Fruit Set of Triploid Watermelons as a
Function of Distance from a Diploid PollenizerThis article by D. Scott NeSmith, Department of Horticulture, Georgia Station,
Griffin, Georgia, and John R. Duval, University of Florida, Dover, Florida,
appeared in "HortScience" 36(1):60-61. 2001.
bstract. During 1998 and 1999, ‘Genesis’ triploid watermelons [Citrullus lanatus (Thunb.) Matsum. & Nak.] were grown in large blocks with a single row of the diploid ‘Ferarri’ planted as a pollenizer in the middle. A once-over harvest each year was made in harvest lanes approximately 0, 5, 10, 15, 20, 25, and 30 feet perpendicular distances from the pollenizer row. Individual fruit were weighed and counted. Data from both years indicated a similar distribution of triploid fruit with respect to distance from the pollenizer row.
Overall, fruit yield for the rows of ‘Genesis’ plants varied depending on their distance from the pollenizer row. The patterns of fruit density across the rows were similar for both years. The pollenizer row itself (0 feet distance) had some triploid watermelons because of vine growth from nearby plants. The first triploid row adjacent to the pollenizer had a substantial number of ‘Genesis’ watermelons, but the greatest number of seedless watermelons per unit area were present in the second row (10 feet distance) away from the pollenizer each year. The number of triploid watermelons diminished by 37 percent to 40 percent from the second to the third row (15 feet distance). The remaining rows (distances of 20, 25, and 30 feet) set very few fruit, suggesting that distances of 20 feet or greater from the pollenizer row are too great for adequate pollination, either because of the distance from the pollen source, or pollen dilution and/or lack of bee visits.
Directionally-biased pollen flow was not apparent in the planting blocks of these experiments. Fruit yields were similar for triploid rows planted equal distances on either side of the pollenizer row. Also, there were no differences in average individual fruit weight or percentage of marketable fruit from the different harvest lanes, only in total fruit number per unit area.
Using the fruit density results from the 1998 and 1999 field experiments, yield projections for different pollenizer-to-triploid ratios were calculated. Estimates of fruit yield/A increased with an increasing number of triploid rows up to a ratio of one pollenizer to four triploid rows in both years. A trend toward declining yields/A was apparent as the number of triploid rows per pollenizer row increased beyond four. Triploid yield (fruit/A) for the current commonly used ratio of 1:2 (every third row a pollenizer) was 25 percent less than that resulting from the 1:4 ratio in 1998 and 1999.
The triploid yield estimates in these experiments were based on 5 feet row widths. This would probably be very acceptable for triploid watermelons, since vine-coverage area tends to be smaller than that of traditional seeded watermelons. Earlier reports show that diploid watermelons grown in 5-feet wide rows at in-row spacings of 3 feet yielded 29 percent to 34 percent more than did watermelons planted at in-row spacings of 7 feet. When deciding on pollenizer ratios, using data from the current study, one must consider that increasing row width beyond 3 feet may slightly modify calculations of yields. The current data indicated that when distance from the pollenizer row approached 20 feet, triploid fruit numbers declined sharply. Therefore, if growers us 6-feet row widths, perhaps a ratio of 1:3 would be best.
In summary, triploid watermelons do require a pollenizer and adequate pollinator-insect activity for successful fruit set. Growers should realize that exceeding distances of 20 feet from the diploid pollenizer will probably reduce yields. Also, planting too many pollenizers (i.e., ratios of 1:1 and 1:2) will reduce triploid yields. The results presented here suggest that triploid yields per unit land area would be optimized using a ratio of 1 pollenizer row to 4 triploid rows for 5-feet row widths.
