Biology
AgriculturalAndFoodSciences,1970-2015-Agricultural And Food Sciences-2014.jsonl.gz.gz
Agricultural And Food Sciences
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Flowering Patterns of Pollenizer and Triploid Watermelon Cultivars

The past 10 years has seen a steep increase in production of seedless watermelon (Citrullus lanatus) in the United States. Seedless fruit is produced on triploid plants that require pollination from diploid pollenizers for fruit set. Synchronization of the staminate flowers on the pollenizers with the appearance of pistillate flowers on the triploids is a fundamental requirement for this production system. Previous research suggested that pistillate flowers reach peak production early in the season, but data are only available for a small number of triploid cultivars. We compared the flowering patterns of 29 triploid cultivars and 20 pollenizers, including 10 harvested pollenizers, during the first 6 weeks after transplanting over 2 years. The average number of days from transplanting (DAT) to the first staminate flower was between 5.3 days and 19.1 days in 2012 and 9.7 days and 24.4 days in 2013 for the pollenizers and between 18.7 days and 27.6 days and 22.1 days and 32.7 days for the pistillate triploid flowers in the 2 years, respectively. K-means clustering of the weekly percentage of plants with staminate and pistillate flowers for the different cultivars shows that different triploid and pollenizer cultivars have different flowering patterns and that some combinations have better synchronized flowering than others. Growers should take particular care when choosing pollenizers for early-flowering triploid cultivars. Harvested pollenizers are better suited to late-flowering triploids and growers should choose triploid and pollenizer cultivar combinations with flowering patterns that best satisfy their specific production goals. Watermelon (Citrullus lanatus) production acreage in the United States in 2010 was 132,600 acres with a value of $500 million. The percentage of watermelon production devoted to seedless fruit has increased dramatically from 51% in 2003 to 85% in 2009 (U.S. Department of Agriculture, 2011). The seedless fruit is produced on triploid plants, but because pollination and fertilization are required for fruit set, and these plants produce negligible amounts of viable pollen, diploid pollen sources (pollenizers) are required (Boyhan et al., 2000; Maynard, 1992; Maynard and Elmstrom, 1992). Growers interplant the triploid cultivars and diploid pollenizers in the production field and are then dependent on the pollenizers producing staminate flowers on the same days the triploids produce pistillate flowers. The system is complicated by the monoecious nature of watermelon with cultivars producing approximately one pistillate flower for every seven staminate flowers (Wehner, 2008). If a pistillate flower is not pollinated on the day it opens, it will abort and it may take days before the next pistillate flower opens, leading to delayed fruit set. Growers use either elite seeded cultivars as pollenizers (harvested pollenizers) or specialized non-harvested pollenizers developed specifically for this purpose. These specialized pollenizers are usually compact plants (so as not to compete with triploids), producing small inedible fruit with a rind pattern that can easily be distinguished from the triploid during harvesting. The choice of using edible or specialized pollenizers depends on whether the grower has a market for the seeded varieties. The choice of pollenizer affects yield (Dittmar et al., 2010; Fiacchino and Walters, 2002). There are several traits that are considered desirable for pollenizers such as compact growth habit (Freeman et al., 2007b) and flower attractiveness to pollinators (Freeman and Olson, 2007b). However, the most basic requirement is synchronized flowering patterns between the pollenizer cultivar and triploid cultivar (Dittmar et al., 2009, 2010). The goal is for the pollenizer to have plentiful staminate flowers at the time the triploid plant produces pistillate flowers, simulating the flowering pattern of a single plant on two different plants. The choice of pollenizer–triploid combination is critical for timely production (Dittmar et al., 2010; Freeman et al., 2007a; Maynard and Elmstrom, 1992). Dittmar et al. (2009) compared flowering patterns of two triploids and 13 pollenizers by collecting data for the number of pistillate and staminate flowers from 4 to 9 weeks after transplanting and found that peak performance of pistillate flowers was often in Week 5 or 6, which was earlier than the peak production of staminate flowers for the pollenizers. In 2005 one of the triploid cultivars, Tri-X-313, already had a large number of pistillate flowers when the study started. If this is a common phenomenon, it could mean less than optimal amounts of pollen are available for early-flowering triploids. The aim of the current study was to compare the flowering patterns of a large number of popular pollenizer and triploid cultivars early in the season to determine which triploid cultivars and pollenizers have complementary flowering patterns. Materials and Methods Plant material. In 2012, 17 pollenizers and 17 triploid cultivars were included and in 2013, 29 triploid and 20 pollenizer cultivars were included in this study (Table 1). In both years, 10 of the pollenizers were non-harvested pollenizers. Seeds were sown in seedling trays in the greenhouse on 23 Apr. 2012 and 29 Apr. 2013, and plants were hand-transplanted in the field at the Durham Horticulture Farm (Watkinsville, GA; sandy loam soil) on 21 May 2012 and 23 May 2013 after hardening off for 1 week. One plant per cultivar was planted per block in a completely randomized block design with 10 blocks. Plants were grown according to University of Georgia Cooperative Extension Service recommendations on plastic mulch with between-row spacing of 1.83 m and in-row spacing of 0.9 m. In both years, one-third of the total fertilizer for the 6-week study duration (100.8N–44P– 83.7K kg·ha) was applied pre-plant and the rest using weekly fertigation. Drip tape was used for irrigation in both years. Four applications of chlorothalonil (1.9 L·ha a.i.) were applied over the 6-week period, starting the second week after transplanting. Fields were scouted for insects and Asana XL (0.63 L·ha) or Brigade 2EC (0.45 L·ha) was applied to control squash bugs and cucumber beetles as needed. Weeds were controlled early in the season by one application of glyphosate (18.6 mL·L a.i.) in the row middles and handweeding during the rest of the season. In 2012, the vines were turned once a week to make data collection easier. In 2013 high rainfall prevented turning the vines before data collection. Data collection. Data were collected three times a week, for six weeks after transplanting, except for the first week when data were collected twice. For all pollenizers, data were collected on the number of open staminate flowers on that particular day for each plant, whereas the presence of open pistillate flowers was recorded for triploids and harvested pollenizers. Any hermaphroditic flowers were scored as pistillate flowers. Statistical analysis. The number of days from transplanting to the first open flower and number of staminate flowers per flowering plant were analyzed using JMP Pro Version 10.0.1 (SAS Institute, Cary, NC). Analysis of variance was used to determine the significance of the cultivar and year main effects and their interactions. Tukey’s honestly Received for publication 8 Jan. 2014. Accepted for publication 7 Apr. 2014. We thank Jeremy Ray, Allen Ray, and Dusty Martin for their contributions to this research as well as Bayer, Harris Moran Seed Company, Hazera Genetics, Monsanto Vegetable Seeds, Sakata, and Syngenta Seeds Inc. for supplying seed for this study. To whom reprint requests should be addressed; e-mail cmcgre1@uga.edu. 714 HORTSCIENCE VOL. 49(6) JUNE 2014 significant difference test was used to separate the least square means of significant effects. K-means clustering of the weekly percentage of flowering plants for each cultivar was carried out using Euclidian distance with Cluster, Version 3.0 (de Hoon et al., 2004; Eisen et al., 1998). To determine the number of clusters, the sum of squared error was plotted for a number of cluster solutions in R (R Core Team, 2013) and the ‘‘elbow’’ point in the plot was used as a starting point. Flowering profiles and average cluster profiles for different numbers of clusters was then visually investigated for uniformity. Results and Discussion Data were collected 17 times during the 6-week period after transplanting in both years. In the first week, data were collected only two times and for all following weeks, data were collected three times a week. The only exception was in 2012 when data were collected twice in Week 3 and four times in Week 4. To determine synchronized flowering patterns, we examined three traits for each cultivar: 1) the number of days from transplanting to the first staminate and/or pistillate flower; 2) the percentage of plants with staminate and/or pistillate flowers; and 3) the number of staminate flowers per flowering plant for pollenizers. There was a significant year effect for the traits (data not shown) and therefore data are presented separately for the 2 years. The average number of DAT for the first staminate flower was between 5.3 d (‘Ace’) and 19.1 d (‘Jenny’) in 2012 and 9.7 d (‘Ace’ and ‘Minipol’) and 24.4 d (‘SP 6’) in 2013 (Table 2). For appearance of the first pistillate flower on triploids, the number of days to first flower was between 18.7 d (‘Bold Ruler’) and 27.6 d (‘Fascination’) in 2012 and 22.1 d (‘Serval’) and 32.7 d (‘SuperSeedless 7197’) in 2013 (Table 3). For several cultivars, the number of plants used for analysis was less than 10 (Tables 2 and 3). There were several reasons for this, including poor germination (‘Bold Ruler’, 2012), crows pulling out seedlings (2012), deer damage (2013), and flooding (2013). In some cases, plants were lost after data collection for the first staminate flower was completed, but not for the first pistillate flower, leading to different numbers of plants used for the two data sets (Tables 2 and 3). Pistillate flowering data were also collected for harvested pollenizers to compare natural flowering patterns on diploids. Table 1. The triploid and pollenizer watermelon cultivars used in this study. Cultivar Company Description Flower data collected Staminate Pistillate Accomplice Harris Moran Seed Company Non-harvested pollenizer X Ace Sakata Non-harvested pollenizer X ACR 10319DP Bayer Non-harvested pollenizer X Affirmed Sakata Triploid X AU Producer Hollar Harvested pollenizer X X Bold Ruler Sakata Triploid X Citation Sakata Triploid X Crimson Sweet Seedway Harvested pollenizer X X Crunchy Red Harris Moran Seed Company Triploid X Declaration Bayer Triploid X Exclamation Syngenta Triploid X Extazy Hazera Genetics Triploid X Fascination Syngenta Triploid X Gladiator Bayer Non-harvested pollenizer X Imagination Syngenta Seeds, Inc. Triploid X Jenny Bayer Non-harvested pollenizer X Leopard Hazera Genetics Triploid X Liberty Bayer Triploid X Majestic Monsanto Vegetable Seeds Triploid X Melody Syngenta Seeds, Inc. Triploid X Mickylee Hollar Harvested pollenizer X X Minipol Hazera Genetics Non-harvested pollenizer X Nun01007 Bayer Triploid X Nun01009 Bayer Triploid X Polimax Bayer Non-harvested pollenizer X Pollen Pro Syngenta Seeds, Inc. Non-harvested pollenizer X Revolution Bayer Triploid X Serval Hazera Genetics Triploid X Side Kick Seed Company Non-harvested pollenizer X SP-5 Syngenta Seeds, Inc. Non-harvested pollenizer X SP-6 Syngenta Seeds, Inc. Non-harvested pollenizer X SSX8585 Sakata Harvested pollenizer X X Starbrite Monsanto Vegetable Seeds Harvested pollenizer X X StarGazer Monsanto Vegetable Seeds Harvested pollenizer X X Sugar Coat Syngenta Seeds, Inc. Triploid X Sugar Heart Syngenta Seeds, Inc. Triploid X Summer Flavor 720 Bayer Harvested pollenizer X X Summer Flavor 790HQ Bayer Harvested pollenizer X X Summer Flavor 800 Bayer Harvested pollenizer X X Summer Sweet 5244 Bayer Triploid X SuperSeedless 6177 Plus Bayer Triploid X SuperSeedless 7197 HQ Bayer Triploid X SuperSeedless 9651 HQ Bayer Triploid X SuperSeedless 7167 Bayer Triploid X SuperSeedless 7187HQ Bayer Triploid X Sweet Gem Syngenta Seeds, Inc. Triploid X SWT7829 Sakata Triploid X Traveler Harris Moran Seed Company Triploid X Troubadour Harris Moran Seed Company Triploid X WT2527 Monsanto Vegetable Seeds Harvested pollenizer X X HORTSCIENCE VOL. 49(6) JUNE 2014 715 CROP PRODUCTION

Abstract. The past 10 years has seen a steep increase in production of seedless watermelon (Citrullus lanatus) in the United States. Seedless fruit is produced on triploid plants that require pollination from diploid pollenizers for fruit set. Synchronization of the staminate flowers on the pollenizers with the appearance of pistillate flowers on the triploids is a fundamental requirement for this production system. Previous research suggested that pistillate flowers reach peak production early in the season, but data are only available for a small number of triploid cultivars. We compared the flowering patterns of 29 triploid cultivars and 20 pollenizers, including 10 harvested pollenizers, during the first 6 weeks after transplanting over 2 years. The average number of days from transplanting (DAT) to the first staminate flower was between 5.3 days and 19.1 days in 2012 and 9.7 days and 24.4 days in 2013 for the pollenizers and between 18.7 days and 27.6 days and 22.1 days and 32.7 days for the pistillate triploid flowers in the 2 years, respectively. K-means clustering of the weekly percentage of plants with staminate and pistillate flowers for the different cultivars shows that different triploid and pollenizer cultivars have different flowering patterns and that some combinations have better synchronized flowering than others. Growers should take particular care when choosing pollenizers for early-flowering triploid cultivars. Harvested pollenizers are better suited to late-flowering triploids and growers should choose triploid and pollenizer cultivar combinations with flowering patterns that best satisfy their specific production goals.
Watermelon (Citrullus lanatus) production acreage in the United States in 2010 was 132,600 acres with a value of $500 million. The percentage of watermelon production devoted to seedless fruit has increased dramatically from 51% in 2003 to 85% in 2009 (U.S. Department of Agriculture, 2011). The seedless fruit is produced on triploid plants, but because pollination and fertilization are required for fruit set, and these plants produce negligible amounts of viable pollen, diploid pollen sources (pollenizers) are required (Boyhan et al., 2000;Maynard, 1992;Maynard and Elmstrom, 1992).
Growers interplant the triploid cultivars and diploid pollenizers in the production field and are then dependent on the pollenizers producing staminate flowers on the same days the triploids produce pistillate flowers. The system is complicated by the monoecious nature of watermelon with cultivars producing approximately one pistillate flower for every seven staminate flowers (Wehner, 2008). If a pistillate flower is not pollinated on the day it opens, it will abort and it may take days before the next pistillate flower opens, leading to delayed fruit set.
Growers use either elite seeded cultivars as pollenizers (harvested pollenizers) or specialized non-harvested pollenizers developed specifically for this purpose. These specialized pollenizers are usually compact plants (so as not to compete with triploids), producing small inedible fruit with a rind pattern that can easily be distinguished from the triploid during harvesting. The choice of using edible or specialized pollenizers depends on whether the grower has a market for the seeded varieties. The choice of pollenizer affects yield (Dittmar et al., 2010;Fiacchino and Walters, 2002). There are several traits that are considered desirable for pollenizers such as compact growth habit  and flower attractiveness to pollinators . However, the most basic requirement is synchronized flowering patterns between the pollenizer cultivar and triploid cultivar (Dittmar et al., 2009(Dittmar et al., , 2010. The goal is for the pollenizer to have plentiful staminate flowers at the time the triploid plant produces pistillate flowers, simulating the flowering pattern of a single plant on two different plants. The choice of pollenizer-triploid combination is critical for timely production (Dittmar et al., 2010;Maynard and Elmstrom, 1992). Dittmar et al. (2009) compared flowering patterns of two triploids and 13 pollenizers by collecting data for the number of pistillate and staminate flowers from 4 to 9 weeks after transplanting and found that peak performance of pistillate flowers was often in Week 5 or 6, which was earlier than the peak production of staminate flowers for the pollenizers. In 2005 one of the triploid cultivars, Tri-X-313, already had a large number of pistillate flowers when the study started. If this is a common phenomenon, it could mean less than optimal amounts of pollen are available for early-flowering triploids.
The aim of the current study was to compare the flowering patterns of a large number of popular pollenizer and triploid cultivars early in the season to determine which triploid cultivars and pollenizers have complementary flowering patterns.

Materials and Methods
Plant material. In 2012, 17 pollenizers and 17 triploid cultivars were included and in 2013, 29 triploid and 20 pollenizer cultivars were included in this study (Table 1). In both years, 10 of the pollenizers were non-harvested pollenizers. Seeds were sown in seedling trays in the greenhouse on 23 Apr. 2012 and 29 Apr. 2013, and plants were hand-transplanted in the field at the Durham Horticulture Farm (Watkinsville, GA; sandy loam soil) on 21 May 2012 and 23 May 2013 after hardening off for 1 week. One plant per cultivar was planted per block in a completely randomized block design with 10 blocks. Plants were grown according to University of Georgia Cooperative Extension Service recommendations on plastic mulch with between-row spacing of 1.83 m and in-row spacing of 0.9 m. In both years, one-third of the total fertilizer for the 6-week study duration (100.8N-44P-83.7K kg · ha -1 ) was applied pre-plant and the rest using weekly fertigation. Drip tape was used for irrigation in both years. Four applications of chlorothalonil (1.9 L · ha -1 a.i.) were applied over the 6-week period, starting the second week after transplanting. Fields were scouted for insects and Asana XL (0.63 L · ha -1 ) or Brigade 2EC (0.45 L · ha -1 ) was applied to control squash bugs and cucumber beetles as needed. Weeds were controlled early in the season by one application of glyphosate (18.6 mL · L -1 a.i.) in the row middles and handweeding during the rest of the season.
In 2012, the vines were turned once a week to make data collection easier. In 2013 high rainfall prevented turning the vines before data collection.
Data collection. Data were collected three times a week, for six weeks after transplanting, except for the first week when data were To whom reprint requests should be addressed; e-mail cmcgre1@uga.edu. significant difference test was used to separate the least square means of significant effects.
K-means clustering of the weekly percentage of flowering plants for each cultivar was carried out using Euclidian distance with Cluster, Version 3.0 (de Hoon et al., 2004;Eisen et al., 1998). To determine the number of clusters, the sum of squared error was plotted for a number of cluster solutions in R (R Core Team, 2013) and the ''elbow'' point in the plot was used as a starting point. Flowering profiles and average cluster profiles for different numbers of clusters was then visually investigated for uniformity.

Results and Discussion
Data were collected 17 times during the 6-week period after transplanting in both years.
In the first week, data were collected only two times and for all following weeks, data were collected three times a week. The only exception was in 2012 when data were collected twice in Week 3 and four times in Week 4.
To determine synchronized flowering patterns, we examined three traits for each cultivar: 1) the number of days from transplanting to the first staminate and/or pistillate flower; 2) the percentage of plants with staminate and/or pistillate flowers; and 3) the number of staminate flowers per flowering plant for pollenizers. There was a significant year effect for the traits (data not shown) and therefore data are presented separately for the 2 years.
The average number of DAT for the first staminate flower was between 5.3 d ('Ace') and 19.1 d ('Jenny') in 2012 and 9.7 d ('Ace' and 'Minipol') and 24.4 d ('SP 6') in 2013 (Table 2). For appearance of the first pistillate flower on triploids, the number of days to first flower was between 18.7 d ('Bold Ruler') and 27.6 d ('Fascination') in 2012 and 22.1 d ('Serval') and 32.7 d ('SuperSeedless 7197') in 2013 (Table 3). For several cultivars, the number of plants used for analysis was less than 10 (Tables 2 and 3). There were several reasons for this, including poor germination ('Bold Ruler', 2012), crows pulling out seedlings (2012), deer damage (2013), and flooding (2013). In some cases, plants were lost after data collection for the first staminate flower was completed, but not for the first pistillate flower, leading to different numbers of plants used for the two data sets (Tables 2  and 3). Pistillate flowering data were also collected for harvested pollenizers to compare natural flowering patterns on diploids.  (Tables 2 and 3).
Harvested pollenizers generally tended to flower later than non-harvested pollenizers with 'Mickylee' being the notable exception. Flowers appeared significantly later in 2013 than 2012 (pistillate 4.81 d later; staminate 4.6 d later). There are many possible reasons for the delay in flowering in 2013, but the most obvious is the very high rainfall during the experimental period in 2013 (100 mm) compared with 2012 (350 mm) (Fig. 1).
In an effort to condense the data for the percentage of flowering plants for each cultivar into a form that is easier to interpret, we converted the daily data into weekly data (percentage of plants that flowered during a particular week for each cultivar). K-means clustering was then used to group cultivars with similar flowering patterns together Week 2 to 4 in 2013. It is possible that these cultivars were more severely affected by the heavy rains during this period (Fig. 1) than the other cultivars. Together with the data from Dittmar et al. (2010) that showed decreased triploid yields when 'Summer Flavor 800' was used as a pollenizer, it suggests that this cultivar is probably not the optimum choice for pollenizer and should only be used when advantage can be taken of the diploid fruit it produces through a reliable market for seeded fruit (Dittmar et al., 2010).
Pistillate flowering percentages increased later in the season, reached its highest values at Weeks 4 and 5, and then declined. Flowering was later in 2013 and was still increasing at the end of the study period for cultivars in cluster 2013I (Fig. 3). To simplify the comparison of triploid and pollenizer flowering patterns, we plotted the averages for the individual clusters (Figs. 2 and 3) for staminate and pistillate flowers together (2012, Fig. 4A, and 2013, Fig. 4B). In both years flowering patterns show that most of the pollenizers reach high percentages of flowering well before the pistillate triploids and would make appropriate pollenizers. However, for clusters 2012E (Figs. 2E and 4A)  Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 In an effort to evaluate the validity of recommendations made using this clustering methodology, we compared the staminate and pistillate flowering patterns of harvested pollenizers. If our interpretation is correct, we would expect harvested pollenizers with staminate flowers in cluster 2012D (Figs. 2D and 4A) to have staminate flowers in cluster 2012F (Fig. 2F), 2012G (Fig. 2G), or 2012H (Fig. 2H) (not group 2012E; Fig. 2E). Likewise, we would expect harvested pollenizers with staminate flowers in cluster 2013D (Fig. 3D) to have staminate flowers in clusters 2013G (Fig. 3G), 2013H (Fig. 3H), or 2013I (Fig. 3I) (not 2013E or 2013F;Figs. 3D and 3F). Based on the clustering methodology for percentage of flowering plants, the following are early triploids cultivars where caution should be taken when choosing a pollenizer: Affirmed, Bold Ruler, Citation, Extazy, Imagination, Liberty, Melody, Serval, Summer Sweet 5244, Sweet Gem, and Troubadour. Appropriate pollenizers for early (2012E and2013E;Figs. 2E and 3E) triploids are those that are clustered in 2012A ( Fig. 2A), 2012B (Fig.  2B), or 2012C (Fig. 2C) and 2013A (Fig. 3A) or 2013B (Fig. 3B)   might also be appropriate, but data were only available for 1 year for these two cultivars.
In addition to the percentage of flowering plants, we also calculated the average number of staminate flowers per flowering plant for each cultivar (Table 4) (Dittmar et al., 2009;, although a lower absolute number of flowers was observed in the current study. The data for the number of pistillate flowers are not shown. Because the vast majority of plants usually have only one or two pistillate flowers at a time, these data add little to what is already reflected by the percentage of flowering plants. The current study focused on early flowering and specifically aims to make recommendations for synchronization of pollenizer flowering patterns with the peak period of triploid pistillate flowering. However, growers may want to extend the length of the harvesting window and that would require pollenizer cultivars that flower consistently for a long period of time (Dittmar et al., 2009;Maynard and Elmstrom, 1992). At the end of our study at Week 6, most of the pollenizer plants were still flowering at a high level and other studies have shown that the number of flowers per plant is still increasing at this stage (Dittmar et al., 2009;. Although we cannot make any recommendation that goes beyond the duration of our study, it should be noted that for most triploid cultivars, there is a decline in the number of flowering (pistillate) plants by Week 6 and thus the flowering pattern of the triploid cultivar might also play a role in the success of efforts to extend the harvesting season. Dittmar et al. (2010) observed higher yield for earlier harvests and the pistillate flowering patterns we observed provide one possible explanation for their observations.
In the present study, the number of plants used per cultivar was limited because our aim was to compare a large number of cultivars. Although we have shown that the genetic factors influencing flowering time can be determined using such an experimental design (McGregor et al., 2014), future studies comparing synchronized flowering patterns over time should endeavor to use a larger number of plants per cultivar. In addition,   1.2 a 1.0 b 2.6 b 5.0 b 5.6 cd z Harvested pollenizers are indicated with italics. y Values followed by the same letters within each column are not significantly different (P < 0.05) by Tukey's honestly significant difference test. studies comparing yield of triploid cultivars pollinated by different pollenizers (Dittmar et al., 2010;Fiacchino and Walters, 2002;) often use only one or two triploid cultivars. This is certainly understandable given the space and isolation requirement for such experiments. However, given the different clustering patterns (Figs. 2E-G and 3E-I) of the triploids, it would be prudent to use cultivars representing each of the pistillate flowering cluster patterns in such studies to limit the confounding effect of the triploid cultivar flowering pattern.
Although synchronized flowering of triploids and pollenizers is a fundamental requirement for fruit set (Dittmar et al., 2009), it is by no means the only factor that determines fruit set and ultimate yield.  showed that all pollenizers are not equally attractive to pollinators. So just because a pollenizer plant has open staminate flowers, it does not guarantee successful pollination and triploid fruit set.
Our data show that different pollenizers and triploid cultivars have specific flowering patterns both in the percentage of plants flowering and the number of (staminate) flowers per plant. A good pollenizer should have a high percentage of plants flowering and a high number of flowers per plant at the time that the triploid cultivar is producing pistillate flowers. Based on our results, certain combinations of triploids and pollenizers meet these criteria better than others. Growers have to be especially careful when choosing pollenizers for the early-flowering triploids and most harvested pollenizers are better suited to later flowering triploids or when growers want to extend their harvest season.