Successful rearing of whiteleg shrimp Litopenaeus vannamei larvae fed a desiccation‐tolerant nematode to replace Artemia

The nematode Panagrolaimus sp. was tested as live feed to replace Artemia nauplii during first larval stages of whiteleg shrimp Litopenaeus vannamei. In Trial 1, shrimp larvae were fed one of four diets from Zoea 2 to Postlarva 1 (PL1): (A) Artemia nauplii, control treatment; (NC) nematodes enriched in docosahexaenoic acid (DHA) provided by the dinoflagellate Crypthecodinium cohnii; (N) non‐enriched nematodes; and (Algae) a mixture of microalgae supplemented in C. cohnii cells. In Trial 2, shrimp were fed (A), (NC) and a different treatment (NS) with nematodes enriched in polyunsaturated fatty acids (PUFAs) provided by the commercial product S.presso^®, until Postlarva 6 (PL6). Mysis 1 larvae fed nematodes of the three dietary treatments were 300 μm longer (3.2 ± 0.3 mm) than control larvae. At PL1, control shrimp were 300 μm longer (4.5 ± 0.3 mm) than those fed DHA‐enriched or PUFAs‐enriched nematodes. No differences were observed in length and survival at PL6 between control larvae and those fed DHA‐enriched nematodes (5.1 ± 0.5 mm; 33.1%–44.4%). Shrimp fed microalgae showed a delay in development at PL1. This work is the first demonstration of Panagrolaimus sp. suitability as a complete substitute for Artemia in rearing shrimp from Zoea 2 to PL6.     

Composition of the stubble weed flora and its role for Heterodera schachtii in the year preceding sugar beet production

In Germany, sugar beet is often rotated with 2 years of cereal. Extensive fallow periods between cereal harvest and autumn primary tillage allow for a weed flora to develop. Broad‐leaved weeds could potentially be alternate hosts for the common nematode Heterodera schachtii, one of the most important pests of sugar beet. Between 2009 and 2012, annual weeds developing in cereal stubble fields during July to mid‐October in the season prior to sugar beet were surveyed, including known hosts of H. schachtii. Yearly weather patterns and agronomic practices possibly impacted weed species composition and weed population densities. During September, Chenopodium album, Cirsium arvense, Convolvulus arvensis, Mercurialis annua, Polygonum spp., Solanum nigrum and Sonchus spp. occurred at the highest frequencies. Weed hosts of H. schachtii were present, but densities, frequencies and uniformity were limited. In 2010 and 2011, staining for nematodes in roots revealed juvenile penetration of some weeds but few adult stages. No indication of nematode reproduction of H. schachtii was found on these weed hosts. A fairly stable weed flora was detected on stubble fields that could provide some carry over for weed species. An elevated risk for nematode population density build‐up on these weeds was not found and management of these weeds at the observed densities during the stubble period for nematological reasons appeared unnecessary.     

A SCAR marker linked to the N gene for resistance to root knot nematodes (Meloidogyne spp.) in pepper (Capsicum annuum L.)

The root-knot nematodes (Meloidogyne spp.) are important nematode pests and cause serious diseases in pepper in the world. No molecular markers linked to the nematodes resistance N gene have been reported. In this paper, ‘Carolina Wonder’ (Capsicum annuum L.), a sweet pepper line resistant to root-knot nematode with N gene, ‘20080-5-29’ (C. annuum L.), an inbred line susceptible to root-knot nematode with good horticultural characteristics, and their F₂ progeny with 320 individuals were used as materials. Evaluation of resistance and susceptibility of parental lines, F₁ and F₂ progeny inoculated with root-knot nematodes (Meloidogyne incognita) were carried out. ‘Bulked segregant analysis’ method was used to search for polymorphic markers from 512 pairs of AFLP primers. Based on the assessment of resistance and susceptibility and polymorphism of the AFLP marker in F₂ population, the genetic linkage distance between the AFLP marker and the N gene was estimated. One AFLP marker E39/M41-339 was obtained and transferred to a SCAR marker amplifying a 315 bp DNA fragment linked to the N resistant allele and a 331 bp fragment linked to the N⁺ susceptible allele. The distance between the molecular marker and the nematodes resistance N gene is 6.3 cM. This research delivered a valuable tool for the marker assisted selection of nematodes resistance in pepper.     

Population dynamics of the potato cyst nematode,Globodera pallida,in relation to temperature,potato cultivar and nematicide application

The impact of increasing temperatures on the population dynamics of the soil-dwelling nematode Globodera pallida, a persistent and economically important pest of potatoes, was investigated. The reproductive factor (final population⁄initial population) and length of life cycle were found to be temperature sensitive. Pot experiments performed over 4 months allowed comparison of the effect on development of G. pallida of two temperature regimes: an average temperature comparable to current field conditions (14.3 °C) and an average temperature above current field conditions (17.3 °C). A larger second generation of juveniles was observed at 17.3 °C compared to 14.3 °C. Multiplication of G. pallida at field sites in Shropshire and East Lothian (average soil temperatures of 15.5 and 14.1 °C, respectively, during potato cropping) was also examined. A quantitative PCR assay and visual examination of roots were used to monitor the dynamics of the G. pallida populations in both field sites at 4-weekly intervals. Four cultivars, Desirée, Cara, Maris Piper and Estima, were grown with and without nematicide treatments. Nematicide treatments suppressed population increases at both sites. Females were observed on the roots of cvs Cara and Desirée at the end of the growing season in Shropshire, but not at East Lothian, and are likely to represent a second generation.     

根瘤内生细菌对大豆胞囊线虫及根腐病菌的影响

为了明确大豆根瘤内生芽孢杆菌Snb2对大豆胞囊线虫的毒性和大豆根腐病菌的抑制作用,用菌悬液处理和对峙培养法分别测定了Snb2对两种病原微生物的作用效果.结果表明:Snb2的菌悬液能够明显抑制大豆胞囊线虫胞囊的孵化,相对抑制率达到94.9%;菌悬液处理J2 96 h时死亡率达到66.7%;Snb2菌株对4种大豆根系病原真菌表现不同程度的拮抗作用,对尖孢镰刀菌和茄腐镰刀菌的拮抗作用最明显,抑菌圈达到10 mm左右,抑制作用可持续10 d;经细菌悬浮液浸种测定,处理后的大豆子叶节到根尖的距离为9.1±4.54 cm,较对照增加了15.19%%,对幼苗生长有明显的促进作用;通过温室盆栽防效试验,进一步表明Snb2菌悬液进行种子浸种对大豆胞囊线虫病有明显的抑制作用,防治效果达到62.5%.     

贝加尔针茅草原土壤线虫与微生物群落特征及其相互作用

分析了在施氮环境下内蒙古贝加尔针茅草原土壤微生物和土壤线虫群落特征及相互作用。结果表明,不同的施氮水平显著影响土壤微生物真菌和细菌群落结构和数量,但对土壤微生物群落总量的影响并不显著;对土壤线虫食细菌类群（Bacterivores）、食真菌类群（Fungivores）和植物寄生性类群（Plant parasites）数量影响显著,同时影响土壤线虫的物种丰富度（SR）和群落结构的稳定性。土壤中的植物寄生性类群线虫与土壤中细菌群落、真菌群落和真菌/细菌之间呈显著正相关,土壤真菌群落与土壤线虫群落的丰富度（SR）、均匀度（J'）和结构指数（WI）也有明显的相关性。施氮对土壤真菌群落的影响大于对土壤细菌群落的影响,土壤中的真菌群落与土壤中植物寄生性类群线虫具有相互促进的作用,增加了植物受线虫感染的几率,同时施氮也改变了土壤线虫的群落结构。     

玫瑰黄链霉菌对根结线虫的防效及对土壤微生物区系的影响

利用玫瑰黄链霉菌Men-myco-93-63 菌株的固、液体发酵物防治设施番茄和黄瓜根结线虫,研究其对根结线虫的防效以及施用生防菌对土壤微生物区系的影响。结果表明：Men-myco-93-63 菌株固体发酵物1 V∶200 V对黄瓜和番茄根结线虫病的防效分别达到了65.62% 和57.69%;施用生防菌使得植株根际土壤中细菌数量增加了19.57%,放线菌数量增加了316.67%,真菌数量降低了28.57%,以上3 种可培养微生物总量由7.4×10⁶ cfu·g^-1增加到16.75×10⁶ cfu·g^-1,增加了126.35%。     

Chemical mutagenesis and soybean mutants potential for identification of novel genes conferring resistance to soybean cyst nematode

The resistance of soybean (Glycine max (L.) Merr.) to soybean cyst nematode (SCN, Heterodera glycines Ichinohe), which is a devastating pathogen in soybean production and causes a large quantity of annual yield loss worldwide, can shift during the long-term interaction and domestication. It is vital to identify more new resistance genetic sources for identification of novel genes underlying resistance to SCN for management of this pathogen. In the present study, first, two ethane methylsulfonate-mutagenesis soybean M2 populations of PI 437654, which shows a broad resistance to almost all of SCN races, and Zhonghuang 13, which is a soybean cultivar in China conferring strong resistance to lodging, were developed. Many types of morphological phenotypes such as four- and five-leaflet leaves were observed from these two soybean M2 populations. Second, 13 mutants were identified and confirmed to exhibit alteration of resistance to SCN race 4 through the forward genetic screening of 400 mutants of the PI 437654 M2 population, the rate of mutants with alteration of SCN-infection phenotype is 3.25%. Third, these identified mutants were further verified not to show any changes in the genomic sequences of the three known SCN-resistant genes, GmSHMT08, GmSNAP18 and GmSANP11, compared to the wild-type soybean; and all of them were still resistant to SCN race 3 similar to the wild-type soybean. Taken together, we can conclude that the 13 mutants identified in the present study carry the mutations of the new gene(s) which contribute(s) to the resistance to SCN race 4 in PI 437654 and can be potentially used as the genetic soybean sources to further identify the novel SCN-resistant gene(s).     

不同根际细菌对南方根结线虫抑制效果的研究

采用稀释平板涂布方法从番茄根结土壤中初步筛选出对明胶有水解作用的菌株。通过各菌株发酵上清液对南方根结线虫二龄幼虫死亡率和虫卵孵化率抑制作用,以及拮抗菌悬浮处理番茄根系30 d后观察番茄根结数量变化,进一步筛选获得高效菌株。通过16S rDNA基因序列分析,对能显著抑制根结线虫生长的2株菌株进行了鉴定。结果表明:筛选出了10株对明胶有明显水解圈的细菌,其中菌株BTG和X5具有较强的明胶水解能力。菌株BTG和X5发酵的上清液处理二龄幼虫24 h后的死亡率比无菌上清液处理死亡率提高了72.13%和62.14%;而用菌株上清液处理14 d后的虫卵孵化率比无菌上清液处理的孵化率降低了38.62%和30.73%。菌株BTG和X5的菌悬液处理的番茄根结数比不加菌悬液对照处理根结数分别降低了80.49%和73.17%。经16S rDNA基因序列分析表明,菌株BTG和X5都属于芽孢杆菌。通过比较各株细菌对二龄幼虫(J2)死亡率,虫卵孵化率及番茄根结数量的影响,筛选出了2株可用于生物防治作物根结线虫的芽孢杆菌。     

Impact of soil fumigation practices on soil nematodes and microbial biomass

This study was designed to understand the impact of methyl bromide (MB) (CHaBr) and its alternatives on both free-living and root-knot nematodes in the soil. A randomized complete block experiment with six treatments and 4 replicates (each replicate in a separate greenhouse) was established in Qingzhou, Shandong Province, China. In addition to MB and untreated control (CK) treatments there were four alternative soil fumigation practices including MB virtually impermeable films (VIF), metam sodium (MS), MS VIF and soil solarization combined with selected biological control agents (SS BCA). Two tomato (Lycopersicum esculentum Mill.) cultivars, cv. Maofen-802 from the Xian Institute of Vegetable Science, China, and cv. AF179 Brillante from the Israeli Hazera Quality Seeds, were selected as test crops. The results indicated that Rhabditidae was the most dominant population with percentage abundance as high as 85% of the total number of identified free-living nematodes, followed by that of Cephalobidae. Methyl bromide and its alternatives except for the non-chemical SS BCA treatment controlled the target pest, root-knot nematodes. Also, the impact of the three chemical alternatives on free-living nematode number and functional group abundance was similar to the impact associated with a typical methyl bromide application. Chemical fumigation practices, especially that with MB, significantly reduced the number of nematodes in the soil and simultaneously significantly reduced the number of nematode genera thereby reducing nematode diversity. All the four soil chemical fumigation activities decreased soil microbial biomass and had an obvious initial impact on microorganism biomass. Furthermore, both plant-parasitic and fungivore nematodes were positively correlated with soil microbial biomass.