of about 5 months after planting. A higher number of stolons was obtained at low plant densities. Tuber formation hastened when supplied N was reduced. Experiments on harvesting intervals (7, 10, and 14 days) indicated that for a density of 60 plants/m2, both number of minitubers and yield increased as harvesting interval decreased. Best results were achieved harvesting every 7 days: a total tuber yield of 118.6 g per plant was obtained (four times higher than for 100 plants/m2). Such a yield was composed, on the average, of 13.4 tubers with a mean tuber weight of 8.1 g. Harvesting intervals did not have an effect on the number of minitubers and yield for a density of 100 plants/m2. The best productivity obtained in this study was 800 minitubers/m2 for weekly harvests and a low plant density (60 plants/m2). We also studied the field performance of aeroponically produced minitubers vs those produced by hydroponics. Minituber behavior under field conditions was independent from the technique used for its production.

Relative susceptibility of five strawberry cultivars to Meloidogyne hapla under three soil water deficit levels

The relative susceptibility of five strawberry (Fragaria x ananassa Duch.) cultivars to the root-knot nematode (Meloidogyne hapla) was tested under three different soil water deficit levels and three nematode densities. 'Bounty' was the most susceptible cultivar and 'Glooscap' the least susceptible for parasitism by M. hapla. Percent water deficit had a positive linear effect on the number of galls on strawberry roots, and on egg production and number of M. hapla larvae in the soil, regardless of cultivar type. Different population densities of the nematode had no effect on the final number of strawberry flower clusters, stolons and crowns. The initial M. hapla population had a quadratic effect on the number of galls on strawberry roots and on the number of larvae in the soil, but had a positive linear effect on M. hapla egg production. The harmfulness of this species to strawberry total yield and fruit size is questionable and requires further investigation.

Plant Regeneration and an Analysis of Somaclonal Variation from TifEagle and TifSport Bermudagrass Cultivars

`TifEagle' (2n = 3x = 27) hybrid bermudagrass [Cynodon dactylon (L.) Pers. (2n = 4x = 36) × Cynodon transvaalensis Burtt-Davy (2n = 2x = 18)] is an ultradwarf cultivar for greens, and `TifSport' (2n = 3x = 27) is a more versatile hybrid used on fairways, athletic fields, and lawns. To develope a transformation system and determine if somaclonal variation was present in regenerated plants, both cultivars were tested for their ability to produce embryogenic callus from which plants could be regenerated. Sliced nodes of both cultivars and immature inflorescences from `TifSport' were used as the explant sources. Cultures were initiated on Murashige and Skoog medium supplemented with 6.79 μm 2,4-D and 0.044 μm BA (`TifSport' and `TifEagle') or 6.79 μm 2,4-D plus 200 mg.L-1 casein hydrolysate (`TifSport'). In total, 51 plants were regenerated from callus of a single node of `TifEagle'. Nodes from `TifSport' did not produce embryogenic callus. In total, 29 plants were regenerated from callus of `TifSport' produced from immature inflorescences. These plants were grown in the field for at least one season, and 5-cm-diameter plugs were harvested, repotted in a greenhouse, and allowed to reestablish. Data on canopy height, leaf width, leaf length, and number of stolons were collected. Seven `TifEagle'-derived entries (14%) were not significantly different (α = 0.05) from `TifEagle' harvested from the breeder plot in Tifton, Ga., for all measured traits, and 41%, 24%, and 22% differed by one, two, or three measurements, respectively. Flow cytometry indicated that 33% (13 plants) of the `TifEagle' regenerants were hexaploid (2n = 6x = 54) and the rest remained triploid. One `TifSport' regenerant was significantly different (α = 0.05) for plant height.

Root mass and depth, stolons and roots formed on stolons in four cultivars of potato under water stress

Four potato cultivars ( Solanum tuberosum L.) differing in their precocity and contrasted for their drought tolerance were investigated in the field and two of them in the greenhouse. They were subjected to two water treatments, well irrigated and droughted. We followed the evolution of stolon number, stolon length, mass of roots and the adventitious roots which are formed on stolons. Our objective was to check the response of those characters to water shortage throughout the cycle, and examine if they could have, especially the adventitious roots on stolons, contributed to drought tolerance. All physiological and agronomical studied parameters were sensitive to drought. Maximum root dry mass was reduced by drought. Stolon number was enhanced by drought but the total length of stolons, was reduced. The number of the adventitious roots on stolons was reduced by drought and negatively related to root dry mass of the plant. Fresh tuber yield was significantly correlated to root dry mass in the field and drought tolerance index was significantly associated to root depth in the field, but in stressed conditions only.

Morphological and Seed Set Characteristics of Centipedegrass Accessions Collected in China

Greater than two-fold differences were observed between the lowest and highest means for stolon number and length characteristics. A 60% difference in total length was observed between the longest stolon of accessions. There was a 42% difference between the accessions with the fastest and slowest growing stolons. Accession with the longest and shortest internode differed by 28%. Small differences were observed for leaf length and width. Seed set under selfing was less than 7% indicating high self-incompatibility. Open-pollinated seed set ranged from 37% to 87%. Coefficients of variation for the various characteristics measured indicate that the Chinese accessions should provide more variation for genetic improvement in this species. Data showed that measuring total stolon length at five weeks after transplanting was adequate for evaluating all of the stolon length and number characteristics in this study. The Chinese accession appear to be a valuable source of new germplasm for this species.

The effect of environmental heterogeneity on clonal behaviour of Prunella vulgaris L.

We studied the response of a clonal herb, Prunella vulgaris, to its position in a gap, the identity of neighbouring graminoid species, and simulation of competition for light. The growth characteristics, such as stolon length, internode length and number of stolons were recorded in competitive environments with graminoid bunches of Molinia caerulea, Juncus effusus and Nardus stricta and in different types of gaps in a manipulative field experiment. Two pot experiments studied the effect of reduced light and of low red/far red ratio (R/FR) on the plant growth characteristics. In both field and pot experiments we monitored stolon orientation in a treatment divided into two parts (competition/shaded or gap/unshaded). Methods of circular statistics were used to evaluate stolon orientation. The graminoid bunches had equivalent effects on plant vegetative growth – plants had longer stolons and internodes than plants growing in gaps. The effects of treatments on other characteristics (amounts of stolons and leaves) were not significant. In divided treatment, plants responded by accumulation of stolons and leaves in vegetation removed part, and avoided the vegetated part. In the pot experiments the plant biomass and stolon number decreased in low R/FR and in low irradiance treatments, but the internodes in low R/FR were 26% longer compared to the control. Centroids were uniformly distributed in divided low R/FR treatment contrary to low irradiance treatment where they showed preference for unshaded part. No dependency of stolon length on its orientation was found in divided treatments of both experiments. Prunella vulgaris in heterogeneous environment distinguished favourable and less favourable conditions and produced more stolons with shorter internodes under favourable conditions. This resulted in concentration of resource acquiring structures in favourable patches.

Infection by the systemic fungus Epichloë glyceriae and clonal growth of its host grass Glyceria striata

Many plant species have the ability to expand laterally through space by clonal growth. Plant pathogens can affect clonal growth characteristics thereby altering the success of host plants within populations and of clonal species within communities. We conducted a greenhouse experiment to determine the effects of the systemic fungal pathogen, Epichloe glyceriae, on clonal growth patterns of its host grass, Glyceria striata. We found that infected and uninfected plants produced similar total biomass and numbers of tillers plus primary stolons per mother ramet. However, biomass allocation to tillering (vegetative growth) vs stolon production (clonal growth) was significantly affected by pathogen infection. Infected plants produced more stolons and clonal growth biomass than uninfected plants while mother ramets of uninfected plants produced more tillers and biomass than infected plants. Stolon architecture of infected and uninfected plants also differed. In two of three populations, infected plants produced stolons with greater biomass and shorter spacer lengths, even though mean stolon lengths were similar for infected and uninfected plants. These results contrast strongly with most other clonal plant-pathogen systems where infected plants are less vigorous and have reduced clonal growth compared to uninfected plants. Greater clonal growth may be an effective mechanism for host genotypes to persist and spread when seed production is prevented, as is the case with castrating pathogens like Epichloe glyceriae.

Reproductive Development of White Clover (Trifolium repens L.) is Not Impaired by a Moderate Water Deficit That Reduces Vegetative Growth: I. Inflorescence, Floret, and Ovule Production

Field experiments have shown that water deficit can either increase or decrease white clover (Trifolium repens L.) seed yield depending on its intensity. In order to explain this behavior, we evaluated the effect of water deficit intensity on the components of plant reproductive potential: number of reproductive stolons produced per plant (NSr), inflorescences per reproductive stolon (NI), viable florets per inflorescence (NFv) and ovules per floret (NO). Four experiments were conducted in greenhouse or growth chamber on white clover plants grown in large or small soil columns, or in small pots with vermiculite. Water supply was managed to maintain relatively constant values for predawn soil water potential and midday leaf relative water content (RWC) during the deficit period (20 to 68 d). Water deficit treatments were classified as moderate (M) or severe (S) on the basis of the reduction of RWC compared with the well‐watered plants (C) and of previously established relationships between RWC, soil water potential and vegetative growth. The development of inflorescences, florets and ovules were largely unaffected in M plants, while vegetative growth was depressed by reductions in leaf number per stolon (up to 30%), leaf area (30 to 40%), and by inhibition of stolon branching. Moderate water deficits induced an increase in the percentage of reproductive stolons per plant and reproductive phytomers per stolon. Although this positive effect on the reproductive to vegetative balance was generally observed with S water deficit, the reproductive potential of S plants was strongly depressed relative to C and M plants because of reduced stolon branching, phytomer production, and increased inflorescence and floret abortion. These results show that inflorescence, floret and ovule development of white clover were not impaired by a moderate water deficit that reduced vegetative growth, and suggest good prospects to manage optimal soil‐plant status to maximize potential of seed production.

Root and shoot plasticity of the stoloniferous herb Ajuga reptans L. planted in a heterogeneous environment

Summary In a greenhouse experiment, single ramets of Ajuga reptans, a stoloniferous herb, were planted on the divider of two halves of trays. The two halves of a tray had the same or different nutrient supply. The aim was to study root and shoot plasticity and the placement of ramets and roots in response to the heterogeneous nutrient environment. Number of primary stolons, number of secondary stolons, stolon internode length, number of leaf ramets, total root length (including fine and coarse roots) and root dry weight were greater, but biomass allocation to fine and coarse roots and specific coarse root length were lower under the homogeneous nutrient-rich (the HH-treatment) than under the homogeneous nutrient-poor (the LL-treatment) conditions. No significant response was observed in specific stolon length and specific fine root length. In the heterogeneous nutrient environment (the HL-treatment), total root length, root dry weight, root biomass allocation and specific root length did not differ between the nutrient-rich and the nutrient-poor halves of the trays for both fine and coarse roots. The same response pattern was found for the number of primary and secondary stolons, the number of leaf ramets, spacer lengths between leaf-ramets (internode length) and specific stolon length. Only the number of shoot ramets was larger in the nutrient-rich than in the nutrient-poor patch. Ajuga reptans responded strongly to the different homogeneous nutrient supplies (the HH-treatment vs. the LL-treatment) in terms of morphology and growth of roots and shoots. In the heterogeneous environment (the HL-treatment), the differences in response to local nutrient conditions seemed to be reduced due to intraclonal physiological integration. Predictions of an increase in root mass in the nutrient-rich patch as compared to root mass in the homogeneous HH-treatment or even in the nutrient-poor patch of the HL-treatment were not confirmed by the results. Apparently, behaviour of clonal plants in a heterogeneous environment cannot be simply predicted from their behaviour in different homogeneous environments.

Reproductive Development of White Clover ( L.) is Not Impaired by a Moderate Water Deficit That Reduces Vegetative Growth

Field experiments have shown that water deficit can either increase or decrease white clover (Trifolium repens L.) seed yield depending on its intensity. In order to explain this behavior, we evaluated the effect of water deficit intensity on the components of plant reproductive potential: number of reproductive stolons produced per plant (NSr), inflorescences per reproductive stolon (NI), viable florets per inflorescence (NFv) and ovules per floret (NO). Four experiments were conducted in greenhouse or growth chamber on white clover plants grown in large or small soil columns, or in small pots with vermiculite. Water supply was managed to maintain relatively constant values for predawn soil water potential and midday leaf relative water content (RWC) during the deficit period (20 to 68 d). Water deficit treatments were classified as moderate (M) or severe (S) on the basis of the reduction of RWC compared with the well-watered plants (C) and of previously established relationships between RWC, soil water potential and vegetative growth. The development of inflorescences, florets and ovules were largely unaffected in M plants, while vegetative growth was depressed by reductions in leaf number per stolon (up to 30%), leaf area (30 to 40%), and by inhibition of stolon branching. Moderate water deficits induced an increase in the percentage of reproductive stolons per plant and reproductive phytomers per stolon. Although this positive effect on the reproductive to vegetative balance was generally observed with S water deficit, the reproductive potential of S plants was strongly depressed relative to C and M plants because of reduced stolon branching, phytomer production, and increased inflorescence and floret abortion. These results show that inflorescence, floret and ovule development of white clover were not impaired by a moderate water deficit that reduced vegetative growth, and suggest good prospects to manage optimal soil-plant status to maximize potential of seed production.

Variation in life history characteristics between clones of Ranunculus repens grown in experimental garden conditions

Ranunculus repens L. is a clonal perennial that occurs in a wide range of environmental conditions. This species is also a notorious weed of disturbed habitats. Life history parameters of clones from 24 Irish populations of R. repens from ruderal, marsh and turlough (temporary lake) habitat types were measured in an experimental garden across a growing season. Mother rosettes with a greater number of leaves produced a greater amount of primary stolons. Ramet production was higher in plants that produced a greater number of secondary and tertiary stolons. Growth and production of vegetative and sexual offspring did not vary with habitat types from which the clones were derived. High variability was evident between clones for all parameters measured. The extent and success of colonization by this species is therefore highly dependent on the productivity of the initial pioneer.

The role of vegetative spread and seed dispersal for optimal life histories of clonal plants: a simulation study

Sexual and vegetative reproduction of clonal plants phenotypically differ in dispersal distance, in the phenology of offspring production and establishment, and in the success of establishment. We applied a combination of analytical and of spatially explicit individual-based simulation modelling to calculate long-term fitness. We predicted optimal clonal plant life histories in a parameter space spanned by stolon number, stolon internode length, and relative allocation to sexual and vegetative reproduction. For a given allocation to sexual reproduction and number of stolons, fitness was optimised for rather short internode lengths under small disturbances, and for the longest possible internodes under larger disturbances. A trade-off between length and number of vegetative spacers drew parameters away from their unrestricted optima. Now, intermediate length and number of spacers led to maximum fitness under large disturbances. Simultaneous trade-offs between sexual and vegetative reproduction and between the length and number of spacers could also lead to fitness optima at intermediate parameter values, depending on the success of seedling establishment. We demonstrated that spatial habitat structure (1) selects for an efficient use of available space either by optimum internode length or by investment into seeds, which disperse farther than vegetative spacers, and (2) leads to an interaction between trade-offs. We conclude, that dispersal distance, i.e. a spatial life-history component, and trade-offs must be included in considerations on adaptive evolution of clonal life histories.

The effect of nitrogen on stolon and ramet growth in four genotypes of Fragaria chiloensis L.

Plant foraging response is a process in which clonal plants proliferate in nutrient-rich sites by shortening stolon length and increasing ramet density. Conversely, stolon length increases and ramet density decreases in nutrient-poor sites. Four genotypes of strawberry ( Fragaria chiloensis (L.) Duch.) were grown in a greenhouse for 10 weeks and treated with different concentrations of nitrogen. Genotypes differed in plant size, stolon and ramet production, and nitrogen distribution between parent and ramets. Genotype Q18 were the smallest plants with the greatest number of stolons and ramets, typical of the phalanx morphology. The other genotypes had fewer but longer stolons, typical of the guerrilla morphology. Number of stolons and ramet density increased with increased N more in Genotype Q18 than the other genotypes. Results indicate that vegetative growth changed in response to increasing N treatment of the parent plant by shortening the average stolon length, increasing the number of stolons, and increasing the number of ramets while maintaining total stolon length. Foraging response characteristics were observed in strawberry but varied among genotypes.

Comparison of Thidiazuron and Two Nitroguanidines to Kinetin on Potato Microtuberization in vitro under Short and Long Days

Thidiazuron and many nitroguanidines (for example, AC239,604 and AC243,654) act as cytokinins similar to kinetin in many bioassays. Potato tuber initiation effects by thidiazuron, and AC239,604 and AC243,654 have not been investigated. These compounds were compared with kinetin for tuber initiation on nodal segments in vitro under short and long photoperiods. Potato plantlets from "Atlantic" tubers were grown in vitro under 16-h days on Murashige-Skoog (MS) medium with 2.5% sucrose. After 2 months, nodal segments were removed and cultured on MS medium containing 6% sucrose and a test compound. Half the nodal segments remained under 16-h days (long photoperiod) and half under 8-h days (short photoperiod). Kinetin was added to the MS medium at 2 mg/L. The test treatments were 0.1 mg thidiazuron/L, 0.01 mg AC239,604/L, and 1.0 mg AC243,654/L, Stolon number and length, root length, stem length, time to microtuber initiation, and microtuber size and number were recorded at 5-day intervals up to 80 days after culture. Thidiazuron behaved much like kinetin in promoting the percent of nodal segments producing stolons and inhibiting the growth of stems and roots under both long and short photoperiods. Thidiazuron and kinetin delayed the onset of tuber initiation and lessened tuber production compared with untreated nodal segments under long days. Under short days, thidiazuron and kinetin increased the rate of stolon elongation, hastened tuber initiation, and increased tuber production. The two nitroguanidines were not as active on stolons, roots, and stems as kinetin. But, under long days, AC243,654 and, to a lesser extent, AC239,604 increased microtuber production without changing the time to tuber initiation. Under short days, the nitroguanidines, as with kinetin, also hastened the onset of tuber initiation but did not increase the number of microtubers produced. Thidiazuron acted like kinetin, promoting tubers under short days, but the nitroguanidines acted differently, promoting tuber production primarily under long days.

195 Sexual and Vegetative Performance of Native and Cultivated Day-neutral Strawberries under Moderate and High Temperatures

A common complaint with day-neutral strawberries is that they perform poorly in mid-summer heat. Since most modern day-neutral cultivars are derived from the same Fragaria virginiana ssp. glauca clone from Utah, we felt it prudent to search for alternate sources of day-neutrality that were more heat-tolerant. We compared the sexual and vegetative performance of nine F. virginiana clones from a wide range of environments including the Utah site, and four F. × ananassa day-neutral types (`Aromas', `Fort Laramie', `Ogallala', and `Tribute') under constant temperatures of 18, 22, 26, and 30 °C and 12-h days. `Aromas' and `Tribute' carry the Utah source of day-neutrality, while `Fort Laramie' and `Ogallala' are old cultivars that have a different, complex background. After a 4-week period of acclimation, we counted the number of crowns, inflorescences, flowers, stolons, and daughter plants that emerged over a 10-week period, and measured the dry weights of component parts. ANOVA tables revealed that temperature regime (T), genotypes (G), and T*G were significant for flower number (FLN) and total dry matter accumulation, while species and T*G were significant for daughter plant number (DPN). Mean FLNs across the four temperatures were 6.8, 3.7, 3.3, and 1.2, while mean DPNs were 0.7, 0.9, 0.7, and 1.8. F. virginiana clones averaged 3.8 FLNs and 1.8 DPNs, while the F. × ananassa clones averaged 4.1 FLNs and 0.2 DPNs. There was generally more variability among the F. virginiana clones than the F. × ananassa clones, but the F. × ananassa cultivars, `Fort Laramie' and `Ogallala', performed best at 30 °C. The Wasatch clone did not flower in any treatment, suggesting it is not day-neutral.

Chloris gayana cultivars: RAPD polymorphism and field performance under salinity

Variability in the response to salinity within Chloris gayana (Rhodes grass) germplasm was evaluated under field conditions, and random amplified polymorphic DNA (RAPD) markers were used to assess genetic relatedness among cultivars/accessions. RAPD analysis showed a clustering of cultivars of known relatedness: cv. Pioneer and accessions Local and Trancas (derived from an old Pioneer pasture established in saline soil) belonged to the same cluster, Katambora to another and tetraploid Boma and Callide could be further separated, Boma belonging to a fourth, distant cluster. Field experiments were laid out in two types of plots: control [with electrical conductivity of the saturation extract (EC) = 3·64 dS m−1] and saline (EC=13·10 dS m−1) and two experiments were carried out: one to evaluate the effects of salinity on emergence and establishment, and the other, with a uniform number of plants per plot, to evaluate yield under saline conditions. All cultivars/accessions had salinity‐associated decreases in dry‐matter (DM) production during the establishment phase. After this stage, 1‐year DM yield was similar in all cultivars within each salinity level and production in the saline plots was significantly lower than in controls only in cv. Callide and accession Trancas. Second‐year production in the non‐saline plots increased by 30% on average over the previous year, whereas an average 40% reduction was observed in the saline plots. Thus, salinity had a negative effect on Rhodes grass establishment and persistence. The cultivars could not be ranked unequivocally by production under saline conditions, but tetraploids Boma and Callide may be said to be less tolerant than the rest on the basis of an increased proportion of dead leaves and decreased number of stolons observed in the saline plot.