Isolation and Characterization of a Novel Arabidopsis thaliana Mutant Unable to Develop Wilt Symptoms After Inoculation with a Virulent Strain of Ralstonia solanacearum

ABSTRACT To characterize host genes required for a compatible interaction, we identified a novel recessive Arabidopsis thaliana mutant, nws1 (no wilt symptoms), that failed to develop wilt symptoms in response to virulent strains of the phytopathogenic bacterium, Ralstonia solanacearum. The absence of wilting in nws1 plants was not correlated with a cell death phenotype or a constitutive expression of salicylic acid-, jasmonic acid- or ethylene-associated genes. In addition, this mutation, which conferred a symptomless phenotype in response to all the R. solanacearum strains tested, was highly specific to this pathogen, because nws1 responses to other plant pathogens, including oomycetes, nematodes, viruses, and other bacteria, were identical to those of wild-type Col-5 plants. Finally, the lack of disease development was shown to be different than RRS1-R-mediated resistance. The identification of mutants such as nws1, that are unable to develop disease, should lead to the isolation of target host factors required for pathogen growth or fitness, or of factors modified by the invading microorganism to avoid or inactivate plant defense mechanisms, and should bring a better understanding of bacterial wilt diseases.     

三株拮抗细菌对烟青枯病的抑制效果

烟草青枯病 (Ｒａｌｓｔｏｎｉａｓｏｌａｎａｃｅａｒｕｍ)是湖南烟草的一种重要病害。根据调查 ,发病面积380 0ｈｍ2 ,一般发病率 1 0 %～ 2 0 % ,重达 80 %～ 90 % ,损失极为严重。烟草青枯病是一种难防治的土传病害 ,国内外都在研究生物防治方法[1～ 6] ,并取得一定的效果 ,但大多还停留在大田小区试验 ,未能大面积推广。我们 1 995年在 2 3个烟区 ,6 2块烟地根际与根表土壤中分离筛选了一批拮抗细菌 ,进行了室内抑菌测定、温室初筛和培养发酵条件研究[7,8] ,本文报道该研究筛选的 3个拮抗菌湘 1 2、湘 2 3和 2 轻 9的进一步试验结果…     

防治青枯病工程菌Hrp-菌株的固体剂型研究

本文对工程菌 Hrp-菌株的固体剂型进行了初步研究。经载体、保护剂和抑菌剂的筛选,最终得出固体菌剂的制作方法。具体为将发酵菌液以5000 r/min离心10 min后弃上清,收集菌泥;将菌泥加至石蜡油中,振荡15～20 min使其在石蜡油中充分分散,制成菌悬液;再将此菌液按1：1比例与灭菌后的草炭混合均匀,制成固体菌剂;再向这种固体菌剂中加入杂菌抑制剂乳酸链球菌素（0.75 g/kg）和纳他霉素（0.075 g/kg）,并混合均匀。制作的固体菌剂在pH值5.3左右、含水量35%、不抽真空及温度25℃的条件下保存6个月,存活率为44.4%,有效活菌量为1.12×1010 cfu/g。     

Bacterial wilt of bellflower caused by Ralstonia solanacearum in Japan

A sudden wilt of bellflower (Campanula lactiflora) was observed in Japan in 1997. A bacterium that formed white fluidal and mucoid colonies resembling those of Ralstonia solanacearum was isolated from the infected plants. The bacterium was bacteriologically identified as biovar 3 of R. solanacearum. This is the first report of R. solanacearum affecting a plant species of the Campanulaceae family.     

Bacterial Wilt of China Aster Caused by Erwinia chrysanthemi

In July 2000, a bacterial wilt was found on China aster (Callistephus chinensis Nees) on Hokkaido, Japan. Bacteriological characteristics of the isolated bacteria were identical to Erwinia chrysanthemi. This is the first report on bacterial wilt of China aster caused by E. chrysanthemi. Received 4 June 2001/ Accepted in revised form 6 September 2001     

防治青枯病工程菌Hrp-菌株的发酵培养基配方优化

在摇瓶发酵条件下,采用全因子实验设计法和正交实验设计法对工程菌Hrp-菌株的培养基碳、氮源配方进行优化,确定了最适碳源为葡萄糖、细玉米面,最适氮源为硫酸铵、细豆饼粉;对这四个碳氮源因子的浓度进行L9（34）的正交试验,最终确定出该菌的最适发酵培养基碳、氮源配方为（g/L）：葡萄糖8g、细玉米面5g、细豆饼粉35g、硫酸铵2g。优化后的培养基配方使摇瓶发酵液菌量从1.34×10^10cfu/ml提高至3.30×10^10cfu/ml。     

Resistance to Taiwanese race 1 strains of Ralstonia solanacearum in wild tomato germplasm

A total of 252 wild Solanum accessions and one population of 49 introgression lines of LA716 were screened for resistance to a race 1/biovar 4/phylotype I strain Pss186 of Ralstonia solanacearum. Most wild tomato accessions were highly susceptible. However, five accessions of S. pennellii, i.e. LA1943, LA716, LA1656, LA1732 and TL01845 were resistant to strain Pss186. These accessions were then challenged against two other race 1/phylotpye I strains Pss4 and Pss190, which were more aggressive. All the five S. pennellii accessions were susceptible to Pss4, but displayed high to moderate resistance to Pss190 with a percentage of wilted plants ranging from 0% to 60%. Pss190 is an aggressive strain that made a resistant tomato line Hawaii 7996 susceptible. Thus, the results found in this study provide evidence of the presence of strain-specific resistance. LA3501, which has an introgression segment on chromosome 6, was found to be resistant to Pss186 among the screened introgression lines. This confirms the importance of resistance trait loci on chromosome 6 that have been identified by other studies. This is the first report of S. pennellii being resistant to bacterial wilt. These new resistant sources will provide breeders with more resources to breed for stable resistance to bacterial wilt of tomato.     

Expression of Human Lactoferrin cDNA Confers Resistance to Ralstonia solanacearum in Transgenic Tobacco Plants

ABSTRACT A construct containing a human lactoferrin cDNA was used to transform tobacco (Nicotiana tabacum) using an Agrobacterium-mediated DNA-transfer system to express this human protein in transgenic plants. Transformants were analyzed by Southern, Northern, and Western blots to determine integration of the cDNA into the plant genome and lactoferrin gene expression levels. Most transgenic plants demonstrated significant delays of bacterial wilt symptoms when inoculated with the bacterial pathogen Ralstonia solanacearum. Quantification of the expressed lactoferrin protein by enzyme-linked immunosorbent assay in transgenic plants indicated a significant positive relationship between lactoferrin gene expression levels and levels of disease resistance. Incorporation of the lactoferrin gene into crop plants may enhance resistance to other phytopathogenic bacteria as well.     

Molecular typing of Japanese strains of Ralstonia solanacearum in relation to the ability to induce a hypersensitive reaction in tobacco

The genetic diversity of 120 Ralstonia solanacearum strains isolated from a variety of host plants across Japan was assessed on the basis of hypersensitive response (HR) in tobacco leaves and phylogenetic analyses of endoglucanase gene egl, hrpB, and gyrB. Phylogenetic analysis of egl revealed that only three strains belonged to phylotype IV, and 117 strains belonged to phylotype I. Partial sequences of HrpB were identical among phylotype I strains except for one strain. Analyses using the partial nucleotide sequences of the gyrB and egl gene fragments grouped phylotype I strains into 11 gyrB and 8 egl types, respectively, whereas analyses using the partial amino acid sequences of GyrB and Egl grouped phylotype I strains into 4 GyrB and 5 Egl types, respectively. Using multilocus sequence typing of GyrB and Egl, we identified 10 unique sequence types within the Japanese phylotype I strains. Strains belonging to the GyrB42 or GyrB66 type caused wilt in tobacco, and strains belonging to GyrB2 or GyrB9 type elicited HR, demonstrating that HR induction in tobacco is genetically differentiated in the Japanese strains of R. solanacearum.     

Pine Wilt Disease Caused by the Pine Wood Nematode: The Induced Resistance of Pine Trees by the Avirulent Isolates of Nematode

Since the beginning of the 20th century, pine trees in Japan have been seriously damaged by the pine wilt disease. This disease is caused by the pine wood nematode, Bursaphelenchus xylophilus, which is transmitted by the Japanese pine sawyer, Monochamus alternatus. The control of disease depends to a large extent on chemicals, but the public is now demanding environmentally friendly control methods. The virulence of B. xylophilus varies very widely. Pre-inoculation of young pine trees in a nursery with avirulent B. xylophilus has induced systemic resistance of trees against a subsequent inoculation with virulent B. xylophilus. This induced resistance was considered a hopeful means for developing a biological control for the disease. The induced resistance by the avirulent nematodes was also expressed in mature pine trees in a forest where the disease was naturally epidemic. However, the effects of induced resistance were not satisfactory for practical biological control. Since the inoculation with higher concentrations of the avirulent B. xylophilus induced the resistance more effectively, the pre-inoculation method will need to be improved to develop the biological control. The induced resistance of pine trees by avirulent B. xylophilus should be one of the candidate biological control methods against pine wilt disease. This induced resistance also provides an experimental system to clarify physiological interactions between the nematodes and pine trees.     

Bacterial Wilt of Russell Prairie Gentian Caused by <Emphasis Type="Italic">Burkholderia caryophylli</Emphasis>

A new bacterial disease of Russell prairie gentian (Eustoma grandiflorum) was found in Fukuoka Prefecture, Japan, in 1997. This disease was characterized by wilting and yellowing of the foliage. A cross section of the stem of a diseased plant revealed a tan to yellow-brown discoloration of the vascular tissue. A nonfluorescent, aerobic, Gram-negative bacterium was consistently isolated from infected plants. The bacteriological characteristics of 10 isolates of the bacterium coincided with those of the reference strains of Burkholderia caryophylli that were isolated from carnations. The bacterium, as well as the reference strains, attacked Russell prairie gentian and carnation after artificial inoculation and reproduced the symptoms similar to those after natural infections. On the basis of bacteriological characteristics and pathogenicities, the bacterium was identified as B. caryophylli. This is the first report of a disease caused by B. caryophylli on Russell prairie gentian ; therefore, bacterial wilt of Russell prairie gentian is proposed as the name of the disease. Received 5 April 2000/ Accepted in revised form 11 July 2000     

A Review of Fusarium Wilt of Oil Palm Caused by Fusarium oxysporum f. sp. elaeidis

ABSTRACT Vascular wilt is the most destructive disease of oil palm in Africa and causes severe losses in some areas. Symptoms include initial wilting followed by desiccation of the fronds, which finally break and hang around the trunk. Internally, characteristic browning of the vascular elements is seen both in adult palms and in seedlings. Two disease syndromes are commonly seen in the field in adult palms-"acute wilt" where the palm dies within a few weeks and "chronic wilt" where the palm may remain alive for many months and even years but becomes progressively stunted. The pathogen (Fusarium oxysporum f. sp. elaeidis) is a soilborne fungus and the perennial nature of the crop ensured that, in the past, disease management was difficult. Over a period of 30 to 40 years, screening for resistance at the nursery stage was introduced in many plantations and research stations, and successful breeding programs in West Africa, notably in Ivory Coast, have resulted in more resistant oil palm material becoming available. The disease has not yet been detected in South East Asia (largest producer of palm oil) and rigorous quarantine measures have been imposed to prevent introduction of the pathogen into these highly productive areas.     

蜡样芽孢杆菌ANTI-8098A在番茄内的定殖和对青枯病的防治研究

本文研究了生防菌ANTI-8098A在番茄植株内的定殖及其对青枯病的生防特性,采用激光共聚焦显微技术观察了GFP标记菌株ANTI-8098A:pCM20在番茄根系的分布.ANTI-8098A及其标记菌株可很好地定殖于番茄植株内,在根内定殖浓度最高,达104～105cfu·g-1,茎部、叶片内次之,达103～104cfu·g-1;ANTI-8098A处理后番茄根系PPO活性显著提高,对番茄叶绿素含量有短期效应;处理后5～15d番茄根际微生物数量略低于对照,其后逐渐与对照趋于一致;ANTI-8098A及其标记菌株对青枯病的防效存在一定差异,平均防效为57.1%～100%.     

Fusarium Wilt of Banana Is Caused by Several Pathogens Referred to as Fusarium oxysporum f. sp. cubense

ABSTRACT Fusarium wilt of banana (also known as Panama disease) is caused by Fusarium oxysporum f. sp. cubense. Where susceptible cultivars are grown, management is limited to the use of pathogen-free planting stock and clean soils. Resistant genotypes exist for some applications, but resistance is still needed in other situations. Progress has been made with this recalcitrant crop by traditional and nontraditional improvement programs. The disease was first reported in Australia in 1876, but did the greatest damage in export plantations in the western tropics before 1960. A new variant, tropical race 4, threatens the trades that are now based on Cavendish cultivars, and other locally important types such as the plantains. Phylogenetic studies indicate that F. oxysporum f. sp. cubense had several independent evolutionary origins. The significance of these results and the future impact of this disease are discussed.