**2. Varieties**

The modern strawberry, *Fragaria* x *ananassa*, was first found in the 1760s in Versailles gardens, France, via a cross of *Fragaria virginiana* from eastern North America and *Fragaria chiloensis*, which was brought from Chile [1]. Typically to species originated in temperate climate regions, temperature and photoperiod are the most important environmental factors that regulate the transition from vegetative to floral growth in strawberries [2]. Under temperate climate conditions, strawberry plants usually enter a vegetative phase and develop runners during the warmer and longer summer days. With the decreasing temperature and day length during autumn, flower initiation and dormancy are simultaneously induced in the young developing crowns [3, 4]. These young crowns, called daughter plants, are rooted and planted towards spring, develop a foliar canopy and realize their reproductive potential during early summer (June-yielding types). Nevertheless, the modern strawberry harbors substantially broad genetic diversity, including a wide sensitivity ranges to photoperiod or temperature [4–7]. Moreover, individual plants may possess significant plasticity in response to combinations of temperature and photoperiod.

To obtain significant early fruiting, two prerequisites must be fulfilled: early and extensive reproductive induction; and, avoided bud dormancy. The first has been met by breeding within the SD strawberry types. This way, young crowns that are detached from the mother plant on the end of August, when the declining photoperiod is still long (13 h), will continuously exhibit floral induction throughout the young plant establishment from August to October. Bud dormancy in many strawberry cultivars is facultative or considered a quantitative trait; hence, avoiding the conditional dormancy could be gained by breeding, by which genotypes that yield continuously for 7 months from November to May are selected.

Four decades ago, a few Californian varieties, mostly 'Fresno', 'Tioga', 'Douglas' and 'Tuft', the harvest of which began in late January, dominated the Israeli market. The breakthrough in obtaining earlier fruiting was accomplished through the establishment of a local (ARO, Israel) breeding program led by Izsak and Izhar [8], in which day neutral (DN) types were hybridized with SD strawberry types, resulted in the release of the first Israeli cultivars 'Nurit' and 'Rachel' in 1977, and during the 1990s—the commercial cultivars 'Tamar', 'Hadas', 'Yael' and 'Malach'. All these are very early cropping cultivars patented as infra short-day (ISD) strawberry types [9]. Unlike the Californian short-day types, the Israeli varieties are less sensitive to temperature and can initiate their reproductive phase under the relatively warm and long-day conditions prevailing in Israel during August and September.

Over the last two decades, the ARO breeding program has been renewed in an attempt to enhance the already high commercial value of the previously developed local varieties [10]. The ARO's in-house germplasm collection has been restored and its genetic base extended with new cultivars from different sources. As a part of this program, approximately 60 specific crosses have been carried out every year, resulting in 6000–10,000 seedlings that have been screened each year under various commercial conditions. While early fruiting is indeed compulsory for strawberry breeding programs in Israel, many other traits are carefully overlooked in order to develop cultivars bearing premium quality fruits suited for local and European markets. These traits include: plants with open canopies and long fruit pedicels for easier harvest; attractive fruit appearance with a bright red color, medium to large size, and a conical or heart

shape; firm texture with extended shelf life; and, desired sweet/sour balance with excellent aromatic flavor. On top of these, tolerance to Powdery mildew (*Sphaerotheca macularis*) and anthracnose fruit rot (*Colletotrichum acutatum*), two major diseases affecting plant vigor and postharvest quality gains an increasing attention as a strategic means to overcome the challenge. Since there are no simple selectable markers for the resistance against these diseases, at least one resistant parent is always combined in the basic crosses, and clones with good field tolerance to those diseases are selected.

The attempts made by the ARO strawberry breeding programs, as well as simultaneous efforts made by the private sector, have yielded a growing number of qualified cultivars, all of which bearing early fruiting and desired quality trait (**Figure 2**). Among

### **Figure 2.**

*Representative cultivars released by the Israeli ARO strawberry breeding program for commercial use in the recent decade.*

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

cultivars released at about 2005, 'Tamir' was selected as a vigorous, early-ripening, and highly productive cultivar, with orange-red, large, pretty, and very sweet fruit. 'Tamir' also does very well in hanging, soil-less growing systems. 'Barak' has a medium growth habit and long fruit stalks, which make it easier to harvest. It also exhibits good resistance to powdery mildew and mites. Its fruits are uniform in size, medium, and have an attractive appearance, with a strong red color, excellent flavor and aroma, and extended shelf-life. 'Yasmin' is one of the earliest Israeli cultivars, the harvest of which can begin by mid-November. It has a moderate-sized canopy and continuous waves of flowering and fruiting. The fruits are large to medium-sized, bright red, juicy and sweet. Yasmin's sibling-cultivar Shani has a large, erect growth habit. It produces relatively high annual yields of firm, large, juicy fruit. The cultivars Gili, Matan and Rocky were released in 2015; these three are characterized by a medium-size canopy bearing firm, large, red, and sweet fruits with an extended shelf-life. In addition, Rocky displays good tolerance to powdery mildew and high and stable yields along the season.

The most recently released (2020) cultivars of the ARO breeding program are Tammuz and Lavi (**Figure 2**); both cultivars exhibit vigorous growth habits, long fruit pedicels, early fruiting (late-November to early-December), high yield, continuous and stable production course, and above all, highly attractive fruit appearance, sweetness (Brix 8.5-10) and rich flavor, firm texture, and long shelf life. In addition, private breeders released competitive commercial strawberry cultivars based on the same genetic origin, among which 'Aya1', 'Daniel', 'Peles', 'Shaked', and 'Rotemi' (Yosef's Farm, Israel), and 'Yuval', 'Orly', 'Noa' and '6050' (Fertiseeds Ltd., Israel) have been evaluated and are available for growers.

Along with the continuing challenge to enhance early yielding cultivars, several points require special attention. Most of the breeding programs, including at ARO, are carried out under the traditional low-tunnels cultivation rather than on the advanced hanging soilless culture technology (which will be discussed below). Certain cultivar traits may significantly differ fitting to either set of conditions. For instance, while a vigorous plant canopy is undesired in the traditional cultivation, as it decreases the access for pollinating insects, promotes foliar diseases and makes harvest less efficient, this trait is considered an advantage in the hung soilless system, the fruits and vegetative canopy of which are separated, as it leads to higher yields and to better fruit quality. Concurrently, early strawberry plants grown under greenhouse conditions are more exposed to powdery mildew infection and red spider mites, and hence, more resistant cultivars are preferred [11]. In addition, considerable year-to-year variations in the weather conditions, particularly during the critical autumn season, and the impatient strawberry industry, both prevent the desired adequate long-term evaluation of new cultivars. On the one hand, the rapid rotation among the leading cultivars makes it difficult to point to uniquely promising and stable ones. On the other hand, simultaneously growing several sound cultivars in a season appears a good strategy to deduct failures in the performance of one cultivar or another and accomplish an acceptable operation over a whole season.
