A Histological Evaluation of Induced Resistance to Phytophthora infestans (Mont.) de Bary in Potato Leaves

Systemically induced resistance against Phytophthora infestans in the potato cultivar ‘Bintje’ was studied histologically at the light microscopy level on the leaf surface, in the epidermis and in the mesophyll of challenged potato leaves. Systemic disease resistance was induced by a local pre-infection with the same fungus. On the leaf surface of induced plants, the germination of cysts was enhanced. In the epidermis of induced plants, papilla deposition increased and penetration decreased, whereas in the mesophyll of induced plants the spread of hyphae was reduced. It is suggested that the reduction of disease severity in induced plants is the result of the combined action of several successive defence reactions.     

Changes in Sugar Content During Induction of Systemic Acquired Resistance to Late Blight Caused by Phytophthora infestans (Mont.) de Bary in Potato

Resistance of plants to their pathogens may be systemically enhanced by a localized induction treatment, a characteristic named systemic acquired resistance (SAR). Changes in amounts and proportions of sucrose, glucose and fructose were examined in induced and noninduced potato plants ( Solarium luberosum L. ev. Matilda) before, and 1–9 days after challenge inoculation. The potato plants were induced and challenged with Phytophthora infesians (Mont.) de Bary. Plants which were non-induced and non-challenged were also tested (referred to as non-treated). The sugars were analysed using high-performance anion exchange chromatography with pulsed electrochemical detection, HPAE-PED (Dionex system). The amounts as well as the proportions of sucrose, glucose and fructose were similar throughout the experimental period in the non-treated plants. In induced plants, before challenge inoculation, the amount of sucrose was 44% lower than in non-treated plants. One day after challenge inoculation, the amount of sucrose had decreased by 79% in non-induced plants compared with non-treated plants, while the induced plants were much less affected. The total amount of all sugars were approximately the same 1 day hefore and 9 days after the challenge inoculation in ail treatments. However, 1 day after challenge inoculation, a 65% decrease in total amount was observed in the non-induced plants compared with the smaller reduction of 37% in the induced plants. The large differences in sugar amounts and proportions between the different treatments are discussed.     

The Influence of Temperature on Phytophthora infestans (Mont.) de Bary

The influence of temperature on the growth rate, sporulation density and zoospore release of Phytophthora infestans, cultivated on rye agar, has been studied. Temperature significantly influenced all the features of the fungus mentioned above. The highest yield of sporangia per 1 cm² of aerial mycelium occurred at 24°C while the highest percentage of sporangia releasing zoospores was observed when the fungus was grown at 15 °C. When considering the size of the fungal colony the highest production of sporangia was obtained at 20°C. It was concluded that the temperature at which the fungus was cultured predetermined the way it germinated.     

Cell-Wall Changes in Potato Tuber Tissue 4Phytophthora infestans (Mont.) De Bary

Examination of the carbohydrates of cell walls prepared fromtuber discs of a susceptible variety of potato showed an increase,with time, in all the polysaccharide fractions in control discs,but a slower increase in the pectic fraction and a more rapidincrease in the extraction residue to discs infected with Phytophthorainfestans. These differences were related to the monosaccharidecomposition of hydrolysates; there was no increase in galactose,found predominantly in the pectic fraction, but a rapid increasein glucose which is confined almost exclusively to the extractionresidue. Part of the increased glucose was due to an accumulationof hyphal wall of P. infestans which contains mainly an alkali-insolubleglucan. Galactanase activity, which was demonstrated in infecteddiscs, could account for the divergence of galactose contentfrom that of the controls. There was an enhanced accumulationof a lignin-like polymer associated with the cell-wall fractionof infected discs.     

Tuber Blight Development in Potato Cultivars in Response to Different Genotypes of Phytophthora infestans

Migrations or introduction of new genotypes of Phytophthora infestans to a specific region imposes a different perspective for potato production. During 2009–2010, a late blight epidemic affected the Northeastern United States, which quickly spread through several states. The epidemic was characterized by the appearance of a new genotype of P. infestans designated US‐22, which was isolated from tomato and potato. Potato tubers are an essential component of late blight epidemics where the pathogen cannot overwinter on Solanaceous plants. Six potato cultivars were inoculated with 12 isolates of P. infestans (five different genotypes), including isolates of the genotype US‐22. Tuber blight development was characterized in terms of tissue darkening expressed as area under the disease progress curve values and lenticel infection. The responses indicated that US‐8 was more aggressive than US‐22, but US‐22 isolates obtained from potato were more aggressive on potato than those acquired from tomato. Tuber periderm responses to infection were limited, yet US‐8 isolates infected the periderm more often than US‐22 isolates. There were significant differences among the cultivars tested but cv. Jacqueline Lee was the most resistant overall. Although isolates of P. infestans genotype US‐22 were less aggressive in comparison with US‐8 isolates, US‐22 isolates still infected potato tubers and were as aggressive us US‐8 isolates on some cultivars. Management of late blight caused by isolates of US‐22 through host resistance may be feasible but imposes a different set of criteria for consideration from those that US‐8 imposed.     

Effect of Some Factors on Detectability of Virulence Genes in Phytophthora infestans (Mont.) de Bary

Abstract Inoculum concentration, length of incubation period and passages on leaves of potato R–genotypes were found to influence the detectability of virulence genes in Phytophthora infestans.
At lower inoculum concentrations, only a few virulence genes were detected, these were usually 1 and 4. Coupled with an increase of the inoculum dose a gradual increase was found in the number of detected genes and their multiple combinations. An increased incubation time also resulted in the detection of additional virulence genes and their combinations. Two successive passages on respective potato R-genotypes produced a 2--3 fold rise in the number of detected genes.
To explain this phenomenon, a hypothesis has been proposed which suggests that for a virulence gene to be detected, certain infection thresholds have to be reached, which may be different for particular differential host genotypes or virulence genes.     

Phosphohydrolases of the phytopathogenic fungus Phytophthora infestans (Mont) de Bary]

ATPase, pyrophosphatase and tripolyhosphatase activities were found in a cell-free Phytophtora infestans micelium extract. No polyphosphatase activity, hydrolyzing high molecular weigh polyphosphates to orthophosphate, was observed in the fungi. It was demonstrated that, unlike ATPase, the activity of pyrophosphatase was inhibited by Ca2+ at concentrations from 0.1 to 20 mM, and it was considerably decreased in the presence of a Ca2+ transport inhibitor, ruthenium red (0.01--0.1 mM). Possible relation of Ph. infestans pyrophosphatase activity with the process of active calcium transport is suggested.     

Genetic Diversity of Phytophthora infestans (Mont.) de Bary in the Eastern and Western Highlands of Uganda

Eight isolates of Phytophthora infestans were recovered from late blight infected samples collected from the districts of Mbale and Mbarara in the Eastern and Western highlands of Uganda in 2001 and analysed using mitochondrial deoxyribonucleic acid (DNA) haplotype and Amplified Fragment Length Polymorphism (AFLP) markers. Polymerase chain reaction amplification with the P2 primer followed by digestion with MspI yielded a three‐fragment pattern characteristic of isolates belonging to the US‐1 clonal lineage; the polymorphism was confirmed by DNA sequencing. AFLP analysis yielded 60 markers, analysis of which clustered the Ugandan isolates with reference to US‐1 isolates (US930258 and US940501). These results suggest that the examined Ugandan isolates belong to the US‐1 clonage lineage.     

RNA silencing of the anionic peroxidase gene impairs potato plant resistance to Phytophthora infestans (Mont.) de Bary

Potato Solanum tuberosum L. plants expressing an antisense M21334 fragment were obtained by agrobacterial transformation. A manifold decrease in activity of anionic isoperoxidase with pI ～ 3.5 in the transformed plants demonstrated that the enzyme is encoded by M21334. The transformed plants showed a decrease in lignin accumulation and a dramatically lower resistance to the late blight agent Phytophthora infestans, implicating the enzyme in the response to P. infestans infection.     

Effect of Bacillus Bacteria on Hydrogen Peroxide Content and Gene Expression of Hydrolase Inhibitors in Potato Plants Infected with Phytophthora infestans (Mont.) de Bary

Russian Journal of Plant Physiology - Late blight of potato (Solanum tuberosum L.) caused by the oomycete Phytophthora infestans (Mont.) de Bary was studied in respect to the disease resistance...     

Factors involved in resistance to blight (Phytophthora infestans (Mont.) de Bary) in potatoes and assessment of resistance using detached leaves

In leaves of potatoes inoculated with Phytophthora infestans early in the growing season, more but smaller lesions with later onset of sporulation and fewer sporangia developed than on those inoculated later. None of these factors was uniform on detached leaves of all clones, so could not be used separately to forecast field resistance satisfactorily; when considered together, a reasonable prediction was feasible. With some clones, tests of detached leaflets gave a better indication of behaviour in the field than laboratory tests of whole plants.     

Changes in Photosynthetic Electron Transport in Potato Cultivars with Different Field Resistance after Infection with Phytophthora infestans

The estimation of field resistance of potato cultivars to Phytophthora infestans are usually carried out in expensive and time consuming field experiments over several years. Therefore, a procedure is required for the fast and objective determination of qualitative and quantitative field resistance of new cultivars. This study correlated level of field resistance to P. infestans in leaf discs or leaflets of various potato cultivars to characteristic changes of Chlorophyll-a fluorescence (CF) parameters F _m (maximal fluorescence) and F _v (maximal variable fluorescence). Two different inocula, both containing virulence genes 1-11 were tested. The results were achieved when leaf discs from greenhouse or field plants were each inoculated with a P. infestans spore suspension and incubated for 24 h. In field measurements, comparable results were obtained 48 h after inoculation. The estimation of field resistance by measuring specific CF parameters could be an economical and rapid procedure to reduce or substitute visual lesion assessment for determining cultivar field resistance.     

利用马铃薯晚疫病菌粗毒素离体筛选马铃薯抗晚疫病无性系

以3个马铃薯品种叶片外植体的愈伤组织为材料、马铃薯晚疫病病菌培养粗毒素为筛选压力进行马铃薯抗晚疫病细胞变异无性系筛选。结果表明,不同品种的叶片、愈伤组织对毒素有不同的忍耐力。“费乌瑞它”最大忍耐的粗毒素浓度为40％,“东农303”、“早大白”则为50％。马铃薯晚疫病病原菌粗毒素对愈伤组织的诱导、生长、不定芽的分化及再生苗生根有显著的抑制作用,而且浓度越大,抑制作用越强。筛选结果抗性鉴定表明,经过粗毒素筛选的细胞无性系及其再生植株对高浓度粗毒素的抗性能力显著高于对照。     

Effects of infection by Phytophthora injestans (Mont.) de Bary on the stomata of potato leaves

Phytophthora injestans infection of potato leaves causes abnormal opening of the stomata in the tissue colonized by the fungus before sporangiophores emerge through them. The affected area, which may be up to 7 mm wide, extends from the necrotic tissue to within 1–2 mm of the advancing edge of the colonizing mycelium. These stomata open wider than those in uninfected parts of the leaf, and do not close in the dark, but closure can be induced experimentally by a high water deficit. Affected guard cells have an increased osmotic value, reduced starch content, and show degradation of the chloro-plasts. No direct infection of the guard cells has been observed. Autoradiography of infected leaflets which had been exposed to ¹⁴CO₂ in the light, showed that a zone of increased photosynthesis occurs in the region of wide-open stomata.