Forecasting Crop Damage by Nematodes: Nematode Population Dynamics1

Factors affecting the ease or difficulty of forecasting and modelling cyst, root-ectoparasitic and soil surface nematodes are mentioned. To relate pre-planting to post-harvest populations of cyst nematodes, a version of the logistic curve is derived from first principles and modified to take account of the injury done to root systems as numbers increase, and of eggs carried over to the following year. Egg hatch, when potato or other crops are grown, appears to be independent of population density. So also does root invasion over the population densities encountered in field plots. In the absence of enemies, population density is determined by competition for feeding sites induced by females in the root system, and by the size of the root system. Population oscillations about the equilibrium point are affected mainly by the proportion of the population that fails to hatch and the damage to the root system. The process of model building and the parameters required are outlined. The model includes hypotheses relating to intraspecific (genetic) competition and interspecific competition. The limitations of models and the need to make them stochastic are discussed. L'article fait état des possibilites et difficultés rencontrees dam la prévision et la modelisation des populations de nematodes a kystes, de nematodes ectoparasites des racines, et de nematodes de surface. Afin detablir la relation entre les populations de nematodes a kystes avant le semis et apres la recolte, il est recouru a la courbe logistique, derivee des principes fondamentaux. Celle-ci se trouve modifiee afin de tenir compte des degits croissants subis par les racines en fonction de I'augmentation des populations et de la survie d'une partie des ceufs d'une annee a I'autre. L'eclosion des ceufs semble être independante de la densite des populations dans les champs de pommes de terre et de toute autre culture. Ceci s'applique egalement a I'invasion des racines, dans le cas des densites de populations observees dans les parcelles experimentales. En I'absence dennemis, la densite est determinee par la competition pour L'acces aux sites de nutrition que les femelles preparent dans les racines, et par L'importance du systeme radiculaire. Les ecarts de population observes a partir dun equilibre sont principalement dus a la proportion de la population non eclose et aux deggts subis par les racines. I1 est fait etat d'une modelisation, basee sur certains parametres essentiels. Le modele repose sur L'hypothese d'une concurrence intraspecifique (genetique) et interspecifique. Les limites des modeles sont considerees, ainsi que la necessite de passer a une approche stochastique.     

Drivers,challenges and opportunities of forage technology adoption by smallholder cattle households in Cambodia

Forage technology has been successfully introduced into smallholder cattle systems in Cambodia as an alternative feed source to the traditional rice straw and native pastures, improving animal nutrition and reducing labour requirements of feeding cattle. Previous research has highlighted the positive impacts of forage technology including improved growth rates of cattle and household time savings. However, further research is required to understand the drivers, challenges and opportunities of forage technology for smallholder cattle households in Cambodia to facilitate widespread adoption and identify areas for further improvement. A survey of forage-growing households (n = 40) in July–September 2016 examined forage technology adoption experiences, including reasons for forage establishment, use of inputs and labour requirements of forage plot maintenance and use of forages (feeding, fattening, sale of grass or seedlings and silage). Time savings was reported as the main driver of forage adoption with household members spending approximately 1 h per day maintaining forages and feeding it to cattle. Water availability was reported as the main challenge to this activity. A small number of households also reported lack of labour, lack of fencing, competition from natural grasses, cost of irrigation and lack of experience as challenges to forage growing. Cattle fattening and sale of cut forage grass and seedlings was not found to be a widespread activity by interviewed households, with 25 and 10% of households reporting use of forages for these activities, respectively. Currently, opportunities exist for these households to better utilise forages through expansion of forage plots and cattle activities, although assistance is required to support these households in addressing current constraints, particularly availability of water, if the sustainability of this feed technology for smallholder cattle household is to be established in Cambodia.     

PG99S智能型喷灌机的调试及维护

在蔬菜、花卉的工厂化育苗生产中,准确控制肥水的浓度和喷洒的均匀性显得尤为重要,而喷灌设备作为智能型连栋育苗温室的主要浇灌设备,被广泛应用于现代化育苗温室中。该设备自动作业,水量控制精准。本文就PG99S型智能喷灌机介绍其调试方法和故障维修。     

Trivalent metal (Cr, Y, Rh, La, Pr, Gd) sorption in two acid soils and its consequences for bioremediation

The recent addition of trivalent metals to soil and their subsequent movement within the biosphere are of concern. For this reason, the sorption of chromium (Cr), yttrium (Y). rhodium (Rh), lanthanum (La), praseodymium (Pr) and gadolinium (Gd) in two contrasting acid soils has been determined. Except for Rh, the sorption of the other trivalent metals conformed well to the Langmuir equation with derived sorption parameters similar for all the trivalent species tested. Calculation of the buffer powers indicated that under both small (0·01 mmol kg^?1) and large (1 mmol kg^?1) trivalent metal soil loadings > 99·5% of the metals will be associated with the exchange phase with small quantities present in the bulk soil solution (<0·5%). It seems that the slight availability of metals within the bulk soil solution will slow the rate of trivalent metal bioremediation of contaminated sites.     

栽培稻种间近等基因系杂种育性研究

 为了研究亚洲栽培稻与非洲栽培稻种间杂种不育的遗传基础，以亚洲栽培稻品种WAB56-104为测验种与来自种间回交组合WAB56-104/CG14//WAB56-104///WAB56-104的14个种间近等基因系测交，对亲本及杂种的花粉及小穗育性研究表明，这14个近等基因系带有来自非洲栽培稻品种CG14的3个互不等位的配子消除位点和2个互不等位的花粉不育基因位点, 其中至少有2个配子消除位点未曾报道过。     

The effect of drying techniques on formononetin concentration in red clover

Oven-drying at 60°, 80° or 105°C was compared with microwave and freeze-drying as a method of preparing samples for the estimation of formononetin, the major oestrogenic factor in red clover. There was no significant difference in the formononetin concentration of clover samples either oven-dried at 60°C or freeze-dried. The formononetin concentration was reduced by drying at higher temperatures and by microwave-drying but was not affected by wilting for up to 8 h after harvesting. The routine determination of formononetin in ten varieties of red clover showed no significant differences between samples cold stored at – 18°C prior to oven-drying at 60°C and samples freeze-dried.     

Comparison of responses to floret and seedling inoculation in wheat- Ustilago tritici and barley- U. nuda combinations

The floret and seedling methods for inoculating wheat and barley with Ustilago tritici and U. nuda, respectively, were optimized and then compared. Floret inoculation gave higher infection levels than did seedling inoculation, especially for wheat, but problems of plant mortality and standardization of tissue age were greater with the former method. Floret inoculation identified wheat and barley varieties exhibiting embryo resistance (class 1 or 2 resistance) or seedling resistance (class 3), but only class 3 wheat and barley varieties (and one class 2 wheat variety) were resistant to seedling inoculation. Using near-isogenic wheat lines expressing different levels of partial resistance to floret inoculation, positive correlations were obtained between percentage infection levels resulting from the two inoculation protocols. In addition, race-specific host-pathogen interactions such as hypersensitivity and partial smutting were expressed following both floret and seedling inoculation, indicating that these interactions operate in the developing plant. The potential value of the seedling inoculation method in fundamental and applied research into the cereal-loose smut interaction is discussed.