Synergistic interaction of arbuscular mycorrhizal fungi and mycorrhiza helper bacteria improving antioxidant activities in Troyer citrange and Cleopatra mandarin under low moisture stress

Abstract

A glasshouse experiment was conducted to investigate the influence of arbuscular mycorrhizal fungi (AMF) and mycorrhiza helper bacteria (MHB) on growth, osmotic adjustment, and antioxidant activities in Troyer citrange and Cleopatra mandarin in pot culture under well-watered (WW) and water stress (WS) conditions. After 270 days of inoculation with microbial culture(s), half of the seedlings of each genotype were subjected to water stress and the other half were WW for 20 days. During the moisture stress mycorrhizal root colonization showed a durative reduction. No mycorrhizal colonization was observed in the roots of non-AM seedlings. Troyer citrange and Cleopatra mandarin recorded significantly highest root colonization just before imposing differential water treatment (83.34 and 80.00%, respectively) and after 20 days of differential water treatment (66.67 and 62.50%, respectively) under WS and (87.50 and 83.33%, respectively) under WW, when dually inoculated with Glomus intraradices and PSB. Glomus intraradices in association with PSB or Azospirillum accumulated higher concentration of osmolytes like total phenols, proline and total soluble sugars and antioxidant metabolites (carotenoids and ascorbic acid) in leaves of citrus seedlings under WS. Nekkare < Kurukkan < Terpentine < Olour.