Use of potassium bicarbonate (Armicarb) on the control of powdery mildew (Sphaerotheca mors-uvae) of gooseberry (Ribes uva-crispa)

Powdery mildew (Sphaerotheca mors-uvae) severely infects young shoots, stems and fruits of gooseberry (Ribes uva-crispa). Environmental friendly and biological control measures are being sought throughout the world. Especially in organic gooseberry growing effective control measures are needed, because powdery mildew infections may result in a total loss of the crop. In organic currant growing the number of adequate control methods is very limited. Sulphur as a fungicide against powdery mildew in e.g. gooseberry or table grape growing is not recommendable due to possible bleaching of berries and scorching of tender shoots. Various bicarbonate salts are suggested as a good option to control powdery mildew. In a field trial the effect of potassium bicarbonate (Armicarb) on the on the control of powdery mildew of gooseberry was evaluated. Four treatments; i.e. two preventive strategies and two curative strategies, were applied. PLants were sprayed until runoff. The percent of infected fruits and disease severity were assessed. In the unsprayed control plots very high disease incidences were observed; on average more than 90% of the berries were infected with powdery mildew. The weekly (preventive) spray applications with potassium carbonate reduced the disease incidences on fruits significantly. On average approximately 10% of the fruits were affected by powdery mildew. However, the number of spray applications was high. In conclusion, our results indicate that applications of potassium bicarbonate (as Armicarb) are effective in reducing the incidence and severity of American powdery mildew in gooseberry. Early spray applications are necessary to protect berries against powdery mildew infections. Future research will focus on reducing the number of applications, e.g. warning models based on powdery mildew of rose (Sphaerotheca pannosa).     

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.     

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.     

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.     

Linkage between genes for resistance to downy mildew (Bremia lactucae) in lettuce

Data are presented for the joint segregation of the gene combinations: Dm-2/Dm-3, Dm-3/Dm-6, Dm-2/Dm-6 and Dm-6/Dm-8, following inoculation with five races of B. lactucae. It is postulated that Dm-2, 3 and 6 comprise a tight linkage group but that Dm-6 and Dm-8 are not linked as has been proposed previously. Information on the reaction of some resistant lettuce cultivars to certain B. lactucae races and some new postulated host genotypes is also presented.     

亚蔬中心绿豆品种(系)抗白粉病评价

采用苗期人工接种鉴定法,在大棚种植条件下对12个亚蔬中心(AVRDC)绿豆品种白粉病抗性进行了鉴定评价。结果显示,VC1560C、V4785和VC2768A三个品种高抗(HR)白粉病,VC6173-14、V1132为中抗(MR)白粉病品种。其它品种对白粉病表现高度感病。在田间种植条件下对亚蔬中心16个抗豆象回交9代品系(BC9)进行了成株期白粉病抗性鉴定。与对照感病品种 VC1973、VC1178A 相比,VC6459-3-6-37和 VC6458-6-3-16对白粉病具有一定抗性,但白粉病感染程度仍很严重,其它14个 BC9品系均对白粉病表现高度感病。     

Linkage analysis of genes for resistance to downy mildew (Bremia lactucae) in lettuce (Lactuca sativa)

Summary The genetics of specific resistance was studied in F₂ populations which segregated for either one or two resistance genes. The resistance factors 1, 11 and 14 which had not previously been characterized genetically segregated as single dominant genes (Dm). Resistance was determined by three linkage groups; R 1/14, 2, 3, and 6 in the first, R 5/8, and 10 in the second and R 4, 7 and 11 in the third. Cultivars of lettuce commonly used in the differential series to detect virulence to R3 and R10, were demonstrated to carry two tightly linked resistance genes. Implications of this linkage arrangement to the manipulation and characterization of these resistance genes are discussed.     

Antisense expression of peach mildew resistance locus O (PpMlo1) gene confers cross-species resistance to powdery mildew in Fragaria x ananassa

Powdery mildew (PM) is one of the major plant pathogens. The conventional method of PM control includes frequent use of sulfur-based fungicides adding to production costs and potential harm to the environment. PM remains a major scourge for Rosaceae crops where breeding approaches mainly resort to gene-for-gene resistance. We have tested an alternate source of PM resistance in Rosaceae. Mildew resistance locus O (MLO) has been well studied in barley due to its role in imparting broad spectrum resistance to PM. We identified PpMlo1 (Prunus persica Mlo) in peach and characterized it further to test if a similar mechanism of resistance is conserved in Rosaceae. Due to its recalcitrance in tissue culture, reverse genetic studies involving PpMloI were not feasible in peach. Therefore, Fragaria x ananassa LF9 line, a taxonomic surrogate, was used for functional analysis of PpMlo1. Agrobacterium-mediated transformation yielded transgenic strawberry plants expressing PpMlo1 in sense and antisense orientation. Antisense expression of PpMlo1 in transgenic strawberry plants conferred resistance to Fragaria-specific powdery mildew, Podosphaera macularis. Phylogenetic analysis of 208 putative Mlo gene copies from 35 plant species suggests a large number of duplications of this gene family prior to the divergence of monocots and eudicots, early in eudicot diversification. Our results indicate that the Mlo-based resistance mechanism is functional in Rosaceae, and that Fragaria can be used as a host to test mechanistic function of genes derived from related tree species. To the best of our knowledge, this work is one of the first attempts at testing the potential of using a Mlo-based resistance strategy to combat powdery mildew in Rosaceae.     

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.     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

Glycogen and degeneration in the pyloric gland of Dendrodoa grossularia (Ascidiacea,Tunicata)

Summary Degeneration is observed in cells of the pyloric gland of Dendrodoa grossularia in which glycogen storage occurs. The ultrastructure of four phases of the degeneration cycle is described. Natural senescence seems to be the cause of the degeneration. Glycogen storage might be the result of metabolic disturbance, but its presence reveals the importance of glycogen in the function of the organ. The role of the pyloric gland is discussed.     

Transference of resistance to black-currant gall mite, Cecidophyopsis ribis, from gooseberry to black currant

Field and insectary tests confirmed that the black-currant gall mite (Cecidophyopsis ribis) is unable to survive on gooseberry and red currant. A dominant gene Ce, controlling resistance to the gall mite, has been transferred from gooseberry to black currant. Resistant, large-fruited, self-fertile black currants of commercial potential have been obtained in the third backcross. One accession of Ribes bracteosum and three of R. americanum proved field susceptible to the gall mite, but twenty-four accessions of other Ribes species remained free from galled buds for at least 3 years in an infection plot.     

Breeding for partial resistance in dry beans (Phaseolus vulgaris) to bean rust (Uromyces appendiculatus)

Significant differences in susceptibility of 23 bean cultivars were found after natural infection by a single-pustule isolate of bean rust in field trials over three seasons. These differences were not related to differences in the number of adaxial or abaxial acicular leaf hairs, latent period in primary leaves or a difference in pustule size. Forty-five large-seeded bean lines with partial resistance to a single-pustule isolate were developed by recurrent selection for commercial evaluation.