Erland Liljeroth

Induced resistance in potato to Phytphthora infestans —effects of BABA in greenhouse and field tests with different potato varieties

We have investigated to what degree induced resistance with β-aminobutyric acid (BABA) can protect potato from late blight infection under Swedish field conditions and if synergistic interactions occur if BABA is applied in combination with a commonly used fungicide, Shirlan. In greenhouse experiments we also investigated the durability of BABA induced resistance, the dose-response relationships in susceptible (Bintje) and partially resistant (Ovatio, Suberb) cultivars and effects of combined applications of BABA and fungicides. We found a clear effect of BABA on P. infestans infection of greenhouse grown potato plants. The lesion sizes were reduced by on average 40–50% compared to untreated control. However, this effect lasted for only 4–5 days after BABA treatment and then the efficacy was lower. When BABA was given in combination with the fungicides it appeared to have an additive effect both in greenhouse and field experiments. Higher concentrations of BABA gave a stronger protective effect. The partially resistant cultivars Ovatio and Superb reacted to lower concentrations of BABA where no effect was found in susceptible Bintje. According to our field data, 20–25% reduction of the fungicide dose in combination with BABA gave on average the same result on late blight development as full dose Shirlan alone; while reduced dose of Shirlan alone sometimes resulted in less effective protection. Our results indicate that induced resistance could be used in practice in combinations with fungicides in order to reduce the amount of toxic compounds under north European conditions.

Stability of transgene integration and expression in subsequent generations of doubled haploid oilseed rape transformed with chitinase and β-1,3-glucanase genes in a double-gene construct

A double-gene construct with one chitinase and one β-1,3-glucanase gene from barley, both driven by enhanced 35S promoters, was transformed into oilseed rape. From six primary transformants expressing both transgenes 10 doubled haploid lines were produced and studied for five generations. The number of inserted copies for both the genes was determined by Southern blotting and real-time PCR with full agreement between the two methods. When copy numbers were analysed in different generations, discrepancies were found, indicating that at least part of the inserted sequences were lost in one of the alleles of some doubled haploids. Chitinase and β-1,3-glucanase expression was analysed by Western blotting in all five doubled haploid generations. Despite that both the genes were present on the same T-DNA and directed by the same promoter their expression pattern between generations was different. The β-1,3-glucanase was expressed at high and stable levels in all generations, while the chitinase displayed lower expression that varied between generations. The transgenic plants did not show any major impact on fungal resistance when assayed in greenhouse, although purified β-1,3-glucanase and chitinase caused retardment of fungal growth in vitro.

Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans

BackgroundPotato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss. We investigated the transcriptome of Solanum tubersoum (cv. Desiree) and characterized the secretome by quantitative proteomics after foliar application of the protective agent phosphite. We also studied the distribution of phosphite in planta after application and tested transgenic potato lines with impaired in salicylic and jasmonic acid signaling.ResultsPhosphite had a rapid and transient effect on the transcriptome, with a clear response 3 h after treatment. Strikingly this effect lasted less than 24 h, whereas protection was observed throughout all time points tested. In contrast, 67 secretome proteins predominantly associated with cell-wall processes and defense changed in abundance at 48 h after treatment. Transcripts associated with defense, wounding, and oxidative stress constituted the core of the phosphite response. We also observed changes in primary metabolism and cell wall-related processes. These changes were shown not to be due to phosphate depletion or acidification caused by phosphite treatment. Of the phosphite-regulated transcripts 40% also changed with β-aminobutyric acid (BABA) as an elicitor, while the defence gene PR1 was only up-regulated by BABA. Although phosphite was shown to be distributed in planta to parts not directly exposed to phosphite, no protection in leaves without direct foliar application was observed. Furthermore, the analysis of transgenic potato lines indicated that the phosphite-mediated resistance was independent of the plant hormones salicylic and jasmonic acid.ConclusionsOur study suggests that a rapid phosphite-triggered response is important to confer long-lasting resistance against P. infestans and gives molecular understanding of its successful field applications.

Identification of Colletotrichum species associated with anthracnose disease of coffee in Vietnam

Twenty-three isolates of Colletotrichum gloeosporioides, five isolates of C. acutatum, two isolates of C. capsici and six isolates of C. boninense associated with anthracnose disease on coffee (Coffea spp.) in Vietnam were identified based on morphology and DNA analysis. Phylogenetic analysis of DNA sequences from the internal transcribed spacer region of nuclear rDNA and a portion of mitochondrial small subunit rRNA were concordant and allowed good separation of the taxa. We found several Colletotrichum isolates of unknown species and their taxonomic position remains unresolved. The majority of Vietnamese isolates belonged to C. gloeosporioides and they grouped together with the coffee berry disease (CBD) fungus, C. kahawae. However, C. kahawae could be distinguished from the Vietnamese C. gloeosporioides isolates based on ammonium tartrate utilization, growth rate and pathogenicity. C. gloeosporioides isolates were more pathogenic on detached green berries than isolates of the other species, i.e. C. acutatum, C capsici and C. boninense. Some of the C. gloeosporioides isolates produced slightly sunken lesions on green berries resembling CBD symptoms but it did not destroy the bean. We did not find any evidence of the presence of C. kahawae in Vietnam.

Paranoid potato: phytophthora-resistant genotype shows constitutively activated defense.

Phytophthora is the most devastating pathogen of dicot plants. There is a need for resistance sources with different modes of action to counteract the fast evolution of this pathogen. In order to better understand mechanisms of defense against P. infestans, we analyzed several clones of potato. Two of the genotypes tested, Sarpo Mira and SW93-1015, exhibited strong resistance against P. infestans in field trials, whole plant assays and detached leaf assays. The resistant genotypes developed different sizes of hypersensitive response (HR)-related lesions. HR lesions in SW93-1015 were restricted to very small areas, whereas those in Sarpo Mira were similar to those in Solanum demissum, the main source of classical resistance genes. SW93-1015 can be characterized as a cpr (constitutive expressor of PR genes) genotype without spontaneous microscopic or macroscopic HR lesions. This is indicated by constitutive hydrogen peroxide (H2O2) production and PR1 (pathogenesis-related protein 1) secretion. SW93-1015 is one of the first plants identified as having classical protein-based induced defense expressed constitutively without any obvious metabolic costs or spontaneous cell death lesions.

Late blight on potato is suppressed by the biosurfactant-producing strain Pseudomonas koreensis 2.74 and its biosurfactant

Potato late blight disease caused by the zoospore-producing pathogen Phytophthora infestans (Mont.) de Bary is one of the most destructive plant diseases world-wide and currently its management mainly relies on the frequent use of fungicides. This study investigated the possibility of reducing potato late blight by biocontrol with the biosurfactant-producing strain Pseudomonas koreensis 2.74. Significant disease reduction with the biosurfactant-producing strain and its biosurfactant was observed in greenhouse trials using a detached-leaf assay. A direct effect of the biosurfactant on zoospores of P. infestans was also observed, whereas the biosurfactant only caused a minor reduction in mycelial growth rate and had no effect on the rate of sporangia production in pure culture.

Sugar beet extract induces defence against Phytophthora infestans in potato plants

The aim of this study was to find a natural and cheap agent that could induce defence responses in potato plants to combat Phytophthora infestans, which causes late blight disease that is one of the most devastating plant pathogens in agriculture. We tested whether a sugar beet extract (SBE), derived through a simple extraction procedure from a large-scale plant waste product, induced resistance under green-house conditions. In three potato genotypes differing in their level of resistance to P. infestans (two susceptible genotypes: Desiree and Bintje and one partially resistant: Ovatio), treatment with SBE resulted in significant reduction of the size of the infection lesions in a pattern similar to that seen with application of a known defence-inducing compound, β-aminobutyric acid (BABA). Lower sporangial production was also observed on SBE-treated leaves, but the reduction in sporangial production was more pronounced after BABA treatment. SBE had no apparent toxic effect on the hyphal growth of the pathogen or on the germination of sporangia. Instead, SBE triggered pathogenesis-related protein (PR-1 and PR-2) induction which suggests that the protection conferred by SBE could be via induced resistance. An array of phenolic metabolites was found in the SBE that may contribute to the defence response.

Pathogenic variation and sexual reproduction in Swedish populations of Bremia lactucae.

SummaryThe host-pathogen interaction between lettuce (Lactuca sativa) and downy mildew (Bremia lactucae) is mainly differential and the resistance so far utilized in the host is vertical. As in many other obligate parasites, the introduction of cultivars with new vertical resistance has exerted a strong selection pressure on the pathogen resulting in significant changes in virulence frequencies and in the establishment of races with new combinations of virulence. Genetic diversity in pathogen populations may arise through mutation and gene flow, and new virulence genotypes may then be established through parasexuality and sexual recombination. In Swedish populations of Bremia lactucae, the pattern of variation in the parasite agrees well with that which might be expected in a diploid, outcrossing organism with frequent sexual reproduction. This is supported by: two or more isolates, different in virulence and mating type, may occur together on the same lettuce leaf; zygotes (oospores) are formed in all populations investigated and the frequency varies from 22% to 98%; oospores germinate rather frequently under suitable conditions. To breed for resistance in dynamic host-pathogen systems such as this one is difficult and the program should preferably be based on race-non-specific resistance.

Cut-off shoots method for estimation of partial resistance in apple cultivars to fruit tree canker caused by Neonectria ditissima

Fruit tree canker, caused by the fungus Neonectria ditissima, is an economically devastating disease in apple orchards, especially in north-western Europe. Complete resistance has not yet been reported in apple, but variation in levels of partial resistance has been described and could be valuable in plant breeding programmes. A screening method based on spore inoculation of manually inflicted leaf scars on cut shoots was evaluated for reliability and repeatability in discrimination of 11 apple cultivars during two years – 2012 and 2013 – in two different facilities – biotron and standard greenhouse – and different time periods (February–May). The resulting cankers were counted (infection percentage), first appearance noted (incubation period) and lesion size measured at regular intervals during a period of 25–29 days for comparison of resistance levels. Results of two-way analysis of variance and correlation analyses showed that the area under the disease progress curve yielded the most robust data. This parameter was then applied for screening 30 apple cultivars using the same cut-shoot method. ‘Elise’ showed very high susceptibility, while the ornamental ‘Prairifire’ showed the highest level of partial resistance. Results suggested that cut shoots can be used to assess levels of resistance among cultivars, but great care must be taken to provide stable experimental conditions.

Plant Resistance Inducers against Pathogens in Solanaceae Species—From Molecular Mechanisms to Field Application

This review provides a current summary of plant resistance inducers (PRIs) that have been successfully used in the Solanaceae plant family to protect against pathogens by activating the plant’s own defence. Solanaceous species include many important crops such as potato and tomato. We also present findings regarding the molecular processes after application of PRIs, even if the number of such studies still remains limited in this plant family. In general, there is a lack of patterns regarding the efficiency of induced resistance (IR) both between and within solanaceous species. In many cases, a hypersensitivity-like reaction needs to form in order for the PRI to be efficient. “-Omics” studies have already given insight in the complexity of responses, and can explain some of the differences seen in efficacy of PRIs between and within species as well as towards different pathogens. Finally, examples of field applications of PRIs for solanaceous crops are presented and discussed. We predict that PRIs will play a role in future plant protection strategies in Solanaceae crops if they are combined with other means of disease control in different spatial and temporal combinations.