Arbuscular mycorrhizal colonization promotes plant growth and regulates biochemical and molecular defense responses against Pythium myriotylum and Meloidogyne incognita in ginger (Zingiber officinale Rosc.)

Abstract

This study investigated the effects of arbuscular mycorrhizal fungi (AMF) inoculation on growth, nutrient uptake, and defense mechanisms against Pythium myriotylum and Meloidogyne incognita in ginger (Zingiber officinale Rosc.). Structural colonization of AMF was confirmed in inoculated ginger roots, with colonization rates of 90 % and 80 % at two and six months, respectively. AMF significantly enhanced plant height and number of tillers compared to non-inoculated controls. Nutrient uptake was notably higher in AMF-inoculated plants, with increased levels of nitrogen (27.81 g wt plant⁻¹), phosphorus (3.89 g wt plant⁻¹), potassium, calcium, magnesium, and micronutrients. AMF inoculated plants demonstrated 50 % reduction in disease incidence when challenged with P. myriotylum. Similarly, AMF preinoculated ginger plants showed no Meloidogyne incognita (J2s) penetration in the roots, unlike plants treated only with M. incognita (J2s). Additionally, protray experiment was conducted to study the possible correlation between the disease resistance traits of AMF using biochemical and molecular methods. In this study, the enhanced activity of antioxidant enzymes, such as peroxidase, catalase, and β-1,3-glucanase, was observed in AMF-primed plants under pathogen inoculation, particularly with combined infections of P. myriotylum and M. incognita, indicating improved systemic resistance. At the molecular level, AMF priming altered the expression of key defense-related genes. In AMF-treated plants, the NPR1 gene, which regulates systemic acquired resistance, was notably upregulated in roots with P. myriotylum, while TGA and AP2, involved in salicylic acid signaling and stress response, exhibited strong expression in the presence of AMF and M. incognita. In leaves, LOX2, a key enzyme in jasmonic acid biosynthesis, showed the highest expression with M. incognita, whereas AOC, essential for jasmonate signaling, steadily increased in AMF-primed plants with P. myriotylum. These findings indicate that AMF colonization supports nutrient uptake, plant growth, and systemic defense, thereby enhancing resistance to pathogen infections in ginger.