Insights on cisgenic plants with durable disease resistance under the European Green Deal.

Significant shares of harvests are lost to pests and diseases, therefore, minimizing these losses could solve part of the supply constraints to feed the world. Cisgenesis is defined as the insertion of genetic material into a recipient organism from a donor that is sexually compatible. Here, we review (i) conventional plant breeding, (ii) cisgenesis, (iii) current pesticide-based disease management, (iv) potential economic implications of cultivating cisgenic crops with durable disease resistances, and (v) potential environmental implications of cultivating such crops; focusing mostly on potatoes, but also apples, with resistances to Phytophthora infestans and Venturia inaequalis, respectively. Adopting cisgenic varieties could provide benefits to farmers and to the environment through lower pesticide use, thus contributing to the European Green Deal target.

Broad spectrum late blight resistance in potato differential set plants MaR8 and MaR9 is conferred by multiple stacked R genes.

Phytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this "de-stacking" approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varieties.

Review: Holistic pest management against early blight disease towards sustainable agriculture.

Alternaria species are well-known aggressive pathogens that are widespread globally and warmer temperatures caused by climate change might increase their abundance more drastically. Early blight (EB) disease, caused mainly by Alternaria solani, and brown spot, caused by Alternaria alternata, are major concerns in potato, tomato and eggplant production. The development of EB is strongly linked to varieties, crop development stages, environmental factors, cultivation and field management. Several forecasting models for pesticide application to control EB were created in the last century and more recent scientific advances have included modern breeding technology to detect resistant genes and precision agriculture with hyperspectral sensors to pinpoint damage locations on plants. This paper presents an overview of the EB disease and provides an evaluation of recent scientific advances to control the disease. First of all, we describe the outline of this disease, encompassing biological cycles of the Alternaria genus, favorite climate and soil conditions as well as resistant plant species. Second, versatile management practices to minimize the effect of this pathogen at field level are discussed, covering their limitations and pitfalls. A better understanding of the underlying factors of this disease and the potential of novel research can contribute to implementing integrated pest management systems for an ecofriendly farming system. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Invasion of Phytophthora infestans at the landscape level: how do spatial scale and weather modulate the consequences of spatial heterogeneity in host resistance?

Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with ≥1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions.

No Tangible Effects of Field-Grown Cisgenic Potatoes on Soil Microbial Communities.

DNA modification techniques are increasingly applied to improve the agronomic performance of crops worldwide. Before cultivation and marketing, the environmental risks of such modified varieties must be assessed. This includes an understanding of their effects on soil microorganisms and associated ecosystem services. This study analyzed the impact of a cisgenic modification of the potato variety Desirée to enhance resistance against the late blight-causing fungus Phytophthora infestans (Oomycetes) on the abundance and diversity of rhizosphere inhabiting microbial communities. Two experimental field sites in Ireland and the Netherlands were selected, and for 2 subsequent years, the cisgenic version of Desirée was compared in the presence and absence of fungicides to its non-engineered late blight-sensitive counterpart and a conventionally bred late blight-resistant variety. At the flowering stage, total DNA was extracted from the potato rhizosphere and subjected to PCR for quantifying and sequencing bacterial 16S rRNA genes, fungal internal transcribed spacer (ITS) sequences, and nir genes encoding for bacterial nitrite reductases. Both bacterial and fungal communities responded to field conditions, potato varieties, year of cultivation, and bacteria sporadically also to fungicide treatments. At the Dutch site, without annual replication, fungicides stimulated nirK abundance for all potatoes, but with significance only for cisgenic Desirée. In all other cases, neither the abundance nor the diversity of any microbial marker differed between both Desirée versions. Overall, the study demonstrates environmental variation but also similar patterns of soil microbial diversity in potato rhizospheres and indicates that the cisgenic modification had no tangible impact on soil microbial communities.

Equivalence analysis to support environmental safety assessment: Using nontarget organism count data from field trials with cisgenically modified potato.

This paper considers the statistical analysis of entomological count data from field experiments with genetically modified (GM) plants. Such trials are carried out to assess environmental safety. Potential effects on nontarget organisms (NTOs), as indicators of biodiversity, are investigated. The European Food Safety Authority (EFSA) gives broad guidance on the environmental risk assessment (ERA) of GM plants. Field experiments must contain suitable comparator crops as a benchmark for the assessment of designated endpoints. In this paper, a detailed protocol is proposed to perform data analysis for the purpose of assessing environmental safety. The protocol includes the specification of a list of endpoints and their hierarchical relations, the specification of intended levels of data analysis, and the specification of provisional limits of concern to decide on the need for further investigation. The protocol emphasizes a graphical representation of estimates and confidence intervals for the ratio of mean abundances for the GM plant and its comparator crop. Interpretation relies mainly on equivalence testing in which confidence intervals are compared with the limits of concern. The proposed methodology is illustrated with entomological count data resulting from multiyear, multilocation field trials. A cisgenically modified potato line (with enhanced resistance to late blight disease) was compared to the original conventional potato variety in the Netherlands and Ireland in two successive years (2013, 2014). It is shown that the protocol encompasses alternative schemes for safety assessment resulting from different research questions and/or expert choices. Graphical displays of equivalence testing at several hierarchical levels and their interpretation are presented for one of these schemes. The proposed approaches should be of help in the ERA of GM or other novel plants.

Understanding and exploiting late blight resistance in the age of effectors.

Potato (Solanum tuberosum) is the world's third-largest food crop. It severely suffers from late blight, a devastating disease caused by Phytophthora infestans. This oomycete pathogen secretes host-translocated RXLR effectors that include avirulence (AVR) proteins, which are targeted by resistance (R) proteins from wild Solanum species. Most Solanum R genes appear to have coevolved with P. infestans at its center of origin in central Mexico. Various R and Avr genes were recently cloned, and here we catalog characterized R-AVR pairs. We describe the mechanisms that P. infestans employs for evading R protein recognition and discuss partial resistance and partial virulence phenotypes in the context of our knowledge of effector diversity and activity. Genome-wide catalogs of P. infestans effectors are available, enabling effectoromics approaches that accelerate R gene cloning and specificity profiling. Engineering R genes with expanded pathogen recognition has also become possible. Importantly, monitoring effector allelic diversity in pathogen populations can assist in R gene deployment in agriculture.