Spermidine Pretreatments Mitigate the Effects of Saline Stress by Improving Growth and Saline Excretion in Frankenia pulverulenta

Climatic change, ecosystem imbalance, and soil salinization and desertification are serious obstacles to the restoration of degraded landscapes. Halophyte cultivation could constitute a way of mitigating these problems. Frankenia pulverulenta is used in the remediation and revegetation of areas affected by salinity and as an ornamental plant on saline soils since it can tolerate salt concentrations up to 200 mM NaCl. To increase saline tolerance, different plant growth regulators (auxins, cytokinins, gibberellins, spermidine, and salicylic acid) were tested in hydroponic conditions before the addition of NaCl (300 mM). At 52 days, growth, proline, saline excretion, free polyamines, and ethylene were determined under both saline and non-saline conditions. All growth regulators improved growth in the salt-free pretreatment; however, under conditions of salinity, pretreatment with spermidine (0.5 mM) and then salicylic acid (0.5 mM) were efficient at reversing the inhibitory effect of salt and improved saline excretion in F. pulverulenta. A strong positive correlation of polyamines and proline, and a negative correlation with ethylene, indicate that pretreatments that increase endogenous polyamine content and osmolytes are the most effective in improving salt tolerance of F. pulverulenta and could be used in the technical guidance of the cultivation of this halophyte.

Heterophylly Quantitative Trait Loci Respond to Salt Stress in the Desert Tree Populus euphratica

Heterophylly, or leaf morphological changes along plant shoot axes, is an important indicator of plant eco-adaptation to heterogeneous microenvironments. Despite extensive studies on the genetic control of leaf shape, the genetic architecture of heterophylly remains elusive. To identify genes related to heterophylly and their associations with plant saline tolerance, we conducted a leaf shape mapping experiment using leaves from a natural population of Populus euphratica. We included 106 genotypes grown under salt stress and salt-free (control) conditions using clonal seedling replicates. We developed a shape tracking method to monitor and analyze the leaf shape using principal component (PC) analysis. PC1 explained 42.18% of the shape variation, indicating that shape variation is mainly determined by the leaf length. Using leaf length along shoot axes as a dynamic trait, we implemented a functional mapping-assisted genome-wide association study (GWAS) for heterophylly. We identified 171 and 134 significant quantitative trait loci (QTLs) in control and stressed plants, respectively, which were annotated as candidate genes for stress resistance, auxin, shape, and disease resistance. Functions of the stress resistance genes ABSCISIC ACIS-INSENSITIVE 5-like (ABI5), WRKY72, and MAPK3 were found to be related to many tolerance responses. The detection of AUXIN RESPONSE FACTOR17-LIKE (ARF17) suggests a balance between auxin-regulated leaf growth and stress resistance within the genome, which led to the development of heterophylly via evolution. Differentially expressed genes between control and stressed plants included several factors with similar functions affecting stress-mediated heterophylly, such as the stress-related genes ABC transporter C family member 2 (ABCC2) and ABC transporter F family member (ABCF), and the stomata-regulating and reactive oxygen species (ROS) signaling gene RESPIRATORY BURST OXIDASE HOMOLOG (RBOH). A comparison of the genetic architecture of control and salt-stressed plants revealed a potential link between heterophylly and saline tolerance in P. euphratica, which will provide new avenues for research on saline resistance-related genetic mechanisms.

Screening of Mango Rootstock For Saline Tolerance

An experiment was conducted at Fruit Tree Improvement Project, Fruit Tree Improvement Programme, Bangladesh Agricultural University-Germplasm Center (FTIP, BAU-GPC), Bangladesh Agricultural University (BAU), Mymensingh during the period of April 2020 to June 2020 to study the performance of selected mango rootstocks for the saline area. The two-factor experiment consisted of four mango rootstock varieties such as V1 = BAU Aam-9, V2 = BAU Aam-6, V3 = BAU Aam-4 and V4 = Amropali and six salinity treatments namely control S1 = 0 dSm-1, S2 = 4 dSm-1, S3 = 8 dSm-1, S4 = 10 dSm-1, S5 = 12 dSm-1 and S6 = 14 dSm-1. The experiment was conducted following randomized complete block design with three replications. Results revealed that rootstock line and salinity levels had significant influences on various rootstock characters viz. length of rootstocks, number of leaves and percent rootstocks success and survivability. In case of varietal effect, the highest number of leaves (32.44) found in BAU Aam-6 and the lowest number of leaves was recorded in Amropali (22.55) at 90 days after transplanting. The longest rootstock length observed in 90 DAT which (54.83 cm) found in BAU Aam-9and shortest rootstock recorded in Amropali (47.94 cm). The highest survivability (51.44%) was recorded in BAU Aam-9 and the lowest survivability recorded in Amropali (33.88%). In case of salinity treatments, the highest survivability (95.83%) was recorded in control and the lowest survivability (0.00%) recorded in 14 dsm-1 at 90 DAT. Interaction of rootstock varieties and different salinity treatments showed significant variation on the length leave and survivability of rootstocks at 90 DAT. The maximum number of rootstock leaves recorded in V2S2 (46.33) and lowest number of leave recorded in V4S6 (7.66). The highest rootstock length was found in V1S3 (78.00 cm) and lowest in V1S2 (21.66 cm). The highest Survivability (100 %) observed in V1S1, V1S2, V2S1, V2S2 and V4S1. From the above mentioned it can be said BAU Aam - 9 and BAU Aam – 6 rootstock varieties performed best from 0-8 dSm-1 salinity. The overall salinity tolerance was graded as follows: BAU Aam - 9>BAU Aam – 6> BAU Aam-4>Amropali rootstock line. SAARC J. Agric., 19(1): 93-102 (2021)

A novel WD40-repeat protein involved in formation of epidermal bladder cells in the halophyte quinoa

Halophytes are plants that grow in high-salt environments and form characteristic epidermal bladder cells (EBCs) that are important for saline tolerance. To date, however, little has been revealed about the formation of these structures. To determine the genetic basis for their formation, we applied ethylmethanesulfonate mutagenesis and obtained two mutants with reduced levels of EBCs (rebc) and abnormal chloroplasts. In silico subtraction experiments revealed that the rebc phenotype was caused by mutation of REBC, which encodes a WD40 protein that localizes to the nucleus and chloroplasts. Phylogenetic and transformant analyses revealed that the REBC protein differs from TTG1, a WD40 protein involved in trichome formation. Furthermore, rebc mutants displayed damage to their shoot apices under abiotic stress, suggesting that EBCs may protect the shoot apex from such stress. These findings will help clarify the mechanisms underlying EBC formation and function.

Evaluation of black gram genotypes for saline tolerance at seedling stage

Black gram [Vigna mungo (L.) Hepper] is the third most important pulse crop in India after chickpea and pigeon pea. Soil salinity is one of the major factor responsible for loss in agricultural production. Forty eight black gram genotypes were evaluated for salt tolerance with six different salinity levels viz., EC0, EC4, EC7, EC10, EC13, EC16 at early seedling stage. All the seedling parameters and salt tolerant index were investigated from four days old seedlings. From the results, it was found that there was a gradual decrease with increasing levels of salinity in all the genotypes studied. Seed germination and dry matter production showed more variations than other parameters studied for all the genotypes at different salinity levels. Based on the results, it may be concluded that the genotypes VNBG 017, AUB 3 AND AUB 20 were saline tolerant and VNBG 022, AUB 31 AND AUB 12 were susceptible to salinity.