Aminoethoxyvinylglycine (AVG) is widely used in commercial apple (Malus ×domestica Borkh.) production to reduce preharvest fruit drop (PFD) and delay ripening for harvest management. Recently, the maximum allowable concentration of AVG was doubled (up to 264 mg⋅L−1). Reports of the relationship between the AVG concentration and fruit growth, size, and quality have been contradictory. We evaluated the relationship between the AVG concentration and PFD, fruit size, fruit quality, and expression of ethylene signaling-related and cell wall modification-related genes. Experiments were conducted in 2019 and 2020 using mature ‘Red Delicious’ in western North Carolina. The AVG treatments [0 and 132 (AVG-1x) and 264 mg⋅L−1 (AVG-2x)] were applied 3 weeks before the expected harvest. The AVG treatments reduced fruit drop and internal ethylene concentration relative to the control in both years. There was no difference in drop between AVG-1x and AVG-2x applications. Only in 2020 did AVG treatments delay fruit softening and starch hydrolysis and reduce soluble solids concentration. There were no effects on red fruit color development. Fruit size was unaffected by AVG in 2019, but it was reduced in 2020 with the AVG-2x application. AVG reduced ethylene synthesis and altered signaling, evidenced by decreased relative expression of genes related to ethylene signaling (ARGOS1, ARGOS2). AVG applications also reduced the expression of EXPA8;1, suggesting that reduced cell wall disassembly was associated with a reduction in fruit softening. These results indicate that preharvest applications of 132 mg⋅L−1 AVG effectively reduced PFD via altering ethylene evolution and signaling. Use of a higher AVG concentration was of limited benefit.
Ficus carica Linn. is an important economic tree species with high developmental prospects and scientific research for edible and medicinal value. The F. carica chloroplast genome has recently been reported; however, the mitochondrial genome is still unexplored. We assembled the complete mitogenome of F. carica using reads from PacBio Biosciences sequencing platforms. The circular mitogenome F. carica has a length of 480,902 base pairs (bp), which contain 46 genes, including 27 protein-coding genes, 16 transfer RNA (tRNA) genes, and three ribosomal RNA (rRNA) genes. The base composition, codon usage, sequence repeats, RNA editing, and selective pressure were examined. We also conducted the phylogenetic analysis based on the mitogenomes of F. carica and 21 other taxa to know the evolutionary and taxonomic status of F. carica. Our analyses provided comprehensive information on the F. carica mitochondrial genome, which would facilitate evolutionary research in other fruit trees in the future.
Multistep chemical thinning programs have been widely recommended in the eastern United States; however, adoption of bloom thinners is limited. With caustic blossom thinners, narrow effective application timings and concerns related to spring frost damage are barriers for commercial use in this region. If effective and safe, use of hormonal blossom thinners for apple would be an attractive alternative. We evaluated the effects and interactions of bloom thinners [6-benzyladenine (BA) and lime sulfur (LS, or calcium polysulfide) + stylet oil (LS+SO)] and a postbloom thinner (NAA) in the context of a multistep, carbaryl-free thinning program across three locations. Experiments were conducted in 2017 and 2018 on mature ‘Gala’ in North Carolina, Massachusetts, and Pennsylvania, USA. In four of six studies, BA at bloom increased the efficacy of postbloom NAA and reduced crop density (P < 0.08). Postbloom NAA generally increased fruit relative growth rate (RGR) and reduced crop density. However, where NAA failed to reduce crop load, there was a negative influence on RGR. BA and LS+SO increased RGR in one of six studies; however, BA was generally ineffective as a blossom thinner, whereas LS+SO was more effective. Nevertheless, BA applied at bloom may have utility as part of a multistep thinning program. As a part of a multistep thinning program, BA applied at bloom may be useful in increasing efficacy of postbloom applications, particularly when use of caustic blossom thinners is not permitted.
Drought is a primary abiotic stressor that markedly impairs pepper growth and quality. This study aimed to investigate the effects of foliar applications of phytohormones, including salicylic acid (SA), jasmonic acid (JA), and root application of arbuscular mycorrhizal fungi (AMF), on severe and moderate drought stress of 38-day-old ‘Anemon F1’ pepper plants. The results showed that drought stress led to a considerable decrease in plant growth parameters, nutrient uptake, leaf water content, and chlorophyll content, and it increased leaf temperature, phenolic and flavonoid contents, and antioxidant enzyme activity. Nevertheless, the combined application of AMF with SA and JA demonstrated substantial synergistic effects, resulting in a notable improvement in the ability to alleviate the detrimental impacts of drought stress. Furthermore, the combined application of AMF and phytohormones exhibited a stronger effect on drought stress compared with the individual application of AMF or phytohormones alone. The application of AMF+SA and AMF+JA not only improves the availability of essential nutrients but also leads to an increase in fresh shoot weight, relative water content, leaf area, and chlorophyll and antioxidant capacity. Consequently, the combined application of SA and JA with mycorrhiza emerged as a promising treatment for enhancing pepper growth under drought-stress conditions. The positive results observed in pepper cultivation through the combined use of phytohormones and mycorrhizae in regions with limited water availability emphasize the importance of investigating the effectiveness of similar approaches in other agricultural crops.