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S. Alan Walters

Honey bees (Apis mellifera L.) are important pollinators of triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]. Pistillate (or female) watermelon flowers require multiple honey bee or other wild bee visitations after visiting staminate (or male) flowers for fruit set, and pollination is even more of a concern in triploid watermelon production since staminate flowers contain mostly nonviable pollen. Six honey bee visitation treatments—1) no visitation control, 2) two visits, 3) four visits, 4) eight visits, 5) 16 visits, and 6) open-pollinated control—were evaluated to determine the effectiveness of honey bee pollination on `Millionaire' triploid watermelon fruit set, yield, and quality utilizing `Crimson Sweet' at a 33% pollenizer frequency. `Millionaire' quality characters (hollow heart disorder or percent soluble solids) did not differ (P > 0.05) between honey bee pollination treatments. The open-pollinated control provided the highest fruit set rate (80%) and the greatest triploid watermelon numbers and weights per plot compared to all other honey bee visitation treatments. Fruit set, and fruit numbers and weights per plot increased linearly as number of honey bee visits to pistillate flowers increased from 0 (no visit control) to the open-pollinated control (about 24 visits). This study indicated that between 16 and 24 honey bee visits are required to achieve maximum triploid watermelon fruit set and yields at a 33% pollenizer frequency, which is twice the number of honey bee visits required by seeded watermelons to achieve similar results. This is probably due to many honey bees visiting staminate triploid watermelon flowers (that are in close proximity) before visiting pistillate flowers thus providing mostly nonviable pollen that is useless for fruit set and development. Therefore, more honey bee visits to pistillate triploid watermelon flowers would be required to achieve maximum fruit set and subsequent development compared to seeded watermelons.

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Joseph H. Connell

California almonds [Prunus dulcis, (Mill.) D.A. Webb, syn. Prunus amygdalus Batsch] are self-incompatible requiring cross-pollination to produce a commercial crop. Within seven known pollen groups, they also display cross-incompatibility. Coincidence of bloom between compatible cultivars is essential for cross-pollination. Since almonds are pollinated primarily by honeybees [Apis mellifera L.], arranging pollinizers in close proximity to one another promotes maximum pollen transfer. Almonds are frequently subject to inclement weather during their February bloom period. Strong honeybee colonies are better able to forage during marginal weather conditions than are weak colonies. Honeybee management can encourage pollen foraging and placement of colonies can affect flight activity and ultimately nut-set. Weather permitting vigorous honeybee flight activity is the most important factor for setting a good crop. Temperature also affects anther dehiscence, pollen germination, and pollen tube growth. The sooner an almond flower is cross-pollinated after opening, the greater the chance of fertilization and nut-set. Optimizing all of these pollination factors is therefore essential to achieve maximum production in almond orchards.

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E. Ortega, J. Egea, and F. Dicenta

In almond [Prunus dulcis (Mill.) D.A. Webb], a high flower density and fruit set rate is important, because yield increases with higher fruit set ratio. Furthermore, because the ovule of some cultivars mature at anthesis, rapid pollination and pollen tube growth along the style are essential to ensure fertilization of a viable ovule. In this work, we studied the effective pollination period (EPP) of four almond cultivars of different bloom time by studying pollen tube growth and fruit set. EPP in almond was longer than in other fruit trees, and its duration was determined by stigma receptivity, which decreased with high temperature. An acceptable fruit set for all cultivars was obtained following pollination from day 0 to day 4 after emasculation.

Open access

Olivia M. Smith, Beverly Gerdeman, Matthew Arrington, Hollis Spitler, and Lisa Wasko DeVetter

total national production and was valued at $287.5 million ( U.S. Department of Agriculture, National Agricultural Statistics Service, 2020 ). Despite the industry’s success, improving pollination and fruit set is a shared goal among growers in the PNW

Open access

Marlee A. Trandel, Penelope Perkins-Veazie, and Jonathan Schultheis

placental tissue, causing hollowing or a cavity to develop in the flesh ( Johnson, 2014 , 2015 ; Kano, 1993 ). Inadequate pollination is thought to be one of the leading causes of HH in watermelon and is generally worse in triploid (seedless) watermelons

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Serge Gudin and Laurence Aréne

Flowers of two cultivars of Rosa hybrida were treated or not with putrescine before being pollinated from 2 to 8 days after anther emasculation. On both cultivars the 10-3 M putrescine treatment extended the effective pollination period, as shown by the best hip formation rates and mean number of seeds per hip. On one cultivar, the 10-5 M putrescine treatment increased fertilization efficiency (more hips obtained). The effect of putrescine was proportionally more important on the cultivar characterized by the highest stigmatic exudate pH. Putrescine also influenced in vitro pollen germination by increasing the length of emitted pollen tubes (10-3 and 10-5 M-putrescine) and the quantity of germinated pollen grains (10-5 M putrescine).

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Michael S. Stanghellini, John T. Ambrose, and Jonathan R. Schultheis

The effectiveness of bumblebees, Bombus impatiens, and honeybees, Apis mellifera, on the pollination of cucumber, Cucumis sativus, was compared at the individual bee level. A correlation between the number of bee visits a flower received and the resultant seed set was established. In both cucumber varieties, `Calypso' and `Dasher II', B. impatiens-visited flowers consistently had higher seed sets than A. mellifera when compared at equal visit numbers. This difference between bee types was found to be highly significant.

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Corey J. Andrikopoulos and James H. Cane

Cultivated red raspberry ( Rubus idaeus L.) is one of the numerous specialty crops dependent upon bees for fruit production ( Klein et al., 2007 ). Although predominantly self-fertile ( Daubeny, 1971 ), raspberry flowers only partially self-pollinate

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Patricio A. Brevis* and D. Scott NeSmith

Rabbiteye blueberries (Vaccinium ashei Reade) often exhibit poor fruit set under commercial field conditions. Problems of low fruit set have been attributed to short periods of flower receptivity in different fruit crops. This study seeks to establish the effective pollination period (EPP, defined as the number of days during which pollination is effective to produce a fruit) in rabbiteye blueberry. The cultivars Brightwell and Tifblue were chosen due to their known difference in fruit set and field performance. Flowers were hand pollinated 0, 2, 4, 6, and 8 days after anthesis (DAA) using self- and cross-pollen. Fruit set, seeds per berry, berry weight and days to ripening were recorded. Fruit set showed a polynomial trend across flower ages. `Brightwell' was highly receptive from the day of anthesis, whereas, `Tifblue' receptivity was low until 2 DAA. `Brightwell' and `Tifblue' flowers produced adequate fruit set (≥50%) over a period of 7 and 5 days, respectively. In `Tifblue', fruit set was limited by the low receptivity of newly opened flowers. The difference in EPP helps to explain the performance of these cultivars in the field. The rate of ripening increased with flower age in both cultivars. The number of seeds per berry was affected by flower age only in `Tifblue'. The effect of flower age on berry weight depended on the cultivar and the pollen source.

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María Engracia Guerra, Ana Wünsch, Margarita López-Corrales, and Javier Rodrigo

controlled pollination is required to avoid the interference of undesired pollen ( Hedhly et al., 2009 ). For fruit breeding purposes, flower emasculation is used to carry out controlled pollinations when the female parent is self-fruitful to avoid self-pollination