Evaluation of an avirulent strain ofPseudomonas solanacearum for biological control of bacterial wilt of potato

An avirulent strain ofPseudomonas solanacearum, B82, was tested for its ability to protect the potato cultivar, Ontario, from bacterial wilt caused by virulent strains of this bacterium. Strain B82 was not antagonistic to 124 virulent strains ofP. solanacearum and was not bacteriocinogenic. When potato seedpieces were soaked for 5 hr in suspensions of B82 (10⁸ to 10⁹ cfu/ml), reduction in disease severity (up to 50%) was noted in some experiments. The treated plants, grown in the greenhouse or growth room for 4–5 wk, were challenged by stem inoculation, soil drenching, or root-to-root infection with virulent strains (276 or Br5) of the bacterium. Protection was not obtained consistently, however, and much of the variability could be attributed to differences in ambient temperature and light conditions in the greenhouse between experiments. In general, high ambient temperatures and/or reduced sunlight resulted in no protection. Protection appeared to depend on the ability of strain B82 to multiply in the vascular system in the crown region and to colonize the rhizosphere of treated plants. Soil temperatures above 24 C affected the ability of strain B82 to survive in the rhizosphere. The close dependence of protection on environmental conditions suggests that this method of control may not be practical under field conditions.     

Optimisation of sample size for the detection of latent infection byRalstonia solanacearum in potato seed tubers in the highlands of Peru

Summary A sampling strategy was evaluated in the Andean highlands of Peru to optimise the detection ofRalstonia solanacearum in seed tubers harvested from symptomless crops. A sensitive and specific serological method developed at CIP was used to detect the pathogen in latently infected tubers. Optimum sample size was evaluated for symptomless crops after analysing various numbers of composite samples and using a binomial distribution model to calculate the detection probabilities.R. solanacearum was detected in all lots from fields with visible symptoms, so validating the detection technique. About half of the seed lots from apparently healthy fields at altitudes of up to 3,100 m were found positive for the pathogen.R. solanacearum was detected with 99% probability in samples of 350 tubers from seed lots from symptomless crops. This number of seed tubers could feasibly be processed in a seed-health test without incurring too high a cost for labour and materials.     

Survival and possibilities for extinction ofPseudomonas solanacearum (Smith) Smith in cool climates

Summary The importance of biovar 2 ofPseudomonas solanacearum (syn.Burkholderia solanacearum; syn.Ralstonia solanacearum) in cool temperate climates has been recently emphasised by outbreaks of potato brown rot disease in some European countries. Dissemination of the pathogen in latently infected potato tubers and in contaminated irrigation water, and overwintering in aquatic roots of the weed hostSolanum dulcamara have been implicated. Evidence from the literature suggests that in cool climates the organism is unlikely to persist long term in soil in the absence of a susceptible host. Effective control strategies rely on the enforcement of quarantine legislation at both national and European Community levels. This requires knowledge of the biology of the pathogen in cool environments, methods for accurate monitoring of its survival and distribution at and around disease outbreak sites and application of effective measures for pathogen exclusion, containment and eventual eradication. This paper reviews current knowledge on the above.     

New disease symptoms observed on field-grown potato plants with potato spindle tuber viroid and potato virus Y infections

Summary Potato spindle tuber viroid (PSTV) and potato virus Y (PVY) were isolated from plants of cultivar Kennebec with severe necrotic symptoms in the field. In the greenhouse, severe necrotic symptoms were reproduced only when potato plants were infected either simultaneously with PSTV+PVY, or with PSTV prior to PVY infection. Thirteen additional potato cultivars were tested in the greenhouse for this synergistic reaction and eight developed necrotic responses similar to cv. Kennebec. PVY concentration was significantly higher in doubly infected plants, compared with those infected with PVY alone.     

Latent infection of potato tubers byPseudomonas solanacearum

Strains ofPseudomonas solanacearum differed in their ability to infect tubers of different resistant potato clones grown in infested soil. When eight resistant clones (Solanum phureja orS.phureja ×S. tuberosum hybrids) were grown at 24–28°C in soil infested with a race 1 or a race 3 strain of the bacterium, relatively few plants had wilt symptoms at harvest, but 26.7% and 9.2% of the tubers harvested from plants infected with the race 1 and race 3 strains, respectively, carried latent infections. Some infected clones never yielded diseased tubers, however. The development of symptoms above ground was not correlated with the incidence of tuber infection in any particular clone. No tuber infection occurred in tolerant or resistant clones grown in infested soil at cool (12–22°C) temperatures. Tubers were inoculated directly in an attempt to evaluate the ability of bacteria to multiply in these tissues at different temperatures. Highly virulent strains ofP. solanacearum survived in susceptible tubers in higher numbers and for longer periods than in resistant ones. Low temperature (4°C) had a deleterious effect on survival of the bacterium in tubers, but did not completely eliminate the pathogen even after 40 days.     

栽培种花生对青枯菌潜伏侵染的反应

通过对国内外已鉴定出的主要抗青枯病花生种质进行人工接种和多克隆抗体检测,研究栽培花生对青枯菌潜伏侵染的反应。根据青枯菌在花生植株体内的潜伏定殖部位,将抗病花生品种划分为５个反应类型,类型间抗性水平和稳定性存在明显差异。通过分析潜伏定殖率与植株生长发育的关系,发现不同花生品种受潜伏侵染影响的程度不同,鉴定出的几个产量水平高而且受潜伏侵染影响较小材料,可以作为进一步育种的抗源亲本。     

Survival of south african strains of biovar 2 and biovar 3 ofPseudomonas solanacearum in the roots and stems of weeds

Summary South African strains of biovar 2 and biovar 3 ofPseudomonas solanacearum were compared for their ability to survive in the roots and stems of ten weed species. After artificial inoculation with a biovar 2 strain none of the weed species developed wilt symptoms, but the pathogen was isolated from one species,Physalis angulata L. Using inoculum of a biovar 3 strain, two of the weed species developed wilt symptoms (Datura stramonium L.,Solanum nigrum L.), and the pathogen was isolated from four species,Eragrostis curvula, Amaranthus hybridus L.,Datura stramonium L. andSolanum nigrum.     

Resistance toPseudomonas solanacearum in potato: Infectivity titrations in relation to multiplication and spread of the pathogen

When several wilt-resistant potato clones were tested against a highly virulent strain from Mexico (No. 276) by standard stem inoculation methods, only one clone ofSolanum phureja was resistant. When different inoculum concentrations were introduced quantitatively for infectivity titrations, however, different levels of resistance were clearly defined among clones previously rated as susceptible. Linear regression was used to estimate the ED₅₀ values (dosage required to wilt 50% of the population) for each of seven clones. These values ranged from 3 and 100 colony-forming units (CFU) for Katahdin and Russet Burbank, respectively, to 2.1 x 10⁶ CFU for S.phureja clone 1386.15. The distribution of bacteria in stems of Russet Burbank plants inoculated with the compatible strains 276 and K-60 and the incompatible strains B1 and S-210 was very different. In all cases, incompatible bacteria were not detected 10 cm above the inoculation point in the stem, even by 12 days after inoculation, whereas compatible strains multiplied rapidly at this site by 6 days. At the inoculation site and at sites immediately adjacent to it, however, incompatible bacteria attained populations that only differed by one order of magnitude from those of compatible bacteria. Similar results were obtained when a resistant clone (MS 118.24) was inoculated with the virulent strain K-60. Thus, resistance was characterized both by reduced acropetal spread and by tolerance to large numbers of the bacterium.     

Virus translocation in two-stemmed potato plants

Summary Inoculation of one shoot ofBintje potato plants with potato virus X resulted in a very low rate of tuber-infection of those tubers produced by a second, non-inoculated shoot of the same plant. A similar experiment with potato virus Y^N resulted in a considerably higher rate of infection of the tubers produced by the non-inoculated shoot than was the case with potato virus X. The results indicate that virus translocation to tubers of non-inoculated shoots is possible, but not as readily as to those produced by the inoculated shoots themselves.

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Zusammenfassung Inokulation eines Triebes von Kartoffelpflanzen der SorteBintje mit Kartoffelvirus X 49 Tage nach dem Auspflanzen bewirkte nur sehr wenig Infektionen bei Knollen, die durch einen zweiten, nicht infizierten Trieb der gleichen Pflanze erzeugt wurden (Tabellen 1 und 3). Ein gleicher Versuch mit Kartoffelvirus Y^N (Inokulation 64 Tage nach dem Auspflanzen) zeigte im allgemeinen einen h?heren Anteil an Knolleninfektionen als im Versuch mit Kartoffelvirus X und eine betr?chtlich h?here Infektionsrate bei den Knollcn, die vom nicht infizierten Trieb hervorgebracht wurden (Tabellen 2 und 4). Die Ergebnisse zeigen, dass Viruseinwanderung in Knollen von nicht infizierten Trieben m?glich ist, aber nicht so leicht vor sich geht wie in Knollen, die von infizierten Trieben erzeugt wurden.

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Résumé L'inoculation d'une pousse de plantes de pomme de terreBintje avec le virus X. 49 jours après la plantation, n'infectait les tubercules produits par une seconde pousse, non inoculée, de la même plante que dans une très faible proportion (Tableaux 1 et 3). Dans une expérience semblable avec le virus Y^N, l'inoculation étant faite 64 jours après la plantation, le taux d'infection des tubercules en général était plus élevé dans l'expérience avec le virus X et le taux d'infection des tubercules produits par la pousse non-inoculée (Tableaux 2 et 4) était considérablement plus élevé. Les résultats indiquent que la translocation du virus aux tubercules des pousses noninoculées est possible, mais non aussi rapide qu'aux tubercules des pousses inoculées.

     

Detectability and translocation of potato virus A in potato plants after artificial inoculation

Summary The tip leaflets of median leaves of plants of different ages of the very susceptible cv. Jara and the less susceptible cv. Krasava were dry inoculated with potato virus A (PVA). Movement of the virus was followed by using the A6 leaf test on different plant perts at intervals after inoculation. The technique was not very reliable but the results showed that in cv. Jara the rate of movement of virus within the plants and into the tubers was greater and less dependent on their age than in the less susceptible cv. Krasava. In cv. Jara. PVA reached the tubers with 6–7 days from inoculation but in cv. Krasava not until after 21 days and not at all if the plants were more than 6 weeks old when inoculated.     

Potato plants transformed with a potato virus Y P1 gene sequence are resistant to PVYO

The cloned P1 sequence of PVY^O was transferred in sense orientation into the potato cultivar Pito usingAgrobacteriummediated transformation. Sixteen of the putatively transformed plants (NPTII positive) were assayed for PVY^O resistance. No PVY^O was detected in four plants, representing two lines, 21 days after two sap-inoculations and 35 days after graft-inoculation, and the plants remained symptomless, whereas other tested plants showed mosaic symptoms and had high PVY titers similar to those of the control plants. No line was resistant to PVY^N and potato viruses A and X. Southern analysis confirmed the presence of the transgene(s) in the two PVY^O-resistant and one susceptible line examined, but no signal was detected in nontransformed Pito. These results suggest a high level of protection against PVY^O in potato transformed with P1 sequence of PVY^O.     

Noise levels in potato packinghouses and dry-grading plants

Work stations in each of seven potato packinghouses and seven dry-grading plants, located in the Red River Valley, were surveyed for sound levels. Nine equipment categories were established in packinghouses and four in dry-grading plants for preliminary sound level determinations. In general, sound levels in packinghouses were acceptable; however, some dry-grading-plant equipment exhibited noise levels above suggested limits and required remedial attention. Follow up studies were then conducted in a representative dry-grading plant. Simple, practical noise-reduction practices such as proper maintenance of equipment were undertaken, and the noise in the plant was substantially reduced by these practices. Further separation from the noise created during the operations of the powered bulk scoop was provided with simple, easily fabricated barriers.     

Variability in the response toPseudomonas solanacearum of transgenic lines of potato carrying a cecropin gene analogue

Summary Transgenic potato plants of cv. Désirée carrying an antibacterial gene, coding for a cecropin lytic peptide analogue, were inoculated with a virulent strain ofPseudomonas solanacearum under controlled conditions. The disease index scored during three repeated infection trials indicated an increased variability in plant response among the transgenic lines which gave either a more susceptible or a more resistant response to the pathogen when compared with untransformed Désirée. Immunity toP. solanacearum was not observed, but it was possible to select a group of transgenic lines that showed resistance levels and disease development curves comparable to the field resistant cv. Cruza 148.     

Detection of potato virus M and potato virus S on test plants

Summary The influence of environment and virus isolate on PVM detection on eight plant species and PVS detection on six plants species was investigated.Lycopersicon chilense was the most reliable test plant for PVM andChenopodium quinoa for PVS. In both cases 12–24 days were required for the symptoms to appear. The most rapid development of PVM symptoms resulted from inoculation onPhaseolus vulgaris Red Kidney (4–8 days) and of PVS symptoms on detached leaves ofSolanum demissum Y (6–8 days). The detectability of the viruses on these test plants was, however, lower than onL. chilense andC. quinoa.

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Zusammenfassung An 8 bzw. 6 Pflanzenarten wurde die Reaktion auf eine Inokulation mit dem Kartoffel-M-virus (PVM) bzw. dem Kartoffel-S-virus (PVS) untersucht. Die Symptome sind in Tabelle 1 beschrieben. Untersuchungen, die in 3 temperaturkonstanten R?umen (16, 22 und 28°C) durchgeführt wurden, ergaben, dass unabh?ngig von der Temperatur nach Inokulation mit PVM aufLycopersicon chilense undSolanum rostratum Symptome auftraten, nach Inokulation mit PVS aufChenopodium quinoa, L. chilense undS. rostratum (Tabelle 2). Tests, die im Winter und im Sommer mit 12 Isolaten des PVM und 8 Isolaten des PVS durchgeführt wurden, ergaben, dass sich aufL. chilense undS. rostratum für PVM und aufC. quinoa für PVS unabh?ngig von der Jahreszeit und vom Virusisolat Symptome bildeten (Tabelle 3). Die am besten geeigneten Testpflanzen warenL. chilense für PVM undC. quinoa für PVS. Insgesamt wurden 200 Versuche zu verschiedenen Zeiten des Jahres durchgeführt (Tabelle 4). Jedoch, die vielleicht am besten geeignete Testpflanze für PVM istPhaseolus vulgaris Red Kidney und für PVS sind es abgeschnittene Bl?tter vonSolanum demissum Y, da die Symptome bereits wenige Tage nach der Inokulation mit allen getesteten Virusisolaten auftreten. Die Schwierigkeit bei der Verwendung dieser Testpflanzen ergibt sich aus der sehr starken Abh?ngigkeit der Symptomausbildung von den Versuchsbedingungen.

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Résumé La réaction au virus M et au virus S, respectivement de 8 et 6 espèces de plante, a été étudiée. Les sympt?mes qui sont apparus sur les plantestests, inoculées avec le virus M et avec le virus S, sont décrits dans le tableau 1. Des expériences conduites dans trois chambres à température contr?lée (16, 22 et 28°C) ont montré, qu'indépendamment de la température, le virus M produisait des sympt?mes surLycopersicon chilense etSolanum rostratum, et le virus S surChenopodium quinoa, L. chilense etS. rostratum (tableau 2). Des tests réalisés en hiver et en été avec 12 isolats de virus M et 8 isolats de virus S ont montré que les plantes-tests qui manifestaient chaque fois des sympt?mes, indépendamment de l'isolat utilisé, étaientL. chilense etS. rostratum pour le virus M, etC. quinoa pour le virus S (tableau 3). Deux cents tests réalisés sur la pomme de terre à différentes époques de l'année ont montré queL. chilense pour le virus M etC. quinoa pour le virus S étaient les plantes-tests les plus s?res (tableau 4). Toutefois, la plante-test la plus prometteuse est peut-être pour la détection du virus M,Phaseolus vulgaris Red Kidney; et pour la détection du virus S, les feuilles deSolanum demissum Y, car les sympt?mes étaient apparus quelques jours seulement après l'inoculation, quel que soit l'isolat testé. La difficulté d'utiliser ces plantestests réside dans le fait que le développement des sympt?mes est hautement dépendant des condition d'environnement.