Seed Priming for Disease Resistance in Plants

Abstract

Crop production is limited by various kinds of diseases throughout the world. The increasing climatic and environmental changes further add to the intensity and severity of diseases in plants. This has created the need for better understanding of various diseases, their mode of spread, level and mechanism of damage, and causes and risk factors in plants. At the same time, there is a need of explanation of plant responses to diseases and their levels and mechanism of tolerance to diseases. The common disease-causing agents are fungi, bacteria, viruses, and nematodes. And the major crop diseases are powdery mildew, downy mildew, Fusarium wilt, and Fusarium root rot that severely damaged and are very common among main crop species of important families especially Poaceae, Cucurbitaceae, Solanaceae, and Fabaceae. However, understanding plant’s natural adaptation and tolerance to diseases by improving the constitutive and inducible factors has progressed prominently. With the passage of time, the demands of better quality food with enhanced supplies are increasing. There is a need to introduce potential synthetic methods that trigger priming of plant tolerance to diseases. Studies have shown that fungal diseases are the most widespread among them and cause great losses in most of the crop species. Keeping in view the current situation, a lot of practices have been adopted for inducing disease tolerance in plants. However, the traditional crop production practices are not up to mark. Plant biologists are in search of innovative techniques for suitable crop improvements or ways to alleviate disease stresses for achieving the crop production goals. Currently, seed priming has gained a substantial attention due to its crucial role in plant growth and development. Furthermore, the effects of seed priming in disease tolerance in plants are evident since many years. The review of studies has described that different seed priming methods can be used for enhancing disease tolerance in plants. Biopriming and hormonal priming are the most appropriate and effective one. Study of mechanisms of disease tolerance shows that mostly the formation of signaling molecules e.g. salicylic acid (SA) and jasmonic acid (JA) are involved, however, β-aminobutyric acid and azelaic acid have also been reported to be involved in disease tolerance. Their involvement in defense-related gene expression and in regulation of disease-induced reactive oxygen species (ROS) is clearly noted. However, salicylic acid has diverse roles in physiological changes of lignification and suberization and biochemical functions. Generally, the enzymes involved in seed priming-induced disease tolerance are phenol oxidase, tyrosine ammonia lyase and phenylalanine ammonia lyase, and antioxidant enzymes, superoxide dismutase, catalase, and peroxidase. Moreover, glucanase, peroxidase, and chitinase are also involved in disease tolerance in plants. However, their nature and amounts depend upon the disease type, plant species, and seed priming method. The main proteins participating in disease tolerance in plants are NPR1, NPR3, and NPR4 that act as salicylic acid receptors; however NPR1 is a bona fide salicylic acid-binding agent. The pathways in the inducing disease tolerance in plants are mainly the salicylic acid-dependent pathways. However, salicylic acid-independent pathway or combinations of both have also been found. In this chapter, we review current progress in the seed priming research in broader context of disease tolerance in plants and discuss its protective mechanisms of plants toward disease tolerance.