Climate Change and Defense against Pathogens in Plants

Disease Management in Regenerative Cropping in the Context of Climate Change and Regulatory Restrictions

Regenerative agriculture as a term and concept has gained much traction over recent years. Many farmers are convinced that by adopting these principles they will be able to address the triple crisis of biodiversity loss, climate change, and food security. However, the impact of regenerative agriculture practices on crop pathogens and their management has received little attention from the scientific community. Significant changes to cropping systems may result in certain diseases presenting more or less of a threat. Shifts in major diseases may have significant implications regarding optimal integrated pest management (IPM) strategies that aim to improve profitability and productivity in an environmentally sensitive manner. In particular, many aspects of regenerative agriculture change risk levels and risk management in ways that are central to effective IPM. This review outlines some of the challenges, gaps, and opportunities in our understanding of appropriate approaches for managing crop diseases in regenerative cropping systems.

Resistant or Susceptible? How Central European Oat (A. sativa L.) Cultivars React to B. graminis f. sp. avenae Infection

In accordance with the postulates of integrated plant protection, the use of cultivars with genetically determined resistance is one of the main strategies for preventing losses caused by fungal pathogens. The development of breeding programs aimed at increasing resistance to pathogens should be preceded by a characterization of the resistance of cultivars grown in a given area. This allows us to determine the number of genes used in breeding and their effectiveness. It also allows us to estimate the pressure that the pathogen may exert on varieties with specific resistance genes. The presented work aimed to determine the level of resistance of oat varieties currently cultivated in Central Europe and the number of effective powdery mildew resistance genes currently used in oat breeding programs. The research showed that out of 46 varieties, only 5 were resistant to powdery mildew. Analysis of the infection profiles allowed us to postulate the presence of the Pm7 gene in four of them. In the Merlin variety from the Czech Republic, it was not possible to determine which of the previously described genes determines resistance to powdery mildew. Due to the observed climate changes and the rapid adaptation of pathogens to new environmental conditions, it is crucial to introduce a wider pool of genes that determine the pathogen resistance of cultivars.

Micronutrients Affect Expression of Induced Resistance Genes in Hydroponically Grown Watermelon against Fusarium oxysporum f. sp. niveum and Meloidogyne incognita

The soil-borne pathogens, particularly Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita) are the major threats to watermelon production in the southeastern United States. The role of soil micronutrients on induced resistance (IR) to plant diseases is well-documented in soil-based media. However, soil-based media do not allow us to determine the contribution of individual micronutrients in the induction of IR. In this manuscript, we utilized hydroponics-medium to assess the effect of controlled application of micronutrients, including iron (Fe), manganese (Mn), and zinc (Zn) on the expression of important IR genes (PR1, PR5, and NPR1 from salicylic acid (SA) pathway, and VSP, PDF, and LOX genes from jasmonic acid (JA) pathway) in watermelon seedlings upon inoculation with either FON or RKN or both. A subset of micronutrient-treated plants was inoculated (on the eighth day of micronutrient application) with FON and RKN (single or mixed inoculation). The expression of the IR genes in treated and control samples was evaluated using qRT-PCR. Although, significant phenotypic differences were not observed with respect to the severity of wilt symptoms or RKN galling with any of the micronutrient treatments within the 30-day experimental period, differences in the induction of IR genes were considerably noticeable. However, the level of gene expression varied with sampling period, type and concentration of micronutrients applied, and pathogen inoculation. In the absence of pathogens, micronutrient applications on the seventh day, in general, downregulated the expression of the majority of the IR genes. However, pathogen inoculation preferentially either up- or down-regulated the expression levels of the IR genes at three days post-inoculation depending on the type and concentration of micronutrients. The results demonstrated here indicate that micronutrients in watermelon may potentially make watermelon plants susceptible to infection by FON and RKN. However, upon infection the IR genes are significantly up-regulated that they may potentially aid the prevention of further infection via SA- and JA-pathways. This is the first demonstration of the impact of micronutrients affecting IR in watermelon against FON and RKN infection.

Multivariate analyses of Ethiopian durum wheat revealed stable and high yielding genotypes

Improving crop adaptation and stability across diverse and changing environmental conditions is essential to increasing grain yield per unit area. In turn, this contributes to meeting the increasing global food demand. Nevertheless, a number of factors challenge the efficiency of crop improvement programs, of which genotype-by-environment interaction (GEI) is one of the major factors. This study aimed to evaluate the performance and phenotypic stability of 385 Ethiopian durum wheat landraces and 35 cultivars; assess the pattern of genotype by environment interaction (GEI) effect, and identify stable and high-yielding landraces or cultivars using the additive main effect and multiplicative interaction (AMMI) and genotype main effect plus genotype by environment interaction biplot (GGE-biplot). The experiment was laid out in an alpha lattice design with two replications at five test sites (Akaki, Chefe Donsa, Holeta, Kulumsa, and Sinana). The combined analysis of variance revealed highly significant effects (P ≤ 0.01) of environments (E), genotype (G), and GEI on a phenotypic variation of traits evaluated, including grain yield. For all traits, the amount of phenotypic variance and GEI explained by the GGE biplot was higher than in AMMI2, but both exhibited significant effects of E and GEI on the genotypes. The AMMI model identified G169, G420, G413, G139, G415, G416, G417, and G418 as stable genotypes across testing sites. Whereas, the GGE biplot identified G169, G420, G415, G139, G106, G412, G413, and G417 as both high-yielding and stable across test sites. Hence, genotypes identified as stable and high yielding in the present study could be used in a durum wheat breeding program aimed at identifying genes and molecular markers associated with the crop’s productivity traits as well as developing stable and high-yielding cultivars for use in East Africa and beyond.

The Transcriptomic Profile of Watermelon Is Affected by Zinc in the Presence of Fusarium oxysporum f. sp. niveum and Meloidogyne incognita

Zinc (Zn) accumulation and deficiency affect plant response to pests and diseases differently in varying pathosystems. The concentrations of Zn in plants aid in priming defense signaling pathways and help in enhanced structural defenses against plant pathogens. Studies are lacking on how concentrations of Zn in watermelon plants influence defense against two important soil-borne pathogens: Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita). In this study a comparative transcriptomics evaluation of watermelon plants in response to high (1.2 ppm) and low (0.2 ppm) levels of Zn were determined. Differential transcript-level responses differed in watermelon plants when infected with FON or RKN or both under high- and low-Zn treatment regimes in a controlled hydroponics system. Higher numbers of differentially expressed genes (DEGs) were observed in high-Zn-treated than in low-Zn-treated non-inoculated plants, in plants inoculated with FON alone and in plants inoculated with RKN alone. However, in the co-inoculated system, low-Zn treatment had higher DEGs as compared to high-Zn treatment. In addition, most DEGs were significantly enriched in hormone signal transduction and MAPK signaling pathway, suggesting an induction of systemic resistance with high-Zn concentrations. Taken together, this study substantially expands transcriptome data resources and suggests a molecular potential framework for watermelon-Zn interaction in FON and RKN.

Cold acclimation by the CBF-COR pathway in a changing climate: Lessons from Arabidopsis thaliana

Cold acclimation is a process used by most temperate plants to cope with freezing stress. In this process, the expression of cold-responsive (COR) genes is activated and the genes undergo physiological changes in response to the exposure to low, non-freezing temperatures and other environmental signals. The C-repeat-binding factors (CBFs) have been demonstrated to regulate the expression of many COR genes. Recent studies have elucidated the molecular mechanisms of how plants transmit cold signals from the plasma membrane to the CBFs and the results have indicated that COR genes are also regulated through CBF-independent pathways. Climate change is expected to have a major impact on cold acclimation and freezing tolerance of plants. However, how climate change affects plant cold acclimation at the molecular level remains unclear. This mini-review focuses on recent advances in cold acclimation in Arabidopsis thaliana and discusses how signaling can be potentially impacted by climate change. Understanding how plants acquire cold acclimation is valuable for the improvement of the freezing tolerance in plants and for predicting the effects of climate change on plant distribution and agricultural yield.

Genetic resistance against viruses in Phaseolus vulgaris L.: State of the art and future prospects

Viruses are obligate parasites that replicate intracellularly in many living organisms, including plants. Consequently, no chemicals are available that target only the virus without impacting host cells or vector organisms. The use of natural resistant varieties appears as the most reliable control strategy and remains the best and cheapest option in managing virus diseases, especially in the current ecological context of preserving biodiversity and environment in which the use of phytosanitary products becomes limited. Common bean is a grain legume cultivated mainly in Africa and Central-South America. Virus diseases of common bean have been extensively studied both by breeders to identify natural resistance genes in existing germplasms and by pathologists to understand the molecular bases of plant-virus interactions. Here we present a critical review in which we synthesize previous and recent information concerning 1) main viruses causing diseases in common bean, 2) genetic resistance to viruses in common bean, 3) the different resistance phenotypes observed and more particularly the effect of temperature, 4) the molecular bases of resistance genes to viruses in common bean, and 5) future prospects using transgenic-engineered resistant lines.

Exploitation of Diversity within Crops-the Key to Disease Tolerance?

Tolerance, defined as the ability of a crop to maintain yield in the presence of disease, is a difficult characteristic to measure, and its component traits are generally undefined. It has been studied as a characteristic of plant genotypes grown singly or in monoculture crop stands. However, it is similarly valid as a characteristic of ecosystems, or mixtures / inter-cropping in crops and this paper seeks to evaluate theoretical and practical aspects of tolerance in this context. Focusing on cereals and fungal pathogens, consideration is given to the process of yield formation, the impact of disease on yield, and how tolerance might be assessed in monocultures. Variation in tolerance traits in monocultures and how such plants might interact in mixtures is considered; specifically the expression of tolerance in mixtures and how plants with contrasting tolerance traits in monocultures combine. Having focused on disease, further consideration is given to the impact of and on other microbial species in the crop environment. Finally the practical approaches that could be adopted to identify and assess the main traits responsible for expressing tolerance are addressed. These focus on the dynamic nature of plant-plant and plant-microbe interactions particularly in response to both biotic and abiotic stress out with the range of optimal or normal crop evaluation environments. It is proposed that by using more extreme factor parameter values in mixed crop evaluation environments the key traits affecting tolerance will be identified.