Reducing bushiness in micropropagated Gerbera

Bushiness in Gerbera is a major problem causing more than 30% loss of production during micropropagation and greenhouse production. We studied two Gerbera cultivars `Rosabella' (bushy) and `Sunset' (non-bushy). Three different types of inocula (main, adventitious and axillary shoots) were investigated. The choice of the inoculum had an important influence on bushiness, the main axis being the most sensitive. Higher KIN concentrations enhanced bushiness. Addition to the fungicide imazalil to the propagation medium reduced bushiness. The appropriate concentration of imazalil depended on the degree of bushiness and the inoculum type.     

Pre- and post-landing response of the parasitoid Encarsia formosa to whitefly hosts on Gerbera jamesonii

One of the factors that may complicate biological control of the greenhouse whitefly on Gerbera jamesonii by Encarsia formosa is the rosette shape of this ornamental, which differs from the vertical shape of most vegetable plants (cucumber, egg plant, tomato, etc.). Therefore, host-habitat location and the behaviour prior to landing on uninfested and infested leaves was studied. Attraction of E. formosa from a short distance by infested leaves could not be detected: the parasitoid females landed at random on uninfested and infested leaves. After the first landing, a redistribution of the wasps occurred on the leaves. After 24 h three times as many wasps were found on the infested leaves than on uninfested ones. In a dispersal experiment with four plants, E. formosa appeared to have no preference for landing on leaves of the medium age class, which is the age class on which most of the whiteflies in a suitable stage for parasitism occur. Twenty percent of the parasitoids were found on the plants 20 min after releasing them. These results were independent of the plant cultivar and the host density on the plants. In the course of 8 h, the number of E. formosa females recovered from plants increased linearly, and this increase was greater on plants where hosts were present and also greater on the plant cultivar with the lowest trichome density. After 24 h, the percentage of females was highest (56%) on plants with the highest host density. E. formosa females were arrested on leaves where hosts were present. Contrary to our expectation, the results from the two G. jamesonii cultivars that differed strongly in leaf hairiness were not significantly different in most experiments. Only at the high host density was parasitism found to be lower on the cultivar with the higher hair density. Parasitoids may walk on top of the `hair coverlet' of cultivars with high trichome density and, therefore, be hampered less than expected.     

Interactions between ammonium and pH of the nutrient solution supplied to gerbera (Gerbera jamesonii) grown in pumice

The interactions between the NH₄-N/total-N supply ratio (N _r) and the pH of the nutrient solution delivered to the plants regarding the nutrient availability and its influence on plant growth and yield were investigated in a gerbera crop grown in pumice. Four treatments obtained by combining a low and a high N _r (0.02 and 0.13 on a molar basis, respectively) with two different levels of nutrient solution pH (5.0 and 5.8, respectively) were compared in a long-term glasshouse experiment. The low N _r resulted in significantly higher pH levels in the rhizosphere, as indicated by the values measured in the drainage water. A high nutrient solution pH further increased pH in the root zone at low N _r but had no influence on it at the higher N _r level. The high pH in the root zone restricted significantly the Cu, Mn, and Zn uptake as indicated by both analytical results and visual symptoms, which were typical for Cu- and Mn-deficiencies. Mn-deficiency was induced only when a low N _r was combined with a high nutrient solution pH. The Cu-deficiency symptoms appeared earlier, were more severe and occurred also when the low N _r was combined with a low nutrient solution pH, but to a lesser extent. As a result of these nutrient deficiencies, both the growth and the flower yield were severely restricted when N _r was low. These results indicate that gerbera is prone to Cu- and Mn deficiencies at pH values above 6 in the rhizosphere. The maintenance of root zone pH below this level in soilless culture is most successfully attained by properly adjusting the NH₄-N/total-N supply ratio rather than the pH of the nutrient solution delivered to the plants.     

Effect of solarization of soil within plastic bags on root rot of gerbera (Gerbera jamesonii L.)

Solarization of soil, (potting mix = coarse sand:Eucalyptus marginata fines = 1∶1) infested with 3 fungi pathogenic to gerbera (Phytophthora cryptogea, Fusarium oxysporum andRhizoctonia solani), for 3 to 4 weeks within transparent polyethylene bags controlled root rot of gerbera. Solarization for 2 weeks however, was less effective. All plants grown in the infested potting mix which had been kept in shade for 2, 3 or 4 weeks were severely attacked. Solarization of soil within plastic bags for 4 weeks also increased availability of nutrients such as NH₄ ⁺-N, PO₄ ⁻ and K⁺ in comparison to bagged soil kept in the shade for the same period.     

Foraging Behavior of the Parasitoid Encarsia formosa on Gerbera jamesonii Leaves

Insight into the foraging behavior of the parasitoid Encarsia formosa Gahan for whitefly hosts was gained by continuous observation of individual parasitoids on leaves of the ornamental plant Gerbera jamesonii, until females left the leaf. Comparison of the parasitoid behavior on three cultivars gave similar results. Mean searching time on uninfested G. jamesonii leaves of three cultivars was 1 h 30 min and the mean percentage of walking activity of the total observation time on those cultivars was 61%. Both parameters were not influenced by different leaf structures of Gerbera cultivars. Encounters with hosts arrested the parasitoids on the leaves. The walking activity and the percentage of host encounters that resulted in an oviposition decreased with decreasing egg load of the parasitoid. In comparison with tomato, where biological control of whiteflies is successful, only minor differences in the foraging behavior occur, except for the residence time of females, which was about three to four times longer on G. jamesonii leaves, but these leaves are about seven times larger than tomato leaves. The facts that (1) the foraging behavior of E. formosa on G. jamesonii is independant of the cultivar and (2) the foraging behavior is, in many aspects, similar to that on tomato suggest that biological control of whitefly on this ornamental plant is a potential option.     

Induction of homozygous Spathiphyllum wallisii genotypes through gynogenesis

In Spathiphyllum wallisii the production of doubled haploids was attempted. Different combinations of growth regulators were tested, as well as different cultivars. The use of TDZ (0.25–1 M) in ovary cultures of Spathiphyllum was required. On the contrary, cytokinins were not crucial during ovule culture; in fact, the use of a too high TDZ concentration induced diploid parthenogenesis in ovules of `Alfa'. The use of the imidazole fungicides IMA, PRO or TRI during ovary culture was not critical, though they enhanced the swelling of ovules during ovary culture, making the isolation of the ovules easier. The ovule cultures yielded different plantlets. Flow cytometry and AFLP-patterns showed that two doubled haploid genotypes could be obtained from `Stefanie'. These plants showed a normal phenotype. We concluded that the induction of homozygous Spathiphyllum through gynogenesis is possible and is genotype dependent.     

LED光质对非洲菊组培苗增殖及生理特性的影响

为提高非洲菊增殖培养的效率并降低生产能耗,通过发光二极管(LED)设置不同比例的红蓝光组合,研究光质对非洲菊离体培养增殖阶段的影响,通过对丛生苗形态指标和生理生化指标的测定,筛选出最适LED光质条件,并初步探讨其生理机制。结果显示:(1)不同LED光质条件下,非洲菊组培苗的增殖系数差异显著,其中RB4(红蓝光比例为4∶1)处理显著高于其他处理。(2)丛生苗的株高在复合光处理下显著低于R(单一红光)和B(单一蓝光)处理;鲜重和干重在红蓝复合光RB2、RB4、RB8(红蓝光比例分别为2∶1、4∶1和8∶1)处理下均显著高于R、B和对照处理。(3)RB4处理下丛生苗的可溶性糖含量显著高于其他处理,比对照提高了89.62%。(4)LED复合光处理下丛生苗的丙二醛含量显著低于对照,并呈现随红光比例增加而不断降低的趋势;RB2、RB4和RB8处理的超氧化物歧化酶活性显著低于其他处理;除R处理外,其他LED光质处理的丛生苗过氧化氢酶活性均显著高于对照,并以RB4处理丛生苗过氧化氢酶活性最强。研究表明,RB2、RB4和RB8处理有助于提高非洲菊组培苗的增殖系数和干鲜重,并能够促进可溶性糖含量的增加,增强植株自身对活性氧的解毒能力,减轻植株的膜脂过氧化作用,且以RB4处理表现最优,其非洲菊丛生苗的增殖系数和可溶性糖含量显著高于其他处理,干鲜重和过氧化氢酶活性均为最高,丙二醛含量显著低于除单一红光外的其他处理。     

多效唑和三唑酮对非洲菊微繁的效应

培养基中加入多效唑0．2,0．4,0．6mg／L,可使非洲菊组培苗健壮、矮化,提高增殖系数,促进继代后生根;在生根培养基中加入0．2～1．0mg／L多效唑,可增加生根量,促进根的增粗,提高移栽成活率。0．1mg／L三唑酮可降低植株高度,提高增殖率。     

Transformation of antisense constructs of the chalcone synthase gene superfamily into Gerbera hybrida: differential effect on the expression of family members

Suppression of gene expression using antisense technology has been successful in various applications. In this paper we report differential inhibition of gene expression of the chalcone synthase (chs) gene superfamily members in transgenic Gerbera hybrida (Asteraceae) plants. We have transformed two different cDNAs of the chs gene family, gchs 1 [4] and gchs2, in antisense orientation under control of the CaMV 35S promoter into gerbera. Gchs1 codes for an enzyme with chalcone synthase activity while gchs2 is a more diverged member of the gene family having distinct structure and expression pattern. Furthermore, gchs2 is evidently not involved in anthocyanin synthesis and encodes an enzyme with novel catalytic properties. In both cases effective blocking of the resident sense gene expression was detected. In addition, the transformation affected differentially the expression of other members of the chs gene family. The degree of inhibition appeared to depend on the sequence homology between the antisense and the target genes. In the unevenly coloured inflorescences detected among anti-gchs1 transformants during their growth, relaxation of the antisense effect was here shown to start from the most distant member of the gene family, further demonstrating the influence of sequence homology in the stability of antisense inhibition.     

影响非洲菊愈伤组织诱导和增殖的因素

以非洲菊(Gerbera jamesonii Bolus)7个品种的叶片和带叶叶柄为外植体,接种到附加0.5、1.5和2.0 mg L-1 2,4-D的MS培养基上培养,各品种均能诱导出愈伤组织并增殖。愈伤组织的诱导和增殖状况均是叶片好于叶柄,但各品种之间存在显著差异。将品种F30和Ⅱ的叶片和带叶叶柄接种到含不同浓度单一细胞分裂素(6-BA、TDZ、KT)的MS培养基上培养,均未能诱导出愈伤组织,而在含2.0 mg L-1 6-BA 0.5 mg L-1 NAA的培养基上可以诱导出愈伤组织,且由品种Ⅱ叶柄诱导产生的愈伤组织可再分化出芽,品种F30诱导的愈伤组织却不能分化,但在其叶柄基部可直接出芽。以上结果说明,生长素是非洲菊愈伤组织诱导和增殖所必须的,非洲菊愈伤组织诱导、增殖和芽再生方式受品种及外植体类型的影响。     

Effect of genotype on somatic embryogenesis from axes of mature peanut embryos

Genotypes representing the three botanical varieties of peanut (Arachis hypogaea L.) were assessed for somatic embryogenesis and subsequent plant conversion from mature zygotic embryo axes. Explants were initially cultured on Murashige and Skoog medium supplemented with 12.42 M 4-amino-3,5,6-trichloropicolinic acid. Individual somatic embryos wer isolated from explant tissue and used to initiate repetitive liquid cultures. There were significant differences among genotypes and varieties for somatic embryo formation and plant regeneration using a single media sequence. Botanical variety fastigiata had a lower embryogenic frequency and produced significantly fewer embryos than either hypogaea or vulgaris, which were similar in response.Abbreviations EA zygotic embryo axes - MS Murashige and Skoog (1962) medium - picloram 4-amino-3,5 - 6 trichloropicolinic acid     

In vitro gynogenesis in Beta vulgaris L.: Effects of plant growth regulators,temperature, genotypes and season

In order to increase the yield of haploid sugarbeet plants obtained from in vitro culture of unfertilized ovules, we have studied several factors: (1) the nature and concentration of various growth hormones, (2) the temperature for the cultured ovules, (3) genotypes and (4) seasonal effects. We found N6 medium [7] supplemented with 2.85 M of indoleacetic acid (IAA) and 0.88 M of 6-benzylaminopurine (BAP) or N6 medium containing 2.3 M of kinetin (KIN) to give the best qualitative and quantitative results for the culture of ovules. A two-step process for the induction and the development of gynogenic embryos was used. For the initiation of the embryos from the cultured ovules, the temperature of 27°C was favoured to that of 24°C. A pronounced and very significant seasonal effect was observed; the month of June was favoured to that of the other summer months tested. The effect of genotype was significant only for certain media. Using the above concentrations and combinations, a yield of viable gynogenic plants (plants/100 cultured ovules) between 6 and 10% (depending on the genotype) was obtained. In each case, 81% of these were haploids.     

Plant regeneration from ryegrass ovules cultivated on endosperm-derived feeder cells

An efficient method for the regeneration of zygote-derived plants via ovule culture is desirable for overcoming postzygotic cross incompatibility as well as for the development of certain methods for genetic manipulation. High-frequency plantlet regeneration from ovules of Italian ryegrass (Lolium multiflorum Lam.) and a hybrid Italian/perennial ryegrass excised 1 to 4 days post pollination was obtained by culture on endosperm-derived feeder cells. Ovules excised 3 or 4 days after anthesis and grown on feeder cells generally regenerated about twice as frequently as ovules grown directly on nutrient medium. In one of the genotypes tested, ovules excised 1, 2 and 3 days post pollination developed into plantlets at percentages of 38.1, 52.0 and 52.8, respectively, using the feeder-cell system.Abbreviations EM endosperm multiplications - OC ovule culture - R regeneration - 2,4-d 2,4-dichlorophenoxyacetic acid     

非洲菊试管苗叶柄愈伤组织的诱导与分化研究

以非洲菊(Gerbera janesonii Bolus)品种‘Sunanda'试管苗幼叶的带叶叶柄为材料,研究了培养基、外植体类型和继代次数等因素对愈伤组织诱导及分化的影响.结果表明:培养基上附加不同植物生长调节剂所诱导出的愈伤组织在形态和分化能力上存在显著差异,叶柄基部诱导愈伤组织的最适培养基是MS+TDZ 0.3 mg L-1+NAA0.1 mg L-1.外植体以叶片长度＞0.5 cm,叶片已舒展,颜色嫩绿的幼叶最佳,继代培养基以MS+KT 1.0 mg L-1较适宜,愈伤组织在分化培养基MS+6-BA 2.0 mg L-1+NAA 0.1 mg L-1上分化出芽的同时还会增殖,分化率达87.4%,继代培养2次的愈伤组织分化率可提高至95%.不定芽在生根培养基1/2MS+IBA0.6 mg L-1上的生根率达100%,试管苗移栽45 d后,成活率达97%以上.     

Effect of anther orientation on microspore-callus production in barley (Hordeum vulgare L.)

Barley anthers from cold pretreated spikes produced no or few calluses when plated with both loculi in contact with the medium (flat). When anthers were plated with only one loculus in contact with the medium (up), a high proportion of the anthers produced calluses. The top loculus of the up anthers was most productive. Flat anthers, when compared with up anthers, were not only slower to produce multicellular pollen grains (MCPs) and microcalluses, but also produced fewer of them and ceased production earlier. The MCPs and microcalluses in flat anthers grew more slowly and few developed beyond the 30 cell stage. These results establish the importance of anther orientation for barley anther culture.     

氯化钙对非洲菊切花的保鲜作用

以 1 0mg ml的CaCl2 溶液作为保鲜液 ,对非洲菊切花进行瓶插试验 ,通过外部形态观察和生理指标测定 ,结果表明 :用CaCl2 溶液瓶插非洲菊切花可以增强花枝的吸水能力 ,增加花枝的鲜重 ,保持切花的水分平衡 ,减少溶质外渗 ,维持膜结构的相对稳定性 ,从而使切花的瓶插寿命比对照延长 3 3d。     

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m⁻²/14 days), and a subsequent 3-month trial with high (100 m⁻²/week) and very high (1,000 m⁻²/week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50–100 juvenile and 50–70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50–70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10–100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.     

Effects of genotype and plant growth regulator on callus induction and plant regeneration in four important turegrass genera: A comparative study

Summary Turfgrass, like other major crop species, is recalcitrant to manipulation in vitro. To perform efficient genetic transformation of turfgrass, it is necessary to optimize tissue culture conditions. In most reports, plant tissue culture techniques have been applied to propagate a single cultivar or several cultivars in one species of turfgrass. In this experiment, four turfgrass genera were used, namely common bermudagrass, Cynodon dactylon [L.] Pers. (California origin); red fescue, Festuca rubra L. var. rubra ‘Shadow’; perennial ryegrass, Lolium perenne L. ‘Barbal’; and Kentucky bluegrass, Poa pratensis L. ‘Merion.’ Mature seeds were surface-sterilized and cultured on basal Murashige and Skoog (MS) media supplemented with 30–250 μM 2,4-dichlorophenoxyacetic acid (2,4-D) for callus induction. Regeneration media consisted of MS supplemented with 5–10 μM 6-benzyladenine (BA). Among the genera, Poa had the higest callus induction percentage (CIP) regardless of 2,4-D concentration, followed by Cynodon, Lolium, and Festuca, respectively. Cynodon and Lolium had the highest callus regeneration percentage (CRP) and overall regeneration rate (ORR). Festuca had a poor CIP, CRP, and ORR compared to other studied genera. Cynodon produced the highest shoot number per explant. Based on the results of the present study, MS medium supplemented with 60 μM 2,4-D (for callus induction) and 7.5 μM BA (for regeneration) can be used in multi-generic transformation studies with the genera used.     

Effect of genotype and medium on wheat (Triticum aestivum L.) anther culture

Four winter wheat (Triticum aestivum L.) and two spring wheat cultivars were evaluated in anther culture on three to four different media for their ability to initiate callus and green plants. Five media were used in the experiment: stored-potato medium with Ficoll 400, fresh-potato medium with Ficoll 400, fresh-potato medium with agar, fresh-potato liquid medium without agar or Ficoll 400, and a one tep 85D12-3 medium. Greatly different frequencies of calli and/or green plants were obtained from different cultivars and media. The callus initiation frequency varied from 2.7% for Arapahoe to 52% for Pavon, both on the stored potato medium with Ficoll 400. The frequency of green plant regeneration ranged from 0% for Arapahoe and Siouxland on the stored-potato medium with Ficoll 400 and 0% for Redland and Arapahoe in the fresh-potato medium with Ficoll 400 to 12% for Chris in the 85D12-3 medium (one-step procedure). Chris and Centurk 78, previously reported as having high levels of response, had significantly higher (P < 0.05) frequencies of green plant regeneration on the 851312-3 medium than the other cultivars. An unexpected observation is that wet MSC^– medium enhanced callus regeneration more than a drier MSC^– medium.     

Influence of Hairiness ofGerbera jamesoniiLeaves on the Searching Efficiency of the ParasitoidEncarsia formosa

To characterize the relationship between the leaf surface ofGerbera jamesoniiHooker cultivars and the searching behavior of the parasitoidEncarsia formosaGahan on a leaf, the trichome density and shape were described, and the walking behavior was quantified. Leaf hair density varied from 80 to more than 1000 trichomes/cm²and the hair shape varied from single erect trichomes to tapestries of entangled trichomes above the leaf surface. The walking activity, speed, and pattern of the parasitoid were tested on leaves with different hair density and shape. In spite of the large differences in leaf surface structure, the walking activity was similar and around 75% on most cultivars. The walking speed was between 0.2 and 0.3 mm/s on all cultivars and was not significantly different from the speed on tomato. On hairless sweet pepper leaves the walking speed is much higher (0.73 mm/s), so the hairs onGerberaleaves do hamper parasitoid females and result in a strong reduction of the walking speed, but the variation in hair density and shape onGerberadoes not lead to differences in walking activity, pattern, and speed. It appears that the hairs ofGerberaare less of an obstacle forE. formosathan the stiff, large hairs occurring in a high density on cucumber, where the walking speed of the parasitoid is less than 0.2 mm/s. A rise of temperature of 5°C gave a significantly higher walking speed (0.39 mm/s) ofE. formosafemales on all cultivars tested. The relative straightness of the walking track was high and the same on all cultivars. Consequences of the results of the searching behavior ofE. formosaonG. jamesoniicultivars are discussed with respect to other host plants. As parasitoid walking speeds are the same onGerberaand tomato, and whitefly reproduction is also similar on these two host plants, we conclude that biological control of whiteflies onGerberais a realistic option. This conclusion is confirmed by the strong increase of commercial biological control onGerberawhich occurred during the past 5 years.