Variation at the b Mating Type Locus of Ustilago maydis

ABSTRACT Population level diversity at the Ustilago maydis b mating type locus was determined in samples from four Minnesota locations using a combination of plate mating techniques and a polymerase chain reaction (PCR)-based assay. The PCR method allows rapid identification of b types from samples of natural populations and utilizes the hypervariable regions of the b locus that determine mating type specificity. Results demonstrated high levels of b diversity within populations, with one population yielding 17 of the total 18 b types found in the study. Pairwise G(ST) values were in the range of 0.02 to 0.05, and common b mating types were found across broad geographic distances. These data demonstrated that very low levels of differentiation among U. maydis populations occur with respect to b locus variation. Consistent with frequency-dependent selection models, b types were represented at approximately equal frequencies within the entire Minnesota population. However, neutral evolutionary models for patterns of geographic distribution and variation at b cannot be entirely excluded. The importance to agricultural practices of understanding population genetic processes is discussed.     

Exposure of four Filipino farmers to parathion-methyl while spraying string beans

Filipino farmers resist wearing protective garments while spraying, preferring to wear long-sleeved cotton polyester shirts and short or long trousers. The exposure of farmers while wearing this attire and spraying was assessed to determine what degree of protection it afforded farmers under tropical conditions. Absorbent pads were placed on the outer and inner wear on various body parts. Applicators sprayed parathion-methyl on fruiting string beans at the recommended rate and residues were analyzed by gas chromatography. Each farmer had a characteristic spraying pattern which resulted in peculiar residue levels in some body parts. Inner exposure did not exceed the tolerable dermal exposure level during warm days while using proper spraying techniques. The use of long-sleeved cotton polyester shirt and thick polyester trousers provides, to a certain degree, protection for farmers during warm days. A change of clothing would be a more acceptable measure for farmers than wearing uncomfortable and impractical protective garments. The following spraying techniques reduced farmer exposure: fully outstretched arm, minimal body twisting and smooth hand movements. The use of thick polyester long trousers, gloves or a suitable substitute and the removal of weeds within the crop area also reduce farmer exposure to insecticides. Re-designing the bottle to include a plastic lip, in order to avoid spillage, is also recommended to reduce exposure during the critical mixing stage. Laundering the shirt immediately after use removes a significant amount of residues (96–97%) and contributes towards the protection of farm workers. These recommendations should provide useful data for incorporation in farmer-training programes on the proper use of pesticides.     

Effect of pea plant architecture on spatiotemporal epidemic development of ascochyta blight (Mycosphaerella pinodes) in the field

The effect of pea canopy structure on epidemics of Mycosphaerella pinodes was investigated in four spring pea cultivars (Bridge, Obelisque, Solara and Athos) in two field experiments. These cultivars had similar levels of susceptibility to ascochyta blight and presented different architectural features (branching, standing ability and stem height). Stem height ranged from 77 to 95 cm in 1999 and from 72 to 92 cm in 2000, while leaf area index (LAI) ranged from 3·8 to 5·1 in 1999 and from 3·8 to 4·7 in 2000. Internode lengths varied from 4·6 to 6·0 in 1999 and from 3·8 to 4·7 in 2000. Mean distance between nodes in the canopy (MDN) ranged from 12·2 to 15·3 cm in 1999 and from 11·2 to 13·9 cm in 2000. Canopies with different architecture differed in disease progression on stipules and mainly on pods. The levels of disease on stipules and pods were strongly correlated. Moreover, if disease was considered as a function of stipule height up the stem, large differences in vertical disease distribution were observed between cultivars. Three architectural features acted on disease development: cumulative LAI above the node on which disease was assessed (LAIcum) and large MDN favouring disease development, and large internode length reducing disease severity. Modifying LAI distribution and plant organization could be one way to reduce the impact of ascochyta blight, by direct or indirect effects on environmental and dispersal conditions.     

Potato cultivars: Genetic variation within putative clones

Four of five major cultivars of the potato (Solanum tuberosum L. ssp.tuberosum) from different sources were found to vary genetically. This variability was detected by an electrophoretic study of enzymatic activity for alkaline phosphatase and glucosephosphate isomerase. An examination of red cultivars from Beltsville, Md. suggests that the apparent intracultivar variability observed for Red Pontiac may be due to cultivar mislabeling rather than mutation or mitotic recombination. The results of this study raise concerns about potato cultivar certification and interpretations of some of the previous cultivar work. We suggest that a more extensive survey of intracultivar variability be carried out. Further, we suggest that these genetic markers and others could be used in cultivar identification.     

Harvest-pruning and trellising of ‘Sultana’ vines. I. Effects on yield and vegetative growth

Yield reductions averaging 10% are reported from 2 experiments in which ‘Sultana’ vines were continuously harvest-pruned for 11 and 9 years respectively. Over the period of the study there was no evidence of the yield reduction increasing with time.Differences between treatments in bunch number, berry weight and total soluble solids did not account for the reduction in yield. However, berry number per bunch was consistently, if not always significantly, lower on treated vines. Harvest-pruned vines had lower pruning-weights than the control vines.Increases in trellis width from 0.30 to 0.45 m to 0.90 m generally led to increases in yield caused by increases in bunch number. A 0.30 m wide T-trellis, with foliage wires added to support the shoots vertically to a height of 2 m, also gave yield increases over the standard 0.30 m trellis in most seasons. Harvest-pruned vines on the 0.90 m wide trellis gave similar yields to control vines on the standard 0.30 m trellis.     

Dysgenesis atypica ovarü bei einer XY-Kalbin. Histologische, biochemische, genetische und Rezeptor-Befunde

Inhalt: Die Phänomene der gonadalen Dysgenese weisen eine erhebliche Bandbreite au Die hier vorgestellte XY-Kalbin hatte ein geringgradig hypoplastisches, weibliches Genitale, in den dysgenetischen Gonaden lagen 2 Primordialrestfollikel vor. Ihre inter-stitiellen Zellen waren hyperplastisch, doch gab es keine Anzeichen für eine tumoröse Entartung, in Art eines Gonadenblastoms oder Dysgerminoms. Das Tier hatte zur Behandlung der bestehenden primären Amenorrhoe keine Hormonbehandlung erfahren. Die Konzentrationen uon Sexualsteroiden (Testosteron, Epitestosteron, Dehydroepian-drosteron) glichen solchen, wie sie im Zyklus des Rindes auftreten, ein Konzentrations-anstieg nach Pregnylapplikation war nichtzu erzielen. Nucleare Rezeptoren für Dihydro-testosteron waren nicht nachzuweisen. Die Persistenz von einzelnen Follikeln und von Keimzellen in den postpartalen resp. postpubertären Gonaden wurde in den letzten Jahren beim Menschen gelegentlich beschrieben, ist jedoch fur die reine gonadale Dysgenese nicht charakteristisch. Contents: Dysgenesis atypica ovarii in a XY-heifer The phenomena of gonadal dysgenesis show a wide range of variations. The XY-heifer described in this article showed low grade of hypoplasia of the inner female genital organes. Two primordial residual follicles were detected in serial sections of the dysgenetic gonads. The interstitial cells were hyperplastic, but there was no indication of tumorous degeneration, such as gonadoblastoma or dysgerminoma. No hormones had been given to treat primary amenorrhoe. Levels of sexual steroids (testosterone, epitestosterone, dehydroepiandrosterone were similar to those occurring in normal bovine cycle; Pregnyl failed to produce any rise in the concentration of sexual steroids. No evidence was found of nuclear receptors for dihydrotestosterone. Persistence of singular follicles and germinal cells in the postpartal and postpubertary gonads resp. of XY females has been sometimes observed (Cussen & Mac Mahon, 1979; Russel et al., 1980; Warner et al., 1985), but this is — by no means —characteristic for pure gonadal dysgenesis.