Arbuscular Mycorrhizal Fungi and Endophytic Fungi Activate Leaf Antioxidant Defense System of Lane Late Navel Orange.

Qiu-Shuang Li,Ya-Chao Xie,Abeer Hashem,Qiang-Sheng Wu,Mohammed Mahabubur Rahman,Elsayed Fathi Abd_Allah

doi:10.3390/jof8030282

Abstract

Arbuscular mycorrhizal (AM) fungi and endophytic fungi collectively symbiose well with plants and, thus, stimulate plant growth; however, it is not clear whether field inoculation of the fungi enhances the resistance potential of plants, particularly in citrus. In the present study, we inoculated AM fungi (Acaulospora scrobiculata, Diversispora spurca, and D. versiformis) and endophytic fungi (Piriformospora indica) on an eight-year-old lane late navel orange (Citrus sinensis (L.) Osb) trees grafted on Poncirus trifoliata in a field, and we analyzed the response of the leaf antioxidant defense system. Approximately 2 years after inoculation, the root fungal colonization rate and soil hyphal length significantly increased. Fungal inoculation significantly increased the activity of leaf antioxidant enzymes, such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, and the content of non-enzymatic antioxidants, such as reduced ascorbic acid and reduced glutathione. As a result, fungi-inoculated plants maintained lower concentrations of hydrogen peroxide and superoxide anion radicals and lower levels of membrane lipid peroxidation (according to malondialdehyde level) in leaves than uninoculated plants. Among them, inoculation of D. spurca and A. scrobiculata showed relatively higher effects in enhancing the antioxidant defense system than the other fungi. Furthermore, inoculation of D. spurca induced expressions of CsFe-SOD, CsMn-SOD, CsPOD, CsCAT1, and CsPRR7; inoculation of A. scrobiculata and D. versiformis induced expressions of CsCAT1; CsCAT1 and CsPOD were also induced by inoculation of P. indica. All four inoculations almost upregulated expressions of CsFAD6. AM fungi had superior effects than endophytic fungi (e.g., P. indica). According to our findings, inoculation with beneficial fungi, specifically mycorrhizal fungus D. spurca, activated the antioxidant defense system of field citrus trees, thus, having potentially superior resistance in inoculated plants.

Highlights

Citrus is an important horticultural crop with a long life cycle, as is one of the most widely planted fruit trees in the world [1]
Cara cara trees grafted on trifoliate orange, inoculation with Glomus mosseae dramatically increased leaf superoxide dismutase (SOD) and CAT activity during soil water deficit and rewatering [18]. These results show the important roles of Arbuscular mycorrhizal (AM) fungi in enhancing the stress tolerance of plants by increasing the antioxidant enzyme defense system
The purpose of this study was to assess the effect of field inoculation with AM fungi and endophytic fungi on root fungal colonization, membrane lipid peroxidation, antioxidant enzyme activity, non-enzymatic antioxidant concentration, and antioxidant enzyme gene expression of the lane late navel orange trees

Summary

Introduction

Citrus is an important horticultural crop with a long life cycle, as is one of the most widely planted fruit trees in the world [1]. The lane late navel orange (Citrus sinensis (L.) Osb) is an important cultivar in the middle region of the Three Gorges Reservoir area in China [4]. The cultivar originates from the limb sport of the Washington navel orange in Australia and it was first documented in 1950 [5]. It has good productivity with highquality fruit and vigorous growth [6]. Fresh fruits of the lane late navel orange are typically harvested from April to June in China, while other fruits are in low supply [7]. Lane late navel orange trees in the field face various biotic and abiotic stresses [8]; it is necessary to enhance the stress resistance of this variety

Objectives

Methods

Results

Discussion

Conclusion