Endocrine changes in the fowl during infection with Eimeria maxima

Plasma concentrations of thyroxine (T4), triiodothyronine (T3), prolactin, growth hormone and corticosterone were measured in immature domestic fowl which were infected with Eimeria maxima, uninfected but given the same amount of food as those infected (pair-fed) or fed ad libitum. Infection with E maxima caused a decrease in plasma T4 concentration whereas pair feeding caused an increase when food intake was minimal. Plasma T3 concentrations were decreased similarly in both infected and pair-fed birds. Infection caused an increase in plasma prolactin concentration, whereas pair-feeding did not. The plasma concentration of growth hormone was not affected by any of the treatments. Plasma corticosterone concentration was markedly increased on days 5 and 6 in pair-fed birds but was not affected by infection with E maxima.     

Grass inflorescence and spikelet culture: An appraisal

Summary Techniques of inflorescence and spikelet culture have been used for three major cereals. In maize, the influence of hormones on sexuality has been demonstrated. For wheat and barley the influence of supplying carbohydrate and nitrogen on grain content has been explored. Although in vitro seed setting is less efficient than in vivo the resulting grains, from optimal treatments, are in almost all respects normal or nearly so. Culture media to achieve this are precisely defined.In reviewing this work a major concern has been to highlight an elegant system of enquiry but at the same time to indicate the remarkably small area of interest to which it has been applied. As a prelude therefore to a consideration of the technical achievements, the range of spikelet form, and more particularly, function are examined. The aim is to encourage the application of inflorescence and spikelet culture to a much wider range of topics than hitherto.     

Relationships between height and yield in near-isogenic spring wheats that contrast for major reduced height genes

The effect of two major dwarfing (Rht-B1b and Rht-D1b) genes varies with environment. Near-isogenic pairs (i.e., tall and semidwarf) of six spring wheat lines, included in the International Adaptation Trial (IAT), were grown in 81 trials around the world from 2001 to 2004. Trial yields ranged from 1 to 8 t ha⁻¹ with a mean of ca. 4 t ha⁻¹. Overall, the yield advantage of the lines possessing the dwarfing gene was ca. 10% and was particularly evident in trials where the mean height of semidwarf isolines exceeded ca. 80 cm. However, the yield advantage was greater in the slightly taller and older lines (Pavon and Galvez) than in the newer lines Nesser and Kauz and the two durum lines. Sixteen pairs of semidwarf/tall near-isolines were grown in six managed drought environment trials at CIMMYT in northwestern Mexico. In these trials, height and yield differences were small and/or negligible in the most droughted environment (2.5 t ha⁻¹) and the slope of yield versus height for each isoline pair became consistently negative with increase in irrigation. In the IAT, the slope of the yield versus height was much more variable at low heights or yields, presumably due to the fact that there were many more factors driving the response. Even at the point where the slope became consistently negative (ca. between 2 and 4 t ha⁻¹), there were some trials where tall isolines equaled or exceeded the yield of semidwarf isolines, particularly in the most recent developed cultivar, Kauz. For submission to Euphytica as part of special issue “Challenges to International Wheat Breeding”. From the International Symposium on Wheat Yield Potential: Challenges to International Wheat Breeding, Days Inn, Ciudad Obregón, Sonora, Mexico, March 19–24th, 2006.     

Genotype by environment effects and selection for drought tolerance in tropical maize. II. Three-mode pattern analysis

A selection program in three tropical maize populations aimed to improve tolerance of mid-season to late season drought environments while maintaining grain yield (GY) potential. The selection process employed other attributes that included maintaining a constant anthesis date (AD) and, under drought, shortening the anthesis-silking interval (ASI) and increasing ear number per plant (EPP). Three-mode (genotypes × environments × attributes) pattern analysis, which consists of clustering and ordination, should be able to collectively interpret these changes from ten evaluation trials. Mixture maximum likelihood clustering identified four groups that indicated the populations' performance had changed with selection. Groups containing the advanced cycles of selection were higher yielding in most environments and had lower ASI and higher EPP, particularly in drought environments. Check entries with no selection for drought tolerance remained grouped with the initial cycles of selection. A 3 × 2 × 3 (genotypes by environments by attributes) principal component model explained 70% of the variation. For the first environmental component, ASI was shown to be highly negatively correlated with both GY and EPP while anthesis date (AD) was virtually uncorrelated with other traits. The second environmental component (explaining 10% of the variation) contrasted droughted and well-watered environments and showed that EPP and GY were better indicators of this contrast (in terms of changes in population performance) than were AD or ASI. Three-mode analysis demonstrated that improvements with selection occurred in both droughted and well-watered environments and clearly summarised the overall success of the breeding program. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differentiation of physical from chemical toxicity in solid waste fish bioassays

This study showed that particulate (i.e., physical) toxicity was responsible for rainbow trout deaths in bioassays with two separate solid wastes. This conclusion was based on: (1) fish necropsies which indicated physical damage to gills but no evidence of chemical damage to liver or kidney, (2) chemical analyses which indicated that levels of Priority Pollutants and other target compounds were too low to cause the observed toxicity, (3) structural and chemical analyses of the waste particles which showed that these consisted of inert materials, and (4) the use of centrifugation techniques to remove most of the suspended particulate material in bioassay tanks resulting in an elimination of most of the toxicity. The particles associated with the lethal effects were approximately 5 to 10 μm in size. Regulatory testing of solid wastes must distinguish physical and chemical toxicity since disposal options can vary depending on the mode of toxicity. For instance, chemical toxicity raises concern regarding leaching through soils into groundwater, whereas if physical particles are responsible for toxicity, such leaching is not of concern.     

Intensive tree planting facilitates tropical forest biodiversity and biomass accumulation in Kibale National Park, Uganda

The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675 kg/ha) than naturally regenerated trees (4560 kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.