Flowering of Sweet Cherries “Prunus avium” in Tunisia

In Tunisia, the development of cherry growing is limited by two major constraints, namely, the chilling requirements and the self-incompatibility of some cultivars. In order to contribute to the development of this high added-value culture, which is capable to play an important socioeconomic role in rural and semi-forestry places, this study has set the main objective, characterization, and selection of best-suited cultivars to mild winter based on the blooming period. The plant materials used for this study are composed of the introduced cultivars, which are “Napoleon,” “Van,” “Moreau,” “Sunburst,” and “Stella,” and unknown cultivars, which are “V1,” “V2,” “V3,” “V4,” and “V5,” and a local one “Bouargoub.” Differential behavior between cultivars was shown for phenological stages (budbreak, flowering, maturity, and leaf fall), and this behavior is dependent in some cases on the cold requirement [chilling requirements (CR)]. The local cultivar “Bouargoub” recorded the lowest “CR” with early flowering and maturity.

Long-day increase of HvVRN2 expression marks the deadline to fulfill the vernalization requirement in winter barley

Vernalization and photoperiod cues are integrated in winter barley plants to flower in the right conditions. We hypothesize that there is a timeframe to satisfy the vernalization needs in order to flower in the optimum moment. Growth and expression of different flowering promoters (HvVRN1, HvCO2, Ppd-H1, HvFT1, HvFT3) and repressors (HvVRN2, HvCO9 and HvOS2) were evaluated in two winter barley varieties under: (1) natural increasing photoperiod, without vernalization, and (2) under short day conditions in three insufficient vernalization treatments. Here, we provide evidence of the existence of a day-length threshold, around 12 h 30 min in our latitudes (Zaragoza, Spain, 41°43’N), marked by the rise of HvVRN2 expression, which defines the moment in which cold requirement must be satisfied to acquire competency to flower. Before that, expression of HvCO2 was induced and might be promoting HvFT1 in both inductive and non-inductive conditions. HvFT3, to be effectively expressed, must receive induction of cold or plant development, through downregulation of HvVRN2 and HvOS2. We emphasize the contribution of HvOS2, together with HvVRN2, in the delay of flowering in vernalization-responsive cultivars. Understanding this complex mechanism of flowering might be useful for breeders to define varieties, particularly in a climate change scenario.

In vitro multiplication of pear tree cultivar Cascatense

One main obstacle to the development and expansion of pear tree cultivation in Brazil has been the lack of cultivars adapted to the edaphoclimatic conditions of regions with the potential for pear production. Intending to overcome this hindrance, Embrapa Clima Temperado (Embrapa Temperate Climate) developed and released the cultivar Cascatense, with a low cold requirement (~400 h) better suited for Rio Grande do Sul`s and Santa Catarina`s climate. Still, seedlings of high genetic and sanitary quality are necessary for the establishment of a high-yield orchard. Plants with both sanitary quality and uniformity can be obtained through in vitro micropropagation. Thus, the present study aimed to assess the influence of different culture media (MS, MS¾, WPM, QL, and Himédia), concentrations of sucrose (0, 15, 30, 45, and 60 g L-1), and concentrations of benzylaminopurine (BAP) (0, 0.4, 0.8, 1.2, and 1.6 mg L-1) upon the in vitro multiplication of cultivar Cascatense, to establish an efficient protocol to enhance its propagation and reproducibility. The study included three sequential experiments in which the number of shoots per explant, the length of shoots, the number of axillary buds per shoot, fresh mass, and dry mass of shoots were evaluated. Cultivar Cascatense can be best propagated in vitro with the use of Himédia medium, supplemented with 0.8 mg L-1 of BAP and 30 g L-1 of sucrose.

Effect of gibberellic acid and ethephon on the germination of European beech dormant and chilled beechnuts

The effect of ethephon (80, 100 and 120 mg·l^–1) and gibberellic acid (GA₃) (40, 300 and 1,000 mg·l^–1) on the germination capacity (GC) and mean germination time (MGT) of European beech (Fagus sylvatica [L.]) dormant beechnuts or beechnuts pre-chilled for four weeks was determined. Compared to the control (dormant untreated seeds) or beechnuts treated with tap water no significant increase in mean GC was detected after the application of ethephon or GA₃ to dormant seeds. Conversely, both ethephon and GA₃ treatments reduced (ethephon significantly) GC when applied to beechnuts chilled for four weeks prior to treatment. The effect of the treatments on germination speed (MGT) and dormancy release significantly improved when beechnuts were chilled for four weeks prior to the application of ethephon or GA₃. However, the effect of GA₃ on MGT of chilled beechnuts was not so distinct compared to dormant untreated seeds. Reduction in MGT was most obvious in seeds hydrated with 1,000 mg·l^–1 GA₃ prior to germination. Their cold requirement time was reduced by three weeks compared to beechnuts hydrated in tap water.

Differing Vernalization Responses of Veronica spicata ‘Red Fox’ and Laurentia axillaris

Many polycarpic herbaceous perennials are known to have a cold-requirement for flowering. To determine the range and relative effectiveness of vernalization temperatures for flower induction, clonally propagated plants of veronica (Veronica spicata L.) ‘Red Fox’ and laurentia [Laurentia axillaris (Lindl.) E. Wimm.] were exposed to temperatures from −2.5 to 20 °C at 2.5 °C increments for 0, 2, 4, 6, or 8 weeks (veronica ‘Red Fox’) and 0, 2.5, 5, 7.5, 10, 12.5, or 15 weeks (laurentia). After treatments, growth and flowering were monitored in a glass greenhouse set at 20 °C with an average daily light integral of ≈5 mol·m−2·d−1. Both veronica ‘Red Fox’ and laurentia exhibited obligate vernalization requirements for flowering, but the temperature–response curves were distinctly different. A minimum of 4 weeks at −2.5 and 0 °C, 6 weeks at 2.5 °C, and 8 weeks at 5 and 7.5 °C was required for complete (100%) flowering of veronica ‘Red Fox’, while a minimum of 5 weeks at 5 to 10 °C, 7.5 weeks at 12.5 °C, and 10 weeks at 2.5 °C were required for complete flowering of laurentia. For veronica ‘Red Fox’, node number under each flower and flower timing were relatively fixed following up to 8 weeks at each temperature, although these values generally decreased at each temperature with extended exposure for laurentia. Based on percent flowering and percentage of lateral nodes flowering, vernalization of veronica ‘Red Fox’ was most effective at 0 and −2.5 °C, while based on percent flowering and flower number, vernalization of laurentia was most effective at 5 to 10 °C.

Effects of Cold and Photoperiod on Flowering of Several Herbaceous Perennial Species

Thirty herbaceous perennial species were treated at 5°C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours plus a 4-hour night interruption. Continuous photo-periodic treatments consisted of 9-hour natural days extended with light from incandescent lamps. Species were categorized into nine response types based on the effects of cold and photoperiod on flowering. Plants had three flowering responses to cold treatment: obligate, facultative, or none. The perennials were obligate long-day, facultative long-day, or day-neutral plants. For example, Campanula carpatica `Blue Clips' had no response to cold and was an obligate long-day plant requiring photoperiods of 16 hours or longer or night interruption for flowering. Rudbeckia fulgida `Goldsturm' had a facultative response to cold and required photoperiods of 14 hours or longer or night interruption for flowering. Veronica longifolia `Sunny Border Blue' had an obligate cold requirement and was day-neutral. Some species responded differently to photoperiod before and after cold. Leucanthemum ×superbum `Snow Cap' flowered as an obligate long-day plant without cold and as a facultative long-day plant after cold. Response categories are discussed.