Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

线虫群落结构对外源添加不同浓度铜污染物的响应

通过盆栽模拟试验的方法研究外源添加铜对土壤线虫群落结构的影响,试验添加Cu浓度分别为50 mg kg-1,100 mg kg-1,200 mg kg-1,400 mg kg-1干土和不施加污染物的对照处理,在小麦的生长关键期取样。试验结果表明:线虫不同营养类群对铜污染物的响应在小麦拔节期比较明显,拔节期捕食/杂食线虫的数量在外源添加400 mg kg-1Cu处理中显著低于对照,而不同浓度铜对食细菌线虫和食真菌线虫的影响则表现为低浓度促进高浓度抑制。线虫的生态指数对不同浓度铜污染物反映比较敏感,在小麦苗期和拔节期,与对照相比,不同浓度铜处理中线虫多样性降低,而优势度增加;自由生活线虫成熟度指数对不同浓度铜反映相对滞后,只在小麦成熟期表现出差异,即高浓度铜处理中线虫成熟度指数显著低于对照。     

不同剂量达虫净对山羊自然感染线虫的驱虫效果试验

按体重5mg/kg、10mg/kg、15mg/kg不同剂量的达虫净对自然感染线虫的山羊进行拌料饲喂驱虫,同时用0.2mg/kg阿维菌素一次皮下注射作药效对照,并设空白对照组。分别于用药前及用药后第7天取粪便进行虫卵计数。用药后第2天起每天检查由粪便中驱出的虫体数至查不出为止。结果表明:各剂量组药物对肺线虫虫卵减少率分别为100%,100%,100%,83.3%,虫卵转阴率分别为100%,100%,100%,66.7%;对捻转血矛线虫等其他线虫虫卵减少率分别为88.9%,100%,100%,100%,虫卵转阴率分别为66.7%,100%,100%,100%。用药后第2天病羊开始排虫,第3天为排虫高峰,第4天排虫减少,第5天仅见有少量虫体,第6天以后未再见虫体排出。     

我国草坪线虫2个新纪录种的记述

对江苏淮安地区草坪根际线虫种类进行调查,鉴定出我国草坪上2个植物寄生线虫新纪录种:粗尾矮化线虫(Tylenchorhynchus crassicaudatusWilliams,1960)和假强壮螺旋线虫(Helicoty-lenchus pseudorobustusGolden,1956)。     

大豆F_1代群体对孢囊线虫3号优势生理小种抗性遗传

本试验采用两个抗孢囊线虫品系84—783、CN210与当地感病的大豆品种绥农6号配制成84—783×绥农6号和绥农6号×CN210二个组合,在大豆孢囊线虫3号生理小种自然感染条件下,分析这些组合的F2代抗感病植株分离比例。结果表明,84—783、CN210的抗性基因对绥农6号的感病基因是隐性的,三对独立遗传的隐性基因控制84—783×绥农6号和绥农6号×CN210两个组合对大豆孢囊线虫3号生理小种的抗性。     

Tephrosia species and provenances for improved fallows in southern Africa

Seeking an alternative to Sesbania spp. tree fallows, a Tephrosia species and provenance trial was conducted at Msekera Research Station, Chipata (Zambia) to evaluate eleven Tephrosia vogelii and three Tephrosia candida provenances. They were tested for biomass production, quality of biomass, resistance to root-knot nematodes, nitrogen release, and for their effects on soil nitrogen dynamics. At the end of 1.5 years, the T. candida provenances 02970, 02971 and 02972 from Madagascar produced two times greater amount of aboveground biomass than the T. vogelii provenances. There was little variability among the T. vogelii provenances in terms of litter and biomass production. Weed growth was significantly greater under T. vogelii than T. candida provenances. While Tephrosia vogelii provenance 98/02 from Zambia and T. candida 02972 were highly tolerant to the Meloidogyne incognita nematodes, T. vogelii provenances 02977, 98/03, 02973 from Kenya, Zambia and Malawi, respectively, were highly susceptible to the nematodes. The Tephrosia species and provenances showed a wide variability in terms of N, lignin and polyphenol concentration in their foliage. Mineralization of N in the foliage of T. candida provenances 02970 and 02971 and T. vogelii provenances 98/04 and 02974 from Malawi occurred rapidly within 14 weeks of incubation. At the end of the 2-year growth period, there was significantly greater total inorganic N under T. candida provenance 02972 (12.5 mg kg⁻¹) than T. vogelii (5 mg kg⁻¹) provenance Mungwi 98/02. Maize (Zea mays L.) yields after T. candida provenances were greater than those after T. vogelii provenances. Further testing of the most promising provenances is needed for their effects on subsequent maize yields under a range of farm conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

High level of treatment failure with commonly used anthelmintics on Irish sheep farms

Background

In 2013 a Technology Adoption Program for sheep farmers was established to encourage the implementation of best management practices on sheep farms in Ireland. There were 4,500 participants in this programme in 2013. As part of this programme, farmers had the option to carry out a drench test to establish the efficacy of their anthelmintic treatment.

Results

Flock faecal samples were collected before and after treatment administration and gastrointestinal nematode eggs enumerated. In total there were 1,893 participants in the task, however only 1,585 included both a pre- and post-treatment faecal sample. Of those, 1,308 provided information on the anthelmintic product that they used with 46%, 23% and 28% using a benzimidazole (BZ), levamisole (LEV) and macrocyclic lactone (ML) product respectively. The remaining farmers used a product inapplicable for inclusion in the task such as a flukicide or BZ/LEV combination product. Samples were included for analysis of drench efficacy if the pre-treatment flock egg count was ≥200 eggs per gram and the interval post-sampling was 10–14 days for BZ products, 4–7 days for LEV products and 14–18 days for ML products. These criteria reduced the number of valid tests to 369, 19.5% of all tests conducted. If the reduction post-treatment was ≥95% the treatment was considered effective. Only 51% of treatments were considered effective using this criterion. There was a significant difference in efficacy between the anthelmintic drug classes with BZ effective in only 30% of treatments, LEV effective in 52% of cases and ML effective in 76% of cases.

Conclusions

Gastrointestinal nematode anthelmintic treatments, as practiced on Irish farms, have a high failure rate. There was a significant difference between the efficacies of the anthelmintic classes with BZ the least effective and ML the most effective.     

Management of Meloidogyne incognita in yam-based cropping systems with cover crops

The effect of intercropping cover crops was with yam was assessed for nematode management both in pot and field conditions in Nigeria. The cover crops were sown with yams in pots containing sterile soil and inoculated with 5000 eggs of Meloidogyne incognita. In the field, each cover crop was separately intercropped with yams inoculated with 10,000 nematodes. From both pot and field experiments, no nematode damage was observed on yam tubers that were intercropped with Aeschynomene histrix, Crotolaria juncea, and Tagetes erecta. Damage in intercropped tubers was reduced by 72.7% with Mucuna pruriens, Centrosema pubescens, and Pueraria phaseoloides and by 58.3% with Stylosanthes guianensis compared to yams planted without cover crops; they also had lower (p ≤ 0.05) nematode populations. Cajanus cajan, Lablab purpureus and Vigna unguiculata however, supported high nematode populations and led to nematode damage in intercropped yams. Tubers from M. incognita-inoculated plants were more damaged and lost 42% more weight (p ≤ 0.05) following three months of storage than tubers from uninoculated plants. Intercropping yams with selected cover crops can be useful in managing M. incognita without reducing yam yields.     

Histopathological changes induced by Meloidogyne incognita in some ornamental plants

Histopathological changes induced by the root-knot nematode (Meloidogyne incognita) in five ornamental plants, specifically, Calendula (Calendula officinalis), Centaurea (Centaurea montana), Papaver (Papaver somniferum), Chrysanthemum (Chrysanthemum morifolium) and Dianthus (Dianthus caryophyllus), were investigated. Based on the galling index (GI), Centaurea was classified as susceptible, Calendula as moderately susceptible, and Papaver as moderately resistant, while Chrysanthemum and Dianthus were highly resistant to M. incognita infection. The histopathology of the galled roots of Centaurea, Calendula, and Papaver during later stages of infection showed that nematodes were localized entirely within the cortex and generally oriented horizontally to the vascular cylinder. Most of the females were mature, and a few of them were associated with egg masses. Giant cells with a variation in cell sizes were observed in the galled roots of all three of the plant species and exhibited a granular cytoplasm and hypertrophied nuclei as a typical reaction to nematode feeding.     

Legacy effects of elevated ozone on soil biota and plant growth

Many studies have examined how human-induced atmospheric changes will influence ecosystems. The long-term consequences of human induced climate changes on terrestrial ecosystems may be determined to a large extend by how the belowground compartment will respond to these changes. In a free-air ozone enrichment experiment running for 5 years, we reciprocally transplanted soil cores from ambient and elevated ozone rings to test whether exposure to elevated ozone results in persistent changes in the soil biota when the plant and soil are no longer exposed to elevated ozone, and how these legacy effects of elevated ozone influenced plant growth as compared to current effects of elevated ozone. After one growing season, the current ozone treatment enhanced plant growth, but in soil with a historical legacy of elevated ozone the plant biomass in that soil was reduced compared to the cores originated from ambient rings. Current exposure to ozone increased the phospholipid fatty acids of actinomycetes and protozoa, however, it decreased dissolved organic carbon, bacterivorous and fungivorous nematodes. Interestingly, numbers of bacterivorous and fungivorous nematodes were enhanced when soils with a legacy of elevated ozone were placed under elevated ozone conditions. We conclude that exposure to elevated [O₃] results in a legacy effect in soil. This legacy effect most likely influenced plant growth and soil characteristics via responses of bacteria and fungi, and nematodes that feed upon these microbes. These soil legacies induced by changes in soil biotic community after long-term exposure of elevated ozone can alter the responses of ecosystems to current climatic changes.