Breeding for resistance to American gooseberry mildew, Sphaerotheca mors-uvae, in the gooseberry (Ribes grossularia)

Strong resistance to American gooseberry mildew (Sphaerotheca mors-uvae) occurred in eight out of ten F₁ progenies from crosses of resistant North American Eugrossularia species with European gooseberry cultivars or seedlings. Bimodal segregations in four of these F₁'s and in one F₁ derived from the wild European Ribes grossularia uva-crispa suggested that each donor carried a major dominant resistance gene. Such a gene, Sph₁ was identified in a first backcross from R. oxyacanthoides. Accessions of R. oxyacanthoides, R. leptanthum and R. watsonianum proved the most promising donors of resistance to mildew and leaf spot (Pseudopeziza ribis).     

Overwintering of Sphaerotheca mors-uvae on black currant and gooseberry

The ability of Sphaerotheca mors-uvae to perennate as cleistocarps, and as mycelium in buds was examined during the winters of 1965-6, 1966-7 and 1967-8 in relation to its two principal hosts, gooseberry and black currant. Cleistocarps on black currant leaves were examined from August 1965 to April 1966 and from July 1966 to March 1967. In 1965 cleistocarps were first observed on the leaves on 5 August; in 1966 on 11 July. These continued to develop through August and September and by October approximately 70% contained well-defined ascospores. The ascospore content remained generally at this level until February 1966 and November 1966; then the numbers of cleistocarps with ascospores fell and by April 1966 and March 1967 few such cleistocarps remained. From 21 March 1966 and 15 February 1967, but not otherwise, discharge of ascospores from the overwintered cleistocarps was readily obtained in laboratory tests. The viability and infectivity of the ascospores was demonstrated by allowing them to discharge on to leaf discs of black currant in the laboratory and also on to leaf discs and plants in the field. Sporulating colonies of S. mors-uvae developed within 8 days. Cleistocarps from shoots of black currant were examined from 4 August 1966 to 9 March 1967, and from 27 July 1967 to 1 January 1968. They developed in a similar manner to those on black currant leaves and by September in both 1966 and 1967 over 60% contained ascospores. This level was not maintained; the number of cleistocarps with ascospores fell gradually and by 8 December 1966 and 1 January 1968 few remained. Only in one laboratory test (21 November 1967) were ascospores discharged from a sample of these cleistocarps. Cleistocarps from shoots of gooseberry were examined from July 1966 to March 1967, and from August 1967 to January 1968. The pattern of ascospore development and subsequent decline in number of cleistocarps with ascospores was similar to that observed for black currant shoots. No discharge of ascospores could be demonstrated in laboratory tests. Evidence that S. mors-uvae perennates in buds of gooseberry was obtained by dissecting buds and by inducing buds on surface-sterilized shoots to burst under conditions which precluded chance infection. Field observations also suggested that bud infection occurred on gooseberry. Similar experiments failed to demonstrate the fungus in buds of black currant, and there was no indication of bud infection of this host in the field.     

Epidemiology and control of powdery mildew (Sphaerotheca pannosa) on roses

In examinations between September 1966 and December 1968 of 741 specimens of rose species and cultivars, cleistocarps of Sphaerotheca pannosa were found on thirty-two cultivars, mostly ramblers and old shrub roses, and on nine of these they were found in two or three successive seasons. On stem pieces placed on soil in each of the winters 1966-7, 1967-8 and 1968-9 the number of cleistocarps with asci and ascospores decreased during November and December and rose slightly in January, but none showed dehiscence. Cleistocarps on rose bushes examined during the winters of 1967-8 and 1968-9 showed a progressive degeneration of ascospores, and by December none was found. Perennation of S. pannosa in buds was demonstrated by field observations, by inducing bursting of dormant buds on surface-sterilized shoots and by dissection of dormant apical buds. In field studies in 1968 of the development of mildew, infected buds were noted on 22 March but secondary infections did not appear until 17 April, though viable conidia and susceptible leaf tissue were present during this period. Low temperatures appeared to be partly responsible for this lag. On detached leaves in the laboratory the fungus developed from germination to sporulation in 4 days at 20°, 7 days at 15°, 11 days at 10° and 28 days at 3°. Keeping inoculated detached leaves at 0° for 10 days apparently did not affect the viability of the conidia. In both 1967 and 1968 there were two host growth periods, each culminating in flowering, between May and September; mildew did not develop on the shoots until the second growth phase, then the disease increased logarithmically on shoots and blooms during August and September. The disease on the shoots was effectively controlled in the field during 1968 by applications of ‘Benlate’ (benomyl) or dinocap, but not by methy-rimol; these fungicides were less effective in controlling mildew on pedicels. Laboratory tests showed that ‘Benlate’ inhibited sporulation of S. pannosa by deforming the conidiophores.     

Overwintering of Sphaerotheca humuli, the cause of hop powdery mildew

The ability of Sphaerotheca humuli to overwinter as cleistocarps in infected hop cones and leaves and in aerial buds on rootstocks was examined during the winters of 1970-1, 1971-2 and 1972-3. Periodical examination of cleistocarps, collected in October and overwintered in Terylene bags on the soil of a hop garden, consistently revealed two periods of maturation ending in November and in March, when over 50% contained eight, well-defined ascospores. In laboratory tests cleistocarps, kept either in the hop garden or dry at 4, 8 or 18^oC during the winter, could not be encouraged to dehisce earlier than April when naturally dehisced cleistocarps were first detected in the field. More ascospores were discharged from cleistocarps, and germination of ascospores in laboratory tests was greater, at 18 than at 4, 8 or 24^oC. Colonies of S. humuli arose on leaves of potted plants exposed to overwintered cleistocarps in the hop garden and were observed microscopically to originate from ascospores. However, a Burkard spore trap, operated amidst the cleistocarps in this garden in 1972 and 1973, failed to detect ascospores. Ascospores, discharged onto susceptible leaves in the laboratory, germinated but failed to produce colonies. It was demonstrated that S. humuli can perennate in aerial, dormant buds on hop rootstocks. Examination of buds in autumn revealed mycelium external to and between the bud scales. At budburst the mycelium was still present internally. Cleistocarps were occasionally associated with hibernating mycelium. Primarily infected shoots arose from plants bearing infected buds in conditions which precluded chance infection. Some evidence was obtained that conditions during the winter determine the success of survival in buds. The fungus appeared to be incapable of infecting a selection of weeds common to hop gardens and their vicinity.     

Observations on the effect of black root rot (Phomopsis sclerotioides) on the susceptibility of cucumber to powdery mildew (Sphaerotheca fuliginea)

Powdery mildew (Sphaerotheca fuliginea) infection of cucumber leaves was earlier and increased more rapidly on plants with black root rot (Phomopsis sclerotioides) than on plants with healthy root systems in the same glasshouse.     

Evaluation of the activity of a number of procaine derivatives and analogous compounds against powdery mildew (Sphaerotheca fuliginea) on cucumber*

About fifty derivatives and analogues of procaine have been prepared and tested in three different tests for activity against powdery mildew of cucumber. Most of the compounds were active but few equalled procaine. The results obtained seem to afford little evidence for simple structure-activity relationship based on physico-chemical or electro-chemical properties.     

硅和白粉菌诱导接种对黄瓜幼苗白粉病抗性影响的研究

研究了硅酸盐和诱导接种白粉菌对黄瓜活性氧代谢、SiO2含量和抗病性的影响．结果表明,诱导接种能使叶片的超氧自由基(O2^-)产生速率、H2O2和丙二醛(MDA)含量升高,加硅接种处理的O2^-产生速率、H202和MDA含量明显低于不加硅接种处理．诱导接种能使叶片的过氧化氢酶(CAT)、过氧化物酶(POD)活性升高,超氧化物歧化酶(SOD)活性降低．加硅接种处理植株叶片的CAT、POD和SOD活性明显高于不加硅接种处理．诱导接种提高叶片的抗坏血酸(AsA)和还原型谷胱甘肽(GSH)含量,加硅处理的AsA含量明显低于不加硅处理,GSH含量高于不加硅处理．无论接种与否,加硅处理的SiO2含量显著高于不加硅处理,病情指数明显低于不加硅处理．     

Antagonistic control of powdery mildew host cell entry by barley calcium-dependent protein kinases (CDPKs)

Calcium-dependent protein kinases (CDPKs) are known to play pivotal roles in intracellular signaling during abiotic and biotic stress responses. To unravel potential functions of CDPKs in the course of barley (Hordeum vulgare)-powdery mildew (Blumeria graminis) interactions, we systematically analyzed the HvCDPK gene family. We found that, according to the existence of respective expressed sequence tags, at least nine paralogs are expressed in the barley leaf epidermis, the sole target tissue of powdery mildew fungi. We exemplarily selected two HvCDPKs with known full-length coding sequence for functional analysis. Transient expression of a putative constitutive active variant of one of these (HvCDPK4) in Nicotiana benthamiana triggered kinase-dependent mesophyll cell death in tobacco leaves. In a barley mlo mutant genotype, a constitutive active variant of the second paralog, HvCDPK3, partially compromised the highly effective resistance to B. graminis f. sp. hordei. A similar break of mlo resistance was seen upon expression of the junction domain of HvCDPK4, supposed to act as a dominant inhibitor of CDPK activity. Expression of a constitutive active HvCDPK3 or HvCDPK4 form also compromised penetration resistance to the inappropriate wheat powdery mildew fungus. Collectively, our data provide evidence for antagonistic roles of individual CDPK paralogs in the control of host cell entry during the early phase of powdery mildew pathogenesis.     

First record of Ribes uva-crispa L. (Grossulariaceae) from the Madonie Mts., a new species of the Sicilian flora

Abstract

In this study, a first record of Ribes uva-crispa L. (Grossulariaceae) – a new species of the Sicilian flora – from the Madonie Mts. is reported. The autochthonous and relict new population of Ribes uva-crispa L. (Grossulariaceae) is found on Mount Carbonara (Madonie Mts., North-Central Sicily), which is several hundred kilometers away from the Central Apenninic and the South Mediterranean locations of its distribution range. R. uva-crispa shows a distribution similar to other taxa extending from the Euro-Asiatic area to the mountains of North Africa with disjunct populations on the main Sicilian reliefs (Madonie and Nebrodi Mts.), testifying ancient phytogeographical connections. This noteworthy record adds a new species – as well as a new genus and new family – to the vascular flora of Sicily. Based on the morphological characters, the population found is to be referred to Ribes uva-crispa L. subsp. austro-europaeum (Bornm.) Bech var. glanduligerum (Lindberg) Maire.     

Powdery mildew (Sphaerotheca fuliginea) resistance in melon is selectable at the haploid level

The major cause of powdery mildew in melons (Cucumis melo L.) is the fungus Sphaerotheca fuliginea. There are several cultivar- and season-specific races of this fungus. In order to control powdery mildew, it is important to introduce resistance to fungal infection into new cultivars during melon breeding. Haploid breeding is a powerful tool for the production of pure lines. In this study, it was investigated whether powdery mildew resistance could be manifested at the haploid level from two disease-resistant melon lines, PMR 45 and WMR 29. the effects of various races of S. fuliginea on diploid and haploid plants of PMR 45 and WMR 29 and of a disease-susceptible line, Fuyu 3 were measured. The responses of haploid and diploid plants to powdery mildew were identical. In addition, haploids that were generated from hybrids between Fuyu 3 and disease-resistant lines were examined. Seven out of 13 haploids from a Fuyu 3xPMR 45 cross and 10 out of 12 haploids from a Fuyu 3xWMR 29 cross were classified as resistant plants because they showed the same responses as their disease-resistant diploid parents to the various fungal races. These results indicate that resistance in PMR 45 and WMR 29 is selectable at the haploid level. All of the plant responses were observed by microscopy. A possible mechanism for generating powdery mildew resistance in two different melon lines is discussed.     

Management of cucumber powdery mildew by certain biological control agents (BCAs) and resistance inducing chemicals (RICs)

The efficiency of some commercial biological control agents (BCAs), Bio Zaid and Bio Arc, and resistance inducers chemicals (RICs) (salicylic acid and Bion) on management of cucumber powdery mildew, caused by Sphaerotheca fuliginea, was evaluated in vitro and in vivo. In vitro experiments revealed that application of the tested BCAs and RICs significantly reduced the disease severity, number of conidia per leaf area unit (cm) and reduced germination of conidiospores of the causal pathogen. Under field conditions, application of BCAs and RICs caused significant decrement in the disease severity with significant increment in the fruit yield compared with check treatments. On the average, application of Bion recorded the highest values, either in reducing the disease severity or in raising the average fruit yield followed by Bio Arc. On the other hand, applying salicylic acid (SA) recorded, on the average, the lowest efficiency in reducing disease severity and low values of fruit yield in both growing seasons.     

Evaluation of biocontrol agents and potassium silicate for the management of powdery mildew of zucchini

Investigations were conducted under greenhouse and field conditions to evaluate the effects of potential biocontrol agents (BCAs) and soluble silicon (Si) on powdery mildew of zucchini caused by Podosphaera xanthii. Five BCAs were applied as foliar sprays to zucchini leaves and Si was drenched weekly into the rhizosphere of these plants.In the greenhouse, all BCAs provided significant control of powdery mildew with fungal isolates, reducing disease levels by up to 90%. Si alone reduced powdery mildew by as much as 35% and improved the efficacy of most of the biocontrol agents. Higher disease pressure reduced the efficacy of Si on powdery mildew but did not affect the performance of the BCAs. In the field, a disease reduction of 10–70% was achieved by BCAs and Si. Lower temperatures and high humidity ranges were suitable for optimal performances. The efficacy of the bacterial BCA, Serratia marcescens – B15 and silicon diminished at temperatures above 25 °C. The fungal BCAs (Clonostachys rosea – EH and Trichothecium roseum – H20) were better suited to higher temperatures (25–30 °C) and were tolerant of low RH values. Application of K₂SiO₂ to zucchini roots increased the level of Si in the leaves, which was responsible for suppression of the disease.     

Effects of powdery mildew on cucumber yields, and its chemical control

Effects of Sphaerotheca fuliginea were deduced from experiments in which cucumber foliage, exposed to naturally occurring inocula, was fungicidally sprayed. Yields increased as the incidence of mildew decreased but the relation was sometimes affected by differing amounts of phytotoxicity. The fungitoxicity and phytotoxicity of a range of chemicals applied as high-volume sprays, fumigants or soil drenches, were tested. Non-phytotoxic concentrations of some fungicides adequately protected cucumber foliage from subsequent attack but were often insufficient to eradicate established infections, the increased amounts needed for this being phytotoxic. Powdery mildew was controlled more effectively when drazoxolon and quinomethionate were applied as sprays with 0·1 and 0·02% a.i. respectively, than when used as fumigants at 2–4 and 1·3 g/28·3 m³(= 1000 ft³). Sprays of drazoxolon (0·1% a.i.) increased yields from 7·0 to 11·2 kg/ plant during 8 weeks picking and in another experiment weights of fruit were increased by applying quinomethionate (0·02% a.i.) from 10·8 to 52·2 kg/plot of four plants. In the former experiment appreciable amounts of phytotoxicity and infection were tolerated before yields decreased but, in the latter, yields were inversely proportional to numbers of dead leaves which were directly related to the incidence of mildew. Spraying with quinomethionate, or drazoxolon plus tetradifon (0·012% a.i.) increased numbers of female flowers from 59·5 in the mildewed controls to 93·0 and 142·8 per plant respectively, and of these 17·6, 32·8 and 16·2 % subsequently produced marketable cucumbers. In addition to decreasing yields, severe S. fuliginea infestations were associated with increased numbers of misshapen cucumbers. Increasing sulphur concentrations from 0·5 to 1·0g/28·3m³during nightly fumigations significantly decreased mildew incidence and increased (a) yields from 35·8 to 52·9 kg during 5 weeks picking, and (b) the proportion of high-quality cucumbers from 49 to 63 %. Similar trends occurred in another trial where sulphur concentrations were increased from 0·75 to 1·0 g/28·3 m³, but comparisons with fortnightly sprays of 0·1% drazoxolon suggest that these sulphur concentrations caused some damage.     

Foliar spray of aqueous extract of neem (Azadirachta indica) cake to control balsam (Impatiens balsaminia) powdery mildew

Neem cake is used as a soil amendment. It releases nutrient into the soil very slowly. It is also an insect repellent. It improves the physical as well as biological conditions of the soil such as soil aeration, water holding capacity and also the microflora in the rhizosphere. Aqueous extract of neem cake was used against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsaminia) in the field at 25, 50, 75 and 100%. The efficacy was observed even at low concentrations (25%). Foliar application of aqueous extract of neem cake induced synthesis of phenolic acids in balsam. Maximum phenolic acid was detected in balsam plant leaves treated with 50% neem cake followed by 75% in both pre-and post-inoculation treatments. The induction of phenolic acid in plants was correlated with the induction of resistance in treated plants against powdery mildew.     

Germination of conidia of poppy powdery mildew (Erysiphe polygoni DC)

Mode of germination and effect of various substrates, temperature, humidities, light and darkness on germination of poppy powdery mildew conidia have been studied.Conidia germinated on all substrates tested. Highest germination (89.41 %) was on agar 2 %. Germination was equally good on dry slide and in water. Generally one, rarely two germ tubes emerged from each conidium from the corner or occasionally from other places. Germination started after two hours of incubation and was almost over in 5 hours. Germination energy was 86.2.Maximum temperature for germination was 32.5 C. Optimum lied near 20 C.Light and darkness did not affect germination.Conidia germinated at all relative humidities tested including 0 and 100 %.Department of Plant Pathology, Agricultural Experiment Station, University of Udaipur, Udaipur, India.Based on a part of Ph.D. thesis of the senior author.     

QTLs for tomato powdery mildew resistance (Oidium lycopersici) in Lycopersicon parviflorum G1.1601 co-localize with two qualitative powdery mildew resistance genes

Tomato (Lycopersicon esculentum) is susceptible to the powdery mildew Oidium lycopersici, but several wild relatives such as Lycopersicon parviflorum G1.1601 are completely resistant. An F2 population from a cross of Lycopersicon esculentum cv. Moneymaker x Lycopersicon parviflorum G1.1601 was used to map the O. lycopersici resistance by using amplified fragment length polymorphism markers. The resistance was controlled by three quantitative trait loci (QTLs). Ol-qtl1 is on chromosome 6 in the same region as the Ol-1 locus, which is involved in a hypersensitive resistance response to O. lycopersici. Ol-qtl2 and Ol-qtl3 are located on chromosome 12, separated by 25 cM, in the vicinity of the Lv locus conferring resistance to another powdery mildew species, Leveillula taurica. The three QTLs, jointly explaining 68% of the phenotypic variation, were confirmed by testing F3 progenies. A set of polymerase chain reaction-based cleaved amplified polymorphic sequence and sequence characterized amplified region markers was generated for efficient monitoring of the target QTL genomic regions in marker assisted selection. The possible relationship between genes underlying major and partial resistance for tomato powdery mildew is discussed.     

Population genetics of the Federally Threatened Miccosukee gooseberry (Ribes echinellum), an endemic North American species

Ribes echinellum (Coville) Rehder (Miccosukee gooseberry; Grossulariaceae) is a Federally Threatened species known from only two localities: Jefferson County (Florida, FL) and McCormick County (South Carolina, SC). This perennial shrub, ca. 1 m tall, is deciduous, and reproduces both vegetatively (clonal growth) and sexually (seed production). Recent surveys of the FL population revealed a dramatic decline in plant numbers. To assist in conservation and management of this species in FL and SC populations, microsatellite genetic markers were used to identify genotypes and assess the genetic structure of R. echinellum. We genotyped seven microsatellite loci in 102 individuals: 74 collected in FL and 28 in SC. Unbiased heterozygosity was between 0.28 and 0.53. All seven loci were polymorphic, showing a range of 1.52–2.13 effective number of alleles per locus (mean = 1.75). The two populations of R. echinellum show low genetic diversity, especially in SC. Clonality was not widespread, but was higher in the SC population. Both populations show signatures of bottlenecks but isolation by distance was not evident. We found significant deviation from HW equilibrium, with higher number of heterozygotes than expected. However when HW test was done for the combined populations as two separate groups, only FL showed a significant HW test and for SC the test was non-significant. Bayesian analysis and F_ST values suggest high genetic divergence between the populations. These results are important for developing a recovery plan and an ex situ and reintroduction conservation programs.