1,721,189 research outputs found
A genetic linkage map of Venturia inaequalis, the causal agent of apple scab
Full text linkBackground
Venturia inaequalis is an economically-important disease of apple causing annual epidemics of scab worldwide. The pathogen is a heterothallic ascomycete with an annual cycle of sexual reproduction on infected apple leaf litter, followed by several cycles of asexual reproduction during the apple growing season. Current disease prevention is achieved mainly through scheduled applications of fungicides. Genetic linkage maps are essential for studying genome structure and organisation, and are a valuable tool for identifying the location of genes controlling important traits of interest such as avirulence, host specificity and mating type in V. inaequalis. In this study, we performed a wide cross under in vitro conditions between an isolate of V. inaequalis from China and one from the UK to obtain a genetically diverse mapping population of ascospore progeny isolates and produced a map using AFLP and microsatellite (SSR) markers.
Findings
Eighty-three progeny were obtained from the cross between isolates C1054 (China) x 01/213 (UK). The progeny was screened with 18 AFLP primer combinations and 31 SSRs, and scored for the mating type locus MAT. A linkage map was constructed consisting of 294 markers (283 AFLPs, ten SSRs and the MAT locus), spanning eleven linkage groups and with a total map length of 1106 cM. The length of individual linkage groups ranged from 30.4 cM (Vi-11) to 166 cM (Vi-1). The number of molecular markers per linkage group ranged from 7 on Vi-11 to 48 on Vi-3; the average distance between two loci within each group varied from 2.4 cM (Vi-4) to 7.5 cM (Vi-9). The maximum map length between two markers within a linkage group was 15.8 cM. The MAT locus was mapped to a small linkage group and was tightly linked to two AFLP markers. The map presented is over four times longer than the previously published map of V. inaequalis which had a total genetic distance of just 270 cM.
Conclusions
A genetic linkage map is an important tool for investigating the genetics of important traits in V. inaequalis such as virulence factors, aggressiveness and mating type. The linkage map presented here represents a significant improvement over currently published maps for studying genome structure and organisation, and for mapping genes of economic importance on the V. inaequalis genome
Plasmopara viticola: a review of knowledge on downy mildew of grapevine and effective disease management
Full text linkThe oomycete Plasmopara viticola is native to North America and was accidentally introduced into Europe at the end of the 19th century, where it caused widespread damage to the grape industry. Since that time, the damage caused by this plant pathogen has generally been controlled with multiple fungicide applications. Modern fungicides applied as prescribed by weather-based warning systems can effectively prevent any damage that might be caused. Alternatives to chemical treatments, such as the use of biocontrol agents or resistant cultivars, currently play a marginal role in controlling this disease. Until the middle of last century, research efforts were mainly concentrated on optimizing the application of copper fungicides and developing new molecules and formulations for controlling the disease. During the second half of the last century, highly efficient products for control were available, so research efforts moved toward optimizing and minimizing chemical control, mostly through the use of weather-based warning systems based on complex biological models. In the last 20 years, parallel to the development of technologies for genomic and transcriptomic analyses, host-pathogen interactions and population genetics have captured the interest of researchers in this field. Breeding for resistance against downy mildew has always coexisted with chemical control. However, the results of these breeding programmes have traditionally been cultivated only in marginal areas and organic production systems. This review traces the history of European knowledge of P. viticola
Vf scab resistance of Malus
Full text linkThe apple production in temperate regions with spring rains, the Scab caused by the fungus Venturia inaequalis is the most important constraint. To produce spotless apples and avoid damage that develops during
storage, growers apply fungicide on a regular or weatherdetermined basis. All major apple cultivars are highly susceptible to this disease. To limit the need for fungicide applications, apple breeders are currently introgressing disease resistance from wild Malus accessions into commercial
lines. The first attempts to do this were made 100 years ago. As apples are self-incompatible, pseudobackcrossing is used to eliminate unwanted traits from wild Malus and select new cultivars that are attractive to both producers and consumers. This process, from the first cross of a commercial cultivar with a wild, disease-resistant Malus, is extremely long due to apple’s long juvenile phase, the need for more than seven backcross steps and the
high heterozygosity of this genus. Therefore, most of today’s scab-resistant cultivars rely on a single introduction
of scab resistance from Malus floribunda 821, referred to as Vf. In this paper, we trace the history of Vf from its initial
identification through its use in breeding and commercial production. We sum up the literature describing how and where Vf resistance has been overcome by new pathotypes of V. inaequalis. Finally, we describe the current knowledge of the genes behind Vf resistance, its mode of action and the use of Vf genes in gene technolog
Isolation of differentially expressed genes in the apple cultivar florina after scab inoculation
No full textNicotinic acid and nicotinamide on pear and apple flowers are not limiting factors for Erwinia amylovora growth when these chemicals are considered in relation to cultivar and flower age
No full textFire blight, caused by Erwinia amylovora, is a devastating disease of pear (Pyrus communis) and apple (Malus × domestica) in many areas of the world. The disease is often initiated by epiphytic populations
that multiply on flowers and colonize the hypanthia. In vitro, E. amylovora requires nicotinic acid (NicAc) and/or nicotinamide (NicNH2) as essential growth factors. The amount of NicAc on pear hypanthia was positively correlated with the altitude of the growing site and was inversely correlated with the sum of the maximum temperatures in the 30 days before flowering. The sum of the amounts of NicAc and NicNH2 on the hypanthia was about 6 to 23 times higher in pear, and about 1.2 to 3.5 times higher in apple, than the amounts of NicAc or NicNH2 necessary to support maximum E. amylovora growth in vitro. No correlation was found between the amounts of NicAc and NicNH2 on the hypanthia of different pear and apple cultivars and at different growth stages and the growth of E. amylovora after experimental inoculation. In conclusion, NicAc and NicNH2 are essential for E. amylovora growth but the amounts of these chemicals on pear and apple flowers do not limit the establishment of the pathogen when competing bacteria are lackin
Effect of temperature on induced systemic resistance on grape against Plasmopara viticola and on pathogen's population
No full textSome biocontrol agents are known to induce systemic resistance (ISR) in plants reducing
the severity of downy mildew disease caused by Plasmopara viticola, but little is known about the effect of temperature on this mechanism. Population genetic studies revealed a considerable diversity of P. viticola in vineyards. The aim of this study is to understand the effect of temperature on
Trichoderma harzianum T39-induced systemic resistance on grape and to study the effect of temperature on populations of P. viticola. Grapevine plants treated with T39 at different temperatures are inoculated with P. viticola and biological effects are evaluated. Leaves are also collected for
ISR/SAR genes expression analysis. P. viticola isolates are genotyped and phenotyped (i.e. incubation time, sporulation amount). Genotypes are co-inoculated at different temperatures and the population is analyzed with microsatellite markers and real time PCR. The results will allow a better understanding of the role of the plant and the pathogen in a view of climate chang
Atoxigenic black aspergilli populations in Trentino: a natural biocontrol threaten by climate change?
No full textOchratoxin A (OTA) is a potent nephrotoxic and carcinogenic mycotoxin. After cereals, wine is considered the second major source of OTA intake in European diet. Responsible of OTA contamination of grapes are members of Aspergillus Section Nigri, also known as black aspergilli, in particular A. carbonarius and A. niger. Due to the relatively high optimum growth temperature of black aspergilli, OTA contamination represents a particularly severe problem in southern, hot environments. In fact, OTA has been never detected in grape musts produced in the region of Trentino (Northern Italy). A survey conducted in vineyards of Trentino during September 2008 and 2009 revealed that only A. japonicus, an atoxigenic species, was present in large quantity; whereas A. carbonarius could not be detected and isolated A. niger strains did not produce OTA. As illustrated by biocontrol experiments using non-aflatoxigenic A. flavus, atoxigenic strains compete with toxigenic strains for the same sites for growth, resulting in a lowered mycotoxin contamination of the agricultural product. We hypothesise that under the present
environmental conditions in Trentino, populations of atoxigenic black aspergilli competitively exclude toxigenic strains, working as natural biocontrol. Observed climate change can have an effect on the interactions of black aspergilli leading to the establishment of toxigenic strains in vineyards of Trentino. This hypothesis will be tested with in vitro experiments to evaluate the effects of temperature on the interactions between atoxigenic and toxigenic black aspergilli strain
Amplification of polyketide synthase gene fragments in ochratoxigenic and nonochratoxigenic black Aspergilli in grapevine
No full textMembers of the Aspergillus section Nigri, also known as black aspergilli produce Ochratoxin A (OTA), a contaminant of wine. Despite potentially severe health effects and economic losses caused by OTA in wine, almost nothing is known about the genetics that lies behind its biosynthesis in black aspergilli in grapevine. In this work, degenerate primer sets were used to amplify 49 Polyketide Synthase (PKS) gene fragments in reference strains of A. carbonarius, A. niger and A. tubingensis. Deduced amino acid sequences were then compared with those of aolc35-12 and aoks1, two PKS genes involved in OTA biosynthesis in A. westerdijkiae. A putative homologue of aolc35-12 was found in A. carbonarius (63% amino acid identity), the main OTA producer on grapes and in an ochratoxigenic A. niger strain (58%). In A. niger this fragment corresponded to an15g07920, a PKS already annotated in the sequenced A. niger CBS 513.88 genome as putatively involved in OTA biosynthesis. No aolc35-12 candidates were found in atoxigenic A. tubingensis isolates and no putative homologues of aoks1 were found in any of the screened strains. A screening of A. niger field isolates using specific primers for an15g07920 indicated that the absence of this gene is apparently related to a failure to produce OTA. The present work gives a first insight into the genetics of OTA biosynthesis in black aspergilli in grapevine and represents a starting point for further investigation of the OTA biosynthesis pathway and the development of molecular methods to detect the producers in vineyards
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