Effects of Exogenous Gibberellic Acid in Huanglongbing-affected Sweet Orange Trees under Florida Conditions – I. Flower Bud Emergence and Flower Formation

Under Florida conditions, sweet orange (Citrus sinensis) affected by Huanglongbing {HLB [Candidatus Liberibacter asiaticus (CLas)]} frequently exhibits irregular flowering patterns, including off-season flowering and prolonged bloom period. Such patterns can increase the opportunity for temporal and spatial proliferation of pathogens that infect flower petals, including the fungal causal agent for postbloom fruit drop (PFD) Colletotrichum acutatum J.H. Simmonds. For the development of strategies to manipulate flowering, the effects of floral inhibitor gibberellic acid (GA3) sprayed monthly at full- and half-strength rates (49 and 25 g·ha−1, or 33 and 17 mg·L−1, respectively) with different regimens, starting from September and ending in November, December, or January, on the pattern of spring bloom were evaluated in field-grown HLB-affected ‘Valencia’ sweet orange at two locations in subsequent February through April for two separate years in this study. To further examine whether GA3 effects on flowering patterns vary in different cultivars, early-maturing ‘Navel’ sweet orange trees receiving no GA3 or full-strength GA3 monthly in September through January were included. Overall, for ‘Valencia’ sweet orange, monthly applications of GA3 at 49 g·ha−1 from September to December not only minimized the incidence of scattered emergence of flower buds and open flowers before the major bloom but also shortened the duration of flowering, compared with the untreated control trees. In addition, exogenous GA3 led to decreased leaf flowering locus t (FT) expression starting in December, as well as reduced expression of its downstream flower genes in buds during later months. When applied monthly from September through January at 49 g·ha−1, similar influences of exogenous GA3 on repressing flower bud formation and compressing bloom period were observed in ‘Navel’ sweet orange. These results suggest that by effectively manipulating flowering in HLB-affected sweet orange trees under the Florida climate conditions, exogenous GA3 may be used to reduce early sporadic flowering and thereby shorten the window of C. acutatum infection that causes loss in fruit production.

Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd

Duckweeds (Araceae: Lemnoideae) are aquatic monocotyledonous plants that are characterized by their small size, rapid growth, and wide distribution. Developmental processes regulating the formation of their small leaf-like structures, called fronds, and tiny flowers are not well characterized. In many plant species, flowering is promoted by the florigen activation complex, whose major components are florigen FLOWERING LOCUS T (FT) protein and transcription factor FD protein. How this complex is regulated at the molecular level during duckweed flowering is also not well understood. In this study, we characterized the course of developmental changes during frond development and flower formation in Lemna aequinoctialis Nd, a short-day plant. Detailed observations of frond and flower development revealed that cell proliferation in the early stages of frond development is active as can be seen in the separate regions corresponding to two budding pouches in the proximal region of the mother frond. L. aequinoctialis produces two stamens of different lengths with the longer stamen growing more rapidly. Using high-throughput RNA sequencing (RNA-seq) and de novo assembly of transcripts from plants induced to flower, we identified the L. aequinoctialis FT and FD genes, whose products in other angiosperms form a transcriptional complex to promote flowering. We characterized the protein-protein interaction of duckweed FT and FD in yeast and examined the functions of the two gene products by overexpression in Arabidopsis. We found that L. aequinoctialis FTL1 promotes flowering, whereas FTL2 suppresses flowering.

Post-Embryonic Lateral Organ Development and Adaxial—Abaxial Polarity Are Regulated by the Combined Effect of ENHANCER OF SHOOT REGENERATION 1 and WUSCHEL in Arabidopsis Shoots

The development of above-ground lateral organs is initiated at the peripheral zone of the shoot apical meristem (SAM). The coordination of cell fate determination and the maintenance of stem cells are achieved through a complex regulatory network comprised of transcription factors. Two AP2/ERF transcription factor family genes, ESR1/DRN and ESR2/DRNL/SOB/BOL, regulate cotyledon and flower formation and de novo organogenesis in tissue culture. However, their roles in post-embryonic lateral organ development remain elusive. In this study, we analyzed the genetic interactions among SAM-related genes, WUS and STM, two ESR genes, and one of the HD-ZIP III members, REV, whose protein product interacts with ESR1 in planta. We found that esr1 mutations substantially enhanced the wus and stm phenotypes, which bear a striking resemblance to those of the wus rev and stm rev double mutants, respectively. Aberrant adaxial–abaxial polarity is observed in wus esr1 at relatively low penetrance. On the contrary, the esr2 mutation partially suppressed stm phenotypes in the later vegetative phase. Such complex genetic interactions appear to be attributed to the distinct expression pattern of two ESR genes because the ESR1 promoter-driving ESR2 is capable of rescuing phenotypes caused by the esr1 mutation. Our results pose the unique genetic relevance of ESR1 and the SAM-related gene interactions in the development of rosette leaves.

Influence of Wild Relative Rootstocks on Eggplant Growth, Yield and Fruit Physicochemical Properties under Open Field Conditions

Eggplant is an essential vegetable crop that is rich in health-related compounds, and the content of these compounds can be increased through grafting. It was reported that grafting with vigorous wild relatives’ rootstocks can improve eggplant’s fruit quality. The study was conducted to investigate the fruit yield, composition and physicochemical traits of Solanum melongena ME, CE, NE and TE scions grafted on wild relatives’ rootstocks of ST, SM and SI. The results show that a notable graft success (100%) was recorded in grafted (TE/ST) and self-grafted (TE/TE) plants using the cleft technique. Growth and yield traits indicated that CE and TE scions grafted onto ST, SM and SI showed better performance in all of the traits mentioned above in an open field across two years, except first flower formation which was displayed on non-grafted CE. In all the rootstocks studied—ST, SM and SI—there was no noticeable effect on carbohydrate, fibre, ash, pH and dry matter content. There was a notable effect of grafting ME/ST, CE/ST, ME/SM, CE/SI, ME/SI, ME/SI and NE/SM on the fruit length, fruit width, total soluble solids, fruit firmness and fat and protein content, respectively. Furthermore, antioxidants such as DPPH (ME/SM), total flavonoids (NE/SM) and total phenolics (TE/SI) had remarkable content of the above-mentioned physicochemical properties. Results show that ST, SM and SI represent a viable rootstock alternative to Solanum melongena or Solanum lycopersicum production.

Gibberellin Induced Transcriptome Profiles Reveal Gene Regulation of Loquat Flowering

Flowering is an integral part of the life cycle of flowering plants, which is essential for plant survival and crop production. Most woody fruit trees such as apples and pears bloom in spring, but loquat blooms in autumn and winter. Gibberellin (GA) plays a key role in the regulation of plant flower formation. In this study, we sprayed loquat plants with exogenous GA3, which resulted in vigorous vegetative growth rather than floral bud formation. We then performed a comprehensive RNA-seq analysis on GA3-treated and control-treated leaves and buds over three time periods to observe the effects of exogenous GA3 application on floral initiation and development. The results showed that 111 differentially expressed genes (DEGs) and 563 DEGs were down-regulated, and 151 DEGs and 506 DEGs were up-regulated in buds and leaves, respectively, upon treatment with GA3. Among those that are homologs of the DELLA-mediated GA signal pathway genes, some may be involved in the positive regulation of flower development, including EjWRKY75, EjFT, EjSOC1, EjAGL24, EjSPL, EjLFY, EjFUL, and EjAP1; while some may be involved in the negative regulation of flower development, including EjDELLA, EjMYC3, EjWRKY12, and EjWRKY13. Finally, by analyzing the co-expression of DEGs and key floral genes EjSOC1s, EjLFYs, EjFULs, EjAP1s, 330 candidate genes that may be involved in the regulation of loquat flowering were screened. These genes belong to 74 gene families, including Cyclin_C, Histone, Kinesin, Lipase_GDSL, MYB, P450, Pkinase, Tubulin, and ZF-HD_dimer gene families. These findings provide new insights into the regulation mechanism of loquat flowering.

PAEONIA EMODI: A THREATENED IMPORTANT MEDICINAL PLANT OF HIGHER HIMALAYAN REGION

Himalaya is well known for its rich biodiversity with respect to medicinal and aromatic plants and Paeonia emodi Wall. ex Royle is one of them locally known as Chandra (family Paeoniaceae). In India, it is distributed in North–West Himalaya from Kashmir to Garhwal-Kumaun regions of Uttarakhand with an altitudinal range of 1800 to 2800 m asl. The whole plant of P. emodi is highly effective for uterine diseases, blood purifier, colic, bilious, backbone ache, headache, dizziness, vomiting, dropsy, epilepsy and hysteria while the seeds are purgative. A present phytosociological study particularly in Garhwal Himalaya, reveals that only few pockets of P. emodi are higher dense in Triyuginarayan and Shyalmi areas (3.80 and 2.72 individual/m2 respectively) while remaining are lower dense under diverse climatic conditions due to invasion by several biotic and abiotic factors. Using available information based on field survey, it assumed that the causes of its degradation are largely overexploitation of immature twigs before flower formation and seed shedding. To conserve the targeted species for future prosperity, Government needs to take immediate and concrete initiatives or imposed the ban on illegal collection or removal of the plant from its natural populations and emphasize the promotion of conservation.

Expansion of the genotypic variability in watermelon by physical mutagenesis

Purpose. Studies have been conducted on 18 promising watermelon genotypes to expand the genotypic variability of watermelon by induced mutagenesis. Materials and methods. Air-dried seeds were irradiated with a closed 60Co γ-source «Doslidnyk» (Department of Molecular and Medical Biophysics, Faculty of Radiophysics, Biomedical Electronics and Computer Systems, V.N. Karazin Kharkiv National University of MES of Ukraine). Results and discussion. Each of the most informative breeding traits was statistically analyzed for their expression patterns and levels by variants of mutagenic treatment (different doses - 150 Gy, 200 Gy, and 250 Gy) in each of the 18 genotypes. The patterns of influence of the irradiation doses on plant growth and development have been determined, both in individual genotypes and for the whole sample. It has been found that γ-irradiation had a depressing effect in the majority of genotypes (late maturation, long or short stems, altered order of the 1st female flower formation, extended phases of the growing period). Genotypes and their groups (clusters), in which expression of traits is opposite (alternative), have been identified. Sources of economically valuable traits have been identified, and the following effective doses of γ-irradiation have been established for genotypes (clusters): 4 genotypes of cluster 4 γ-irradiated at 250 Gy ‑ in breeding for yield capacity; 2 genotypes of cluster 3 γ-irradiated at 150 ‑ 250 Gy – in breeding for marketability; 3 genotypes of clusters 3 γ-irradiated at 150, 200 or 250 Gy – in breeding for large fruits: 1 genotype of cluster 5 γ-irradiated at 150, 200 or 250 Gy – in breeding for late maturation; 2 genotypes of cluster 3 γ-irradiated at 200 or 250 Gy and 5 genotypes of cluster 5 γ-irradiated at 150 or 200 Gy– in breeding for early maturation; 3 genotypes of cluster 3 γ-irradiated at 200 or 250 Gy and 7 genotypes of cluster 5 γ-irradiated at 150, 200 and especially 250 Gy – in breeding for long stems; and 1 genotype of cluster 1 γ-irradiated at 150, 200 or 250 Gy – in breeding for short stems

Physiological Disorders and Fruit Quality Attributes in Pomegranate: Effects of Meteorological Parameters, Canopy Position and Acetylsalicylic Acid Foliar Sprays

Meteorological parameters and occurrences of cracking (CR), russeting (RS), and sun scald (SS) symptoms were monitored in a pomegranate cv. “Wonderful” orchard planted in a W–E orientation, during a 3-year study. Moreover, the efficacy of preharvest foliar sprays with acetylsalicylic acid (ASA; 0.5 mM or 1.0 mM), applied biweekly four to six times, on yield and fruit quality attributes were evaluated in a 2-year study. Fruit from the N-side of the canopy had greater CR and RS, whereas SS symptoms were lower, compared with the S-exposed part of the canopy. The N-side of the canopy had also substantially lower fruit number and yield, suggesting for an important role of light on bisexual flower formation and/or fruit set. Following the occurrences in CR and RS during the fruit maturation period, it was found that temperature fluctuation was the main cause. The presence of RS damages may also be related with increased relative humidity and water movement as symptoms were higher in years with higher values, in the N-side of the canopy and often occurred in the exposed and stylar end of the fruit. The ASA treatment substantially reduced RS by up to 57%, improved the peel red coloration, while anthocyanin, antioxidant capacity, and soluble solid contents in juice were higher. Foliar sprays with ASA did not affect yield, but induced a trend of bigger-sized fruit. In conclusion, planting in a N–S row orientation and selecting an orchard plantation site with a minimum temperature fluctuation and low relative humidity during the fruit-ripening period are measures to control CR and RS in pomegranate. ASA foliar applications proved to have beneficial effects on juice antioxidant contents, but more importantly on fruit appearance.