African spider flower (Cleome gynandra L./Gynandropsis gynandra (L.) Briq.) as a red spider mite (Tetranychus urticae Koch) repellent in cut-flower rose (Rosa hybrida L.) cultivation

Companion planting of Cleome gynandra, of Kenyan origin, in beds of cut-flower roses reduces significantly red spider mite (Tetranychus urticae Koch) infestation without any detrimental effect on productivity or flower quality. The level of reduction is dependent upon the density of the C. gynandra plants with 15 plants in a 1.8 m² bed (8.3 plants m²) being the most effective, planted either around the bed perimeter or within the rows of roses. The relatively high density of C. gynandra plants required may limit the direct application of this technology in export-focused, greenhouse rose production yet may be of significant value as a supplement to other mite-control strategies. The potential benefits of such companion planting for growers of field roses and those involved in some domestic markets are also evident. Research into the nature and extraction of the active, volatile mite-repellant components of C. gynandra is indicated.     

A comparison of monitoring systems used for Ceratitis species (Diptera: Tephritidae) in South Africa

For 16 years a bucket-type trap known as the Sensus fruit fly trap has been used to monitor three fruit fly pest species Ceratitis capitata, Ceratitis rosa and Ceratitis cosyra in South African fruit industries. The relative efficiencies of lures sold for monitoring fruit flies with the Sensus trap in South Africa were determined in field experiments where laboratory-reared C. capitata, C. rosa and C. cosyra were released in a mango orchard within a few metres of Sensus traps containing either Capilure (trimedlure or tert-butyl 4 (or 5) -chloro-2-methylcyclohexane carboxylate), Ceratitislure (protein hydrolysate plus β-caryophyllene) or Questlure (protein hydrolysate plus plant extracts). When using 12-day-old flies, Capilure caught 3 times more C. capitata males than C. rosa males and this difference was more extreme when 3-day-old flies were released. Ceratitislure caught significantly more 12-day-old C. cosyra males than 12-day-old C. capitata males, but the difference was reversed when 3-day-old flies were compared. Questlure showed the least differences between species and age but recovered the lowest proportion of released species. Further comparisons were conducted in an orchard with wild flies using other known attractants in larger yellow Probodelt bucket traps. Capilure caught more male C. capitata than BioLure Fruit Fly 3-component, but BioLure 2-component (trimethylamine and ammonium acetate) was more effective than Questlure for C. capitata females. The 3-component lure was also more effective than both Capilure and Questlure for male and female C. rosa, respectively. Ceratitislure was the most effective lure for male C. cosyra flies and BioLure 3-component was more effective than Ceratitislure and Questlure for female C. cosyra flies. The intervention threshold of 4 flies/trap/week previously used in citrus with Capilure for C. rosa was lowered to 2 C. rosa/trap/week when using the Sensus trap due to the lower sensitivity of this trap-lure combination found for C. rosa in this study. The 3-component lure, or the 2-component combination of trimethylamine and ammonium acetate in a ratio of 1:8 in the Sensus trap capsule, would be more effective for both sexes of all three Ceratitis species than the Questlure that is currently being used.     

Alterations in flower and seed morphologies and meiotic chromosome behaviors of micropropagated rhubarb (Rheum rhaponticum L.) ‘PC49’

Variations in flower and seed and meiotic chromosome behaviors were investigated in micropropagated rhubarb (Rheum rhaponticum L.) ‘PC49’. The results showed that micropropagated plants had significantly higher variations in flower and seed morphologies and chromosome behaviors than plants derived from crown division. The results demonstrated that micropropagated plants grew 2–5 stamens, 8–13 stigmas, and 2–7 seed-wing, compared to 3 stamens, 9 stigmas and 3 (rarely 4) seed-wing in crown-derived plants. Additionally, alteration in chromosome behaviors (i.e. lagging and bridging) was observed only in micropropagated plants. All the results suggest that somaclonal variation may have been involved in micropropagated rhubarb ‘PC49’.     

Effects of temperature on germination and hyphal growth from conidia of Ramularia rhei and Ascochyta rhei, causing spot diseases of rhubarb (Rheum rhaponticum)

Rhubarb leaf and petiole spot disease, caused by Ramularia rhei and Ascochyta rhei , has gradually become more noticeable in the UK field crop. Conidial germination and subsequent colony growth of R. rhei and A. rhei were investigated under in vitro conditions on potato dextrose agar and in vivo on leaf discs. Results indicated that the two fungi responded differently to temperature. Ramularia rhei was better adapted to temperatures ≤ 25°C, with an optimum around 20°C, whereas A. rhei was more adapted to temperatures ≥ 15°C, with an optimum > 25°C. Overall, conidia of R. rhei germinated and subsequent colonies grew at greater rates than those of A. rhei on leaf discs at temperatures ≤ 25°C. These results indicated that it is important to identify the causal agent of leaf and petiole spot diseases in rhubarb field crops in order to estimate disease risks accurately.     

Increased haploid production in Saintpaulia ionantha by anther culture

Anthers of Saintpaulia ionantha containing late-uninucleate stage pollen produced callus from the anther interior after 3–4 weeks culture on Murashige and Skoog medium supplemented with 1 mg l^?1 naphthylene acetic acid (NAA) and 0.5 mg l^?1 1,6-benzylaminopurine (BAP). Shoot regeneration occurred rapidly and up to 200 shoots could be recovered from callus derived from a single anther within 10 weeks. Examination of roottip mitoses from transplanted, established plants demonstrated that, with few exceptions, the plants were haploid, thus indicating that the callus was pollen derived. Exposure of buds to low temperature prior to anther excision was inhibitory to callus production. Shoot regeneration was studied by scanning-electron microscopy.     

Contrasted genetic diversity and differentiation among Mediterranean populations of <Emphasis Type="Italic">Ficus carica</Emphasis> L.: A study using mtDNA RFLP

Patterns of mitochondrial DNA (mtDNA) variation revealed by RFLP were investigated for 63 individuals of the common fig, Ficus carica L., in 15 supposedly natural populations throughout the Mediterranean basin. Fifteen haplotypes were detected using one restriction enzyme (HindIII) and four probes (atp, coxIII, nad3rpsl2 and rps12). Mitochondrial diversity within populations varied from monomorphic to entirely polymorphic and population differentiation was high (F_ST = 0.323, P < 10^–5). Seven groups of populations were defined on the basis of genetic and geographic proximity and lead to significant pairwise F_ST estimates except for the Corsican group which was similar to the Moroccan one. Fig populations were structured into three clusters: Balearic, West and East Mediterranean gene pools. The low diversity and strong differentiation of the Balearic populations strongly supports an ancient origin and the presence of natural populations in this area before domestication. Significant genetic differentiation between the West and East Mediterranean probably also reflects a diversification of the common fig over the Mediterranean basin preceding domestication. In contrast, Italian island populations seem to result from introduced cultivated fig since they present continental haplotypes. Our study represents a first mtDNA polymorphism survey and these indications should be confirmed by analysing local cultivated forms from the Baleares and from Italian islands and further natural populations from the East Mediterranean.     

Acetonitrile (methyl cyanide) emitted by the African spider plant (Gynandropsis gynandra L. (Briq)): Bioactivity against spider mite (Tetranychus urticae Koch) on roses

The African spider plant (Gynandropsis gynandra L. (Briq)) has repellent properties against spider mite on roses (Rosa hybrida L.) when grown as a companion plant. Gas chromatography–mass spectrometry (GC–MS) has been used to identify potential volatile compounds in the foliar emissions of this plant that may contribute to the anti-mite properties. Acetonitrile (methyl cyanide) was the most abundant compound emitted by entire plants and detached leaves of five lines of both glasshouse- and field-grown G. gynandra, with only trace levels emitted by roses grown under similar conditions. A toxicity bioassay was conducted to evaluate the bioactivity of acetonitrile against spider mite, and ≥2.5 μL/L of air rendered 100% of the mites inactive. Removal of the compound after an initial exposure of up to 5.0 μL/L of acetonitrile allowed some 10% of the mites to recover mobility, but above this level no mobility was observed. This study provides a very strong indication that foliar emissions of acetonitrile by G gynandra are responsible, to a significant degree, for the spider mite repellent activity of the plant when used as an intercrop with roses.     

Advantages of storage of potato pollen in liquid nitrogen

Summary Potato pollen stored in liquid nitrogen (−196 C) showed no significant decrease in percentage germination after nine months, whereas pollen stored at −20 C showed a decrease in germination to <1% over the same period.     

Storage of broccoli pollen in liquid nitrogen

Summary Broccoli pollen which had been stored in liquid nitrogen retained its viability, but seed produced using this pollen rapidly lost its germinability. Plants raised from this seed, and their progenies, gave no indication of genetic damage resulting from the low temperature treatment of pollen.