**3.3 Transplantation**

After about 21 days, typically toward the end of September, the root system fully occupies the conical cells, the canopy comprises a few healthy leaves, and the plug plants are ready for transplantation into the final soilless growth system. However, in

### *Winter Strawberries Production in Greenhouse Soilless Culture under an Arid Climate… DOI: http://dx.doi.org/10.5772/intechopen.104390*

case of forecasted heat wave events, it is recommended to keep the seedlings under cool shaded nursery conditions for a longer time and delay the transplantation. The target growbags are carefully prepared: the condensed coir, which serves as the growth medium, is soaked in water to regain maximal volume, washed from excess salts, and recharged with fertilizer. Upon planting, plug plants with roots and growth medium are transferred from the trays and plugged into the new growbag sockets, positioned in a 45 degree angle to maximize canopy spread. This procedure of plug plants preparation is principal for successful transplantation as it minimizes stresses associated with former practices involved with plant uprooting and re-rooting, thus saving the precious time required for recuperation; using the plug plant method, the seedling continues growing with no interruption, with significantly better chances to enhance early production.

#### **3.4 Floral induction**

The concrete ability of well-established strawberry plants to produce considerably early fruit yield depends on the intensity of the floral induction of its crowns' primordia at the earliest stage of development possible. Most of the strawberry cultivars used in Israel for early fruiting are of an ISD origin, which potentially provides floral induction once leaves are exposed to shortening photoperiods of 13 h and below. Nevertheless, temperature is a dominant and not less important determinant of floral induction. High temperatures usually support vegetative vigor in the expense of initial reproductive processes, and *vice versa*. Low temperature, and particularly low night temperature, seem to have a crucial significance promoting the onset of flowering and, furthermore, on the subsequent floral induction of the auxiliary crowns, thus enabling a continuous bloom and fruit production during winter [12].

The response of strawberry cultivars to chilling conditions was extensively studied and significant progress has been made in elucidating the genetic factors and molecular mechanisms underlying its complex flowering responses (for a review see, [13]. However, most of the experiments in Israel that examined the effects of stable low temperature treatment were implemented in cold rooms and failed to produce consistent results. Presumably, the physiological impacts of the circadian rhythm of light and temperature, including seasonal effects on this regime, may be more important than the absolute temperatures alone [14–16]. Light must be adequately supplied during the chilling treatment to avoid carbon deficiency and etiolation. The circadian temperature rhythm is required to support sufficient carbon assimilation during the day under relatively high temperature, as well as its translocation and allocation during the lower night temperature. In Israel, where the autumn nights are cool while the days are still warm enough, both floral induction and carbon supply are favored. Consequently, arid locations at relatively high altitudes are advantageous for the production and establishment of daughter plants, since the cooler nights enhance floral induction and earlier fruit production.

Nevertheless, among the ISD cultivars, the relationships between floral induction and the temperature regime during the seedling establishment phase is yet obscure, due to two major reasons: (1) the substantially fluctuating temperature regime during September–October in Israel; and (2) the rapid rotation of commercial strawberry cultivars. Unequivocally, gaining a precise insight into a cultivar's response to temperature would require 2–3 years of investigation under phytotron conditions that provide various predetermined temperature and photoperiod combinations. In the absence of this kind of research, we conducted a meta-analysis of the early marketable

**Figure 3.**

*Meta-analyses of the relationships between early yield (during November–December) and the ambient cumulative time under cool (hours below 20°C; A) or warm (hours above 32°C; B) during seedlings establishment in August–September of the corresponding years (2013–2021, Ramat Negev).*

yield (November–December) of six commercial cultivars *vs*. the cumulative time under warm (hours above 32°C) or under cool (hours below 20°C) during plug plants establishment (August–September) in the corresponding years (**Figure 3**).

We assumed that greater cumulative cool hours would promote higher early yields, and that the accumulation of warm hours would delay fruit production. Although the expected response to cool temperature could be noticed, it substantially differed between cultivars (**Figure 3A**); only two cultivars (Tamir and 6050) exhibited a significant response, three cultivars responded positively but mildly, whereas one cultivar (Daniel) displayed a clear opposite response. The expected negative response of the early yields to cumulative high temperatures was visible only for Tamir and Rocky, but cultivars Aya1, 6048, and 6050 were unaffected, while 'Daniel', again, exhibited a clear positive response (**Figure 3B**). This rough analysis indicates an extensive variability in the sensitivity or responsiveness of the floral induction to temperature among the Israeli ISD cultivars. Further research is required in order to provide better matching of cultivars to specific climatic conditions.
