The Responses of Physiological Characteristics and Flowering Related Gene to the Different Water Stress Levels of Red-Flesh Pummelo Cultivars (Citrus grandis (L.) Osbeck) Own-Rooted by Air Layering Propagation under Two Growing Conditions

One of the major problems in the fruit production of citrus, including pummelo (Citrus grandis) is controlling flowering induction. Water stress is known to be related to flowering induction via physiological responses related to the flowering gene. However, reports on the mechanisms underlying floral induction by water stress in pummelo are limited. Thus, this study aimed to determine the physiological characteristics and the expression of genes related to flowering induction, CiFT (Citrus Flowering locus T), in pummelo at different levels of water stress. Experiments were conducted under two growing conditions: field and container conditions, each using a 2 × 5 factorial experiment in a randomized complete block. Factor A consisted of two red-flesh pummelo cultivars while factor B consisted of five levels of water stress based on the leaf rolling index. Among the seven characteristics studied, only the data of total nitrogen, CiFT, and flower number were combined for analysis due to their results in a homogeneity test. Although a consistent tendency was not observed for the interaction among environments, genotypes, and water stress levels of all characteristics, ‘KKU-105’ grew more flowers under higher water stress conditions (225 flowers). This result may imply that decreases in total nitrogen (1.48%), stomatal conductance (50.53 m−2s−1), chlorophyll fluorescence (0.30 Fv/Fm), and upregulation of CiFT mRNA level (13.95) may induce flowering in the pummelo cultivar ‘KKU-105’.

Pembuahan Jeruk Siam (Citrus microcarpa L.) di Luar Musim dengan Perlakuan Induksi Pembungaan dan Zat Pemecah Dormansi

Fertilization outside the season of Siam Orange (Citrus microcarpa L.) with Induction of Flowering and Dormancy Breaking Substances. The Siam orange (Citrus microcarpa L.) produces seasonal fruit with the on-season harvest from July to August while the off-season harvest, i.e. from February to September there is hardly any fruit, or very limited supply. The purpose of this study was to examine the response of flowering induction and dormancy-breaking substances to produce off-season fruits of Siam orange. This research began in April to December 2016. The experiment was arranged factorially with two factors using a randomized block design (RBD), with nine combination treatments and six replications. Flowering induction factors consist of three levels, namely Ik = Control, IP = Paclobutrazol at a dose of 7.5 g/l, and Im = cutting the tip of dormant twigs. Dormancy-breaking substances factor consists of three levels, namely Dk = Control, Db = BAP 200 ppm, and Dn = KNO3 300 ppm. The results of the experiment showed that the highest fruit weight per tree at off-season production was obtained by induction with paklobutrazol (28.86 kg) and the lowest was in control (12.75 kg). Flowering induction treatments was not significantly different effect on fruit quality of Siam orange, represented by weight per fruits, fruit diemater, total soluble solid and vitamine C content was not siginificant different among levels of treatment. Dormancy-breaking substances treatment also not significantly effect on fruit quality of Siam orange. Based on this research it is recommended to induce flower for off-season produce of Siam orange by pruning the tips of dormant twigs or by using paklobutrzol.

Analysis of miRNA-mediated regulation of flowering induction in Lilium × formolongi

Background MicroRNAs play pivotal roles in plant vegetative phase change and flowering induction via integrating into multiple flowering pathways. Lilium × formolongi is an important ornamental lily cultivar that can flower within one year after sowing. However, it remains unresolved how miRNA-mediated regulation networks contribute to the L. × formolongi characteristics of a short vegetative growth period and rapid flowering. Results In this study, the small RNA libraries and one degradome library were constructed for L. × formolongi during vegetative growth and flowering initiation, and 366 conserved miRNAs and 32 novel miRNAs were identified. Additionally, 84 miRNAs were significantly differentially expressed during development. A total of 396 targets of 185 miRNAs were identified and validated through degradome sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that functions of the targets were top enriched in the cold and cadmium ion responses, pentose phosphate pathway and carbon fixation in photosynthetic organisms. Furthermore, among 23 differentially expressed miRNA-target pairs, the miR156s-LfSPL2, miR172a-LfAP2 and miR164a-LfNAC pairs as well as miR159a-LfSPL2 were found to be relevant to flowering based on the correlation analysis of expression profiles in the miRNA libraries, degradome and transcriptome. A coexpression regulatory network focused on differentially expressed pairs was also constructed by WGCNA, and 14 miRNAs were considered putative key miRNAs during vegetative development and flowering induction. miR156a/ d/ e showed particularly strong relationships with other miRNAs in the coexpression network. Conclusions This study provides cues for the further exploration of the regulatory mechanisms of short vegetative development and flowering in L. × formolongi.

Flowering induction in mango tree: updates, perspectives and options for organic agriculture

ABSTRACT The artificial flowering induction in mango tree is the most important crop management in mango orchards and requires greater attention from growers. The management involves three steps: stoppage of plant growth, branch maturation and flowering induction with nitrates. The first stage starts with the application of paclobutrazol to the soil. However, problems with the use of excessive concentrations are common and lead to the accumulation of residues in the soil. In addition, the use of paclobutrazol is not allowed in organic agriculture. Therefore, this review article aimed to compile information about the updates and efforts to solve these problems in conventional mango crops, as well as identify alternatives for its organic management. In conventional orchards, the application of fulvic acids in association with paclobutrazol, as an alternative to the single use of paclobutrazol, was identified as a way to improve the absorption of the product by plants and, consequently, reduce the concentrations and residues in the soil. Researches involving pruning, girdling, fertilization and irrigation should be developed as an alternative to the use of paclobutrazol for the organic crop system of mango cultivars in tropical and subtropical regions.

Fruit presence induces polar auxin transport in citrus and olive stem and represses IAA release from the bud

In many fruit trees, heavy fruit load in one year reduces flowering in the following year, creating a biennial fluctuation in yield termed alternate bearing AB). In subtropical trees, where flowering induction is mostly governed by the accumulation of chilling hours, fruit load is thought to generate a signal (AB signal) that blocks the perception of the cold induction. Fruit removal during a heavy-fruit-load year (On-Crop) is effective at inducing flowering only if performed one to a few months prior to onset of the flowering induction period. We previously showed that following fruit removal, content of the auxin indoleacetic acid (IAA) in citrus buds is reduced, suggesting that the hormone plays a role in the AB signal. Here, we demonstrate that fruit presence generates relatively strong polar auxin transport (PAT) in citrus and olive stems. Upon fruit removal, PAT is reduced and allows auxin release from the bud. Furthermore, using immunolocalization, hormone and gene expression analyses, we show that in citrus, IAA level in the bud and, specifically, in the apical meristem is reduced upon fruit removal. Overall, our data provide support for the notion that fruit presence generates an auxin signal in the bud which may affect flowering induction.

Analysis of miRNA-mediated Regulation of Flowering Induction in Lilium × formolongi

Background: MicroRNAs play pivotal roles in plant vegetative phase change and flowering induction via integrating into multiple flowering pathways. Lilium × formolongi is an important ornamental lily cultivar that can flower within one year after sowing. However, it remains unresolved how miRNA-mediated regulation networks contribute to the L. × formolongi characteristics of a short vegetative growth period and rapid flowering.Results: In this study, five small RNA libraries and one degradome library were constructed for L. × formolongi during vegetative growth and flowering initiation, and 366 conserved miRNAs and 32 novel miRNAs were identified. Additionally, 84 miRNAs were significantly differentially expressed during development. A total of 396 targets of 185 miRNAs were identified and validated through degradome sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that functions of the targets were top enriched in the cold and cadmium ion responses, pentose phosphate pathway and carbon fixation in photosynthetic organisms pathway. Furthermore, among 23 differentially expressed miRNA-target pairs, the miR156s-LfSPL2, miR172a-LfAP2 and miR164a-LfNAC pairs as well as miR159a-LfSPL2 were found to be relevant to flowering based on the correlation analysis of expression profiles in the miRNA libraries, degradome and transcriptome. A coexpression regulatory network focused on differentially expressed pairs was also constructed by WGCNA, and 14 miRNAs were considered putative key miRNAs during vegetative development and flowering induction. miR156a/ d/ e showed particularly strong relationships with other miRNAs in the coexpression network. Conclusions: This study provides cues for the further exploration of the regulatory mechanisms of short vegetative development and flowering in L. × formolongi.