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.

Metagenomic analysis provides functional insights into seasonal change of a non-cyanobacterial prokaryotic community in temperate coastal waters

The taxonomic compositions of marine prokaryotic communities are known to follow seasonal cycles, but functional metagenomic insights into this seasonality is still limited. We analyzed a total of 22 metagenomes collected at 11 time points over a 14-month period from two sites in Sendai Bay, Japan to obtain seasonal snapshots of predicted functional profiles of the non-cyanobacterial prokaryotic community. Along with taxonomic composition, functional gene composition varied seasonally and was related to chlorophyll a concentration, water temperature, and salinity. Spring phytoplankton bloom stimulated increased abundances of putative genes that encode enzymes in amino acid metabolism pathways. Several groups of functional genes, including those related to signal transduction and cellular communication, increased in abundance during the mid- to post-bloom period, which seemed to be associated with a particle-attached lifestyle. Alternatively, genes in carbon metabolism pathways were generally more abundant in the low chlorophyll a period than the bloom period. These results indicate that changes in trophic condition associated with seasonal phytoplankton succession altered the community function of prokaryotes. Our findings on seasonal changes of predicted function provide fundamental information for future research on the mechanisms that shape marine microbial communities.

Large seasonal and interannual variations of biogenic sulfur compounds in the Arctic atmosphere (Svalbard; 78.9° N, 11.9° E)

Seasonal to interannual variations in the concentrations of sulfur aerosols (< 2.5 µm in diameter; non sea-salt sulfate: NSS-SO42-; anthropogenic sulfate: Anth-SO42-; biogenic sulfate: Bio-SO42-; methanesulfonic acid: MSA) in the Arctic atmosphere were investigated using measurements of the chemical composition of aerosols collected at Ny-Ålesund, Svalbard (78.9∘ N, 11.9∘ E) from 2015 to 2019. In all measurement years the concentration of NSS-SO42- was highest during the pre-bloom period and rapidly decreased towards summer. During the pre-bloom period we found a strong correlation between NSS-SO42- (sum of Anth-SO42- and Bio-SO42-) and Anth-SO42-. This was because more than 50 % of the NSS-SO42- measured during this period was Anth-SO42-, which originated in northern Europe and was subsequently transported to the Arctic in Arctic haze. Unexpected increases in the concentration of Bio-SO42- aerosols (an oxidation product of dimethylsulfide: DMS) were occasionally found during the pre-bloom period. These probably originated in regions to the south (the North Atlantic Ocean and the Norwegian Sea) rather than in ocean areas in the proximity of Ny-Ålesund. Another oxidation product of DMS is MSA, and the ratio of MSA to Bio-SO42- is extensively used to estimate the total amount of DMS-derived aerosol particles in remote marine environments. The concentration of MSA during the pre-bloom period remained low, primarily because of the greater loss of MSA relative to Bio-SO42- and the suppression of condensation of gaseous MSA onto particles already present in air masses being transported northwards from distant ocean source regions (existing particles). In addition, the low light intensity during the pre-bloom period resulted in a low concentration of photochemically activated oxidant species including OH radicals and BrO; these conditions favored the oxidation pathway of DMS to Bio-SO42- rather than to MSA, which acted to lower the MSA concentration at Ny-Ålesund. The concentration of MSA peaked in May or June and was positively correlated with phytoplankton biomass in the Greenland and Barents seas around Svalbard. As a result, the mean ratio of MSA to the DMS-derived aerosols was low (0.09 ± 0.07) in the pre-bloom period but high (0.32 ± 0.15) in the bloom and post-bloom periods. There was large interannual variability in the ratio of MSA to Bio-SO42- (i.e., 0.24 ± 0.11 in 2017, 0.40 ± 0.14 in 2018, and 0.36 ± 0.14 in 2019) during the bloom and post-bloom periods. This was probably associated with changes in the chemical properties of existing particles, biological activities surrounding the observation site, and air mass transport patterns. Our results indicate that MSA is not a conservative tracer for predicting DMS-derived particles, and the contribution of MSA to the growth of newly formed particles may be much larger during the bloom and post-bloom periods than during the pre-bloom period.

Dust and pyrogenic iron boost phytoplankton blooms in sub-Antarctic waters of the Tasman Sea

&lt;p&gt;Although it is commonly accepted that atmospheric deposition of Fe particles can fertilise phytoplankton, there is yet no clear evidence on how such a fertilisation effect takes place. Several studies have attempted to link individual dust events with surface chlorophyll responses but generally, they do not find a clear correspondence between dust deposition and its impact on chlorophyll. In this work, we use a biogeochemical model to show that the atmospheric deposition of Fe in high-latitude seas, rather than creating instantaneous phytoplankton responses, replenish the upper mixed layer of the ocean during the pre-bloom period, from winter to early summer. The Fe accumulated at the surface boosts the phytoplankton bloom of the following summer, resulting in surface chlorophyll accumulations of up to 3 times larger than the years without atmospheric deposition. We used this mechanism to explain the strong inter-annual variability of the phytoplankton bloom in sub-Antarctic iron-limited waters east of Australia. Putting together more than a 15-years-long record of ocean colour observations and atmospheric aerosols reanalysis we uncovered a strong correlation (r&lt;sup&gt;2&lt;/sup&gt;&gt;0.6) between the dust that crossed the region during the pre-bloom period and the magnitude of the surface chlorophyll bloom. Interestingly, the correlation increased when taking into account pyrogenic aerosols in addition to dust. Our study presents the first observational link between Climate Change-enhanced droughts and wildfires, atmospheric aerosols and primary production of iron-limited waters.&lt;/p&gt;

Unraveling metabolically active fungal-bacterial diversity in commercial organic vineyard soils

&lt;p&gt;This study aims to assess the impact of the pre-bloom and post-harvest periods on the diversity of metabolically active soil-rhizosphere microbiota in a commercial vineyard in Sant Sadurn&amp;#237; d&amp;#8217;Anoia, a typical wine producing region (Pened&amp;#232;s DO, Catalonia, Spain). Thereby, total genomic DNA and RNA was simultaneously monitored to distinguish total from active bacterial-fungal microbiota, by molecular tools in both periods. The studied organic vineyard had 20 years old plants of the white grape variety of Macabeu and 41B as a rootstock. Soil had last been amended (14 tm/ha of composted cow manure) 5 years before.&lt;/p&gt;&lt;p&gt;The soil was monitored in April 2018 in the pre-bloom period (stages 09 to 12 Eichhorn and Lorenz 1977) and the post-harvest period (October 2018) in 2 different plots of the vineyard: Zone1 (loam texture with permanent cover crop) and Zone 4 (sandy-loam without vegetal cover). Samples soils were obtained at a soil depth of30 cm and 20 cm of distance from a plant (n=4 for each plot and sampling event). Each soil sample was submerged in a DNA/RNA preservative solution at 4&amp;#8304;C and afterward stored at -20&amp;#8304;C until the further analysis. In order to quantify and to assess bacterial and fungal diversity (total and active), (RT)qPCR and MiSeq-Illumina analysis (16SrRNA/ITS1rRNA region) were performed.&lt;/p&gt;&lt;p&gt;Results showed that in post-harvest period the bacterial populations were more active in both zones (2 and 5 orders of magnitude in Zone1 and Zone4, respectively) vs. pre-bloom period. Metabolically active fungal population was increased in both plots by 4 orders of magnitude. It is noteworthy to mention that fungal population was present but not active in pre-harvest period. This fact could be explained for the mutualistic microbe interaction and the environmental conditions (soil temperature and soil water content), including grape drop in harvest linked to rainy conditions.&lt;/p&gt;&lt;p&gt;High-throughput sequencing analysis revealed that the microbial diversity was specific for each plot, vine and sampling period. Bacterial population in post-harvest was more diversified but still dominated by Actinobacteria (mainly by Actinomycetales order), Proteobacteria (mainly by Rhizobiales and Pseudomonadales orders). Interestingly, during post-harvest Clostridiales (Firmicutes phylum), present in the pre-bloom period, completely disappeared. Alpha bacterial diversity was higher than fungal one in both plots. Interestingly, the bacterial diversity (H Shannon index) of metabolically active bacteria (cDNA) was higher during post-harvest season compared to April, suggesting more activity and diversity in the former. On the contrary, fungal diversity was smaller and less uniform in both periods. They were predominated by Ascomycota, Basidiomycota and Zygomycota phyla. Noticeably, the relative abundance (RA) of existing fungal population (DNA) in the soil were highly different compared to the RA of active fungal community (cDNA).&lt;/p&gt;&lt;p&gt;In conclusion, simultaneous RNA/DNA-based molecular biology tools could improve the knowledge of metabolically active microbial populations in vineyard soils under different seasons.&lt;/p&gt;&lt;p&gt;Funding: VITIMPAC project (INIA RTA2015-00091-00-00).&lt;/p&gt;

Compatibility Studies in Exotic and Indigenous Almond Varieties/Selections under Temperate Conditions of Kashmir Valley

Almond is a self–incompatible plant and incompatibility are of the gametophytic type requiring pollen transfer between trees of different cultivars for fruit set. The present investigation was carried out for two consecutive years to evaluate cross-compatibility among selected varieties (three exotic) and selections (six indigenous) of a given segment of almond germplasm. Effective bloom period in the genotypes ranged between 8th March to 18th March and 7th March to 19th March in Mukhdoom, Shalimar, KD-03, KD-05, KD-06 and 23rd March to 31st March and 24th March to 2nd April in Pranyaj, Merced, Primorskij and Waris. Fruit set varied with each cross combination, initial fruit-set ranged from 5.55 per cent in Shalimar x KD-03 to 77.77 per cent in Waris x Shalimar in the first year and varied from 11.11 per cent in Merced x Shalimar to 85.71 per cent in Waris x KD-06 in second year. The highest final fruit set of 58.00 per cent was obtained in Merced x KD-05 as compared to lowest fruit set of 1.01 per cent recorded in Shalimar x KD-03 in the first year whereas the final fruit set ranged between 3.23 per cent to 66.00 per cent in Merced x Shalimar and Waris x KD-06 during the second year. Fruit set under open pollination varied from 9.00 to 60.00 per cent among different varieties/selections. No fruit set was observed in any genotype following selfing by bagging. Overall it is observed that the early blooming selections viz. Shalimar, KD-03, KD-05 and KD-06 exhibits maximum compatibility with most of the exotic and indigenous varieties/selections and obtained higher fruit set.

Observational evidence for the formation of DMS-derived aerosols during Arctic phytoplankton blooms

The connection between marine biogenic dimethyl sulfide (DMS) and the formation of aerosol particles in the Arctic atmosphere was evaluated by analyzing atmospheric DMS mixing ratio, aerosol particle size distribution and aerosol chemical composition data that were concurrently collected at Ny-Ålesund, Svalbard (78.5° N, 11.8° E), during April and May 2015. Measurements of aerosol sulfur (S) compounds showed distinct patterns during periods of Arctic haze (April) and phytoplankton blooms (May). Specifically, during the phytoplankton bloom period the contribution of DMS-derived SO42− to the total aerosol SO42− increased by 7-fold compared with that during the proceeding Arctic haze period, and accounted for up to 70 % of fine SO42− particles (< 2.5 µm in diameter). The results also showed that the formation of submicron SO42− aerosols was significantly associated with an increase in the atmospheric DMS mixing ratio. More importantly, two independent estimates of the formation of DMS-derived SO42− aerosols, calculated using the stable S-isotope ratio and the non-sea-salt SO42− ∕ methanesulfonic acid ratio, respectively, were in close agreement, providing compelling evidence that the contribution of biogenic DMS to the formation of aerosol particles was substantial during the Arctic phytoplankton bloom period.