Physiological and biochemical responses of Kinnow mandarin grafted on diploid and tetraploid Volkamer lemon rootstocks under different water-deficit regimes.

Muhammad Fasih Khalid,Shaghef Ejaz,Raphael Morillon,Sajjad Hussain,Alexe Nicolae Ormenisan,Muhammad Akbar Anjum,Hawa Z E Jaafar,Sara T Alrashood,Mubshar Hussain,Shakeel Ahmad

doi:10.1371/journal.pone.0247558

Abstract

Water shortage is among the major abiotic stresses that restrict growth and productivity of citrus. The existing literature indicates that tetraploid rootstocks had better water-deficit tolerance than corresponding diploids. However, the associated tolerance mechanisms such as antioxidant defence and nutrient uptake are less explored. Therefore, we evaluated physiological and biochemical responses (antioxidant defence, osmotic adjustments and nutrient uptake) of diploid (2x) and tetraploid (4x) volkamer lemon (VM) rootstocks grafted with kinnow mandarin (KM) under two water-deficit regimes. The KM/4xVM (VM4) and KM/2xVM (VM2) observed decrease in photosynthetic variables, i.e., photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E), leaf greenness (SPAD), dark adopted chlorophyll fluorescence (Fv/Fm), dark adopted chlorophyll fluorescence (Fv´/Fm´), relative water contents (RWC) and leaf surface area (LSA), and increase in non-photochemical quenching (NPQ) under both water-deficit regimes. Moreover, oxidative stress indicators, i.e., malondialdehyde (MDA) and hydrogen peroxide, and activities of antioxidant enzymes, i.e., superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APx), glutathione reductase (GR) were increased under both water-deficit regimes. Nonetheless, increase was noted in osmoprotectants such as proline (PRO) and glycine betaine (GB) and other biochemical compounds, including antioxidant capacity (AC), total phenolic content (TPC) and total soluble protein (TSP) in VM2 and VM4 under both water-deficit regimes. Dry biomass (DB) of both rootstocks was decreased under each water-deficit condition. Interestingly, VM4 showed higher and significant increase in antioxidant enzymes, osmoprotectants and other biochemical compounds, while VM2 exhibited higher values for oxidative stress indicators. Overall, results indicated that VM4 better tolerated water-deficit stress by maintaining photosynthetic variables associated with strong antioxidant defence machinery as compared to VM2. However, nutrient uptake was not differed among tested water-deficit conditions and rootstocks. The results conclude that VM4 can better tolerate water-deficit than VM2. Therefore, VM4 can be used as rootstock in areas of high-water deficiency for better citrus productivity.

Highlights

Citrus plays a vital role in economy of many developed and developing countries
Kinnow grafted on Volkamer lemon tetraploid showed tolerance against slow and fast drought
We investigated the impact of quick and slow water-deficit stress on the physiological and biochemical responses of 2x and 4x Volkamer lemon (Citrus volkameriana Tan. and Pasq) rootstocks grafted with Kinnow mandarin (Citrus nobilis x Citrus deliciosa)

Summary

Introduction

Citrus plays a vital role in economy of many developed and developing countries. citrus greening disease (Huanglongbing) is decreasing citrus productivity, which affects fruit and juice prices [1]. Citrus rootstocks can behave differently depending on the defence mechanism against water-deficit condition [8]. Tetraploid rootstocks have shorter and thicker roots, which results in slower growth [15,16] All these anatomical and physiological changes do not affect fruit quality of scions grafted on 4x rootstock [17]. Rootstock-scion combination affects growth, yield and induces tolerance against different biotic and abiotic stresses [18]. Climate change is resulting in two types of water-deficit stress, which negatively affect citrus production. These include short and severe stress, and slow and prolonged stress. Few studies have inferred the response of citrus to both types of stresses; none of these analysed the defence machinery of kinnow mandarin grafted on 2x and 4x rootstocks

Methods

Results

Conclusion