Ornamental Bulbs Research Articles

Microbial community responses to disease management soil treatments used in flower bulb cultivation

A number of management practices, such as soil fumigation and flooding, have been employed in efforts to control diseases and weeds in the cultivation of ornamental flower bulbs. However, such treatments may affect the suppression of Pythium root rot, a serious problem in ornamental bulb culture. To gain insight into the nature of Pythium suppression in such soils, we sought to describe the changes that these soil treatments induce in the microbial community in order to determine if particular microbial components of the system could be associated with suppression. Four polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) strategies, two targeting bacteria and two targeting fungi, were used to compare the soil-borne microbial communities of untreated, fumigated, flooded and sterilized, compost-amended soils; the dominant community members were tentatively identified by sequencing of DGGE bands. For all profiling strategies, the compost treatment of sterilized soil appeared to have the most profound effect on the dominant microbial populations in the soil. In general, different primer sets that targeted the same microbial groups, bacteria or fungi, appeared to detect the same microbial taxa, although certain sequence types were detected in only a single profiling strategy. DNA-based microbial community profiles alone were poor predictors of Pythium suppression, as the dominant microbial populations remained mostly intact, even after rigorous soil treatments such as fumigation and flooding. The restoration of suppressive activity against Pythium in compost-amended soil was associated with a different microbial community than observed in untreated, suppressive soils. Thus, although previous studies have shown the suppression of Pythium to be mediated by biological agents, effects of different microbial communities can lead to this suppression.

EFFECT OF GREEN MANURE CROPS AND ORGANIC AMENDMENTS ON INCIDENCE OF NEMATODE-BORNE TOBACCO RATTLE VIRUS

Tobacco rattle tobravirus (TRV) may infect several ornamental bulb crops and is transmitted by trichodorid nematodes. Paratrichodorus teres, P. pachydermus and Trichodorus similis are the main vectors in the Netherlands. In field experiments the effects of various pre-crops and organic amendments on the TRV Infection Potential of Soils (TRV-IPS) and on disease level in tulip and gladiolus were studied. Organic matter amendment of soil at a rate of 1% dry weight has been shown to reduce the host finding activity of P. teres under laboratory conditions. In a field containing viruliferous P. teres dahlia, italian ryegrass, white mustard and fodder radish were grown or the soil was kept fallow and the resulting TRV-IPS prior to the bulbous test crops was measured by a soil dilution bait test method. The application of organic matter was tested after dahlia as pre-crop. Household waste compost (GFT compost) was applied as a soil mix or planting furrow treatment at 12 tons dry weight per ha for tulip and gladiolus. Spent mushroom compost (Champost) was added as planting furrow treatment at 17 or 12 tons dw/ha, respectively, for tulip and gladiolus. The percentage of TRV diseased plants was determined at flowering in all pre-crop and organic amendment treatments. Champost in the planting furrow and fodder radish as a preceding crop reduced the percentage infection in tulip under favourable conditions for TRV infection. In gladiolus most organic amendments, fodder radish as pre-crop and keeping the soil fallow reduced the TRV infection rate of the plants during the first growing season, but not of the plants grown from the corms in the next year.

POTENTIAL USE OF CHLORINE DIOXIDE TO PREVENT THE SPREAD OF FUSARIUM BASAL ROT DURING THE HOT WATER TREATMENT OF DAFFODIL BULBS

POTENTIAL USE OF CHLORINE DIOXIDE TO PREVENT THE SPREAD OF FUSARIUM BASAL ROT DURING THE HOT WATER TREATMENT OF DAFFODIL BULBS

BREEDING FOR RESISTANCE TO BASAL ROT IN NARCISSUS

BREEDING FOR RESISTANCE TO BASAL ROT IN NARCISSUS

Factors affecting direct organogenesis from flower explants of Allium giganteum

A novel method is described for the propagation of Allium giganteum Regel using direct organogenesis resulting in multiple shoot structures formed on mature flower buds or ovaries. A two step induction and differentiation procedure, similar to that described earlier in onion, was tested. Flowers were inoculated on the induction medium for 6 days and extracted ovaries were placed on the differentiation medium. Optimal formation of multiple shoot structures was obtained using modified BDS medium containing 50 g l−1 sucrose solidified by a mixture of agar/gellan-gum, with 8.88 μM benzylaminopurine (BA) and 9.05 μM 2,4 dichlorophenoxyacetic acid (2,4-D) in induction medium and 9.08 μM tidiazuron (TDZ) in the differentiation medium. Five plant sources obtained from different European retailers of ornamental bulbs were tested separately. All tested genotypes produced multiple organogenic structures, although induction percentages clustered in two distinctive groups. Shoots formed tended to become dormant, and attempts to improve their growth and rooting included treatment with fluridone. Dormancy was partly broken when shoots were briefly dipped in 1 μM fluridone. Genetic analysis of plant sources using random amplified polymorphic DNA method showed that 5 retailers actually distribute only two different clones, one of them more and the other less responsive to shoot organogensis.

Suppression of Pythium root rot in bulbous Iris in relation to biomass and activity of the soil microflora

Disease suppression against Pythium root rot can be influenced by management practices applied in ornamental bulb culture. Different levels of suppression were established in sandy soil after several soil treatments. Percentage of infection in Iris caused by Pythium macrosporum was lowest in untreated soil and progressively increased in sterilized soil amended with 1% compost, fumigated soil (methylisothiocyanate) and flooded soil (fumigation and flooding corresponding to the same level of disease severity) and was highest in sterilized soil. The relationship between the level of disease incidence, Pythium growth rate through soil, and various microbial parameters was investigated. Soil microbial biomass and, after amendment of glucose as a non-selective carbon source, dehydrogenase activity, glucose uptake and respiration were determined. By using 14C-labelled glucose, measurement of uptake and assimilation of amended carbon could be distuingished from soil organic matter decomposition. All microbial parameters were negatively associated with Pythium growth rates, indicating that high microbial biomass and activity induced suppression of Pythium growth through soil. However, with neither of the quantitative microbial parameters could changes in disease incidence be fully explained. It is hypothesized that competition for carbon may not be the main mechanism in disease suppression.

Effects of Soil Fumigation and Flooding on Suppression of Pythium Root Rot in Ornamental Bulb Culture

The effects of flooding and soil fumigation with cis-dichloropropene or methylisothiocyanate (MIT) on disease suppression against Pythium spp. were tested in pot and field experiments in sandy soil. Disease suppression was reduced by both flooding and fumigation treatments, resulting in severe infection in Iris and Crocus and reduction of bulb yields. It is demonstrated that the disease suppression has a biological nature, and that disease severity is more related to effects of the soil treatments on the soil microflora than to the initial inoculum density of Pythium. After flooding, disease suppression was restored within the experimental period of two years, whereas after fumigation, disease suppression was only partially restored. The effect of repeated fumigation in two consecutive years on the disease suppression was less severe than the effect of a single fumigation treatment prior to cultivation of a susceptible crop.

Tobravirus isolation and RNA extraction.

AbstractThe tobraviruses have a genome consisting of two positive-sense, single-stranded RNA molecules. The two genomic RNAs, RNA-1 and RNA-2, are encapsidated separately in rod-shaped particles with lengths of 180–215 nm (L particles) and 46–115 nm (S particles), respectively (Fig. 1) (1,2). Both the RNAs are encapsidated by a single species of coat protein (CP) with a mol wt of approx 23 kDa. Tobraviruses can be divided into three serologically distinct subgroups: tobacco rattle virus (TRV), which is the type member, pea early browning virus (PEBV), and pepper ringspot virus (PRV). In the field, these viruses are transmitted by soil-inhabiting nematodes of the family Trichodoridae, and certain isolates are also transmitted through the seed. Tobraviruses can infect a wide range of plant species including economically important crops such as potatoes and ornamental bulbs. Tobravirus structure and genome organization. (ai) Genome organization of RNA-1 of TRV isolate SYM. (aii) Genome organization of RNA-2 of various TRV isolates. (bi and bii) Genome organization of RNA-1 and RNA-2 of PEBV isolate SP5. RNA is shown as a horizontal line and the positions of the open reading frames (ORFs) are indicated by boxes. The numbers inside the boxes are the approximate mol wt in kDa of the proteins encoded by each ORF. The coat protein ORF is denoted by CP. The position of the readthrough termination codon on RNA-1 is indicated by an asterisk. KeywordsCoat ProteinSodium Phosphate BufferTobacco Mosaic VirusTobacco Rattle VirusThioglycollic AcidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

INCIDENCE AND CONTROL OF THRIPS-BORNE TOMATO SPOTTED WILT VIRUS IN DAHLIA IN THE NETHERLANDS

In this study on tomato spotted wilt virus (TSWV) in dahlia various factors involved in the control are dealt with. The overall incidence was in 1992: ca. 15%, 1993: ca. 5%, and 1994: ca. 2%. The virus occurred irrespective of shape and colour of flowers, while substantial differences in susceptibility of cultivars were evident. The regional virus rate per holding precluded the overall effect of long-distance virus spread and of abundant virus sources in herbaceous hosts and other ornamental bulb crops. The symptoms were only occasionally clearly recognisable but mostly did not appear at all, or were temporarily masked. Yield of cuttings per tuber was reduced by up to 20%. Virus detection in leaves was erroneous, but reliable if tubers were tested late during storage. Virus transmission by mechanical deflowering of plants by mowing occurred infrequently or not at all. The thrips-vectored transmission under glass proved circumstantially most unlikely. In the open field the thrips plankton in the air and the adult thrips in leaf and flower material yielded twelve species. Franklinietta occidentalis was not found. Thrips tabaci was assumed and F. intonsa was found to be the virus vector in the field. The numbers of thrips in flowers strongly decreased with sprays of deltamethrin and acefate which were more effective than dimethoate. The control of TSWV-spread was most effective with weekly sprays of deltamethrin (83% reduction of spread), and less with dimethoate (reduction 46%). The impact of various control factors, e.g., symptoms, detection by ELISA in tubers, the fairly rapid propagation via cuttings, and the virus spread by virus vector species and curtailment by insecticide sprays, preferably selectively during the field season, is indicated.

Reviews.

Book reviewed in this article Fens and Bogs in The Netherlands: Vegetation, History, Nutrient Dynamics and Conservation. Ed. by J. T. A. Verhoeven. The Africa-South American Connection. Ed. by Wilma George and Rene Lavocat. Ornamental Bulbs, Corms and Tubers. By A. R. Rees.

花き園芸植物特にラン科植物のウイルス病に関する研究

花き園芸植物特にラン科植物のウイルス病に関する研究

Rhizoctonia tuliparum . [Distribution map

Abstract A new distribution map is provided for Rhizoctonia tuliparum Whetzel & J. M. Arthur. Hosts: Tulip, Iris and other ornamental bulbs and corms. Information is given on the geographical distribution in EUROPE, Austria, Denmark, Finland, Germany, Iceland, Netherlands, Romania, Switzerland, UK, USSR (Moscow district), (Sverdlovsk region), Yugoslavia, NORTH AMERICA, Canada (Ontario), (British Columbia), USA, (Yonkers, New York), (Washington State).

DISEASE INDEXING OF ORNAMENTAL BULB CROPS AND LARGE-SCALE PRODUCTION OF FIRST GENERATION CLEAN MOTHER STOCK THROUGH TISSUE CULTURE

DISEASE INDEXING OF ORNAMENTAL BULB CROPS AND LARGE-SCALE PRODUCTION OF FIRST GENERATION CLEAN MOTHER STOCK THROUGH TISSUE CULTURE

Control of field spread of non-persistent viruses in flower-bulb crops by synthetic pyrethroid and pirimicarb insecticides, and mineral oils

The ability of liquid formulations of synthetic pyrethroid insecticides, a carbamate insecticide, and mineral oils, to limit the spread of non-persistent viruses in lilies, tulips, hyacinths and bulbous irises, was studied under field conditions that favoured rapid virus spread. Bait plants were sprayed and virus source plants were not. Substantial control was consistently achieved by weekly sprays of pyrethroids in moderate amounts of active ingredient. No significant additional control was obtained by increasing rates of application, whereas at low rates the control was inadequate or very variable. Control was generally improved by spraying twice a week, whereas fortnightly spraying was inadequate. Fenvalerate sprays gave slightly better control than permethrin in lilies and bulbous irises. The carbamate insecticide gave inconsistent or no control. Pyrethroids were on average only half as effective as mineral-oil sprays. Application of pyrethroids, unlike that of oil sprays, did not reduce bulb yields. The use of pyrethroids to affect probing behaviour of aphids, and consequently its potential to limit the spread of non-persistent viruses in ornamental bulb crops, is discussed.

球根植物の耐凍性

Freezing tolerance of ornamental bulbs and corms of about 50 species or cultivars which were native to different climates in the world was assessed. Almost all of the bulbs and corms native to the South Africa could not survive freezing below -3 or -5°C. This suggests that the mild oceanic winters do not provide the stimulus to evolve hardy bulbous plant species. Hardy bulbous species native to Mediterranean coast, Asia Minor and East Asia survived freezing between -5°C and -23°C. Allium oreophilum, Fritillaria camtschatcensis and Lilium dauricum were the hardiest of the bulbs tested, tolerating temperatures of to -20°C to -23°C. In the hardy bulbs, the base plate was the least hardy plant part. The flower buds were also far less tolerant than the leaf and stem in many ornamental bulbous plants. Further study on freezing tolerance of flower buds in bulbous plants is required.

Studies on bulbous ornamentals. I. Karyomorphology of diploid and triploid taxa of Pancratium triflorum Roxb.

Somatic chromosomes of two cytotypes of P. triflorum are reported (2n=22 and 2n=33). This is the first report of chromosome number for this species. The position of the satellites and secondary constrictions are the same in both diploids and triploids and on the basis of this and complete morphological identity of the chromosomes an autoploid origin of the triploid is suggested.

Growth regulator treatments to improve the yield of twin-scaled narcissus

Twin-scaling is a method for the rapid propagation of valuable stocks of bulbous ornamentals. Bulbil production from twin-scales cut from narcissus bulbs was investigated by incorporating plant growth regulators into the vermiculite in which the twin-scales were incubated. Gibberellic acid (1–100 p.p.m.) reduced the number and weight of bulbils produced. Abscisic acid (1–100 p.p.m.), indol-3-ylacetic acid (1–10 p.p.m.) and kinetin (1–100 p.p.m.) increased the weight of bulbils produced by stimulating sprouting of the bulbils, some of which normally remain dormant in their first year.

Soil‐borne Pathogens in Ornamental Bulbs as Related to Quarantine Problems

AbstractThe introduction of systemic fungicides belonging to the group of benzimidazoles has greatly improved the available methods for the control of several destructive diseases of ornamental bulbs. This is illustrated on the basis of two diseases of tulips that may be soil‐borne, viz. Botrytis tulipae (Lib.) Lind and Fusarium oxysporum Schl.Benomyl in particular appears to be very active against these and certain other pathogens sometimes carried by planting material. With respect to Fusarium, treated tulip bulbs planted in contaminated soil are protected against infection occurring at high soil temperatures (15°C and higher) shortly after planting. Improved methods of chemical soil disinfection (methylbromide and DD under plastic seal) provide almost complete eradication of nematode populations in sandy soils. Application of these methods will further reduce problems given by stem eelworms (D. dipsaci Kühn and D. destructor Thorne) and free‐living nematodes that transmit soil‐borne viruses (Trichodorus spp.).

Cytogenetics of Tropical Bulbous Ornamentals

Cytogenetics of Tropical Bulbous Ornamentals

Cytogenetics of Tropical Bulbous Ornamentals

Cytogenetics of Tropical Bulbous Ornamentals