Identification of field isolates of Rhizoctonia solani to detect quantitative resistance in rice under greenhouse conditions

The rates of in vitro hyphal growth of Rhizoctonia solani isolates, and their pathogenicity were evaluated to identify R. solani isolates that are suitable to detect quantitative resistance in rice. The isolates of R. solani were purified from the infected rice and two grass species in Arkansas over three years. Among 200 Rhizoctonia-like isolates, 102 isolates were identified as R. solani, and confirmed using a ribosomal DNA internal transcribed spacers’ marker. The rates of in vitro hyphal growth of the 102 R. solani isolates ranged from 1.17 to 1.89 mm/h, of which only 13.7% were significantly different from each other. The rates of in vitro hyphal growth of eight selected isolates were correlated with lesion lengths (r = 0.86 at P = 0.005 9 and r = 0.93 at P = 0.000 1) on the detached leaves of rice cultivars of Jasmine 85 (resistant) and M202 (susceptible), respectively. The eight isolates were selected based on the mean values of the maximal (1.89), median (1.54) and minimal (1.17) rates of hyphal growth. Two isolates that consistently exhibited significant differences in the rates of the hyphal growth were selected to examine the aggressiveness of isolates in micro-chambers. Using a micro-chamber, the slow growing isolates separated susceptible cultivars from moderately resistant cultivars better than the fast growing isolates. In contrast, the differences in disease reactions between both R. solani isolates were undetected using a standard field evaluation method. We suggest that the slow growing isolates are more useful than the fast growing isolates for detecting quantitative resistance with the micro-chamber method.     

Some effects of single and split applications of carbofuran on the incidence of and damage by Locris Maculata,Busseola Fusca and Sesamia Calamistis on maize

Abstract

Studies have been carried out on the efficacy of carbofuran (Furadan 5G) in reducing the incidence of the major insect pests of maize in Nigeria. A single dose of 1.5 kg a.i./ha applied in the planting hole was found to reduce the incidence of spittle bug (Locris Maculata F.) and stem borers (Busseola fusca (Fuller) and Sesamia calamistis (Hmps.)) when compared with split applications of the same dose applied at planting and 40 days after planting. The number of damaged plants was reduced from 40% in the control to 11.7% in the treated plots. Yields of fresh maize cobs were also increased significantly in treated plots. A significant positive correlation was established between the mean number of stem borer larvae and mean percentage damage, and significant negative correlations between the mean yield and mean percentage damage and between the mean yield and mean number of stem borer larvae.     

针叶小爪螨——寄主植物——芬兰钝绥螨相互关系的研究Ⅱ.挥发性物质在寄主植物——针叶小爪螨——芬兰钝绥螨之间的作用

用气相色谱 -质谱联用仪分析了板栗健康叶片、被针叶小爪螨危害过 (除去叶螨 )的叶片和被该叶螨危害并带有该叶螨的叶片挥发性物质的成分和相对含量。在受害和未受害叶片中 ,石竹烯和α 法尼烯均占较大的比例。石竹烯在受害叶中的峰值增高 ;而α 法尼烯在无叶螨的受害叶中的峰值增高 ;1 辛烯在未受害叶片中未检测到 ,但在受害的叶片中则含量均较高 ,尤其有叶螨的受害叶片较无叶螨的受害叶片 1 辛烯的峰值显著增高 ;苯甲酸乙酯在有叶螨的受害叶片中较其余 2种也显著增高 ;3,7,11 三甲基 1 6 10 十二碳三烯 3 醇以有螨的受害叶中含量最高 ,无叶螨的受害叶次之 ,未受害叶含量极微 ,几乎检测不到 ;但 4 溴 2 戊烯却呈现相反的趋势 ,在未受害叶中的含量显著高于受害叶。根据生物测试结果做出如下推断 :叶片受害后 ,挥发性物质的种类和含量发生了变化 ,改变了原来寄主植物气味的化学指纹图 ,使针叶小爪螨在识别寄主植物时遇到困难 ,甚至产生了忌避作用而从受害叶转移到未受害叶上。同时这些物质对引诱芬兰钝绥螨起着重要的引诱作用     

芬兰钝绥螨对针叶小爪螨的捕食作用研究

芬兰钝绥螨的雌成螨对针叶小爪螨幼螨、若螨和成螨的捕食功能反应均属ＨｏｌｌｉｎｇⅡ型。针叶小爪螨的螨态、芬兰钝绥螨的饥饿程度、生境大小等因素均可引起功能反应参数的变化。芬兰钝绥螨的雌成螨喜食针叶小爪螨的幼螨和若螨，而对雌成螨的良能力较弱。     

Molecular tools to investigate Rhizoctonia solani distribution in soil

Real-time PCR protocols were developed to detect and discriminate 11 anastomosis groups (AGs) of Rhizoctonia solani using ribosomal internal transcribed spacer (ITS) regions (AG-1-IA, AG-1-IC, AG-2-1, AG-2-2, AG-4HGI+II, AG-4HGIII, AG-8) or β-tubulin (AG-3, AG-4HGII, AG-5 and AG-9) sequences. All real-time assays were target group specific, except AG-2-2, which showed a weak cross-reaction with AG-2^tabac. In addition, methods were developed for the high throughput extraction of DNA from soil and compost samples. The DNA extraction method was used with the AG-2-1 assay and shown to be quantitative with a detection threshold of 10⁻⁷ g of R. solani per g of soil. A similar DNA extraction efficiency was observed for samples from three contrasting soil types. The developed methods were then used to investigate the spatial distribution of R. solani AG-2-1 in field soils. Soil from shallow depths of a field planted with Brassica oleracea tested positive for R. solani AG-2-1 more frequently than soil collected from greater depths. Quantification of R. solani inoculum in field samples proved challenging due to low levels of inoculum in naturally occurring soils. The potential uses of real-time PCR and DNA extraction protocols to investigate the epidemiology of R. solani are discussed.     

Effects of pesticides on mite predators (Acari: Phytoseiidae) and colonization of apple trees byTetranychus urticae

A 2-year survey of mite populations and pesticide use was carried out in Nova Scotia, Canada, in apple orchards where the two-spotted spider mite (Tetranychus urticae Koch) was the dominant phytophagous mite. Fungicides were the only class of pesticides that affected cumulative number ofT. urticae-days per leaf in tree canopies and colonization success — the ratio ofT. urticae-days to number of immigratingT. urticae caught in sticky bands on tree trunks. In 2000, increased numbers ofT. urticae-days in the tree canopy were associated with more frequent applications of ethylene bis-dithiocarbamate (EBDC) fungicides and with higher fungicide toxicity scores, which indicate cumulative level of suppression of the phytoseiid predatorTyphlodromus pyri Scheuten by all fungicide applications. Higher rates of colonization success were also associated with higher toxicity scores. EBDC’s applied in 2000 promotedT. urticae immigration as indicated by their counts on sticky bands. In 2000 and 2001, number ofT. pyri-days in the tree canopies was decreased by more frequent EBDC applications and by higher fungicide toxicity scores. Promotion ofT. urticae in tree canopies by EBDC’s was attributed to their toxicity toT. pyri. BothT. pyri and another phytoseiid,Amblyseius fallacis (Garman), were found in ground cover vegetation. Hence, increased immigration from the ground cover attributed to the toxicity of EBDC’s toT. pyri and, especially, toA. fallacis, which is a specialist predator of spider mites and an effective natural enemy ofT. urticae. http//www.phytoparasitica.org posting Sept. 13, 2006. Formerly, Atlantic Food and Horticulture Research Centre, now retired.     

Impact of intraguild predation and lambda-cyhalothrin on predation efficacy of three acarophagous predators

This laboratory study reports the interaction of three predators found in commercial apple orchards in Quebec, Hyaliodes vitripennis (Say) (Hemiptera: Miridae), Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Amblyseius fallacis (Garman) (Acarina: Phytoseiidae). First, intraguild predation between H vitripennis and the two other predators was characterized in the absence and presence of their extraguild prey, Tetranychus urticae Koch. The results showed an asymmetrical interaction in favour of the larger predator and the levels of intraguild predation were weak for the two predatory combinations. Presence of the phytophagous mite reduced the intensity of intraguild predation in the predatory combination of H axyridis and H vitripennis. Second, the effects of intraguild predation and the application of lambda-cyhalothrin on predation efficacy of the predators were evaluated. The application of the insecticide reduced prey consumption of H vitripennis and H axyridis but did not affect that of A fallacis. Combination of predators and an insecticide application resulted in two different situations depending on the species involved: a reduced predation efficacy for the combination of H vitripennis and H axyridis due to a knockdown effect caused by the insecticide, and no effect on T urticae consumption for H vitripennis and A fallacis. It is suggested that an integrated pest management program based on H vitripennis, A fallacis and lambda-cyhalothrin may be evaluated to repress phytophagous mites in Quebec orchards.     

从实验种群生命表参数评价胡瓜钝绥螨控制毛竹害螨的能力

本文报道胡瓜钝绥螨AmblyseiuscucumerisOudemans在 2 5℃条件下以毛竹 4种害螨南京裂爪螨chizotetranychusnanjingensisMa&Yuan、竹裂爪螨S .bambusaeReck、竹缺爪螨AponychuscorpuzaeRimando、竹刺瘿螨AculusbambusaeKuang为猎物的实验种群生命表 ,并进行比较结果表明 :①胡瓜钝绥螨能取食上述 4种害螨 ,其世代存活率依次为 90 4%、77 5 5 %、 87 93%、 81 63% ;②每雌总产卵量依次为 38 1 2粒、 45 77粒、 35 5 9粒、 30 76;③胡瓜钝绥螨以南京裂爪螨为猎物其净增殖率R0 =1 6 74低于南京裂爪螨 (R0 =2 0 84) ,但是内禀增长率rm=0 1 5 4是猎物的 1 73倍 (rm=0 0 89) ,世代周期T =1 8 31和种群倍增时间t=4 5 0 88均低于南京裂爪螨 (T =33 35 ,t=7 70 4 ) ,因此在林间当南京裂爪螨离巢、破巢或大量迁移时能有效地控制其种群增长 ;④胡瓜钝绥螨以竹裂爪螨为猎物其净增殖率R0 =2 5 81 ,内禀增长率rm=0 1 5 2 ,周限增长率λ =1 1 64均低于竹裂爪螨 (R0 =39 2 8、rm=0 1 92、λ =1 2 1 2 ) ,而世代周期T =2 1 35种群倍增时间t=4 5 5 2均高于竹裂爪螨 (T =1 9 0 8,t=3 60 3)因此必须在竹裂爪螨处于低密度时释放胡瓜犯绥螨才能有效地控制其种群密度的增长 ;⑤胡瓜钝绥螨以竹裂爪螨为猎物时 ,其     

Characterization of Rhizoctonia solani AG 2 isolates causing bare patch in field grown tulips in the Netherlands

During a spring survey in 1991, 130 isolates of R. solani were collected in 25 commercial flower bulb fields from diseased plants occurring in bare patches. On the basis of hyphal fusion frequency and pathogenicity to flower bulbs, tulip isolates were provisionally assigned to AG 2-t to distinguish these isolates from AG 2-1 isolates which were non-pathogenic to bulbs. Hyphal fusion frequency of a subgroup of 7 AG 2-t isolates was highly variable when paired with 7 AG 2-1 isolates (2-75%), thus making assignment of AG 2-t isolates to AG 2-1 inconclusive. The mean hyphal fusion frequency among AG 2-t isolates was 65% (±6%) indicating AG 2-t to be a relatively homogeneous group. Hyphal fusion frequency among AG 2-1 isolates was highly variable with a mean 51% (±25%) indicating AG 2-1 to be a heterogeneous group. The optimum growth temperature for AG 2-t and AG 2-1 isolates on malt peptone agar was 20-25 °C. The host range of AG 2-t and two AG 2-1 isolates comprised tulip, iris, hyacinth and lily at both 9 and 18 °C, and cruciferous, sugarbeet and lettuce seedlings at 18 °C. Six other AG 2-1 isolates were pathogenic to cruciferous seedlings, but not to any of the bulbous crops. The tested narcissus, Tagetes patula, tomato, potato, wheat, leek and maize cultivars were not susceptible to AG 2-t and AG 2-1 isolates. Statistical analysis using a proportional-odds model revealed significant differences in aggressiveness between R. solani AG 2-t isolates and differences in susceptibility between tulip and iris cultivars. At 18 °C, but not at 9 °C, isolates representing AG 2-2, AG 4, AG 5 and AG BI were pathogenic to bulbous crops. In addition to bare patch causing AG 2-t isolates, other anastomosis groups may cause disease in field grown tulips. For the development of optimal crop rotation schedules, the impact of bulb rot causing isolates under field conditions needs further study.     

新型机油乳剂对尼氏钝绥螨和柑桔的毒性试验

经测定表明,新型机油乳剂对尼氏钝绥螨的毒性极低,不仅比克螨特和三氯杀螨醇低得多,而且比江苏省靖江生化厂的机油乳剂毒性也低得多,对甜橙的夏梢和幼果试验也安全,可以认为是国内对天敌和作物安全性能较高的一种机油乳剂