Enhanced Photosynthetic Capacity, Osmotic Adjustment and Antioxidant Defenses Contribute to Improve Tolerance to Moderate Water Deficit and Recovery of Triploid Citrus Genotypes

Abstract

Currently, drought stress is a major issue for crop productivity, and future climate models predict a rise in frequency and severity of drought episodes. Polyploidy has been related to improved tolerance of plants to environmental stresses. In Citrus breeding programs, the use of triploidy is an effective way to produce seedless fruits, one of the greatest consumer expectations. The current study used physiological and biochemical parameters to assess the differential responses to moderate water deficit of 3x genotypes compared to 2x genotypes belonging to the same hybridization. Both parents, the mandarin Fortune and Ellendale tangor, were also included in the experimental design, while the 2x common clementine tree was used as reference. Water deficit affects leaf water status, as well as physiological and detoxification processes. Triploid genotypes showed a better ability to maintain water status through increased proline content and photosynthetic capacity. Moreover, less oxidative damage was associated with stronger antioxidant defenses in triploid genotypes. We also found that triploidy improved the recovery capacity after a water deficit episode.

Better tolerance to Huanglongbing is conferred by tetraploid Swingle citrumelo rootstock and is influenced by the ploidy of the scion

“…If in CLas- root samples polyphenol contents were quite low, 4x presented higher contents, than those in 2x, whatever the scion. Those results would be in agreement with preadaptation to stress by limiting oxidative stress as previously proposed for polyploid genotypes ( Allario et al., 2013 ; Khalid et al., 2021 ; Lourkisti et al., 2022 ). Interestingly, HLB infections led to a 10-fold increase of the polyphenol contents in 4x rootstocks, compared to 2x.…”

Impact of polyploidy on plant tolerance to abiotic and biotic stresses

“…Several authors reported on higher relative water content in polyploids in comparison with diploids, either when well-watered ( Tal and Gardi, 1976 ) or under water deficit conditions ( Xiong et al, 2006 ; Allario et al, 2011 ; Del Pozo and Ramirez-Parra, 2014 ; Zhang et al, 2015 ). In agreement with this notion, Khalid et al (2021) and Lourkisti et al (2022) , observed an enhanced accumulation of osmolytes under water deficit in different polyploid citrus species. Another, older study on naturally occurring Betula papyrifera polyploids showed that they were more capable of maintaining turgor at low tissue water potentials than the corresponding diploids, although the authors did not provide direct evidence on the existence of osmotic adjustment ( Li et al, 1996 ).…”

Insight into Physiological and Biochemical Determinants of Salt Stress Tolerance in Tetraploid Citrus

“…First, superoxide dismutase (SOD), converts the O 2 ●− radical to hydrogen peroxide (H 2 O 2 ) [ 51 ]. In another study, increased specific SOD activity found in 3x genotypes and Ellendale tangor was related to low MDA levels and, thus, the limitation of the lipid peroxidation process [ 52 ]. The H 2 O 2 formed by SOD can then be converted to oxygen and water by catalase.…”

“…In the first reaction catalyzed by ascorbate peroxidase (APX), ascorbate acts as a reducing agent and oxidizes to monodehydroascorbate [ 54 , 55 ]. In their study, Lourkisti et al (2022) [ 52 ] reported that increased APX and CAT activities in most of the 3x citrus genotypes appeared to be sufficient to prevent oxidative damage by reducing H 2 O 2 accumulation.…”