Factors affecting volatile terpene and non-terpene biotransformation products in plant cell cultures.

Suspension cultures from Peganum harmala were shown to carry out biotransformations of a number of terpenes and non-terpenes. The rate of biotransformation was dependent upon substrate concentration, density of cell suspensions, and the structure and isomeric form of the substrates.     

Airborne inoculum as a major source of Septoria tritici (Mycosphaerella graminicola) infections in winter wheat crops in the UK

The pattern and extent of primary infection by Septoria tritici were compared over a period of 3 years in winter wheat grown at sites with differing histories and from seed stocks obtained in different countries, in the open, under airtight cover and in sterilized soil. Only the airtight cover altered the number of lesions found, substantially reducing it. Lesions were evenly distributed. Lesions were found throughout the autumn and occasionally in the winter and spring on wheat seedlings exposed in trays to the open air for periods of 1 week, then given good conditions for infection to occur. This was true even at a site 0.4 km distant from wheat residues. The results show that the main source of primary infection of winter wheat in these experiments was evenly dispersed and airborne. It probably consisted mainly of ascospores of Mycosphaerella graminicola.     

Apical dominance in the shoot and its possible rôle in the survival of Paspalum distichum L.

Summary. When sequential single-node shoot segments (third to fifteenth node, counting from the apex) of the perennial grass weed Paspalum distichum L. were buried in soil, new shoot growth was significantly correlated with initial segment length. Growth from the youngest segment (third), which was about 2 cm long, was only half as great as that from segments 8 to 15, which were initially 2–3·5 times longer. When 14-node shoot segments were buried in soil, the apical bud exerted a dominating influence on shoot emergence and new shoot growth of axillary buds. The degree of suppression increased gradually up to node 8 and then decreased as the distance from the apex increased. A similar result was obtained in these shoot segments following decapitation. However, the degrees and patterns of apical and bud dominance varied in shoots collected during different seasons and also in shoots with different node numbers, node position, cutting and chilling treatments. A possible role of apical and bud dominance in P. distichum in keeping aerial shocks in reserve under adverse conditions, thus providing a survival mechanism for this weed, is discussed.     

Solarization; a physical control method for weeds and parasitic plants (Orobanche spp.) in Mediterranean agriculture

Summary. Experiments were conducted between 1985 and 1988 to evaluate the effect of duration and time of solarization on the control of two broom rapes ( Orobanche aegyptiaca Pers., O. crenata Forsk.) and other weeds common in the fields of faba bean ( Vicia faba L.) and lentil ( Lens culinaris Medik.) in West Asia. Solarization was performed by applying clear polyethylene sheet to the soil for 0, 10, 20, or 40 days in 1985/86, 0, 30, or 40 days in 1986/87 and 0, 20, 30, 40 or 50 days in 1987/88 during the hot season (July and August) and for 50 days immediately before sowing during milder weather (September and October) in 1986/87. Best control was obtained with solarization for 30–50 days in the hot season. Maximum soil temperature under polyethylene at 5 cm was 55°C in 1985, 48°C in 1986 and 57°C in 1987. Broomrape dry weight decreased in the first experiment by more than 90% in both faba bean and lentil fields. Solarization controlled broom-rape and other weeds in the following two seasons when the soil was left undisturbed during the season of the treatment.     

The bionomics ofLiriomyza Trifolii on Gypsophila and Bean Leaves

A study was carried out to determine the distribution of feeding and oviposition punctures made byLiriomyza trifolii Burgess on gypsophila(Gypsophila paniculata ) and bean(Phaseolus vulgaris) leaves, and the development times of the immature stages on these plants. The absolute number of punctures per leaf area was much greater on bean leaves than on gypsophila leaves. The number of mines per leaf was also higher on beans than on gypsophila, but the ratio of mines/punctures was higher on gypsophila. Gypsophila leaves were punctured on both sides, but most of the punctures were on the distal third of the upper leaf side. On beans the punctures were dispersed uniformly on the upper side of the leaf. The larval period (±SE) at temperatures of 20, 25 and 30°C was 9.9±0.2, 4.4±0.1 and 3.7±0.1, and 5.5±O. l, 3.7±0.1 and 2.4±0.1 days, on gypsophila and bean, respectively. The pupal period at 17, 20, 25 and 30°C lasted 19.9±0.2, 14.7±0.1, 10.4±0.1 and 7.8±0.1 days, respectively.     

The pyrethrins and related compounds. Part XXXV. Esters of aryl-substituted cyclopentane alcohols and analogues

Synthesis of a range of 1-, 2-and 3-phenyl, benzyl and phenethyl substituted cyclopentanols and cyclopentylmethyl alcohols and related unsaturated compounds is reported. Results of bioassays of their esters with known pyrethroidal acids against two species of insect lead to recognition of some structure-activity relationships in this series. The distance and relative orientation between the alcoholic and aryl functions appears crucial, but in other respects the nature of the spacer group between them is less important. The most effective alcoholic components are based on cyclopentenes.     

Present state and prospects of breeding for resistance or immunity to barley yellow mosaic virus1

The BaYMV resistance of German cultivars like Diana, Franka, Gloria or Sonate is due to one recessive gene (‘German gene’), located on barley chromosome 3. This gene and the gene Ym1 are most probably allelic (or tightly linked). Resistance of the American cv. Anson barley is inherited independently of the ‘German gene’ and Ym1. The haploidy technique is an efficient means for approaching major breeding goals: (1) to improve quality characteristics of cultivars carrying‘German resistance' (2) to adapt exotic germplasm carrying the gene Yml to European growing conditions; (3) to broaden the genetic base of BaYMV resistance by incorporating additional ‘new’ resistance genes.     

Control of seed-borne Sclerotinia sclerotiorum by fungicidal treatment of sunflower seed

Treatment of sunflower seeds with benomyl, vinclozolin, iprodione or procymidone virtually eliminated seed-borne Sclerotinia sclerotiorum. Applications of fungicides increased the number of surviving seedlings when seeds were sown in vermiculite or in steam-sterilized soil. With the exception of benomyl, fungicides were significantly more effective when applied in acetone solutions than when 100 g a.i./100 kg of seed was applied as conventional dry dressings. There was no difference in effectiveness between the two application methods when the dry dressings were applied at 200 g a.i/100 kg of seed. The acetone infusion method had no deleterious effects on germination of disease-free seed nor on seedling vigour. For a comparable level of control, less fungicide was needed in the infusion treatment than in the dust treatment. If fungicidal treatment of sunflower seeds is used routinely then the introduction of S. sclerotiorum into uninfested land could be controlled.     

Dormancy studies in three populations of Poa annua L. seeds

Seeds of Poa annua from original collections in Louisiana, Maryland and Wisconsin were grown together in Louisiana over a 3-year period. The freshly harvested seeds and samples stored in moist soil at 30°C were tested for germination at a range of temperatures to compare dormancy and germination characteristics. Seeds of the Louisiana population were dormant over the germination temperature range of 5–25°C, and imbibed storage for 2 weeks did not break dormancy. Freshly harvested seeds of the Maryland population germinated well (78%) at 10°C. With 1 week of imbibed storage at 30°C, germination was good over the range from 5 to 15°C and near 50% at 20°C. Storage for 2 weeks had little further effect. Freshly harvested seeds of two Wisconsin populations germinated above 50% throughout the range of temperatures, and imbibed storage for 2 weeks at 30°C had no effect on germination. The variations in the dormancy of freshly harvested seeds and the varying responses of dormancy breaking from storing imbibed seeds at 30°C suggests that these populations have adapted to avoid high summer temperatures in Louisiana and Maryland but to grow as a summer annual in Wisconsin.