Induction of Systemic Resistance Against Bacterial Wilt in <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> by Fluorescent <Emphasis Type="Italic">Pseudomonas</Emphasis> spp

The ability of selected strains of fluorescent Pseudomonas spp. to cause induced systemic resistance (ISR) in Eucalyptus urophylla against bacterial wilt caused by Ralstonia solanacearum was investigated. Four of the five strains used can produce salicylic acid (SA) in vitro and, therefore, chemical SA, that is known to induce resistance in many plant species, was used as a reference treatment. Whereas a soil drench with SA did induce systemic resistance in E. urophylla, infiltration of SA into leaves did not. None of the fluorescent Pseudomonas spp. strains caused ISR against bacterial wilt when applied to the soil, but two strains, P. putida WCS358r and P. fluorescens WCS374r triggered ISR when infiltrated into two lower leaves 3–7 days before challenge inoculation. A mutant of strain WCS358r defective in the biosynthesis of the fluorescent siderophore pseudobactin, did not cause ISR, while the purified siderophore of WCS358r did, suggesting that pseudobactin358 is the ISR determinant of WCS358. A siderophore-minus mutant of WCS374r induced the same level of disease resistance as its parental strain, but the purified siderophore induced resistance as well, indicating that both the siderophore and another, unknown, inducing determinant(s) of WCS374r can trigger ISR in Eucalyptus. A possible role of WCS374r-produced SA remains uncertain. Transformation of a siderophore-minus mutant of WCS358 with the SA biosynthetic gene cluster from WCS374 did not enable this transformant to cause ISR in E. urophylla.     

Suppression of fusarium wilt of radish by co-inoculation of fluorescentPseudomonas spp. and root-colonizing fungi

In an earlier study, treatment of radish seed with the bacteriumPseudomonas fluorescens WCS374 suppressed fusarium wilt of radish (Fusarium oxysporum f. sp.raphani) in a commercial greenhouse [Leemanet al., 1991b, 1995a]. In this greenhouse, the areas with fusarium wilt were localized or expanded very slowly, possibly due to disease suppressiveness of the soil. To study this phenomenon, fungi were isolated from radish roots collected from the greenhouse soil. Roots grown from seed treated with WCS374 were more abundantly colonized by fungi than were roots from nonbacterized plants. Among these were several species known for their antagonistic potential. Three of these fungi,Acremonium rutilum, Fusarium oxysporum andVerticillium lecanii, were evaluated further and found to suppress fusarium wilt of radish in a pot bioassay. In an induced resistance bioassay on rockwool,F. oxysporum andV. lecanii suppressed the disease by the apparent induction of systemic disease resistance. In pot bioassays with thePseudomonas spp. strains, the pseudobactin-minus mutant 358PSB^– did not suppress fusarium wilt, whereas its wild type strain (WCS358) suppressed disease presumably by siderophore-mediated competition for iron. The wild type strains of WCS374 and WCS417, as well as their pseudobactin-minus mutants 374PSB^– and 417PSB^– suppressed fusarium wilt. The latter is best explained by the fact that these strains are able to induce systemic resistance in radish, which operates as an additional mode of action. Co-inoculation in pot bioassays, ofA. rutilum, F. oxysporum orV. lecanii with thePseudomonas spp. WCS358, WCS374 or WCS417, or their pseudobactin-minus mutants, significantly suppressed disease (except forA. rutilum/417PSB^– and all combinations with 358PSB^–), compared with the control treatment, if the microorganisms were applied in inoculum densities which were ineffective in suppressing disease as separate inocula. If one or both of the microorganism(s) of each combination were applied as separate inocula in a density which suppressed disease, no additional suppression of disease was observed by the combination. The advantage of the co-inoculation is that combined populations significantly suppressed disease even when their individual population density was too low to do so. This may provide more consistent biological control. The co-inoculation effect obtained in the pot bioassays suggests that co-operation ofP. fluorescens WCS374 and indigenous antagonists could have been involved in the suppression of fusarium wilt of radish in the commercial greenhouse trials.Abbreviations CFU colony forming units - KB King's B - PGPR plant growth-promoting rhizobacteria - CQ colonization quotient     

Siderophore-mediated competition for iron and induced resistance in the suppression of fusarium wilt of carnation by fluorescent Pseudomonas spp

The mechanisms of suppression of fusarium wilt of carnation by two fluorescentPseudomonas strains were studied.Treatments of carnation roots withPseudomonas sp. WCS417r significantly reduced fusarium wilt caused byFusarium oxysporum f. sp.dianthi (Fod). Mutants of WCS417r defective in siderophore biosynthesis (sid^–) were less effective in disease suppression compared with their wild-type. Treatments of carnation roots withPseudomonas putida WCS358r tended to reduce fusarium wilt, whereas a sid^– mutant of WCS358 did not.Inhibition of conidial germination of Fod in vitro by purified siderophores (pseudobactins) of bothPseudomonas strains was based on competition for iron. The ferrated pseudobactins inhibited germination significantly less than the unferrated pseudobactins. Inhibition of mycelial growth of Fod by bothPseudomonas strains on agar plates was also based on competition for iron: with increasing iron content of the medium, inhibition of Fod by thePseudomonas strains decreased. The sid^– mutant of WCS358 did not inhibit Fod on agar plates, whereas the sid^– mutants of WCS417r still did. This suggests that inhibition of Fod by WCS358r in vitro was only based on siderophore-mediated competition for iron, whereas also a non-siderophore antifungal factor was involved in the inhibition of Fod by strain WCS417r.The ability of thePseudomonas strains to induce resistance against Fod in carnation grown in soil was studied by spatially separating the bacteria (on the roots) and the pathogen (in the stem). Both WCS417r and its sid^– mutant reduced disease incidence significantly in the moderately resistant carnation cultivar Pallas, WCS358r did not.It is concluded that the effective and consistent suppression of fusarium wilt of carnation by strain WCS417r involves multiple mechanisms: induced resistance, siderophore-mediated competition for iron and possibly antibiosis. The less effective suppression of fusarium wilt by WCS358r only depends on siderophore-mediated competition for iron.     

The enhanced disease susceptibility phenotype of ethylene-insensitive tobacco cannot be counteracted by inducing resistance or application of bacterial antagonists

In an attempt to overcome the enhanced disease susceptibility phenotype that is typical for transgenic ethylene-insensitive tobacco (Tetr), Tetr plants were treated with chemical agents that induce resistance or with antagonistic rhizobacteria. Treatments with β-aminobutyric acid (BABA), benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), methyl jasmonate (MeJA), or salicylic acid (SA) induced PR-genes generally to a lesser extent than in non-transformed plants and did not reduce wilting symptoms upon infection with Pythium sp., except for a marginal effect of SA. In Tetr lines overexpressing PR-1g, PR-5c, or both, no significant reduction in disease development was apparent. Also treatment of Tetr plants with the antagonistic rhizobacteria Bacillus cereus UW85, Pseudomonas aeruginosa 7NSK2, Pseudomonas fluorescens WCS417r or Q8r-196, Pseudomonas putida WCS358r, or antibiotic-producing derivatives of WCS358r, did not reduce symptoms caused by Pythium.     

Induction of systemic resistance byPseudomonas fluorescens in radish cultivars differing in susceptibility to fusarium wilt,using a novel bioassay

Pseudomonas fluorescens-mediated induction of systemic resistance in radish against fusarium wilt (Fusarium oxysporum f. sp.raphani) was studied in a newly developed bioassay using a rockwool system. In this bioassay the pathogen and bacterium were confirmed to be confined to spatially separate locations on the plant root, throughout the experiment. Pathogen inoculum obtained by mixing peat with microconidia and subsequent incubation for four days at 22 °C, yielded a better percentage of diseased plants than a microconidial suspension drench, an injection of a microconidial suspension into the hypocotyl, or a talcum inoculum.Pseudomonas fluorescens strain WCS374 applied in talcum or peat, but not as a suspension drench, induced systemic resistance. A minimal initial bacterial inoculum density of 10⁵ CFU WCS374 root^–1 was required to significantly reduce the percentage diseased plants. At least one day was necessary between bacterization of strain WCS374 in talcum on the root tips and inoculation of the pathogen in peat on the root base, for an optimal induction of systemic resistance. Strain WCS374 induced systemic resistance in six radish cultivars differing in their susceptibility toF. oxysporum f. sp.raphani. Significant suppression of disease by bacterial treatments was generally observed when disease incidence in the control treatment, depending on pathogen inoculum density, ranged between approximately 40 to 80%. Strains WCS374 and WCS417 ofPseudomonas fluorescens induced systemic resistance against fusarium wilt, whereasP. putida WCS358 did not. This suggests that the induction of systemic resistance byPseudomonas spp. is dependent on strain-specific traits.Abbreviations CFU colony forming units - IFC immunofluorescence colony-staining - ISR induced systemic resistance - PBS phosphate buffered saline - SAR systemic acquired resistance     

Heritability Of Rhizobacteria-mediated Induced Systemic Resistance And Basal Resistance In Arabidopsis

Selected strains of non-pathogenic rhizobacteria have the ability to trigger an induced systemic resistance (ISR) response in plants. In Arabidopsis, rhizobacteria-mediated ISR has been extensively studied, using Pseudomonas fluorescens WCS417r as the inducing agent and P. syringae pv. tomato DC3000 (Pst) as the challenging pathogen. To investigate how far expression of ISR depends on the level of basal resistance, 10 different Arabidopsis ecotypes were screened for their potential to express WCS417r-mediated ISR and basal resistance against Pst. Two Arabidopsis ecotypes, RLD and Wassilewskija (Ws), were found to be blocked in their ability to express ISR. This ISR-noninducible phenotype correlated with a relatively low level of basal resistance against Pst. Genetic analysis of crosses between the ISR-inducible ecotypes Columbia (Col) and Landsberg erecta (Ler), on the one hand, and the non-inducible ecotypes RLD and Ws, on the other hand, revealed that ISR inducibility and basal resistance against Pst were inherited as monogenic dominant traits that are genetically linked. Neither ISR inducibility, nor basal resistance against Pst was complemented in the F₁ progeny of a cross between RLD and Ws, indicating that both ecotypes are affected in the same locus. This locus, designated ISR1, was mapped between markers Ein3 and GL1 on chromosome III. Interestingly, ecotypes RLD and Ws also failed to express ISR against the oomycetous pathogen Peronospora parasitica, but they were not affected in their level of basal resistance against this pathogen. Thus, the ISR1 locus controls the expression of ISR against different pathogens but basal resistance only against Pst and not against P. parasitica. Like ecotypes RLD and Ws, ethylene-insensitive mutants showed the isr1 phenotype in that they were unable to express WCS417r-mediated ISR and show enhanced susceptibility to Pst infection. Analysis of ethylene responsiveness of RLD and Ws revealed that both ecotypes exhibit reduced sensitivity to ethylene. Therefore, it is proposed that the Arabidopsis ISR1 locus encodes a component of the ethylene-response pathway that plays an important role in ethylene-dependent resistance mechanisms.     

Responses of cucumber cultivars to induction of systemic resistance against anthracnose by plant growth promoting fungi

Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria     

Development of ascochyta blight (Ascochyta rabiei) in chickpea as affected by host resistance and plant age

Ascochyta blight caused by Ascochyta rabiei, is the most destructive disease in many chickpea growing countries. Disease development varies with the growth stage and host resistance. Hence, disease development was studied in cvs ICCX 810800 (resistant), ICCV 90201 (moderately resistant), C 235 (moderately susceptible), ICCV 96029 and Pb 7 (susceptible) under controlled environment (ICRISAT, Patencheru) and field conditions (Dhaulakuan, Himachal Pradesh) at seedling, post-seedling, vegetative, flowering and podding stages. Under controlled environment, the incubation period and terminal disease reaction (TDR) did not vary significantly at different growth stages against virulent isolate AB 4. Cultivars ICCX 810800, ICCV 90201 and C 235 showed a significantly longer incubation period than the susceptible cv. Pb 7. Cultivar ICCX 810800 showed slow disease progress and the least TDR. Field experiments were conducted during the 2003–2004 and 2004–2005 growing seasons. During 2003–2004, TDR was higher in plants inoculated at podding and the flowering stage and the lowest disease reaction was recorded in ICCX 810800. A severe epidemic during 2004–2005 was attributed to the favourable temperature, humidity and well distributed high rainfall. TDR did not differ significantly at any of the growth stages in susceptible cvs ICCV 96029 and Pb 7. With respect to seeding date and cultivar, the highest yield was recorded in the early-sown crop (1,276.7 kg ha⁻¹) and in ICCV 90201 (1,799.3 kg ha⁻¹), respectively. The yields were greatly reduced in all the cultivars during 2004–2005 and the highest yield was recorded in ICCX 810800 (524.7 kg ha⁻¹). Integrated disease management using resistant cultivars, optimum sowing period and foliar application of fungicides will improve chickpea production. The experiment under controlled environment and field conditions (during the epidemic year) showed a similar disease development.     

Identification of Resistance to Common Bacterial Blight Disease on Bean Genotypes Grown in Turkey

Common bacterial blight (CBB) in edible beans (Phaseolus vulgaris), incited Xanthomonas campestris pv. phaseoli, reduces bean yields and seed quality. The main objective of this study was to determine resistance to common bacterial blight in bean genotypes. Twenty-two bean genotypes grown in Turkey including common and snap bean cultivars/lines were collected from different parts of Turkey and tested for resistance against to Xanthomonas campestris pv. phaseoli strain MFD-11. All the common and snap bean lines/cultivars tested were moderately susceptible, susceptible or highly susceptible, except AG-7117 which was found resistant to Xanthomonas campestris pv. phaseoli. This is the first report of a resistance source in a common bean line (AG-7117) against Xanthomonas campestris pv. phaseoli.     

Benzothiadiazole and BABA improve resistance to <Emphasis Type="Italic">Uromyces pisi</Emphasis> (Pers.) Wint. in <Emphasis Type="Italic">Pisum sativum</Emphasis> L. with an enhancement of enzymatic activities and total phenolic content

Benzothiadiazole (BTH) and DL-β-aminobutyric acid (BABA) induced systemic resistance was investigated in susceptible and resistant pea genotypes against Uromyces pisi. Resistance was characterized by reduced infection frequency mainly due to decreases in appressorium formation, stomatal penetration, growth of infection hyphae and haustorium formation. Changes in β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase and peroxidase activities and in total phenolics content, demonstrate that U. pisi resistance is induced by BTH and BABA treatments at early and late stages of the fungal infection process, but that the chemicals operate via different mechanisms. In fact, our study showed that BTH treatment primed the activity of pathogenesis related-proteins such as β-1,3-glucanase, chitinase and peroxidase in both susceptible and resistant genotypes. On the other hand, BABA treatment did not increase the enzymatic activities in the studied genotypes, but significantly increased their total phenolic contents.     

Assessment of resistance to <Emphasis Type="Italic">Ceratocystis cacaofunesta</Emphasis> in cacao genotypes

Ceratocystis wilt of cacao (caused by Ceratocystis cacaofunesta) is a dangerous disease and results in the death of the plant. This fungus was recently identified in the major cacao-producing regions of Brazil, and was observed to be more aggressive than isolates from other geographical locations. The objective of this study was to develop and test a consistent method to assess cacao genotype response to C. cacaofunesta, based on young plants (seedlings or cuttings). The fungus was inoculated by the deposition of propagule suspensions on cut stems. The parameters to assess disease progress were (a) disease incidence, (b) differences in mortality between the most contrasting cacao genotypes for resistance and susceptibility, (c) disease index, (d) consistency of response over time and (e) relative lesion heights. When seedlings were used for the analyses, the ICS-1 and TSH-1188 genotypes proved to be useful as genetic standards for susceptibility and resistance to C. cacaofunesta, respectively. Inoculum concentrations between 10⁴ and 10⁵ propagules ml⁻¹ and the moment at which the disease incidence stabilized provided appropriate conditions for genotypic comparison. When ten cacao genotypes propagated by cuttings (clones) were assessed, the results confirmed TSH-1188 as the reference genotype for resistance to C. cacaofunesta, while the remaining clones could be grouped as resistant (CEPEC-2008), moderately resistant (CEPEC-2002, CEPEC-2007) and susceptible (CEPEC-2009, CCN-10, CCN-51, HW-25, PH-16, SJ-02). The analytical concepts and results were discussed in terms of their application in breeding programmes aimed at developing genetic resistance to Ceratocystis wilt of cacao.     

Susceptibility of Broccoli Cultivars to Bacterial Head Rot: In Vitro Screening and the Role of Head Morphology in Resistance

Head rot is a major disease of broccoli caused by the soft rot pathogens Pseudomonas fluorescens and Erwinia carotovora. Two in vitro pathogenicity tests were evaluated as a methods to identify broccoli cultivars susceptible or resistant to bacterial head rot. One test used mature heads excised from the plant and inoculated with squares of cotton lint which had been soaked in a bacterial suspension. The other test involved stab-inoculating axenically grown seedlings. With the excised head test, susceptible cultivars showed a black soft rot, whilst less susceptible or moderately resistant cultivars showed only watersoaking, or browning and slight softening of the tissue. No cultivar was completely resistant. Ten cultivars were tested, and their susceptibility ratings corresponded with previously recorded field data, with one exception. This laboratory test could be used to screen for susceptibility to head rot in broccoli breeding programmes. The seedling test distinguished differences in aggressiveness among bacterial isolates but not cultivar susceptibility. Increasing head size correlated negatively with disease resistance. Head shape, i.e. cultivars which showed a domed shape rather than a flat shape, was positively correlated with disease resistance. Thus small domed heads are more resistant to head rot than large flat heads. Other morphological characteristics, viz. floret prominence and number, and sepal stomatal number were not correlated with host resistance.     

Rhizobacteria-mediated Induced Systemic Resistance: Triggering, Signalling and Expression

Selected strains of rhizosphere bacteria reduce disease by activating a resistance mechanism in the plant named rhizobacteria-mediated induced systemic resistance (ISR). Rhizobacteria-mediated ISR resembles pathogen-induced systemic acquired resistance (SAR) in that both types of induced resistance render uninfected plant parts more resistant towards a broad spectrum of plant pathogens. Some rhizobacteria trigger the salicylic acid (SA)-dependent SAR pathway by producing SA at the root surface. In other cases, rhizobacteria trigger a different signalling pathway that does not require SA. The existence of a SA-independent ISR pathway has been demonstrated in Arabidopsis thaliana. In contrast to pathogen-induced SAR, ISR induced by Pseudomonas fluorescens WCS417r is independent of SA accumulation and pathogenesis-related (PR) gene activation but, instead, requires responsiveness to the plant hormones jasmonic acid (JA) and ethylene. Mutant analyses showed that ISR follows a novel signalling pathway in which components from the JA and ethylene response are successively engaged to trigger a defensive state that, like SAR, is controlled by the regulatory factor NPR1. Interestingly, simultaneous activation of both the JA/ethylene-dependent ISR pathway and the SA-dependent SAR pathway results in an enhanced level of protection. Thus combining both types of induced resistance provides an attractive tool for the improvement of disease control. This review focuses on the current status of our research on triggering, signalling, and expression of rhizobacteria-mediated ISR in Arabidopsis.     

Influence of silicon on some components of resistance to anthracnose in susceptible and resistant sorghum lines

This study aimed to evaluate the effect of silicon (Si) rates on some components of sorghum resistance to anthracnose. Two 2×5 factorial experiments, consisting of two sorghum lines (BR005 and BR009, resistant and susceptible, respectively) and five Si application rates (0, 0.06, 0.12, 0.24 and 0.30 g Si kg⁻¹ of soil) were arranged in a completely randomised design with three replications. Plants from both lines were inoculated with a conidial suspension of Colletotrichum sublineolum (1×10⁶ conidia ml⁻¹) 30 days after emergence. The incubation period (IP), latent period (LP₆₀), area under relative infection efficiency progress curve (AURIEPC), area under anthracnose index progress curve (AUAIPC), final disease severity (FDS), percentage of pigmented leaf area (PLA), and percentage of necrotic leaf area (NLA) were evaluated. Silicon and calcium (Ca) content in leaf tissue of both lines was also determined. The content of Si in leaf tissue increased relative to the control by 55 and 58%, respectively, for the susceptible and resistant lines. There was no significant change in Ca content in leaf tissue for either of the lines; therefore the variations in Si accounted for differences in the level of disease response. The IP for the resistant line was not affected by Si application rates. The LP₆₀ was not evaluated in the resistant line due to the absence of acervuli. For the resistant line, Si application rates had no significant effect on AUAIPC, FDS, percentage of PLA, and percentage of NLA. On the susceptible line, a quadratic regression model best described the effect of Si application rates on IP, LP₆₀, AURIEPC, AUAIPC, FDS, percentage of PLA, and percentage of NLA. The correlation between Si content in leaf tissue of the susceptible line and the AURIEPC, AUAIPC, FDS, PLA, and NLA was negatively significant (r = −0.57, −0.37, −0.40, −0.67, and −0.77, respectively). There was no correlation between Si content and IP or LP₆₀. The correlation between the percentage of PLA with the percentage of NLA was negatively significant (r = −0.74). In conclusion, the results from this study underscore the importance of Si in sorghum resistance to anthracnose particularly for the susceptible line.     

No role for bacterially produced salicylic Acid in rhizobacterial induction of systemic resistance in Arabidopsis

ABSTRACT The role of bacterially produced salicylic acid (SA) in the induction of systemic resistance in plants by rhizobacteria is far from clear. The strong SA producer Pseudomonas fluorescens WCS374r induces resistance in radish but not in Arabidopsis thaliana, whereas application of SA leads to induction of resistance in both plant species. In this study, we compared P. fluorescens WCS374r with three other SA-producing fluorescent Pseudomonas strains, P. fluorescens WCS417r and CHA0r, and P. aeruginosa 7NSK2 for their abilities to produce SA under different growth conditions and to induce systemic resistance in A. thaliana against bacterial speck, caused by P. syringae pv. tomato. All strains produced SA in vitro, varying from 5 fg cell(-1) for WCS417r to >25 fg cell(-1) for WCS374r. Addition of 200 muM FeCl(3) to standard succinate medium abolished SA production in all strains. Whereas the incubation temperature did not affect SA production by WCS417r and 7NSK2, strains WCS374r and CHA0r produced more SA when grown at 33 instead of 28 degrees C. WCS417r, CHA0r, and 7NSK2 induced systemic resistance apparently associated with their ability to produce SA, but WCS374r did not. Conversely, a mutant of 7NSK2 unable to produce SA still triggered induced systemic resistance (ISR). The possible involvement of SA in the induction of resistance was evaluated using SA-nonaccumulating transgenic NahG plants. Strains WCS417r, CHA0r, and 7NSK2 induced resistance in NahG Arabidopsis. Also, WCS374r, when grown at 33 or 36 degrees C, triggered ISR in these plants, but not in ethylene-insensitive ein2 or in non-plant pathogenesis- related protein-expressing npr1 mutant plants, irrespective of the growth temperature of the bacteria. These results demonstrate that, whereas WCS374r can be manipulated to trigger ISR in Arabidopsis, SA is not the primary determinant for the induction of systemic resistance against bacterial speck disease by this bacterium. Also, for the other SAproducing strains used in this study, bacterial determinants other than SA must be responsible for inducing resistance.     

Induction of systemic resistance byPseudomonas fluorescens Pf1 againstXanthomonas oryzae pv.Oryzae in rice leaves

When lower leaves of rice plants were inoculated with powder formulation of a saprophytic strain ofPseudomonas fluorescens, Pfl, upper leaves, in addition to the inoculated lower leaves, showed resistance to the rice bacterial blight pathogenXanthomonas oryzae pv.oryzae. When the leaves were challenge-inoculated withX. oryzae pv.oryzae 4 days afterP. fluorescens application on lower leaves, the disease intensity in upper leaves decreased from 6.7 to 1.1. When rice seeds were treated with the formulation ofP. fluorescens Pfl and sown, 30-day-old seedlings showed resistance toX. oryzae pv.oryzae and the disease intensity decreased from 6.8 to 1.2. The induced resistance was transient; leaves sprayed withP. fluorescens Pfl at 30 days after treatment and leaves of 60-day-old seedlings fromP. fluorescens-treated seeds did not show resistance to the pathogen. In field trials, seed treatment followed by foliar application of the powder formulation ofP. fluorescens Pfl effectively controlled rice bacterial blight and increased the yield. In the induced resistant leaves a sharp increase in lignification and activities of peroxidase, phenylalanine ammonia-lyase and 4-coumarate: CoA ligase was observed when the leaves were challenge-inoculated withX. oryzae pv.oryzae. An approximately threefold increase in lignin content, peroxidase activity and phenylalanine ammonia-lyase activity and a fivefold increase in 4-coumarate: CoA ligase activity were observed 5 days after challenge inoculation withX. oryzae pv.oryzae in rice leaves pretreated withP. fluorescens for 5 days. A similar increase in defense-related activities was not observed in susceptible interactions or inP. fluorescens-treated plants at later stages of interactions when no resistance to the pathogen was observed.     

<Emphasis Type="Italic">Ulocladium atrum</Emphasis> as a biological control agent for white mold of bean caused by<Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis>

Field studies were conducted near Lethbridge, Alberta, Canada, in 2001, 2004 and 2005 to determine the efficacy of the antagonistic fungusUlocladium atrum for control of white mold of bean caused bySclerotinia sclerotiorum. Results of the 3 years of field trials showed that, compared with the untreated control, foliar application of a spore suspension ofU. atrum (300 ml m⁻² of 10⁶ spores ml⁻¹ suspension) significantly reduced incidence and severity of white mold, increased seed yield and reduced contamination of bean seed by sclerotia ofS. sclerotiorum. The level of control of white mold observed in the treatment ofU. atrum was similar to that of the mycoparasitic fungusConiothyrium minitans, but lower than the fungicide treatments of Ronilan (vinclozolin) at the rate of 1200 g ha⁻¹ per application in 2001, or Lance (boscalid) at the rate of 750 g ha⁻¹ per application in 2004 and 2005. The potential for use ofU. atrum as a biological control agent for sclerotinia diseases is discussed. http://www.phytoparasitica.org posting Nov. 12, 2006.     

Induced resistance in cotton seedlings against fusarium wilt by dried biomass of<Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> and its water extract

Dry mycelium (DM) of killedPenicillium chrysogenum and its water extract (DME) were used to induce resistance in cotton plants againstFusarium oxysporum f.sp.vasinfectum (Fov). Results showed that the efficacy of either DM or DME in controlling the disease depends on both the concentration and the mode of application. DM amended to the soil at 0.25–2% (w/w) provided 32–75% protection againstFov. Soil drench with 2–5% DME (w/v) and pre-sowing seed soakage with 5–10% DME provided 51–77% and 28–35% protection against the wilt disease, respectively, whereas no protection was obtained with foliar sprays of 1–10% DME. DM and its water extract had no direct antifungal activity on growth ofFov in vitro, suggesting that disease control with DM or DME resulted from the induction of natural defense mechanisms in the cotton plants. Soil drench with 5% DME was as effective as 2% DM powder in inducing resistance againstFov, implying that the resistance-inducing substances were mostly water-soluble. Four cotton cultivars with various genetic resistance levels againstFov were tested at the seedling stage: two resistant ‘Pima’ cultivars and two susceptible ‘Acala’ cultivars. The level of protection achieved in the two susceptible cultivars with DME was equal to, or higher than, that of the two resistant cultivars treated with water. Innate and induced peroxidase activity in cotyledons or hypocotyls and roots coincided with the level of genetic resistance and DME-induced resistance, respectively. Based on our results, an integrated control strategy ofFov with both genetic resistance and induced resistance is suggested.     

Elucidating resistance in cotton genotypes to whitefly, <Emphasis Type="Italic">Bemisia tabaci,</Emphasis> by population buildup studies

Plant resistance has become an important component of integrated pest management (IPM) for management of whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), an important pest of cotton in India. The present studies were undertaken to standardize the plant stage and identify resistant cotton genotypes against whitefly. Nine plant stages of F846, a susceptible cotton genotype, were exposed to whitefly for 25 days under no-choice conditions. The population buildup (eggs, nymphs, pupae and adults) was recorded. The 12-, 14- and 16-leaf stages were suitable for plant resistance studies against whitefly, and the 14-leaf stage was taken for further studies. Ten cotton genotypes of Gossypium hirsutum and two of G. arboreum were covered with split cages in which five pairs of B. tabaci (F₁) were released. The population buildup was recorded to categorize genotypes as resistant, moderately resistant, moderately susceptible or susceptible. The experiment was repeated with F₂ and F₃ generation whiteflies. Based on overall average score of three experiments, LD694 was rated as resistant; LK861, Supriya, RS2013, CNH911 and PA183 as moderately resistant; IS-376/4/1/20/72, NHH44, TxMaroon2-78, Bt 6304 and RS2098 as moderately susceptible; and F846 as susceptible. LD694 was found to be resistant in three consecutive generations of whitefly.     

Bioluminescence reporter assay system to monitor Arabidopsis MPK3 gene expression in response to infection by Botrytis cinerea

The Arabidopsis MPK3 gene product participates in disease resistance mediated by the MAP kinase cascade. The expression of the MPK3 gene is induced by pathogen inoculation and treatment with chemicals such as salicylic acid (SA) and methyl jasmonate (JA), but the detailed expression pattern of the MPK3 gene has been largely unknown. To investigate MPK3 gene expression in response to disease stress, we fused the MPK3 promoter to the firefly luciferase gene to create a real-time monitoring system for regulated gene expression in planta. The results of an in vivo reporter assay using transgenic Arabidopsis plants harboring MPK3::Fluc showed that the MPK3 promoter activity was induced by treatment with chemicals such as SA and benzo(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), that induce defense gene expression. Inoculation with the fungal pathogen Botrytis cinerea resulted in systemic induction of MPK3::Fluc.