Indoleacetic acid enhancement of 14C methionine uptake by tomato cell cultures aids assay of pathogen extracts

Incorporation of one micromolar IAA in the assay system increased the rate of ¹⁴C methionine uptake by tomato cells in suspension and effectively differentiated the rates of uptake such that cells treated with pathogenic and non-pathogenic Fusarium extracts could be easily distinguished in a rapid 3 h assay.     

Distribution of Fusarium wilt of Bambara nut (Vigna subterranea (L.) Verdc.) in farmers’ fields’ of Busia County in Western Kenya and its management using farmyard manure

A study was carried out to determine Fusarium wilt distribution in Bambara nut farmers’ fields and its management using farm yard manure (FYM). Four villages in Busia County were purposively sampled for the study. The data generated were subjected to analysis of variance and treatment means separated by least significant difference test. Fusarium wilt incidence in the fields ranged from 14.63 to 43.56%. In the greenhouse, FYM reduced the disease incidence by 10.2% and severity by 9.5% on the black landrace and 1.9 and 12.8%, respectively, on the red landrace. In the field, FYM reduced disease incidence by 9.1% and severity by 6.9% on the black landrace and 10.4 and 10.4%, respectively, on the red landrace. Farm yard manure had the lowest area under disease progress curve irrespective of the landrace. The study confirmed the presence of the pathogen in the fields and the ability to manage the disease using FYM.     

Spatial pattern of pine wilt disease caused byBursaphelenchus xylophilus (Nematoda: Aphelenchoididae) within aPinus thunbergii stand

To understand the mechanism of spread of pine wilt disease caused by the pinewood nematode, Bursaphelenchus xylophilus, which is vectored by a cerambycid, Monochamus alternatus, the spatial distribution of trees weakened by the nematode was examined within a Pinus thunbergii stand from June to October for 4 years. The weakened trees were distributed in a clumped pattern in 1980 and 1981, at an early stage of infestation. In many cases, they showed a double-clumped pattern. The degree of aggregation was higher in June or July than after August. They were uniformly distributed in June or July 1982 and in June 1983 whereas they showed a double-clumped pattern after August. The trees were frequently weakened in June or July when they were near the trees weakened during the previous year. At quadrat sizes of more than 25 m², spatial overlapping was pronounced between trees weakened during June–July of the current year and those weakened in the previous year. The seasonal changes in spatial distribution of weakened trees were explained by the interaction among M. alternatus, B. xylophilus and Pinus trees.     

Relationships between rhizoplane and rhizosphere bacteria and verticillium wilt resistance in potato

Six cultivars and breeding lines of potato (Solanum tuberosum) differing in susceptibility to verticillium wilt caused by Verticillium dahliae were studied with respect to quantitative and qualitative differences in the bacterial flora of their soil and rhizosphere-rhizoplane. Although, no association was observed between the types of bacteria that inhabited the soil or roots of wilt resistant and susceptible cultivars, quantitative differences were evident. These differences provide the first direct evidence that potato genotypes can influence bacterial populations. Bacterial populations were 9–25-fold higher on roots than in the adjacent soil. As the plants aged, the total number of rootcolonizing bacteria increased between 15 and 245%. Pseudomonas spp. were the most abundant microbes in the soil and rhizosphere-rhizoplane. The bacteria antagonistic to V. dahliae in vitro were identified as members of the genera Bacillus, Pseudomonas, Flavobacterium, and Gluconobacter. A statistically significant trend was evident toward the association of antagonistic bacteria with the more resistant potato cultivars.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

黑籽南瓜NBS类基因CfRFN2的克隆及VIGS验证

黑籽南瓜(Cucurbita ficifolia)是云南特有的具有高抗枯萎病遗传性状的瓜类种质资源。为鉴定黑籽南瓜中NBS-LRR类基因的抗病功能,该研究从其叶片中克隆了NBS类基因CfRFN2 (GenBank ID:MK618462),测序全长为4 303 bp,完整的编码框长度为4 092 bp,编码1 363个氨基酸残基,该基因注释为拟南芥抗病蛋白At4g27190类转录体X1的同源基因,含有1个NB-ARC和2个LRR结构域,属于具有信号肽的可溶性蛋白。核苷酸相似性分析显示,CfRFN2与其他瓜类NBS类基因相似性在87%～98%之间;系统进化树分析表明,CfRFN2蛋白和瓜类的其他NBS类抗病蛋白聚为一个分支,其中CfRFN2蛋白与中国南瓜和美洲南瓜的RPS2、印度南瓜的RPS2-like亲缘关系最近,其次是黄瓜的At4g27190和苦瓜的At4g27220,与甜瓜的Atg27190亲缘关系相对较远;组织表达特性分析表明,CfRFN2基因在黑籽南瓜叶片中表达量最高,其次是茎,而在果皮和根中表达量较低。该研究采用烟草脆裂病毒载体系统,构建了黑籽南瓜VIGS沉默载体pTRV2-CfRFN2,含沉默载体的农杆菌侵染黑籽南瓜幼苗后接种枯萎病菌,qRT-PCR检测表明,接种后2 d和4 d的转pTRV2-CfRFN2沉默组植株的CfRFN2基因表达量比接种后同时期的野生型植株显著降低(分别下降34.75%和98.27%),病情指数增加为野生型的1.32倍,初步证明黑籽南瓜CfRFN2基因具有抗枯萎病的功能,推测该基因可能在黑籽南瓜抗枯萎病防御过程中发挥着重要作用。该研究中NBS类基因CfRFN2的克隆和VIGS验证为黑籽南瓜更多优异基因的克隆和功能验证奠定了前期基础,也为发掘黑籽南瓜优异抗病基因和开展瓜类分子育种提供新信息。     

Integrated management of fusarial wilt of tomato with implementation of soil solarisation

Fusarial wilt of tomato (Lycopersicon esculentum Mill.) is a very common and severe disease occurring in most of the vegetable fields in West Bengal, India. Potenciation and formulation of different fungicidal chemicals and phytoextracts were evaluated against the growth of the pathogen wherein carbendazim (bavistin) and leaf extracts of Azadirachta indica (neem) were recorded to be most effective. Combined treatment with 4 ml neem leaf extract and 1 ml captan (0.01%) or with 4 ml garlic bulb extract and 1 ml captan (0.01%) exhibited 100% growth inhibition of the pathogen. Integrated control of the pathogen with phytoextracts, fungicide and biocontrol agents was carried out. Among the treatments, a combination with extracts of neem, captan (0.01%) and metabolites of Trichoderma harzianum was proved to be superior over the other. Field experiment with three fungicides at 0.5% concentration was carried out in randomised block design where application of bavistin showed up to 62.27% reduction of wilt infection in tomato plants. Soil solarisation of tomato field showed 62.50 and 66.69% reduction of infection during the trial years. However, integration of soil solarisation with the applications of T. harzianum, captan (0.01%) and neem resulted in 100% reduction of infection and thus it was recorded as the most effective treatment in reducing the incidence of the disease.     

Herbivore arthropods benefit from vectoring plant viruses

Plants infected with pathogens often attract the pathogens’ vectors, but it is not clear if this is advantageous to the vectors. We therefore quantified the direct and indirect (through the host plant) effects of a pathogen on its vector. A positive direct effect of the plant‐pathogenic Tomato spotted wilt virus on its thrips vector (Frankliniella occidentalis) was found, but the main effect was indirect; juvenile survival and developmental rate of thrips was lower on pepper plants that were damaged by virus‐free thrips than on unattacked plants, but such negative effects were absent on plants that were damaged and inoculated by infected thrips or were mechanically inoculated with the virus. Hence, potential vectors benefit from attacking plants with virus because virus‐infected plants are of higher quality for the vector's offspring. We propose that plant pathogens in general have evolved mechanisms to overcome plant defences against their vectors, thus promoting pathogen spread.     

与蚕豆萎蔫病毒2号胞间运动和长距离转运相关的寄主细胞超微结构研究

电镜超微结构观察和免疫金标记显示:受蚕豆萎蔫病毒2号(Broad bean wilt virus 2,BBWV 2)中国分离物B935侵染的豌豆(Pisum sativum)和蚕豆(Vicia faba)叶细胞中膜结构增生,形成膜结构增生区,病毒以结晶体和管状体形式存在于细胞质中。在病变早期,叶肉细胞的胞间连丝处连接有小管结构,病毒样颗粒呈纵列排在小管中,穿越胞间连丝的小管能被BBWV 2的金标记抗体特异性标记。维管束组织的薄壁细胞、伴胞及转移细胞内存在膜增生区及病毒管状体,在筛管壁附近存在的病毒样颗粒能被BBWV 2金标记抗体特异性标记。实验结果表明BBWV 2胞间运动形式与豇豆花叶病毒(CPMV)相似,以完整粒子通过在胞间连丝处形成的小管结构穿越胞间连丝;细胞质中存在的直径160nm管状体只是一种病毒聚集体,与胞间运动无直接关系;该病毒在筛管中可能也是以完整粒子形式进行长距离转运的。