Challenges to the exploitation of host plant resistance for Striga management in cereals and legumes by farmers in sub-Saharan Africa: a review

Striga hermonthica, Striga asiatica and Striga gesneroides are obligate root parasites that cause severe yield losses in cereals and legumes in sub-Saharan Africa. Genetic control of Striga through resistance is widely considered to be the most practical and economically feasible method for long term control. The paper presents a comprehensive account of the Striga resistance mechanisms and environmental limitations to their usage in sub-Saharan Africa. Components of Striga resistance in cereals and legumes include low germination stimulant production, low haustorial initiation factor, mechanical barriers, incompatibility, antibiosis and Striga avoidance due to root growth habits. The successful exploitation of resistance has been limited by existence of specificity towards hosts, parasites that have evolved races specific host cultivars, Striga genetic variance which enables parasite to adapt to new resistance alleles and diverse hosts which support the parasite even in the absence of cereals together with low fertility due to nutrient mining in the smallholder sector. The results imply that different resistance mechanism may need to be present in genetically heterogeneous varieties or cereals with different resistance mechanisms may be rotated in the same field. Comprehensive Striga management systems should also address soil fertility in the small holder farmers of sub-Saharan Africa.     

Individual-tree diameter growth model for sugar maple trees in uneven-aged northern hardwood stands under selection system

An individual-tree diameter model was developed for sugar maple (Acer saccharum Marsh.) in northern hardwood stands managed under selection system. We fitted long-term remeasurement data to a linear mixed model to account for the temporal autocorrelation of the remeasurements. The model was evaluated using independent data from two physiographic regions and representing a range of tree diameter classes, residual basal areas and years since cut. We compared our model to several individual-tree models based on data from stands with varied management histories. Several competition indices were also tested for an improvement in model fitting and prediction. Our model had lower bias and prediction error when compared to two previous models, as it better accounted for the increased diameter growth that occurred in trees from appropriately managed stands. The addition of a tree-specific competition index failed to improve model fit and predictive ability over stand-level basal area.     

A comparison of indoor and outdoor calf housing systems using automated and manual feeding methods and their effect on calf health,behavior, growth,and labor

Housing and feeding are integral to calf rearing, and must meet calf needs while remaining functional for the farmer. This study compared health, behavior, growth, and labor requirements of calves housed in groups indoors and fed via an automatic or manual milk feeding system compared to calves manually fed in individual or group hutches outdoors. Seventy-six (49 Holstein Friesian [HF] and 27 HF × Jersey) dairy heifer calves were balanced for birth weight (35.2 ± 4.95 kg), birth date (1 February ± 7.2 d) and breed. The experiment was a randomized block design with four treatments; 1) indoor group housing with automated feeding (IN_AUTO; 12 calves per pen), 2) indoor group housing with manual feeding (IN_MAN; 12 calves per pen), 3) outdoor group hutch with manual feeding (OUT_G_MAN; 8 calves per pen), and 4) outdoor individual hutch with manual feeding (OUT_I_MAN; 6 calves: 1 per pen). Calves in OUT_treatments moved outdoors at 18 d (± 5.9 d). Each treatment was replicated once. Milk allowance increased gradually from 6 to 8 L/day (15% reconstitution rate) with ad libitum fresh water, concentrates, and hay offered from 3 d old. Gradual weaning occurred at 8 wk old. Measurements were divided into period 1; before movement outdoors, and period 2; after movement outdoors. Health was similar among treatments, regardless of period, with the most frequent score being zero (i.e., healthy). Summarized, standing and lying were observed 24.3% and 29.8%, respectively, in OUT_I_MAN calves, compared to 8.0% and 49.1%, for the other systems, which were similar. No difference in bodyweight (BW) existed between treatments, except at weaning where BW was lower for OUT_I_MAN (67.4 ± 2.84 kg) compared to IN_MAN (74.2 ± 2.01 kg), and day 102 where OUT_I_MAN (94.1 ± 2.85 kg) were lighter than IN_AUTO (101.1 ± 2.10 kg) (P = 0.047). Total labor input was greatest for OUT_I_MAN (00:02:02 per calf per day; hh:mm:ss) and least for IN_AUTO (00:00:21 per calf per day) (P < 0.001). The labor for feeding (00:00:29 per calf per day), feeding inspection (00:00:10 per calf per day), and cleaning equipment (00:00:30 per calf per day) was greatest for OUT_I_MAN. All calves showed good health and growth patterns. Differences in behavior expressed by calves in the OUT_I_MAN, compared to other treatments may indicate compromised welfare. Thus, although outdoor group hutches do not negatively impact calves, indoor housing, particularly using automated feeders, can improve labor efficiency.     

Time-series models of sea lice Caligus elongatus (Nordmann) abundance on Atlantic salmon Salmo salar L. in Loch Sunart, Scotland

Most lice infestations on salmon farmed in the North Atlantic are attributed to Caligus elongatus and Lepeophtheirus salmonis. This study reports findings from time‐series analysis conducted on observations of the lesser‐studied C. elongatus, in four farms on the west coast of Scotland over the period 1996–2000. Least‐squares and Poisson regression techniques were applied to one individual site and to the aggregated data of four sites. Models were fitted and tested for goodness of fit using appropriate statistical methods. Findings indicate that infestation levels are highly seasonal with rapidly increasing numbers after week 22 of the year followed by a steady decline from week 40. Abundance is much lower in the second year of the production cycle than the first. Neither of the models indicated that treatment application has a significant effect on C. elongatus infestations.     

The construction and evaluation of a device for mechanomyography in anaesthetized Göttingen minipigs

Objective To devise a method for assessing evoked muscle strength on nerve stimulation [mechanomyography (MMG)] in the anaesthetized minipig. Study design Prospective observational. Animals Sixty male Göttingen minipigs weighing 10.5–26.0 kg. Methods After cadaveric studies, a limb fixation device was constructed which allowed the twitch responses of the pelvic limb digital extensor muscles to be measured by force‐displacement transduction in response to supramaximal train‐of‐four (TOF) stimulation of the common peroneal nerve. The device was tested in 60 minipigs weighing 10.5–26.0 kg positioned in dorsal recumbency. Results The technique recorded the MMG of the common peroneal–pelvic limb digital extensor nerve‐muscle unit for up to 12 hours during which twitch height remained constant in 18 animals in which single twitch duration was <300–500 ms. In 42, in which twitch duration was >300–500 ms, 2 Hz nerve stimulation caused progressive baseline elevation (reverse fade) necessitating a modified signal capture method for TOF ratio (TOFR) computation. However, T1 was unaffected. The mean (range) of the TOFR in pigs with reverse fade was 1.2 (1.1–1.3). Conclusions and clinical relevance The technique allowed MMG recording in unparalysed pigs in response to TOF nerve stimulation and revealed a hitherto unreported complication of MMG monitoring using TOF in animals: reverse fade. This complicated TOFR calculation.     

Hydrolyzable tannin structures influence relative globular and random coil protein binding strengths

Binding parameters for the interactions of pentagalloyl glucose (PGG) and four hydrolyzable tannins (representing gallotannins and ellagitannins) with gelatin and bovine serum albumin (BSA) have been determined from isothermal titration calorimetry data. Equilibrium binding constants determined for the interaction of PGG and isolated mixtures of tara gallotannins and of sumac gallotannins with gelatin and BSA were of the same order of magnitude for each tannin (in the range of 10(4)-10(5) M(-1) for stronger binding sites when using a binding model consisting of two sets of multiple binding sites). In contrast, isolated mixtures of chestnut ellagitannins and of myrabolan ellagitannins exhibited 3-4 orders of magnitude greater equilibrium binding constants for the interaction with gelatin (approximately 2 x 10(6) M(-1)) than for that with BSA (approximately 8 x 10(2) M(-1)). Binding stoichiometries revealed that the stronger binding sites on gelatin outnumbered those on BSA by a ratio of at least approximately 2:1 for all of the hydrolyzable tannins studied. Overall, the data revealed that relative binding constants for the interactions with gelatin and BSA are dependent on the structural flexibility of the tannin molecule.     

Social Heterogeneity and Community Forestry Processes: Reflections from Forest Users of Dhading District, Nepal

Community forestry has been characterized as a successful model of community-based forest governance in Nepal that shifts forest management and use rights to local users, often socially heterogeneous in caste, gender and wealth status. This heterogeneity forms the basis of social groups, which differ in their needs, priorities and perceptions regarding community forestry implementation processes. This paper explores the dynamics of three community forestry processes—users’ participation, institutional development, and decision-making and benefit-sharing—among forest user groups as perceived by three social groups of forest users—elite, women and disadvantaged—from eight community forests of Dhading district, Nepal, using qualitative and quantitative techniques. It is found that social groups have differing levels of perception about community forestry processes occurring in their user groups. In particular, social elites differ from women and disadvantaged members of the group in users’ participation in community forestry activities and institutional development of forest user groups. An important policy implication of the findings is that social inclusiveness is central to the effective implementation of community forestry processes, not only to safeguard its past successes but also to internalize the economic opportunities it poses through reducing deforestation and forest degradation in the future.     

A novel P106L mutation in EPSPS and an unknown mechanism(s) act additively to confer resistance to glyphosate in a South African Lolium rigidum population

Glyphosate resistance evolution in weeds is a growing problem in world agriculture. Here, we have investigated the mechanism(s) of glyphosate resistance in a Lolium rigidum population (DAG1) from South Africa. Nucleotide sequencing revealed the existence of at least three EPSPS homologues in the L. rigidum genome and identified a novel proline 106 to leucine substitution (P106L) in 52% DAG1 individuals. This mutation conferred a 1.7-fold resistance increase to glyphosate at the whole plant level. Additionally, a 3.1-fold resistance increase, not linked to metabolism or translocation, was estimated between wild-type P106-DAG1 and P106-STDS sensitive plants. Point accepted mutation analysis suggested that other amino acid substitutions at EPSPS position 106 are likely to be found in nature besides the P106/S/A/T/L point mutations reported to date. This study highlights the importance of minor mechanisms acting additively to confer significant levels of resistance to commercial field rates of glyphosate in weed populations subjected to high selection pressure.