Pruning management of mini-stumps for mass propagation of blueberry

The objective of this work was to evaluate the influence of the pruning management of mini-stumps of the Climax blueberry cultivar, when weekly fertigated, on the productivity of the clonal mini-garden and on the rooting and root vigor of the mini-cuttings. The high survival of the mini-stumps (100%) and production of the mini-cuttings (182.9 mini-cuttings per square meter per month) evidence the high adaptability of the material to successive samplings and to the nutritional conditions provided to the clonal mini-garden, resulting in a high multiplication rate. The rooting percentages obtained at the different samplings remain stable, with a high average of rooted mini-cuttings, reaching 81.7%.

The Submergence of the Graft Union Causes the Death of Grafted Mango Trees (Mangifera indica L.) under Flooding

The risk of flooding has increased as a result of climate change inspired by global warming. In this study, the difference in tolerance to flooding between grafted trees and seedlings was investigated in mango trees (Mangifera indica L.). Two levels of flooding treatment were established, in addition to a non-treated control. One was “30-flood,” in which trees were submerged up to 30 cm from the soil surface, and another was “10-flood,” in which trees were submerged up to 10 cm from the soil surface. Grafted trees treated with the 30-flood were submerged up to 5 cm above the graft union. Only the grafted trees in the 30-flood treatment began to decrease Fv/Fm and the root sugar content during treatment, then died after the completion of treatment. In grafted trees and seedlings alike, both flooding treatments also reduced root vigor, as determined by triphenyl tetrazolium chloride reduction tests and root starch content. However, root vigor and root starch content in grafted trees treated with the 10-flood as well as seedlings treated with both 10- and 30-flood recovered within two months after the completion of treatment, so that no significant differences were detected between the control. These results suggest that the submergence of the graft union into water causes the decline in photosynthesis of the scion first and the death of the grafted trees as a result.

Root system traits impact early fire blight susceptibility in apple (Malus × domestica)

Background Although it is known that resistant rootstocks facilitate management of fire blight disease, incited by Erwinia amylovora, the role of rootstock root traits in providing systemic defense against E. amylovora is unclear. In this study, the hypothesis that rootstocks of higher root vigor provide higher tolerance to fire blight infection in apples is tested. Several apple scion genotypes grafted onto a single rootstock genotype and non-grafted ‘M.7’ rootstocks of varying root vigor are used to assess phenotypic and molecular relationships between root traits of rootstocks and fire blight susceptibility of apple scion cultivars. Results It is observed that different root traits display significant (p < 0.05) negative correlations with fire blight susceptibility. In fact, root surface area partially dictates differential levels of fire blight susceptibility of ‘M.7’ rootstocks. Furthermore, contrasting changes in gene expression patterns of diverse molecular pathways accompany observed differences in levels of root-driven fire blight susceptibility. It is noted that a singular co-expression gene network consisting of genes from defense, carbohydrate metabolism, protein kinase activity, oxidation-reduction, and stress response pathways modulates root-dependent fire blight susceptibility in apple. In particular, WRKY75 and UDP-glycotransferase are singled-out as hub genes deserving of further detailed analysis. Conclusions It is proposed that low root mass may incite resource-limiting conditions to activate carbohydrate metabolic pathways, which reciprocally interact with plant immune system genes to elicit differential levels of fire blight susceptibility.

Root system traits impact early fire blight susceptibility in apple (Malus × domestica)

Background Although it is known that resistant rootstocks facilitate management of fire blight disease, incited by Erwinia amylovora, the role of rootstock root traits in providing systemic defense against E. amylovora is unclear. In this study, the hypothesis that rootstocks of higher root vigor provide higher tolerance to fire blight infection in apples is tested. Several apple scion genotypes grafted onto a single rootstock genotype and non-grafted ‘M.7’ rootstocks of varying root vigor are used to assess phenotypic and molecular relationships between root traits of rootstocks and fire blight susceptibility of apple scion cultivars.Results It is observed that different root traits display significant (p < 0.05) negative correlations with fire blight susceptibility. In fact, root surface area partially dictates differential levels of fire blight susceptibility of ‘M.7’ rootstocks. Furthermore, contrasting changes in gene expression patterns of diverse molecular pathways accompany observed differences in levels of root-driven fire blight susceptibility. It is noted that a singular co-expression gene network consisting of genes from defense, carbohydrate metabolism, protein kinase activity, oxidation-reduction, and stress response pathways modulates root-dependent fire blight susceptibility in apple. In particular, WRKY75 and UDP-glycotransferase are singled-out as hub genes deserving of further detailed analysis.Conclusions It is proposed that low root mass may incite resource-limiting conditions to activate carbohydrate metabolic pathways, which reciprocally interact with plant immune system genes to elicit differential levels of fire blight susceptibility.

QUALITY OF CLONAL SEEDLINGS OF Tectona grandis Linn F. ROOTED IN DIFFERENT CONCENTRATIONS OF INDOLEBUTYRIC ACID

The general objective of this paper is to evaluate the effect of different IBA concentrations on greenhouse, shade and full sun survival, root vigor and seedling quality in Tectona grandis. To do so, mini-cuttings were prepared containing two pairs of leaves reduced to 25% of their original size (7.0 ± 1.0 cm) in length and bevel cut at the base. They were submitted to five treatments with different concentrations of indolebutyric acid (0, 500, 1000, 1500 e 2000 mg L-1), remaining in greenhouse, house of shade and in full sun for 30, 20 and 15 days, respectively. Survival was evaluated in greenhouse, house of shade and full sun; radicial vigor, height, diameter of the neck, ratio between shoot height and diameter, root dry mass, aerial, and total mass. The experimental design was in randomized blocks, with five replications of 15 plants and five treatments. Data were submitted to the normality test, Bartlett test and polynomial regression of the second degree. As a result, it was verified that the use of IBA did not influence root vigor and survival, however, it provided seedlings with a higher dry mass, being the best the 2000 mg L-1 treatment.

The Recretohalophyte Tamarix TrSOS1 Gene Confers Enhanced Salt Tolerance to Transgenic Hairy Root Composite Cotton Seedlings Exhibiting Virus-Induced Gene Silencing of GhSOS1

The salt overly sensitive 1 (SOS1) gene encodes the plasma membrane Na+/H+ antiporter, SOS1, that is mainly responsible for extruding Na+ from the cytoplasm and reducing the Na+ content in plants under salt stress and is considered a vital determinant in conferring salt tolerance to the plant. However, studies on the salt tolerance function of the TrSOS1 gene of recretohalophytes, such as Tamarix, are limited. In this work, the effects of salt stress on cotton seedlings transformed with tobacco-rattle-virus-based virus-induced gene silencing (VIGS) of the endogenous GhSOS1 gene, or Agrobacterium rhizogenes strain K599-mediated TrSOS1-transgenic hairy root composite cotton plants exhibiting VIGS of GhSOS1 were first investigated. Then, with Arabidopsis thaliana AtSOS1 as a reference, differences in the complementation effect of TrSOS1 or GhSOS1 in a yeast mutant were compared under salt treatment. Results showed that compared to empty-vector-transformed plants, GhSOS1-VIGS-transformed cotton plants were more sensitive to salt stress and had reduced growth, insufficient root vigor, and increased Na+ content and Na+/K+ ratio in roots, stems, and leaves. Overexpression of TrSOS1 enhanced the salt tolerance of hairy root composite cotton seedlings exhibiting GhSOS1-VIGS by maintaining higher root vigor and leaf relative water content (RWC), and lower Na+ content and Na+/K+ ratio in roots, stems, and leaves. Transformations of TrSOS1, GhSOS1, or AtSOS1 into yeast NHA1 (Na+/H+ antiporter 1) mutant reduced cellular Na+ content and Na+/K+ ratio, increased K+ level under salt stress, and had good growth complementation in saline conditions. In particular, the ability of TrSOS1 or GhSOS1 to complement the yeast mutant was better than that of AtSOS1. This may indicate that TrSOS1 is an effective substitute and confers enhanced salt tolerance to transgenic hairy root composite cotton seedlings, and even the SOS1 gene from salt-tolerant Tamarix or cotton may have higher efficiency than salt-sensitive Arabidopsis in regulating Na+ efflux, maintaining Na+ and K+ homeostasis, and therefore contributing to stronger salt tolerance.

A Comparative Study on Root Traits of Spring and Winter Canola (Brassica napus L.) under Controlled and Water Stressed Conditions

Root system in canola (Brassica napus L.) varies largely in different growth habit types. A study was conducted with five winter and five spring types of canola germplasm. The objective was to identify the gradual change of root traits at different growth habits stages under controlled and water stressed conditions. Two experiments, controlled and water stressed, were conducted in a greenhouse. Data on different root traits were collected at 30, 40, 50 and 60 days after planting. In controlled experiment, no significant difference was observed for root traits between winter and spring types at 30 days after planting. However, significant variations were appeared for taproot length (F = 10.17***) and root dry weight (F = 16.96***) between winter and spring types at 40 days after planting. All other root parameters such as basal taproot diameter (F = 22.14***), bottom taproot diameter (F = 4.59*), primary root branches (F = 78.70***) and root vigor (F = 47.18***) were significantly higher in the winter types compared to those of the spring types at 60 days after planting. Growth pattern curves indicated that all the root traits of spring types increased in a steady fashion, where the root traits of winter types increased rapidly after 40 days of planting. In water stressed experiment, the water stress was applied from 20 to 60 days after planting, and data was taken at 60 days after planting. All the root parameters except taproot length were significantly (P < 0.001) lower in the stressed spring and winter plants compared to the control plants. The root growth reduction in stressed winter type germplasms was higher. Basal taproot diameter, bottom taproot diameter, primary root branches, root vigor, and root dry weight were decreased by 43%, 63%, 19%, 31% and 53%, respectively in stressed winter type plants. In contrast, the root growth reduction of the spring type germplasms were relatively lower. This study indicated that winter type canola generates vigorous root system in comparison to spring types under normal growing conditions, but ceases its root growth rate more than the spring types under water stressed conditions.

EX VITRO SYSTEM FOR Acer palmatum PLANTS PROPAGATION BY MINI-CUTTINGS TECHNIQUE

ABSTRACT This study presents an efficient system with high productivity and quality for Acer palmatum propagation. We evaluated the efficiency of mini-cuttings technique, management of mini-stumps, production of shoots, rooting and root vigor of mini-cuttings on two seasons. The mini-stumps were planted in pots of two liters, put up in two environments (full sunlight area and shade house) and submitted to weekly fertigation. Over six collections, we evaluated the survival and productivity of clonal mini-garden (Experiment I). From these, we performed two experiments with mini-cuttings: Experiment II - mini-cuttings originated from two environments, with 8±1 cm, put to root in two seasons (Spring and Summer); Experiment III - mini-cuttings originated from full sunlight area, with 4±1, 6±1, 8±1, 10±1 cm, put to root in Summer. The mini-cuttings planting was made in plastic tubes of 55 cm³, filled with fine vermiculite and carbonized rice hulls (1:1 v/v), in a greenhouse with intermittent irrigation system. The high rooting (95.0%), mini-stumps survival (100%) and mini-cuttings production (217.5 mini-cuttings m-2 month-1) in clonal mini-garden conducted in full sunlight area shown the technique viability for the species. Mini-cuttings of 8±1 cm favored rooting (96.3%). The mini-cuttings technique is viable for Acer palmatum propagation.