Importance of the seed bank for population viability and population monitoring in a threatened wetland herb

Although demographic models have become increasingly important tools in plant conservation, few models have considered the implications of seed banks for population persistence. Based on a 15-year study of the threatened herb, Helenium virginicum, we created a stage-class transition matrix to model the population dynamics of the plant. Our goal was to determine the role of the seed bank in population persistence and in the design of monitoring programs for the plant. Using data from marked plants, a long-term study of seed viability, and a seed bank census, we created a deterministic model and three stochastic models. The stochastic models were a model in which yearly correlations among parameters were retained, a model in which parameters were uncorrelated, and a model in which parameters were derived from log-normal distribution. We also constructed a fourth model in which we assumed a minimum seed lifetime consistent with the seed viability data. Both elasticity and perturbation analysis suggested that seed survival within the seed bank had by far the largest effects on the population growth rate (λ), with 47-64% of the change in λ being controlled by seed survival. Correlations among life history parameters had little effect on λ in the original models, but substantially reduced λ (from 0.97 to 0.86) when seed survival was limited. Given the importance of the seed bank and the high yearly variability in adult plant density, we used simulations to compare power to detect declines with seed bank samples versus censuses of adult plants. The power of adult plant censuses was extremely low (13-22%). The power of seed bank censuses was substantially higher (48-59%), but was limited by large pulses of recruitment to the seed bank in good years. Power was only moderately reduced when seeds were sampled every two or four years instead of yearly (from 59% to 48%). Together, our results suggest that seed survival is crucial to persistence of Helenium populations and that future empirical studies should focus on understanding the factors that affect seed survival. In addition, managers should consider seed bank censuses rather than above-ground plants when designing monitoring programs for plants in variable environments where above-ground plants vary greatly from year to year.     

Novel expression of Haemonchus contortus vaccine candidate aminopeptidase H11 using the free-living nematode Caenorhabditis elegans

With the problem of parasitic nematode drug resistance increasing, vaccine development offers an alternative sustainable control approach. For some parasitic nematodes, native extracts enriched for specific proteins are highly protective. However, recombinant forms of these proteins have failed to replicate this protection. This is thought to be due to differences in glycosylation and/or conformation between native and recombinant proteins. We have exploited the free-living nematode Caenorhabditis elegans to examine its suitability as an alternative system for recombinant expression of parasitic nematode vaccine candidates. We focussed on Haemonchus contortus aminopeptidase H11 glycoprotein, which is enriched in a gut membrane fraction capable of inducing significant protection against this important ovine gastrointestinal nematode. We show that H. contortus H11 expressed in C. elegans is enzymatically active and MALDI mass spectrometry identifies similar di- and tri-fucosylated structures to those on native H11, with fucose at the 3- and/or 6-positions of the proximal GlcNAc. Some glycan structural differences were observed, such as lack of LDNF. Serum antibody to native H11 binds to C. elegans recombinant H11 and most of the antibody to rH11 or native H11 is directed to glycan moieties. Despite these similarities, no reduction in worm burden or faecal egg count was observed following immunisation of sheep with C. elegans-expressed recombinant H11 protein. The findings suggest that the di- and tri-fucosylated N-glycans expressed on rH11 do not contribute to the protective effect of H11 and that additional components present in native H11-enriched extract are likely required for enhancing the antibody response necessary for protection.     

Mapping QTLs for pre-harvest sprouting traits in the spring wheat cross ‘RL4452/AC Domain’

Pre-harvest sprouting (PHS) in spring wheat (Triticum aestivum L.) is a major downgrading factors for grain producers and can significantly reduce end-use quality. PHS resistance is a complex trait influenced by genotype, environment and plant morphological factors. A population of 185 doubled haploid (DH) lines from the spring wheat cross ‘RL4452/AC Domain’ were used as the mapping population to detect quantitative trait loci (QTLs) associated with three PHS traits, germination index (GI), sprouting index (SI) and falling number (FN). Six major QTLs linked with PHS traits were mapped on bread wheat chromosomes 3A, 3D, 4A (2 loci), 4B and 7D. ‘AC Domain’ alleles contributed to PHS resistance on 3A, 4A (locus-2) and 4B, and ‘RL4452’ alleles contributed resistance on 3D, 4A (locus-1) and 7D. QTLs detected on chromosome 4B controlling FN (QFN.crc-4B), GI (QGI.crc-4B) and SI (QSI.crc-4B) were coincident, and explained the largest amount of phenotypic variation in FN (22%), GI (67%) and SI (26%), respectively.     

Assessing evidence on the agronomic and environmental impacts of turfgrass irrigation management

In recent years, rising competition for water coupled with new environmental regulations has exerted pressure on water allocations for turfgrass irrigation. In this article, we reviewed published scientific and industry evidence on the agronomic and environmental impacts of turfgrass irrigation using a robust systematic review methodology. Our focus was on the links between (i) irrigation management (amount and frequency), (ii) agronomic responses to irrigation (turf quality, growth rates and rooting) and (iii) environmental impacts (nitrogen leaching). Based on an initial screening of 653 studies and data extracted from 83 papers, our results show that in most cases, under moderate levels of deficit irrigation (50%–60% of actual evapotranspiration), turf quality can be maintained at an acceptable level but with lower water consumption compared to irrigating back to field capacity. Irrigation beyond field capacity was found to increase the risk of nutrient leaching. However, evidence also showed that the concentration and total loss of in leachate were influenced more by nitrogen (N) rates, soil characteristics, turfgrass species and turfgrass growth rates than by irrigation practices. Our analyses suggest that turfgrass irrigation should be scheduled to apply water at moderate levels of deficit irrigation, sufficient to maintain turfgrass quality but limited to promote a deep and extensive rooting system. The findings provide new insights and valuable evidence for both scientists and practitioners involved in turfgrass research and management.     

Modelling impacts of precision irrigation on crop yield and in-field water management

Precision irrigation technologies are being widely promoted to resolve challenges regarding improving crop productivity under conditions of increasing water scarcity. In this paper, the development of an integrated modelling approach involving the coupling of a water application model with a biophysical crop simulation model (Aquacrop) to evaluate the in-field impacts of precision irrigation on crop yield and soil water management is described. The approach allows for a comparison between conventional irrigation management practices against a range of alternate so-called ‘precision irrigation’ strategies (including variable rate irrigation, VRI). It also provides a valuable framework to evaluate the agronomic (yield), water resource (irrigation use and water efficiency), energy (consumption, costs, footprint) and environmental (nitrate leaching, drainage) impacts under contrasting irrigation management scenarios. The approach offers scope for including feedback loops to help define appropriate irrigation management zones and refine application depths accordingly for scheduling irrigation. The methodology was applied to a case study in eastern England to demonstrate the utility of the framework and the impacts of precision irrigation in a humid climate on a high-value field crop (onions). For the case study, the simulations showed how VRI is a potentially useful approach for irrigation management even in a humid environment to save water and reduce deep percolation losses (drainage). It also helped to increase crop yield due to improved control of soil water in the root zone, especially during a dry season.     

The effects of urea supplementation on production and parasitological responses of sheep infected with Haemonchus contortus and Trichostrongylus colubriformis.

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH3-N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.     

Sequential histopathologic changes of type I, pre-type II and type II ostertagiasis in cattle

Yearling cattle in Louisiana were examined at monthly intervals for abomasal nematode burdens and histological lesions over a year. Tracer calves were grazed for 3 to 4 weeks and removed from pasture for 2 to 3 weeks, then slaughtered; a few animals were killed in extremis shortly after removal from pasture. Histological changes were correlated with worm burdens and characterized according to the type of Ostertagia ostertagi infection present. In cattle with acute Type I ostertagiasis, changes varied from eosinophil infiltration to glandular dilation and slight mucous cell hyperplasia with submucosal edema. During the summer months the cattle had worm burdens that were primarily early 4th stage larvae (EL4), with changes characterized by minimal glandular dilation and mucous cell metaplasia and moderate lymphoid cell proliferation and with intramucosal migration of EL4. In the autumn, the maturation of EL4 produced the Type II syndrome with severe glandular changes, prominent mucosal hyperplasia and marked lymphoid cell accumulation. With increased duration of the pre-Type II interval, there was greater development of the subepithelial lymphoid tissue and increased frequency of epithelial globule leukocytes. The lymphoproliferation which occurred during the prolonged pre-Type II interval appeared to be related to the increased severity and mortality seen with the Type II ostertagiasis syndrome.     

Effect of housing system and boar exposure on estrus expression in weaned sows

Reproductive efficiency depends on detection of estrus, which may be influenced by housing and boar exposure. This experiment investigated the effects of housing system and boar contact on measures of estrus in weaned sows. Mixed-parity sows were randomly assigned to be weaned into gestation crates away from boars (AWC, n = 45), into pens away from boars (AWP, n = 42), or into pens adjacent to a mature boar (ADJ, n = 46). Estrus detection was initiated at approximately 0700 (0 h) and again at 0.25-, 0.5-, 1-, 2-, 4-, and 8-h intervals beginning on d 4 and continuing through d 7 following weaning. Estrus detection involved observation of the standing response after application of nose-to-nose boar exposure, backpressure, and side rubbing. For the AWC sows, a mature boar was moved to the front of the crates for a 10-min period and then removed. Sows housed in AWP were moved approximately 15 m to an empty pen adjacent to a mature boar for a 10-min period, and then returned to their pen. Sows housed ADJ were not moved and estrus detection was performed in their home pen for a 10-min period. The proportion of sows expressing estrus within 7 d from weaning was lowest for ADJ (80%, 37/46) compared with AWP (98%, 41/42) and AWC (96%, 43/45; P < 0.05). There was an effect of interval from weaning to estrus on the percentage of sows expressing estrus, but there was no interaction with treatment. Sows in AWC and AWP (4.7 d) had decreased (P = 0.01) intervals from weaning to estrus compared with ADJ (5.2 d). The duration of estrus was also shorter (P < 0.001) for ADJ (45 h) compared with AWC (58 h) or AWP (62 h). There was a treatment x interval x day of estrus effect for the percentage of sows expressing estrus. After detection of the first standing response on the first day of estrus, only 62 to 82% of sows were detected standing over the next 2 h for all treatments. However, at 4 to 8 h, this increased to 85 to 98% for the AWC and AWP sows, but <73% of the ADJ sows were detected during this period. On the second day of estrus, estrus expression was not influenced by interval for the AWC and AWP sows and was between 90 to 100% during the 8-h period, whereas ADJ sow detection rates were between 68 to 88%. These data suggest that housing sows adjacent to boars negatively affects estrus expression and detection. In addition, refractory behavior occurs in approximately 30 to 40% of sows and is influenced by housing relative to the boar, day of estrus, and interval from last boar exposure.