16-hour Photoperiod Research Articles

The obtaining potato microtubers on the basis of optimization of <i>in vitro</i> cultivation conditions

Search work for optimization of such conditions for in vitro cultivation of potatoes as photoperiod, volume of nutrient medium, choice of a source of carbohydrate nutrition and its concentration, as well as growth regulators of auxin and cytokinin nature, was carried out in 2018-2020. Potato microplants of early-ripening (Alena, Latona, Red-Scarlett), middle-early (Adretta, Charodei, Svitanok Kievsky) and mid-season (Naiada, Ladozhskiy, Skarb) varieties were cultivated at illumination of 75-85 mMol/m2 s-1, 6500 K, air temperature 22...25 °C, relative air humidity 70-75 % and photoperiod from 4 to 16 hours. The results of three years of research have shown that the Murashige-Skooga nutrient medium modified by the Russian Potato Research Center with a 6 % sucrose concentration in a volume of 10 ml per microplant and a 12-hour photoperiod were optimal for micro-tuberization during in vitro cultivation of potatoes of all ripeness groups. The interaction of these cultivation conditions made it possible to obtain an average of 2.5 pcs. of microtubers per microplant of early-ripening potato varieties, 2.4 pcs. - middle-early and 3.2 pcs. - mid-season varieties. Optimal methods of in vitro cultivation of potatoes served as the basis for a new technique for obtaining potato microtubers. If this method was followed, the share of microplants with microtubers of early-ripening varieties increased by 6 %, middle-early varieties - by 12 % and mid-season ones - by 9 %. In addition, the duration of the micro-tuberization period in middle-early varieties was reduced by 14 days, in early-ripening and mid-season potato varieties by 28 days. Microplants of early-ripening and middle-early potato varieties formed larger microtubers, while mid-season varieties were in the lead in terms of quantitative yield.

Optimizing Temperature and Photoperiod in a Home Cultivation System to Program Normal, Delayed, and Hastened Growth and Development Modes for Leafy Oak-Leaf and Romaine Lettuces

As the risk of open-field cultivation increases with climate change, some analysts say that the day when ordinary vegetables will be produced at home is not far away. Moreover, due to the recent coronavirus outbreak, outdoor activities are becoming difficult, leisure activities that can be done at home have become more necessary, and the demand for home gardening has increased. This study was conducted to improve the technology for hydroponics at home. We experimented with whether the harvest time can be hastened or delayed by environmentally controlling the growing season, and what conditions are appropriate. Experiments were conducted with leafy vegetables (Lactuca sativa L. ‘Oak-leaf’ and Lactuca sativa L. var. longifolia, or romaine) that can easily be grown in a closed plant cultivator in which the external air can circulate, and the temperature/photoperiod can be controlled. Two settings for the temperature (25/18 °C and 20/15 °C; day/night) and three settings for the photoperiod (10, 14, and 18 hours; day/night) were employed. It took a total of four weeks from sowing to harvest, and the appropriate harvest time was predicted from the yield. As a result, although there was a difference depending on the vegetable variety, a temperature setting of 25/18 °C and a photoperiod of 14 hours were the most suitable for hastened growth, and a 20/15 °C temperature and 18 hours of photoperiod were suitable for the delayed growth.

First Report of Leaf Spot of Weigela florida Caused by Epicoccum layuense in China.

Weigela florida (Bunge) A. DC. is a dense, rounded, deciduous shrub commonly planted in landscapes. It is also used in Chinese medicine to treat sore throat, erysipelas, cold, and fever (Zheng et al. 2019). In May 2019, leaf spots were observed on approximately 50% of W. florida plants grown in the Wisdom Plaza Park of Anhui Agricultural University in Hefei, Anhui Province, China. Leaf spots begun as small light brown and irregular lesions, enlarged, turned reddish brown, coalesced to form large blighted areas, and eventually covered the entire leaf surface. Five pieces of tissues were removed from the lesion margins of each diseased leaf (five leaves from five different plants), chopped into several 3-4 mm2 pieces, disinfected with 1.5% NaOCl for 2 min, rinsed 3 times with sterile distilled water for 1 min, plated onto Potato Dextrose Agar (PDA) medium containing 50 μg/ml of ampicillin and kanamycin, and incubated at 25°C with a 12-hour photoperiod for 5 days. One segment of the fungal growth from the growing edge of the colony was transferred onto a fresh PDA plate for purification and incubated under the same conditions for another 5 days. The colony morphology of one representative isolate (AAU0519) was characterized by a pale orange cushion in the center surrounded by irregular pink margin, diffusing red orange pigments into the PDA medium. Isolate AAU0519 was cultured on PDA medium for 7 days at 25°C in the dark to induce sporulation. The produced conidia were globose, subglobose to pyriform, golden brown to brown, and with a diameter of 7.7 - 23.8 μm. Both cultural and morphological characteristics suggested that isolate AAU0519 was an Epicoccum species, according to the description by Chen et al. 2017. Amplification and sequencing of the internal transcribed spacer (ITS), beta-tubulin, and 28S large subunit ribosomal RNA (LSU) gene fragments from the extracted genomic DNA of AAU0519 were performed using primer sets ITS1/ITS4 (White et al. 1990), Bt2a/Bt2b (Glass and Donaldson 1995), and LSU1Fd/LR5 (Crous et al. 2009; Vilgalys and Hester 1990), respectively. A phylogenetic tree was constructed by the maximum-likelihood method with 1,000 bootstrapping replications based on the concatenated ITS, beta-tubulin, and LSU sequences from isolate AAU0519 and representative strains of 22 species of the genus Epicoccum (Chen et al. 2017). Isolate AAU0519 clustered with ex-holotype CGMCC 3.18362 of Epicoccum layuense Qian Chen, Crous & L. Cai (Chen et al. 2017). All obtained sequences were deposited into GenBank under accession numbers MK983497 (ITS), MN328723 (beta-tubulin), and MN328724 (LSU). A pathogenicity test was conducted on leaves of five 3-year-old W. florida cultivar "Red Prince" planted in the field (five leaves for each treatment and control per plant) by spraying 30 ml of a spore suspension (106 spores/ml) of isolate AAU0519 as treatment or sterilized distilled water as control. Before the inoculation, the leaves were disinfected with 70% ethanol. After inoculation, the leaves were wrapped with a plastic bag to keep high relative humidity. The average air temperature was about 28°C during the period of pathogenicity test. The experiment was repeated once. Ten days after inoculation, the fungal-inoculated leaves developed light brown lesions resembling those of naturally infected leaves, control leaves did not develop any symptoms. E. layuense was recovered from leaf lesions and its identity was confirmed by morphological and sequence analyses as described above. To our knowledge, E. layuense has been previously reported as a pathogen of Perilla sp. (Chen et al. 2017), oat (Avena sativa) (Chen et al. 2019), and tea (Camellia sinensis) plants (Chen et al. 2020), but this is the first report of E. layuense causing leaf spot on W. florida in China. This pathogen could pose a threat to the ornamental value of W. florida plants. Thus, it is necessary to adopt effective management strategies against leaf spot on W. florida.

Breeding of sunflower lines resistant to race G of Broomrape

Relevance. Over the past decades, new and extremely virulent races have appeared in the southern regions of the Russian Federation, which overcame the resistance of domestic and foreign sunflower range of varieties. The most effective, long-term, and biologically safe way to protect sunflower from broomrape is to develop varieties and hybrids resistant to new races.Methods. We identified broomrape seeds of race G using internationally accepted differentiator lines: Record 1-3 (C), S-1358 (D), P-1380 (E), LC1093 and P96 (F). We used sunflower lines and hybrids of the breeding of V.S. Pustovoit All-Russian Research Institute of Oil Crops as a parent material. We carried out the evaluation of broomrape resistance by the method of A.Ya. Panchenko. To develop an infectious background, we introduced seeds of broomrape race G into boxes with a soil and sand mixture at the rate of 200 mg per 1 kg of the mixture, distributing them evenly. We grew sunflower plants at a temperature of 25-27 °С and a 16-hour photoperiod. In 25-30 days after the emergence if seedlings, we dug up plants and counted the broomrape specimens on their roots by a scale.Results. We developed sunflower lines resistant to races of broomrape from A to G. All of them are of branched form, with different lengths of the period from germination to flowering, they differ in height and oil content. The line L 82 is distinguished by a high content of oleic acid in oil — 91%. The lines have a high combinability. We obtained experimental hybrid combinations using these lines.

Timing of Stolon Removal Alters Daughter Plant Production and Quality in the Ever-bearing Strawberry ‘Albion’

Commercial strawberry (Fragaria ×ananassa Duch.) plants propagate through the development of stolons (runners) with attached daughter plants. While it is known that temperature and photoperiod affect strawberry propagation, little knowledge exists on whether cultural methods may influence stolon and daughter plant development. The objective of this study was to characterize the impact of three stolon removal treatments on the development of daughter plants in the ever-bearing strawberry ‘Albion’. Treatments included 1) stolon removal every 7 days, nine times total; 2) stolon removal every 21 days, three times total; and 3) one-time stolon removal after 63 days. Strawberry plants were grown in a controlled environment (26 °C, 507 μmol⋅m–2⋅s–1 photosynthetic photon flux density, 14-hour photoperiod) in soilless media and fertilized with a customized nutrient solution. Mother plants in the 63-day treatment produced more daughter plants (102 per plant), than in the 21-day treatment (33 per plant) and the 7-day treatment (16 per plant). In the 63-day treatment, daughter plants and stolons accumulated to 86.6% of the total biomass, to 42.9% in the 7-day treatment and to 60.6% of total biomass in the 21-day treatment. Mother plant organs (including roots, crown, and leaves) had less dry weight in the 63-day treatment compared with the 7-day treatment and 21-day treatment, respectively. Furthermore, the daughter plants produced at the 63-day treatment had smaller crown diameters (0.65 cm) and less dry weight (0.51 g) and a higher number of fully expanded leaves (2.9) and visible roots (13.4) compared with the 21-day treatment and the 7-day treatment. The results of this study show daughter plant production of strawberry plants declines significantly with shorter stolon removal intervals, indicating the need to adjust stolon removal in strawberry nurseries for optimal daughter plant production.

Features of seed growth and development of sproutings of the russian dereza (Lycium ruthenicum Murr.) under laboratory conditions and in culture in vitro

Russian dereza (Lycium ruthenicum Murr.) is a shrub plant that spreads on the territory of the dried Aral Sea in conditions of high soil salinity, dry and sharply continental climate. The fruits were collected and the features of germination of seeds of the russian dereza halophyte (Lycium ruthenicum Murr.) Under sterile and non-sterile conditions were studied. The optimal temperature and illumination regime for the germination of annual seeds of this species is a 16-hour photoperiod and a temperature of 25 °C, the germination of seeds in nonsterile conditions was: 4-year-old – 46 %; 2-year – 83; one-year – 96 %. It has been shown that L. ruthenicum plants remain viable for up to 4 years or more, on this basis, we attributed the seeds of this species to truly orthodox. When introduced into culture in vitro, it has been shown that multi-stage sterilization significantly reduces the viability of seeds and seedlings of Lycium ruthenicum Murr., which leads to a decrease in seed germination by up to 40 %. The optimal nutrient medium for the stable development of microshoots without anomalies, callus formation and initiation of root formation was MS with the addition of 1.0 mg/l 6-BAP to the nutrient medium, without sucrose. Maintaining the samples in the in vitro collection is carried out on a half-MS medium without hormones, without sucrose at a low positive temperature of 4 °C, illumination of ~500 lx and a photoperiod of 8 hours. The samples of L. ruthenicum in vitro can be used to develop methods of clonal micropropagation; for genotyping of samples and identification of molecular biomarkers of plant resistance to soil salinity; in the ex vitro morpho-biological study of plants resistant to salt stress.

Storage of Simarouba amara Aubl. seeds

Prior knowledge about the physiological behavior of seeds under storage conditions allows the use of appropriate techniques to maintain viability. The goal of the present study was to classify the behavior of Simarouba amara seeds regarding their physiological potential during storage. The seeds were obtained from mature fruits, collected from five parent plants located at the Joanes-Ipitanga Environmental Protection Area (EPA) (Simões Filho, Bahia) in January 2018. Two experiments were carried out in a completely randomized design. In the first one, seed desiccation tolerance was evaluated with seven moisture contents: 5%, 7.5%, 10%, 12.5%, 15%, 25% and 35.6% (initial moisture). A germination test was carried out to evaluate the seeds’ vigor. In the second experiment, the seeds were stored with moisture contents of 7.5%, 12.5% and 35.6% at temperatures of 8 °C, 15 °C and 20 °C) for two storage periods, two and four months, and samples were taken to determine moisture content and conduct the germination test. Germination tests were performed in BOD chambers at 30 °C and with 12-hour light photoperiod. Daily counts were performed for the number of germinated seeds. We measured germination percentage, mean germination time, uncertainty index, percentage of normal seedlings, and percentage of unviable seeds. Simarouba amara seeds tolerate desiccation up to 7.5% moisture content, but lost viability when stored under this condition. At four months of storage all seeds lost viability. Simarouba amara seeds are recalcitrant and lose viability before reaching two months of storage.

Plant growth chamber with integrated air conditioning system, periodic irrigation, and adjustable photosynthetic light wavelength

The increase in the average temperature due to climate change affects the crop yield production and it can lead to food insecurity. Rapid breeding helps increase crop yield production and improve the overall crop quality. The researchers designed a plant growth chamber with integrated air conditioning system, periodic irrigation, and adjustable photosynthetic light wavelength. The growth rate of the representative plant, green span lettuce, grown in the plant growth chamber is compared to conventional planting. Factors such as growth period rate, dry weight, and overall produce quality are considered. It was found that implementing a 24-hour photoperiod, drip irrigating 50 mL per plant every 2 days, adding vermicast to the cocopeat at a ratio of 1:1 and maintaining a temperature range of 20 to 25 degrees Celsius produced a higher relative growth rate. In consideration of additive nutrients, the addition of vermicast added a substantial increase in the relative growth rate. Quality was also improved due to the correlation of the relative growth rate and plant quality.

Second regrowth phase generative characteristics of alfalfa (Medicago sativa L.) with addition of lighting duration and dolomites

This study determines generative growth characteristics of alfalfa in second regrowth with the addition of dolomite and extended photoperiod. This study used a completely randomized design tested via Least Significant Difference. Dolomite was added at 0, 6 and 12 ton/ha. Photoperiod was varied at 12, 14 and 16 hours. The results conclude that extended photoperiod promoted alfalfa growth. Lengthier exposure to lighting promoted faster flowering and greater proportions of pod emergence and pod ripening. The addition of dolomite levels did not affect generative growth, except in the percentage of pods per plants. The addition of 16-hour lighting duration improved the second regrowth stage of alfalfa as compared to 14 and 12-hour photoperiods. The result yielded 61.63% seed purity and 13.33% seed viability.

Effects of photoperiod on performance, ovarian morphology, reproductive hormone level, and hormone receptor mRNA expression in laying ducks

We investigated the effect of photoperiod on performance, ovarian morphology, reproductive hormones levels, and their receptors mRNA expressions in laying ducks. After adaption, 300 252-day-old Jinding laying ducks were randomly allocated to 5 groups, receiving 12L:12D, 14L:10D, 16L:8D, 18L:6D, or 20L:4D, respectively. Each treatment had 6 replicates of 10 birds each. The feeding trial lasted 8 wk. Egg production, egg mass, and ADFI increased linearly and quadratically with increasing photoperiods (P < 0.05), and the higher values of them occurred in photoperiods ≥ 16 h, compared with 12L:12D (P > 0.05). Initial and bare stroma weight increased quadratically, while total large white follicle (LWF) number and weight increased linearly and quadratically, with increasing photoperiods (P < 0.05). The higher values of them occurred in 16L:8D and 18L:6D treatments as well as the higher total LWF weight also occurred in 20L:4D, compared with 12L:12D (P > 0.05). Besides, 16.93 and 16.93 h were the optimal photoperiods for bare stroma (follicles ≥ 2 mm in diameter removed) weight and total LWF weight, respectively, calculated from reliable regression equations (R2 ≥ 0.5071). Compared with 12L:12D, the higher levels of estradiol, progesterone, follicle-stimulating hormone (FSH) as well as the higher expressions of estrogen, luteinizing hormone (LH) and progesterone receptors were observed in ≥16 h photoperiods (P < 0.05), while the higher LH level and FSH receptor expression only occurred in 16L:8D and 18L:6D (P < 0.05). In the hypothalamus, higher mRNA expression of gonadotropin-releasing hormone occurred in 16L:8D and 18L:6D groups (P < 0.05). Meanwhile, gonadotropin-inhibitory hormone and prolactin increased in 20-hour photoperiod (P < 0.05), and the latter may be due to theup-regulation of vasoactive intestinal peptide expression (P < 0.05). To sum up, an appropriate photoperiod could improve the performance and reproductive organ and ovarian follicles development through reproductive hormones and their receptors, and 16.56 to 10.93 h is an adequate photoperiod for laying ducks.

Age Polyethism in Atta sexdens (Linnaeus) (Hymenoptera: Formicidae)

This study aimed to verify age polyethism occurrence in medium-sized (cephalic capsule = 2.3 ± 0.21 mm) and small-sized (cc = 1.4 ± 0.10 mm) workers from Atta sexdens (Linnaeus) colonies. Four laboratory colonies were used, and they were maintained at 25 ± 2 °C, with 75 ± 3% relative humidity and a 12-hour photoperiod. Workers from these colonies were marked after their emergence and observed throughout their lifetime to determine which tasks they performed. The number of ants performing each activity was analyzed using linear mixed-effect models (LME), considering the temporal effect and the block design (colonies). We found that fungal garden maintenance tasks were frequent for both sizes, but their occurrence decreased significantly from the ninth week. The foraging activity occurred gradually in both sizes, with stabilization in the number of workers from the fourth week onwards and declined in the last three weeks of lifespan. Waste management tasks occurred throughout life but were more frequent during the first two weeks of life, in both medium and small workers. Therefore, age polyethism may be related to all activities; however, foraging tasks presented a distinct pattern compared to tasks in the fungus garden and refuse dump, where younger ants were more frequently observed.

THE INFLUENCE OF HYDROGEN SULFIDE ON WHEATGRASS (Triticum æstivum L.) DE‐ETIOLATION

Hydrogen sulfide (H2S) is involved in many physiological processes and responses to the abiotic types of stress. The aim of the study was to determine the effect of sodium hydrogen sulfide (NaHS) and the time of application on the physiological properties of etiolated wheatgrass plants. Two genotypes of wheatgrass were grown under controlled conditions for five days without light and then with a 12-hour photoperiod, watered for three consecutive days with 100, 200, and 500 mM NaHS solutions. The plants were watered in three variants, 7-9, 10-12, and 13-15 days after sowing, respectively. The highest content of phenols, flavonoids, and hydrogen peroxide was found in wheatgrass plants watered with 100 mM of NaHS solution. The highest proline content and lipid peroxidation levels were found in the plants at 500 mM of NaHS solution. Also, the significant influence of the watering period on the examined physiological parameters was determined. The results show that H2S significantly affects the de-etiolation process and concentration of physiologically active compounds in wheatgrass plants.

Shortening the Production Cycle of Clematis

Clematis (Clematis ×hybrida) is among the flowering plants well-recognized by the retail consumer; however, production has not traditionally fit into standard greenhouse production systems. One reason is the relatively long 2-year production cycle from propagation to flowering. Four experiments were conducted with clematis ‘H.F. Young’ to understand the factors that influence shoot development and flowering of clematis so that strategies could be developed for bulking, providing a cold treatment, and flowering the plants with a shortened production time. The first experiment showed an increase in shoot and flower numbers and a decrease in time to flower as the duration of cold treatment increased from 0 to 9 weeks and the photoperiod increased from 9 to 16 hours. The second experiment resulted in greater shoot and flower numbers when plants were forced at 21 °C as compared with 27 °C. The third experiment showed that the application of ethephon (500 or 1000 mg·L−1) during bulking increased shoot formation (branching) as compared with the control or 500 mg·L−1 benzylaminopurine treatments. The fourth experiment showed that applications of 500 mg·L−1 ethephon along with a 16-hour photoperiod during the bulking period improved shoot number and flowering of the finished crop. The combined results provide guidelines for producing a well-branched, flowering clematis crop within 1 year from the start of propagation to the time of the first open flower.

Research and Development of Process Conditions for Growing Young Plants Iris sibirica L. Aimed at Bio-Synthesis of Tannins, Flavonoids and Xanthones

The reported paper presents process conditions providing a maximal output of biomass and accumulated biologically active substances when growing young plants Iris sibirica (Sterh variety): growth medium composition according to Murashige and Skoog Media Formulation, growth medium pH 5.6-5.8, temperature of growing 24-26 0C, 16-hour photoperiod, illumination intensity (2000 - 4000 lux), and relative air humidity 70%. It is recommended to use growth media containing 1.0-2.5 uM BAP and auxin compounds 1.0 uM NAA+0.1 uM IB A for an optimal build-up of biomass and phenol compounds (flavonoids, tannins, xanthones) in Iris sibirica.

Differences in Inflorescence Numbers and Endogenous Gibberellic Acid Levels in ‘Afterglow’ Bougainvillea

Bougainvillea (Bougainvillea sp.) plant inflorescence number will vary in response to multiple cues such as changes in temperature, water, light intensity, pruning, and photoperiod. Previous research reports that the application of plant growth regulators (PGRs) to bougainvillea grown under varying photoperiods improved inflorescence number, probably as a result of changes in gibberellic acid (GA) levels. There are many bioactive plant GAs, but we chose to investigate differences in gibberellic acid 3 (GA3) levels and inflorescence number in response to the application of ethephon (2-cholorethylphosponic acid) or abscisic acid (ABA) to ‘Afterglow’ bougainvillea (Bougainvillea ×buttiana) grown under 14-hour photoperiod [long-day (LD)] conditions. Plants were 5 inches tall with seven visible lateral nodes and were grown in a greenhouse in 4-inch pots filled with 5-mm coarse aquarium zeolite. Ethephon was applied as a foliar spray at 0.05, 0.07, 0.10, 0.15, or 0.20 mg/plant. ABA was applied as a soil drench at 1, 1.5, 3, 6, 8, or 10 mg/plant. Endogenous levels of GA3 were measured 1 and 48 days after treatment to calculate the change in GA3 (∆GA3). A short day (SD) control of 8 hours was included to measure differences in inflorescence number and ∆GA3 between photoperiods. ‘Afterglow’ plants grown under SD conditions had the greatest decrease in ∆GA3 (–1.09 µg·g–1) over 48 days and the most inflorescences (10.6) compared with LD control plants with a decrease in ∆GA3 of –0.09 µg·g–1 and fewer inflorescences (1.0). Plants grown under LD conditions and treated with 0.05 mg/plant ethephon had inflorescence numbers (9.6) and levels of ∆GA3 (–0.74 µg·g–1) similar to the SD control. As ethephon rate increased to more than 0.05 mg/plant, inflorescence number on LD plants decreased and ∆GA3 increased. Exogenous ABA rates of 1 mg/plant produced inflorescence numbers (1.4) and ∆GA3 (–0.10 µg·g–1) similar to the LD control. As the rate increased, ∆GA3 increased and inflorescence number decreased. Plants treated with ABA rates of 3 mg/plant and more were defoliated and had no inflorescences.

Zinc - rooting cofactor in rubber tree mini-cuttings

The rubber tree (Hevea brasiliensis Müell. Arg.) is a species of significant economic interest in the natural rubber industry in Brazil and the world. This species presents recalcitrance to rooting, and its cuttings are difficult to propagate. This study aimed to evaluate the effect of the pre-conditioning of rubber tree mini-cuttings with zinc on the improvement of the adventitious rooting of rootstocks. Mini-cuttings were standardized with 45 mm length and submitted to preconditioning by immersion of the mini-cutting base in solutions containing 0.00; 0.04; 0.08; 0.16; 0.32 and 0.64 mg L-1 of Zn, for 24 hours. The experimental design was randomized blocks with six treatments and four replicates of 10 mini-cuttings. The rubber tree mini-cuttings were placed in a fitotron-type growth chamber, at 25 °C, with 12-hour photoperiod, 5,000 K intensity, and 95% of relative air humidity, for 60 days. The survival rate, number of buds, percentage of mini-cuttings that had leaf abscission, the percentage of mini-cuttings with callogenesis in the root meristem, the percentage of rooted mini-cuttings, the number of primary roots and root length were evaluated. The highest values of survival rate, the number of buds, the number of primary roots, the percentage of mini-cuttings with callogenesis in the root meristem, the percentage of rooted mini-cuttings and root length were observed with 0.16 to 0.26 Mg L-1 of Zn. The use of zinc in the mini-cuttings of rubber tree reduces linearly the percentage of mini-cuttings that had leaf abscission and the formation of callogenesis in the root meristem.&#x0D; &#x0D; The rubber tree (Hevea brasiliensis Müell. Arg.) is a species of a large economic interest in the natural rubber industry in Brazil and the world. This species presents recalcitrance to rooting, and its cuttings are difficult to propagate. This study aimed to evaluate the effect of the pre-conditioning of rubber tree mini-cuttings with zinc on the improvement of the adventitious rooting of rootstocks. Mini-cuttings were standardized with 45 mm length and submitted to preconditioning by immersion of the mini-cutting base in solutions containing 0; 0.04; 0.08; 0.16; 0.32 and 0.64 mg L-1 of Zn, for 24 hours. The experimental design was randomized blocks with six treatments and four replicates of 10 mini-cuttings. The rubber tree mini-cuttings were placed in a fitotron-type growth chamber at 25 °C, with 24-hour photoperiod, 5,000 K intensity and 95% relative humidity for 60 days. The survival rate, number of buds, percentage of mini-cuttings that had leaf abscission, the percentage of mini-cuttings with callus, the percentage of rooted mini-cuttings, the number of primary roots and root length were evaluated. The highest values of survival rate, the number of buds, the number of primary roots, the percentage of mini-cuttings with callus, the percentage of rooted mini-cuttings and root length were verified with 0.16 to 0.26 Mg L-1 of Zn. The use of zinc in the mini-cuttings of rubber tree reduces linearly the percentage of mini-cuttings that had leaf abscission and the formation of root calluses.

Effect of Extended Photoperiod with a Fixed Mixture of Light Wavelengths on Tomato Seedlings

Light is an abiotic factor, and its quality, quantity, and photoperiod can be modulated to work as eustress inductors to regulate plant processes. It is known that red (R), blue (B), far-red (FR), and ultraviolet-A wavelengths can promote photomorphogenesis and secondary metabolite production in plants. Several ratios of R:B and the addition of end of-day FR, separately, have beneficial effects on plant development, whereas adding ultraviolet-A enhances the production of secondary metabolites such as phenols. However, the effects of extended photoperiods with a mixture of these four wavelengths and extra end-of-day FR have not been evaluated for plants of commercial interest. The objective of this study was to determine the effects on tomato seedlings (‘Saladette’, CORDOBA F1) of different overnight photoperiods using a fixed combination of R (625 nm), B (460 nm), FR (720 nm), and ultraviolet-A (410 nm). We expected increases in the production of specialized metabolites and the generation of beneficial changes in the seedling biomass and morphology. Four treatments involving overnight artificial light provided by a light-emitting diode (LED) module were established: TC (control), 0 h; T1, 4 hours; T2, 8 hours; and T3, 12 hours. All treatments were subjected to a 12-hour natural photoperiod and 12 hours of overnight artificial light. The experiment lasted 4 weeks, and plants were sampled every week for physical and phytochemical measurements. In general, seedlings subjected to 4-hour and 8-hour treatments presented better results than those subjected to the control and 12-hour overnight photoperiod treatments. Seedlings subjected to treatments with an 8-hour overnight photoperiod presented large accumulation of biomass in the stem rather than in the leaves because they had large stem dry weight, stem weight, and elongation and higher first, second, and third internode lengths; however, they had lower leaf area, leaf dry weight, and health index. Seedlings subjected to treatment with a 4-hour overnight photoperiod were visually bigger, with large leaf expansion, total length, stem weight, total weight, and specific leaf area; however, this treatment had a negative impact on the biomass accumulation, with lower leaf weight, stem dry weight, and health index. The 12-hour treatment had a negative impact on the leaf area, and thus the specific leaf area, of seedlings; however, the biomass accumulation was large, with higher leaf dry weight, total dry matter, and specific leaf area, but no difference in stem dry weight compared with the control. At the end of the experiment, the total phenolic content increased in all treatments compared with the control, but the flavonoid content decreased. Moreover, the antioxidant capacity was higher for T2 during the last 2 weeks of the experiment. Results are discussed according to the possibilities of using this light strategy for seedling production.

The influence of environmental factors on seed germination of Xanthium strumarium L.: Implications for management.

Xanthium strumarium L. (Common cocklebur) is a noxious weed prevailing in different ecosystems around the world. It incurs significant yield and economic losses in different cropping systems globally. Successful management of any weed species depends on sound knowledge of seed germination biology. However, detailed knowledge on seed germination biology of the species is missing. Therefore, we investigated the impact of different environmental factors on seed germination and seed burial depths on seedling emergence of two X. strumarium populations. The impact of different sorghum mulch doses (0–10 t ha-1) on seedling emergence of the tested populations was also explored. Seed germination was evaluated under different photoperiods (0, 12 and 24), constant temperatures (0–50°C with 5°C stepwise rise), and different levels of pH (3–12), salinity (0–600 mM) and osmotic potential (0 to -1.6 MPa). Seedling emergence was observed for seeds buried at different depths (0–15 cm). Seeds of both populations proved non-photoblastic; however, higher germination was recorded under 12-hour photoperiod. The seeds germinated under a wide range of constant temperatures (10–45°C), pH (4–10), osmotic potentials (0 to -0.8 MPa) and salinity levels (0–400 mM NaCl). However, the highest germination was observed under 30–31°C temperature and neutral pH (7.51–7.52). Seeds were able to withstand 400 mM salinity and -1.00 MPa osmotic potential. Seedling emergence was initially improved with increasing burial depth and then a sharp decline was noted for the seeds buried >3 cm depth. Most of the seeds of both populations did not emerge from >8 cm depth. Different sorghum mulch doses linearly suppressed seedling emergence of tested populations, and 5.83–5.89 t ha-1 mulch application suppressed 50% of seedling emergence. Seedling emergence was completely retarded with 8 t ha-1 sorghum mulch. The tested populations germinated under diverse environmental circumstances indicating that the species can become troublesome in marginal habitats and cropped lands. Deep burial of seeds and application of sorghum mulches suppressed seedling emergence. Thus, deep burial followed by shallow tillage and application of sorghum mulches could be used as a successful strategy to manage the species in agricultural fields. Nonetheless, management strategies must be developed to control the species in other habitats.

Longer Photoperiods with the Same Daily Light Integral Improve Growth of Rudbeckia Seedlings in a Greenhouse

Supplemental light can increase growth and accelerate production of greenhouse crops, but it can be expensive if not provided in a way that promotes efficient use of the light. Dimmable light-emitting diode (LED) fixtures have the potential to reduce lighting costs because the output can be precisely controlled to meet crop needs. Because light is used more efficiently to drive photosynthesis at lower photosynthetic photon flux densities (PPFDs), we hypothesized that providing Rudbeckia fulgida var. sullivantii ‘Goldsturm’ seedlings with the same daily light integral (DLI), spread out over a longer photoperiod and at lower PPFDs, should improve growth. A DLI of 12 mol·m−2·d−1 was provided in a greenhouse over 12, 15, 18, or 21-hour photoperiods from a combination of sunlight and supplemental light from LEDs, using adaptive lighting control. Plants grown without supplemental light had an ≈12-hour photoperiod and received an average DLI of 5 mol·m−2·d−1, ≈58% less light than the four lighting treatments. Lengthening the photoperiod from 12 to 21 hours increased shoot dry mass (30%), root dry mass (24%), plant height (14%), leaf area (16%), and chlorophyll content index (48%), and decreased specific leaf area (26%). There was no significant effect of photoperiod on root mass fraction or compactness. Growth parameters of plants without supplemental light were 26% to 90% smaller compared with those in the 12-hour photoperiod treatment. Treatment effects on canopy size, seen as early as 2 weeks into the study, were correlated with final shoot dry mass. Longer photoperiods did not induce a shade-avoidance response, based on specific leaf area and compactness data. The 24% increase in root dry mass for the plants in the 21-hour photoperiod suggests that cropping cycles can be shortened by 1 to 2 weeks compared with the 12-hour photoperiod. This could result in more crop turns per year and increased profits. In addition, fewer lights would be needed for adequate growth, reducing the capital cost of the lighting system.

First Report of Neopestalotiopsis rosae causing foliar and fruit spots on pomegranate in Florida.

Foliar and fruit spots were observed on pomegranate trees (Punica granatum L.) planted in orchards located at Balm and Zolfo Springs, FL, in 2019. Symptoms on leaves and fruits included dark brown to black irregular spots, ranging from 0.2 to 1.5 cm, with gray centers. Visible pycnidia were present in the center of the lesions. Leaves became chlorotic and prematurely dropped from the trees. In a disease survey performed on 24 pomegranate cultivars, all of the trees were infected and the disease severity ranged from 2 to 80%. The cultivars Bhagwa and Mridula were the most susceptible. Symptoms on the fruit were similar to those on the leaves; however incidence on the fruits was less than one percent. To isolate the pathogen, small pieces (5 mm2) of symptomatic leaves and fruits were excised from the area between diseased and healthy tissue. Excised tissue pieces were surface disinfested in 70% ethanol solution for 30 seconds, followed by 10% sodium hypochlorite (NaOCl) solution for 2 minutes, rinsed in sterilized distilled water three times, dried on a paper towel, placed onto potato dextrose agar and incubated at 25°C under 12-hour photoperiod for seven days. Fungal cultures formed white cottony aerial mycelium with undulated edges and abundant black pycnidia. Four-septate conidia were fusiform or clavate, straight or slightly curved measuring on average 29.1 (23.3- 34.4) µm long × 6.3 (5.1- 6.8) µm wide (n = 100). Conidia had three median cells which were dark brown, with a single basal hyaline appendage, 5.9 (4.1- 7.7) µm long, and two or four (usually three) apical hyaline appendages 20.3 (14.8- 24.5) µm long. Morphological features were consistent with those of the genus Neopestalotiopsis (Maharachchikumbura et al., 2014). Single-spore cultures were obtained and genomic DNA was extracted from seven isolates (one from fruit, GEV3523, and six from leaf, GEV3426 - GEV3431). Internal transcribed spacer (ITS) region, partial sequences of elongation factor (TEF), and β-tubulin (TUB2) were amplified with the respective primer pairs ITS4 and ITS5, EF1-1567 and EF1-536, and Bt-2a and Bt-2b (Maharachchikumbura et al., 2014). BLAST analysis of the fruit isolate, GEV3523, showed homology of 100% for ITS, 100% for TEF and 99.8% for TUB2 to fungal pathogen Neopestalotiopsis rosae isolate CBS 101057 obtained from a rose plant in New Zealand (Accession Nos. MT587806, MT605118 and MT597152, respectively), whereas the six leaf isolates were 100% identical, GEV3426- GEV3431, showing homology of 100% for ITS, 99.8% for TEF and 98.4% for TUB2 to the same fungal species. Accession numbers: GEV3423 (MT587806, MT605118, MT597152) and GEV3427 (MT587804, MT605120, MT597150); for ITS, TEF and TUB2, respectively. Maximum likelihood phylogenetic analysis, based on the combined alignment of ITS, TEF, and TUB2, differentiated the leaf isolates from other species, suggesting a new Neopestalotiopsis cryptic species. Three-month-old rooted pomegranate cuttings, cultivars Bhagwa and Mridula, were inoculated with two isolates GEV3523 and GEV3527. Each cutting was treated as two distinct halves; one half was wounded by gently rubbing sterilized sand on the leaves to cause abrasions and the other half remained intact. Four cuttings from each pomegranate cultivar were spray inoculated with a spore suspension (105 conidia mL-1) and four control plants were sprayed with sterilized water. The experiment was performed once on each cultivar. Inoculated cuttings were covered with a transparent plastic bag to maintain 100% humidity and incubated for 36 hours at 26°C under 12-hour photoperiod in a growth chamber. Leaves began to show symptoms of small, irregular, brown spots with a gray center three days after inoculation. The pathogen started to produce pycnidia in the center of the lesions one week after inoculation. Symptoms developed on both wounded and unwounded inoculated leaves with 100% disease incidence on both pomegranate cultivars inoculated separately with GEV3527 and GEV3523. Disease severity on wounded leaves ranged from 10 - 25% for 'Bhagwa' and 30 - 60% for 'Mridula' and on intact leaves from 2 - 5% and 5 - 12%, respectively. Furthermore, the fruit isolate, GEV3523, caused an average disease severity of 8 and 3.5 %, on wounded leaves of 'Bhagwa' and 'Mridula', respectively, whereas the leaf isolate GEV3427 caused 19 and 45% disease severity, respectively. No symptoms were observed on control plants and no fungal growth was observed on the re-isolations performed on the control plants. Neopestalatiopsis spp. were re-isolated from leaves fulfilling Koch's postulates. To our knowledge, this is the first report of Neopestalotiopsis rosae infecting pomegranate in Florida as well as in the United States. This pathogen could represent a threat to pomegranate production in Florida due to its ability to cause premature defoliation.