Resistance of tomatoes to late blight (Phytophthora infestans)

Race T₁ of Phytophthora infestans was first isolated in Central Europe. Tomato varieties carrying the dominant gene Ph were easily infected by T₁ but showed a different degree of field resistance. In September 1967 more than 80% of all isolations from the experimental plots at Greifswald were determined as the aggressive race T₁. This race was also isolated in a large screening test over several provinces of the GDR from potato and tomato fields where no plants carrying dominant resistance genes were present in the neighbourhood. The fungus was able to pass from potato leaves or tubers to detached tomato leaves or intact tomato plants (cv. Fanal) without any reduction in sporulation. The field-resistant tomato variety Ru?ový Ker and the highly field-resistant variety Atom were crossed. In F₂ and subsequent generations, young plants were selected following inoculation of 14 mm leaf-discs. Weak sporulations on the leaf-discs were almost invariably correlated with a reduced level of infection of fruit in the field. Data from crosses of Atom with more or less susceptible varieties suggested the presence of incompletely dominant genes. It is concluded that at least two genes in the variety Atom control field resistance and the gene-symbols Phf and Phf-2 are proposed for them.     

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.     

Characterization of Kenyan Isolates of Fusarium udum from Pigeonpea [Cajanus cajan (L.) Millsp.] by Cultural Characteristics, Aggressiveness and AFLP Analysis

Isolates of Fusarium udum from pigeonpea (Cajanus cajan) plants with wilt symptoms were collected from various districts in Kenya and were characterized using cultural characteristics, aggressiveness and amplified fragment length polymorphism (AFLP). The 56 isolates of F. udum showed a high level of variability in aerial mycelia growth, pigmentation and radial mycelia growth (colony diameter) on potato dextrose agar. The aggressiveness of 17 isolates of F. udum on seven pigeonpea varieties varied and five aggressive groups were observed in the present study. There were no relationships among cultural characteristics and aggressiveness. AFLP analysis of the 56 isolates was tested for genetic variability using seven primer combinations. A total of 326 fragments was generated of which 121 were polymorphic. Ten AFLP groups were identified among the Kenyan isolates and, although they were not genetically distinct, six AFLP subgroups were genetically distinct. AFLP had no relationship with cultural characteristics, aggressiveness and geographical origin of the isolates. This is the first report on the study of genetic variability of F. udum using DNA analysis.     

Transgenic potato plants overexpressing the pathogenesis-related STH-2 gene show unaltered susceptibility to Phytophthora infestans and potato virus X

The STH-2 gene is rapidly activated in potato leaves and tubers following elicitation or infection by Phytophthora infestans. However, its biochemical function remains unknown. In order to ascertain if STH-2 protein is directly involved in the defense of potato against pathogens, the STH-2 coding sequence under the control of the CaMV 35S promoter was introduced into potato plants. Transgenic plants expressing the STH-2 gene were analyzed for an altered pattern of susceptibility to a compatible race of P. infestans and to potato virus X. Results indicate that constitutive expression of the STH-2 gene did not reduce susceptibility of potato to these pathogens.     

Role of Protease Inhibitors in Potato Protection

Mechanical wounding or infection of potatoes with Phytophthora infestans caused an accumulation of only serine protease inhibitors in exudates of potato tubers. Among them, proteins prevailed that are structurally similar to those present in healthy tubers: a 22-kDa trypsin inhibitor, a 21-kDa serine protease inhibitor consisting of two polypeptide chains, and a 8-kDa potato chymotrypsin I inhibitor produced de novo. The accumulated proteins inhibited the growth of hyphae and germination of zoospores of P. infestans. Treatment with elicitors, jasmonic and arachidonic acids, intensified the accumulation of these inhibitors in tubers in response to the wound stress, whereas salicylic acid blocked this process. These results suggest that lipoxygenase metabolism plays a substantial role in signal transduction of the protective system of resting potato tubers.     

Exoproteinases of the Oomycete Phytophthora infestans

When grown in a medium containing heat-stable potato tuber proteins, the oomycete Phytophthora infestans (Mont.) de Bary produces a set of exoproteinases active at neutral and mildly basic pH values. These extracellular proteinases have been shown (by SDS-PAGE in the presence of gelatin) to include at least six components differing in molecular weight. Inhibitory analysis and studies of the effects of the enzymes on various synthetic substrates show that the culture liquid of P. infestans contains mainly serine proteinases (specific for trypsin and subtilisin) and metalloproteinases. Their activity is suppressed by proteinase-inhibiting proteins from potato tubers. It is suggested that exoproteinases of P. infestans may be the metabolic target for natural proteinase inhibitors from potato.     

Untersuchungen zur Lagerung und Aggressivität von Peronospora parasitica und Ergebnisse im Hinblick auf die Sortenanfälligkeit des Erregers an Winterraps

Results on preservation and aggressiveness of Peronospora parasitica and results with regard to the disease reistance of the paAogen on winter oilseed rape Laboratory-tests showed, that a long-time preservation of Peronospora parasitica-coiaia in a freezer at - 21° C for a period of 1 year was possible using glycerine, poiyethylenglycol (PEG) 400 or PEG 1000 as cryoprotective agents. Glycerine in a concentration of 20% was ascertained as most suitable additive with germination-rates of 21% after a storage of 1 year. Using a cotyledon-test a simple and non-time-consuming method could be established to find out differences in winter oilseed rape varieties and differences in the aggressiveness of different P. parasitica isolates. Of 32 winter-oilseed rape varieties Synra was the least susceptible variety to the pathogen; Diadem, Doublol and Accord were the most susceptible varieties. The research on aggressiveness of different isolates gave evidence, that only the British isolate P003. differed in aggressiveness from the other isolates.     

Effect of methyl jasmonate on arachidonic acid-induced resistance of potato to late blight

Methyl ester of jasmonic acid (Me-JA) influences the induced resistance of potato tubers to late blight caused byPhytophthora infestans. Treatment of potato tuber disk surfaces with Me-JA solution or exposure to an atmosphere containing Me-JA vapors (10⁻⁶–10⁻⁵ M) increased the rate of rishitin biosynthesis induced by arachidonic acid orP. infestans. Methyl jasmonate increased the sensitivity of potato tissue to arachidonic acid. As a result, in the presence of Me-JA, the protective properties of arachidonic acid were observed at lower concentrations than in the absence of Me-JA. In addition, Me-JA reduced the adverse effects of lipoxygenase inhibitors (salicylhydroxamic acid and esculetin) on the induced resistance of potato tubers to late blight. Therefore, the synergistic interaction of Me-JA and biogenic elicitors can be regarded as part of a mechanism of potato defense against diseases.     

Microsatellite markers reveal two admixed genetic groups and an ongoing displacement within the French population of the invasive plant pathogen Phytophthora infestans

Potato late blight is an example of a re‐emerging disease of plants. Phytophthora infestans was first introduced into Europe during the 19th century, where it caused the Irish potato famine. During the 20th century several additional introduction events have been suspected, especially in the mid‐70s due to the import of large quantities of potato needed after the shortage caused by drought in 1976. Here, we investigate the genetic population structure of Phytophthora infestans, at the first stages of a recent invasion process in France. A total of 220 isolates was collected from 20 commercial fields of the potato susceptible cultivar Bintje, during two consecutive years (2004 and 2005). Clustering analyses based on eight recently developed microsatellite markers reveal that French P. infestans populations are made of two differentiated genetic clusters of isolates (F_ST = 0.19). This result suggests multiple introductions of P. infestans into France, either through the introduction of a composite population of isolates or through the successive introduction of isolates having differentiated genetic backgrounds. Both clusters identified have a strong clonal structure and are similar regarding genetic diversity and mating type composition. The maintenance of differentiation between the two genetic clusters should result from the low or non‐existent contribution of sexual reproduction in French P. infestans populations.     

Role of Energy in Pathogenic Variability of Pyricularia oryzae

Pyricularia oryzae Cav. reacts differently to different varieties. IB race group attacked Zenith for three consecutive years for both rabi and kharif seasons under artificial inoculation condition. Three different isolates were obtained in IB race which differed in their pathogenicity giving a constant susceptible reaction to Zenith. The difference in energy potential of three isolates of P. oryzae was tested biochemically. Total sugar, protein and protein patterns were studied following modern methods. W isolate contained maximum amount of total sugar (18.3 μg/g), total protein (23.8 μg/g albumin equivalent) and seven distinct protein bands on polyacrylamide disc electrophoretic gel which was directly correlated with maximum infection value. So it was concluded that the aggressiveness of P. oryzae depends on its energy potentiality in terms of total protein and protein patterns.     

Tuber surface microorganisms influence the susceptibility of potato tubers to late blight

Potato tubers (cvs Cara and Bintje) were grown in compost in a glasshouse and immature tubers harvested 57, 68 and 78 days after planting. Two moisture levels were imposed after the first harvest by disconnecting the water supply to one of the treatments and allowing the soil in that treatment to dry naturally. Tubers from wetter compost (59.4% moisture holding capacity) were more resistant to Phytophthora infestans than those from drier compost (14.7% moisture holding capacity) 78 days after planting. The potential causes of this difference were investigated. Aqueous extracts of wet compost did not inhibit the growth of P. infestans. The susceptibility of the internal tuber tissue, from which the periderm had been removed, was different to whole tuber susceptibility. The internal tissue of tubers from wet compost was more susceptible (cv. Cara), or as susceptible (cv. Bintje) as that of tubers from dry compost 78 days after planting. Fungi were isolated from the surface of whole tubers and there were no differences between the populations of potentially antagonistic fungal genera on tubers from wet and dry compost. As the experiment progressed, the number of bacteria per gram fresh weight on tubers grown in wet compost increased, whereas that on tubers from drier compost decreased (cv. Bintje) or remained similar (cv. Cara). There were significantly (P= 0.008) more bacteria on the surface of tubers from wet compost 78 days after planting. When P. infestans was co-cultured in Petri dishes with randomly selected tuber surface bacteria, some isolates (≤ 16.7%) inhibited the growth of the fungus. The percentage of the total bacterial population that was antagonistic to P. infestans was not significantly affected by soil moisture level (P= 0.368). The greater numbers of bacteria, of which a proportion are antagonistic to P. infestans, on the surface of tubers grown in wet compost may account for the greater resistance to tuber blight in that instance.     

Effect of proteinaceous proteinase inhibitors from potato tubers on the growth and development of phytopathogenic microorganisms

We studied the effect of two proteins, PSPI-21 and PKSI, on the growth and development of phytopathogenic microorganisms (Phytophthora infestans oomycete and Fusarium culmorum fungus). Both proteins were isolated from potato tubers (Solanum tuberosum L., cv. Istrinskii) and served as inhibitors of serine proteinases. These proteins differed in the ability to inhibit growth of Phytophthora infestans oomycete and Fusarium culmorum fungus. PSPI-21 was the most potent in modulating the growth of oomycete mycelium. PKSI primarily affected the growth of the fungal mycelium. The proteins under study induced complete destruction of oomycete zoospores and partial destruction of fungal macroconidia. Our results suggest that these proteins are involved in the protection of potato plants from phytopathogenic microorganisms.     

Phenotypic markers of Phytophthora infestans

Abstract

Phytophthora infestans is one of the most destructive pathogens of potato and causal agents of notorious disease late blight. Different chemicals are used to control the pathogen of late blight but the most commonly used is metalaxyl; its extensive use of has caused decreased sensitivity in the P. infestans population. The metalaxyl sensitivity of the Pakistani population of P. infestans is investigated in the present study. For this purpose, 178 isolates of P. infestans were obtained from the lesions of diseased potato leaves and stems, and samples were collected from the different potato-growing areas of Pakistan, where late blight is a problem. Sensitivity of the isolates of P. infestans was investigated by metalaxyl sensitivity test and with the help of test isolates were divided into three categories, i.e. sensitive, intermediate and resistant, based on their Co-efficient of mycelial growth inhibition (CMGI) values. During the study, highest percentage (50.17%) of resistant isolates was observed in the population of Punjab (zone 2), whereas the lower percentage (33.33%) was observed in the population of Swat valley (zone 6b). In the present study, it was discovered that P. infestans late blight-causing fungus has adopted more resistance against metalaxyl because of its wide use.     

Phosphite uptake and distribution in potato tubers following foliar and postharvest applications of phosphite‐based fungicides for late blight control

Foliar and postharvest applications of phosphite (Phi)‐based fungicides are used to control the oomycete Phytophthora infestans which is responsible for the occurrence of late blight in potatoes. Optimisation of the usage of Phi‐based fungicides for disease control during the growing season and in subsequent storage can lead to improved potato production and processing quality. In order to assess the efficiency of Phi translocation to tubers, following foliar and postharvest treatments of potato crops with the Phi‐based fungicides, the amount of Phi in tubers was determined by a high‐performance ion chromatography method. The quantity of Phi found in tubers increased with the total amount of Phi‐based fungicides applied during the growing season. Foliar applications of Phi resulted in an uneven distribution of Phi in the three tuber regions analysed, with high concentrations being identified in the tuber cortex (32.5–166.4 µg g^?1 fresh tissue) and medulla regions followed by the skin area. Postharvest treatment of tubers led to a different distribution of Phi, with the highest concentrations of Phi found in the skin (411.0–876.6 µg g^?1 fresh tissue) followed by the cortex and medulla regions. As foliar treatments are essential to protect the aerial parts of the plants during the growth season, the best disease management practices of tubers should include the postharvest treatment in addition to foliar applications. The use of both types of treatments ensures that concentrations of Phi in excess of 100 µg g^?1 fresh tissue are present in tuber skin and cortex areas; such concentrations are needed to suppress the growth of P. infestans on tubers during storage.     

Development of potato blight Phytophthora infestans after planting infected seed tubers

About 1000 blight-infected seed potato tubers, usually of the cultivar King Edward, were planted for 9 yr and the subsequent plants examined until the disease had developed in the plots. Haulm infection originated each year from the seed tubers and occurred first on basal leaves. When tubers were inoculated with a complex race of P. infestans this race was recovered from the leaves and from the soil near the seed tuber. Transmission of infection from soil to leaves was demonstrated by splash of artificially contaminated soil to leaves suspended above the soil. In 4 yr, plants were grown on flat rows as well as on ridges. In 2 yr, when emergence was almost complete, infected stems were observed on otherwise normal plants. In the first year 0.6% grew on ridges and 3.0% on the flat and in the second all grew on the flat (5.3%). Only seven of the 43 plants had more than one infected stem. Flat plots had a significantly higher number of stemdplant than ridge plots, but this bore no relation to numbers of infected stems. When flat plots which had developed affected plants had soil replaced as ridge plots, no further infected stems were observed. Such stems continued to develop on flat plots. No prematurely dead stems were observed below soil level when all plants were dug. Underground portions of most infected stems showed little evidence of P. infestans which was found only at about soil level. Infection appeared to occur first in this area.     

Biochemical reactions of different tissues of potato (Solanum tuberosum) to zoospores or elicitors from Phytophthora infestans

The time courses of sesquiterpenoid phytoalexin accumulation were examined in compatible and incompatible interactions of leaves and tubers from five different R genotypes of potato (Solanum tuberosum) with corresponding pathotypes of Phytophthora infestans, as well as in non-host interactions of all five potato cultivars with Phytophthora megasperma f. sp. glycinea and in elicitor-treated tubers from five, and cell suspension cultures from two, of the cultivars. In tubers, rishitin and several structurally related sesquiterpene derivatives accumulated rapidly in non-host incompatible interactions, less rapidly in host incompatible interactions, and more slowly in compatible interactions. Treatment of tubers or cell cultures with fungal culture filtrate or arachidonic acid elicited in most cases a transient accumulation of the sesquiterpenoid phytoalexins. None of these compounds was detectable under any of the applied conditions either in infected or in elicitortreated leaves. Sesquiterpenoid phytoalexins might therefore be helpful, but appear not to be essential, in disease resistance of potato.Abbreviations CF concentrated culture filtrate of Pi - cv. cultivar - Pi Phytophthora infestans (numbering indicates pathotypes corresponding to R genes in potato) - Pmg Phytophthora megasperma f. sp. glycinea     

Untersuchungen zur pathogenität und mykotoxinbildung von<Emphasis Type="Italic">Fusarium sambucinum</Emphasis>, dem erreger der trockenfäule an kartoffeln

Investigation into virulence and mycotoxin formation of the dry rot causing pathogen Fusarium sambucinum on potatos 11 strains ofFusarium sambucinum were isolated from tubers with dry rot symptoms from three different depots in the Land Brandenburg and Saxony-Anhalt. All isolates produced diacetoxyscripenol in artificially infected potato tubers. Additionally, two isolates produced T-2 and HT-2 toxins as well. The virulence and mycotoxin formation of the isolates was dependent on the potato varieties ‘Sieglinde’ and ‘Berber’ used in the experiment. The amount of diacetoxyscripenol in diseased tissue was positively correlated with the virulence of theF. sambucinum isolate and the susceptibility of the potato variety as well.     

致病疫霉PiSAK1的生物学功能分析

【背景】致病疫霉是引起世界范围内马铃薯晚疫病的重要病原菌。Stress-activated protein kinases (SAPKs)是一类胁迫激活的mitogen-activated protein kinases (MAPKs),研究表明真菌SAPKs在调控细胞应答外界胁迫等方面有重要作用。致病疫霉中存在一个SAPK,即PiSAK1,其生物学功能并不明确。【目的】探究PiSAK1在致病疫霉生长发育、抵抗外界胁迫及侵染马铃薯过程中发挥的生物学功能。【方法】利用生物信息学手段分析PiSAK1的特性,通过RT-qPCR分析明确致病疫霉PiSAK1在不同发育阶段及侵染马铃薯不同时期的表达量,最后构建PiSAK1沉默、过表达菌株并测定其各项生物学表型。【结果】PiSAK1具有丝裂原活化蛋白激酶典型的Ser/Thr蛋白激酶催化结构域,并且与其他卵菌的SAPKs同属一个进化分支。致病疫霉PiSAK1分别在休止孢阶段、侵染马铃薯48 h时表达量最高,且0.3 mol/L NaCl及3 mmol/L H2O2胁迫刺激0.5 h后PiSAK1的表达量均显著升高。构建PiSAK1沉默、过表达菌株并测...     

Aggressiveness analysis of foliar fungi to leaves of wheat and rice crops

Abstract

The investigations were based on two surveys of wheat and one survey of rice. Alternaria alternata, Curvularia lunata, Helminthosporium tetramera and Bipolaris sorokiniana were isolated and identified from foliage and soil of both wheat and rice crops and their aggressiveness was studied by aggressiveness analysis screened out into different aggressiveness classes. The aggressiveness of isolated fungi was studied on wheat varieties (Inqalab-91 and Chakwal-86) and rice varieties (Basmati-385 and IRRI-6) under controlled conditions. In the foliar aggressiveness test of A. alternata, the overall number of aggressive isolates was higher on wheat varieties than rice. Bipolaris sorokiniana isolates showed foliar blight symptoms on wheat but not on rice varieties. In C. lunata, the overall number of aggressive isolates was higher on wheat. In the foliar aggressiveness test of H. tetramera, the number of non-aggressive isolates was almost the same on wheat and rice varieties. In the present study it became clear that A. alternate, B. sorokiniana, C. lunata and H. tetramera are common foliar pathogens in rice and wheat crops and can cause soil-borne and foliar diseases.