Breeding for increased yield in cucumber has been an important objective of many cucumber breeding programs since the 1900s (Staub et al., 2008). Yield of pickling cucumber has been improved by breeding for disease resistance, as well as through the use of improved cultural practices (Lower and Edwards, 1986; Peterson, 1975; Staub et al., 2008; Wehner, 1989). The increased yield of cucumber cultivars has also been achieved through improvements in gynoecious sex expression, improved fruit color (improved percentage of marketable fruit), and direct yield improvement (Wehner, 1989).
Although cucumber plants produce different sex phenotypes (Staub et al., 2008), the wild type is monoecious with staminate flowers appearing first, followed by pistillate flowers at later nodes. ‘NC-Sunshine’ is a monoecious, early maturing, and high yielding slicing hybrid with a high percentage of pistillate nodes. The plant has medium dwarf size vines with short hypocotyls and dark green leaves, and a dwarf-determinate plant type (Wehner, 2005). ‘NC-Sunshine’ is a F1 hybrid of NC-62 (dwarf-determinate, monoecious) × NC-63 (dwarf-determinate, monoecious). These inbreds were developed at North Carolina State University. The fruit of ‘NC-Sunshine’ have good fresh market quality and good keeping ability with very dark green fruit averaging 8 inches in length. ‘NC-Sunshine’ is resistant to anthracnose (Colletotrichum sp.), powdery mildew (Sphaerotheca fuliginea), and scab (Cladosporium cucumerinum).
The amount of pollen required for fruit set depends on the number of pistillate flowers produced by the cucumber cultivar. Generally, monoecious cucumber plants are planted in the field, and plants produce enough pollen for fruit set. Since ‘NC-Sunshine’ produces more pistillate flowers than regular monoecious cultivars, it might need more pollen for effective pollination and fruit set. An important aspect of the pollenizer is the ability to produce enough staminate flowers to pollinate the available pistillate flowers, and ≈12% to 15% monoecious pollenizers are used in the field to pollinate highly gynoecious cultivars. However in comparison, ≈25% to 33% of pollenizer is planted to ensure adequate pollen supply for triploid watermelon (Citrullus lanatus) production (Fiacchino and Walters, 2003; Walters, 2005). Therefore, it is important to determine if planting a pollenizer in the field will significantly increase yield of ‘NC-Sunshine’.
Cucumber is an allogamous crop that requires frequent pollinators (bees) visit to carry pollen for fertilization. Honeybees (Apis mellifera) and bumblebees (Bombus terrestris) are the main pollinators in cucumbers (Gajc-Wolska et al., 2011). The absence of sufficient pollinators can result in low fruit set and reduced fruit size (Walters and Taylor, 2006). Moreover, pistillate flowers require multiple bee visitations after visiting male flowers (Stanghellini et al., 1997, 1998). In triploid seedless watermelon, 16 to 24 honeybee visits are required to achieve maximum fruit set at a 33% pollenizer frequency (Walters, 2005).
Climatic factors have also been reported to influence pollen flow (Gingras et al., 1999; Whitakar and Bohn, 1952). Wind velocity, temperature, and other environmental factors may influence honeybee behavior thereby affecting pollination; and unfavorable environmental conditions such as extreme temperature, moisture stress, and low irradiance can result in flower abortion and low fruit set (Kalbarczyk, 2009). Wehner and Jenkins (1985) reported that the mean rate of natural outcrossing varied from 23% to 77% across three locations in cucumber families. Therefore, it is imperative to study the effect of pollenizers in different environmental conditions (locations) and the interaction of pollenizer with location.
‘NC-Sunshine’ was planted in field plots with ‘Poinsett 76’ as the pollenizer and ‘Gray Zucchini’ squash as the control. ‘Poinsett 76’ is a monoecious slicing cucumber type with excellent color and is resistant to downy mildew (Pseudoperonospora cubensis), powdery mildew, anthracnose, and angular leaf spot (Pseudomonas syringae pv. lachrymans). ‘Gray Zucchini’ is an early maturing squash with a bushy habit similar to ‘NC-Sunshine’ and also has long, straight fruit. The objective of this study is to evaluate the effect of the pollenizer ‘Poinsett 76’ on fruit set and yield of ‘NC-Sunshine’ cucumber.
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