Triploid (seedless) watermelon production requires the use of diploid (seeded) cultivars to ensure pollination (Dittmar et al., 2010; Fiacchino and Walters, 2003; Maynard and Elmstrom, 1992; Rhodes et al., 1997). This is accomplished by planting a diploid watermelon cultivar in the field with the triploid watermelon plants. These pollenizer plants can be planted in a number of patterns including dedicated rows adjacent to the seedless rows or interplanting them within the rows with the seedless plants at various rates (Dittmar et al., 2010; Fiacchino and Walters, 2003; Maynard and Elmstrom, 1992; Rhodes et al., 1997). The typical ratio of pollenizer plants to the seedless plants ranges from 1:2 to 1:4 pollenizer:seedless plants (Dittmar et al., 2010; Fiacchino and Walters, 2003; Nesmith and Duval, 2001; Rhodes et al., 1997). Regardless of the planting arrangement or the ratio of diploid (seeded) plants to the seedless plants in a given area, a proportion of the total population of watermelon plants per acre must be dedicated to the pollenizer plants to ensure growth and development of both staminate flowers and fruit of diploid plants (Dittmar et al., 2009). Growers can market acceptable seeded watermelon; however, demand for these fruit continues to decline in proportion to that of seedless fruit (Lucier and Lin, 2001). Seeded fruit typically bring lower prices than the more desirable seedless fruit (U.S. Department of Agriculture, 2003), and the presence of the diploid cultivars used as the pollenizer plants restricts the number of more valuable triploids that can be planted.
Therefore, many growers interplant older diploid cultivars, which have lower seed prices, within the seedless rows. The purpose of this system is to plant the entire acreage with seedless plants at normal production spacing and interplant pollenizer plants without regard to their fruit production and value. Seed companies have responded to this demand by developing pollenizer cultivars that produce inferior fruit quality (e.g., unacceptably small fruit or soft rinds) and unique growth habits or flowering characteristics. These newer pollenizer culitvars, because of their compact growth habit, also offer less competition with triploid cultivars than the traditional diploid culitvars used as pollenizers.
The use of these newly developed pollenizers is relatively recent. Characteristics important for these exclusive pollenizers are staminate flower production and disease resistance. Previous works have shown that flowering characteristics of these pollenizers varies considerably (Dittmar et al., 2009, 2010; Fiacchino and Walters, 2003; Freeman and Olson, 2007; Maynard and Elmstrom, 1992; Rhodes et al., 1997). The production of sufficient staminate flowers that are easily accessible to bees at the same time as seedless pistillate flower production is critical to successful fruiting. Research has shown that daily staminate flower production is highly variable among cultivars (Dittmar et al., 2010; Fiacchino and Walters, 2003; Freeman and Olson, 2007; Maynard and Elmstrom, 1992; Rhodes et al., 1997; Stanghellini and Schultheis, 2005; Stanghellini et al., 1998).
We also have observed significant variability in the susceptibility of these dedicated pollenizers to fusarium wilt, caused by the soilborne fungus FON, in commercial fields. Pollenizers susceptible to fusarium wilt appear to produce fewer staminate flowers making them less effective as pollenizers. We have observed that watermelon plants often exhibit symptoms of fusarium wilt within 3 to 4 weeks of transplanting (Kleczewski and Egel, 2011), considerably before flowers are produced. While studies ranking the susceptibility of watermelon hybrids to fusarium wilt are available (Elmstrom and Hopkins, 1981; Martyn and McLaughlin, 1983; Zhang et al., 1995; Zhou and Everts, 2004), the relative host resistance rankings of these specialized diploids is not known. Management of fusarium wilt is difficult without good genetic resistance. For example, many triploid hybrids lack adequate host resistance (Egel and Hoke, 2007). The usefulness of crop rotations is limited because chlamydospores of FON may survive many years in the soil. Additionally, soil fumigation is considered too expensive to be useful to most watermelon producers (Egel and Martyn, 2007); thus, host resistance is the most economically useful strategy for management of fusarium wilt of watermelon.
The purpose of this study was to compare staminate flower production of dedicated pollenizers in a commercial watermelon field and evaluate the host resistance of dedicated pollenizers to fusarium wilt in the field as well as in a greenhouse inoculation study.
Dittmar, P.J., Monks, D.W. & Schultheis, J.R. 2009 Maximum potential vegetative and floral production and fruit characteristics of watermelon pollenizers HortScience 44 59 63
Dittmar, P.J., Monks, D.W. & Schultheis, J.R. 2010 Use of commercially available pollenizers for optimizing triploid watermelon production HortScience 45 541 545
Egel, D.S., Harikrishnan, R. & Martyn, R. 2005 First report of Fusarium oxysporum f. sp. niveum race 2 as causal agent of fusarium wilt of watermelon, in Indiana Plant Dis. 89 108
Egel, D.S. & Hoke, S. 2007 Evaluation of triploid watermelon for resistance to fusarium wilt, 2006 Plant Dis. Mgt. Rpt. 2 V020 doi: 10.1094/PDMR01
Egel, D.S., Lam, W.K.F., Foster, R. & Maynard, E. 2006 Midwest vegetable production guide for commercial growers. Coop. Ext. Serv., Purdue Univ. ID-56
Egel, D.S. & Martyn, R.D. 2007 Fusarium wilt of watermelon and other cucurbits Plant Health Instructor, doi: 10.1094/PHI-I-2007-0122-01
Esposito, R. & Fletcher, A. 1961 The relationship of pteridine biosynthesis to the action of copper 8-hydroxy-quinolate on fungal spores Arch. Biochem. Biophys. 93 369 376
Fiacchino, D.C. & Walters, S.A. 2003 Influence of diploid pollenizer frequencies on triploid watermelon quality and yields HortTechnology 13 58 61
Freeman, J.H., Miller, G.A., Olson, S.M. & Stall, W.M. 2007 Diploid watermelon pollenizer cultivars exhibit varying degrees of performance with respect to triploid watermelon yield HortTechnology 17 518 522
Freeman, J.H. & Olson, S.M. 2007 Characteristics of watermelon pollenizer cultivars for use in triploid production Intl. J. Veg. Sci. 13 73 80
Kleczewski, N.M. & Egel, D.S. 2011 A diagnostic guide for fusarium wilt of watermelon Plant Health Prog., doi: 10.1094/PHP-2011-1129-01-DG
Lucier, G. & Lin, B.H. 2001 Vegetables and specialties situation yearbook. Econ. Res. Serv. U.S. Dept. Agr., Washington, DC
Martyn, R.D. 1987 Fusarium oxysporum f. sp. niveum race 2: A highly aggressive race new to the United States Plant Dis. 71 233 236
Martyn, R.D. & McLaughlin, R.J. 1983 Effects of inoculum concentration on the apparent resisitance of watermelons to Fusarium oxysporum f. sp. niveum Plant Dis. 67 493 495
Nesmith, S. & Duval, J. 2001 Fruit set of triploid watermelon as a function of distance from a diploid pollenizer HortScience 36 60 61
Shaner, G. & Finney, R.E. 1977 The effect of nitrogen fertilization on the expression of slow-mildewing resistance in Knox wheat Phytopathology 67 1051 1056
Stanghellini, M.S., Ambrose, J.T. & Schultheis, J.R. 1998 Seed production in watermelon: A comparison between two commercially available pollinators HortScience 33 28 30
Stanghellini, M.S. & Schultheis, J.R. 2005 Genotypic variability in staminate flower and pollen grain production of diploid watermelons HortScience 40 752 755
U.S. Department of Agriculture 2003 Vegetables and melons outlook. U.S. Dept. Agr., Econ. Res. Serv. VGS-296
Zhang, X.W., Jiao, D.L., Na, L., Huang, X.S. & Gu, Q.S. 1995 A preliminary report on screening the resistance of watermelon cultivars to fusarium wilt Acta Hort. 402 45 47
Zhou, X.G. & Everts, K.L. 2004 Quantification of root and stem colonization of watermelon by Fusarium oxysporum f. sp. niveum and its use in evaluating resistance Phytopathology 94 832 841