A significant linkage for sustainable crop protection
Complete and balanced nutrition has always been the first line of plant defense due to the direct involvement of mineral elements in plant protection. Mineral elements affect plant health directly by modulating the activity of redox enzymes or improving the plant vigor indirectly by altering root exudates, and changing microflora population dynamics, rhizosphere soil nutrient content, pH fluctuation, lignin deposition, and phytoalexin biosynthesis. Nitrogen (N) is one of the most important macronutrients having a significant impact on the host-pathogen axis. N negatively affects the plant’s physical defense along with the production of antimicrobial compounds, but it significantly alleviates defense-related enzyme levels that can eventually assist in systemic resistance. Potassium (K) is an essential plant nutrient, when it is present in adequate concentration, it can certainly increase the plant’s polyphenolic concentrations, which play a critical role in the defense mechanism. Although no distinguished role of phosphorus (P) is observed in plant disease resistance, a high P content may increase the plant’s susceptibility toward the invader. Manganese (Mn) is one of the most important micronutrients, which have a vital effect on photosynthesis, lignin biosynthesis, and other plant metabolic functions. Zinc (Zn) is a part of enzymes that are involved in auxin synthesis, infectivity, phytotoxin, and mycotoxin production in pathogenic microorganisms. Similarly, many other nutrients also have variable effects on enhancing or decreasing the host susceptibility toward disease onset and progression, thereby making integrative plant nutrition an indispensable component of sustainable agriculture. However, there are still many factors influencing the triple interaction of host-pathogen-mineral elements, which are not yet unraveled. Thereby, the present review has summarized the recent progress regarding the use of macro- and micronutrients in sustainable agriculture and their role in plant disease resistance.
Introduction
Crop production remains delimited by an array of biotic and abiotic factors that can eventually reduce crop yield, quantity, and quality (Wang M. et al., 2013). Among the biotic factors, phytopathogens such as bacteria, fungi, nematodes, and viruses, have considerable impacts on agricultural productivity and sustainability. Sustainable agriculture can be said as the utilization of the agricultural ecosystem in a way that enables the perfect balance of biological diversity, productivity, and regeneration capacity so that the present and significant future demands can be fulfilled without harming other ecosystems (Lewandowski et al., 1999) and at the same time by managing plant diseases along with an increased yield and improved product quality (Camprubi et al., 2007). Developing along with evolution course, plants have developed multi-layered defense systems enabling them to resist and/or tolerate pathogen invasion and resist infection (Sun et al., 2020). The mineral nutrients play a potential role in supporting plant wellness that is influenced by various abiotic factors, such as light, humidity, temperature, and mineral nutrients (Velasquez et al., 2018) The N status can be affected by high soil temperature as it increases the overall N availability in soils (Lukac et al., 2011) and also increases the plant metabolic rate, thereby positively correlating N uptake with temperature (Dong et al., 2001). The K demands are observed to increase under low moisture conditions, which may sequester a higher reactive oxygen species (ROS) production leading to increased disruption of the plant cell organelles (Wang Y. et al., 2013). The P availability was reported to decrease during high light intensity, which subsequently increased the root length and fine root hair production (Wen et al., 2017). Mineral nutrients are particularly and directly involved in plant protection as structural components and metabolic regulators (Huber, 1980). As imparting the primary defense line, the plant’s nutritional status can play a deciding role in determining the plants’ susceptibility or resistance toward the invading pathogens (Walters and Bingham, 2007; Marschner and Marschner, 2012). The mineral elements can potentially influence plant health either directly by activating the enzymes involved in the synthesis of defense metabolites (callose, glucosinolates, lignin, phenols, and phytoalexins) or indirectly by altering the microbial activity, root exudates composition, and rhizosphere pH modulation (Datnoff et al., 2007). For controlling and managing plant disease, balanced nutrition had always been the primary component, yet its importance remains to be unraveled. The importance of mineral nutrition on plant disease management can be highlighted as (a) fertilization effect on the incidence or severity of a particular pathogen/host pathosystem, (b) mineral nutrition effect in imparting resistance or susceptibility to plant when provided in different concentration, and (c) effect of specific nutrient availability or starvation on disease in consortium with the growth stage of the plant, environmental conditions, and biological activity, which can eventually affect the outcomes (Meena et al., 2015). A healthy plant will certainly have high vigor and improved resistance and hereby mineral nutrients show their capabilities in disease management (Ojha and Jha, 2021). Mineral nutrients, such as the primary macronutrients, nitrogen (N), phosphorus (P), and potassium (K); the three secondary macronutrients, calcium (Ca), sulfur (S), and magnesium (Mg); and the micronutrients, boron (B), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), and silicon (Si), are significant in imparting disease resistance and healthy growth to the plant (Datnoff et al., 2007; Gupta et al., 2017) (Figures 1, 2). Some key mineral elements have a greater impact on plant disease, for instance, N, which can limit the pathogen growth and may also affect the plant defense elicitation and deployment. Moreover, the availability of different N forms (NH4+ and NO3–) also shows varied effects on plant disease resistance using the assimilatory and metabolic pathways (Bolton and Thomma, 2008; Mur et al., 2017). Similarly, K is particularly a critical element required for plant growth and metabolism and contributes greatly to plants’ survival under various biotic stresses (Pettigrew, 2008) by assisting them in multiple plant defense enzyme functioning, regulating the higher plants’ metabolite patterns, and eventually altering the metabolite concentrations (Mengel, 2001). It can be noted that a particular nutrient may have opposite impacts on different diseases and in different environments, i.e., the same nutrient may increase the incidence of one disease but at the same time may decrease the incidence of others (Agrios, 2005) (Table 1).
This review presents the recent advances bridging the implications of mineral nutrients in sustaining plant health, with a focus on nutrient signaling and disease resistance. In addition, an attempt has been made to unravel the linkage between plant macro/micronutrients involved in the disease onset and progression, thereby ensuring sustainable crop production.
- 1Department of Plant Pathology, College of Agriculture, G. B. Pant University of Agriculture and Technology, Pantnagar, India
- 2Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
- 3ICAR – Central Citrus Research Institute, Nagpur, Nagpur, Maharashtra, India
- 4Division of Bioenergy, Biorefinery and Green Chemistry (BBC-BIC), Department of Energy Technologies and Renewable Resources (TERIN), Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Bari, Italy
- 5Faculty of Chemical Sciences, Benemerita, Autonomous University of Puebla, Puebla, Mexico
