Feeding nymphs of the silverleaf whitefly, Bemisia argentifolii (formerly known as Bemisia tabaci Gennadius, B strain), cause a physiological disorder known as squash silverleaf (SSL) in summer squash (Cucurbita pepo L.). This disorder is characterized by a progressive silvering on the upper leaf surface caused by the development of large air spaces between the palisade mesophyll cells and the adaxial epidermis. Severely symptomatic plants can exhibit stunting and fruit yield reduction. A University of Florida C. pepo breeding line, designated Zuc76, confers resistance to this disorder and its inheritance was characterized. Data from F1, F2, and backcross progeny from crossing a SSL disorder-susceptible zucchini squash (C. pepo) with Zuc76 indicated resistance is conferred by a single recessive gene. Determining the mode of inheritance of SSL disorder resistance found in Zuc76 will contribute to future studies to develop SSL disorder-resistant C. pepo cultivars with superior horticultural potential.
Kristen Young and Eileen A. Kabelka
Rachel A. Itle and Eileen A. Kabelka
Carotenoids play an important role in human health by acting as sources of provitamin A or as protective antioxidants. Pumpkins and squash (Cucurbita spp.) are excellent dietary sources of carotenoids. The diversity and range of carotenoid types and concentrations within pumpkins and squash provide a means to increase the nutritional value of this crop through plant breeding. Breeding requires reliable estimates of carotenoid types and concentrations to distinguish differences among breeding material. One method used for carotenoid identification and quantification is high-performance liquid chromatography (HPLC). It is a highly sensitive and reproducible method but expensive and time-consuming. In contrast, colorimeters objectively describing visible color are relatively inexpensive and easy to use. The objective of this research was to determine if the carotenoid content within pumpkin and squash measured by HPLC was correlated with colorimeter L*a*b* color space values. Cultigens (cultivars, heirlooms, and PIs) representing white, yellow, and orange flesh color were grown at multiple locations using a randomized complete block design with two replicates at each location. Fruit flesh of each cultigen was evaluated using HPLC and colorimetric analysis. Strong correlations were found between color value a* and total carotenoids (r = 0.91) and color value b* and chroma with lutein (r = 0.87). Regression equations based on these correlations will be useful for estimating carotenoid type and concentrations. These close associations will also assure that breeding for enhanced carotenoid content within pumpkins and squash can be achieved using an easy-to-use and inexpensive method.
Josh H. Freeman, Stephen M. Olson, and Eileen A. Kabelka
In the Spring and Fall 2006, the pollen viability of four diploid watermelon pollenizers was evaluated in Quincy, FL. Triploid watermelon plants [Citrullus lanatus (Thunb.) Matsum. & Nakai.] do not produce sufficient viable pollen to pollenize themselves and a diploid cultivar must be interplanted as a pollen source. Recent studies have illustrated differences in triploid watermelon yields as a result of the pollenizer cultivar used. The viability of the pollen produced by pollenizer cultivars may greatly influence the fruit set and fruit quality in the triploid watermelon crop. Pollen samples were taken from ‘Companion’, ‘Jenny’, ‘Mickylee’, and ‘SP-1’ and were stained to determine their viability. There were no significant differences in pollen viability among cultivars and all cultivars had high average viability. Pollen viability was never lower than 95% for any cultivar. This study indicates that pollen viability of the cultivars evaluated should not influence their effectiveness as pollenizers.
Les D. Padley Jr, Eileen A. Kabelka, and Pamela D. Roberts
The various disease syndromes caused by Phytopthora capsici Leonian can be devastating to squash (Cucurbita spp.) production areas of the United States. In some growing seasons, yield loss has been reported up to 100%. A recently developed University of Florida Cucurbita breeding line, #394-1-27-12, resistant to the crown rot syndrome of P. capsici, was used to determine the inheritance of resistance to this disease. Data from F1, F2, and backcross progeny from crosses of a P. capsici-susceptible butternut-type winter squash (C. moschata) with #394-1-27-12 indicated that resistance is conferred by three dominant genes. The introgression of P. capsici crown rot resistance from #394-1-27-12 into morphologically diverse domesticates within Cucurbita will aid in the management of this economically important pathogen.
Dario J. Chavez, Eileen A. Kabelka, and José X. Chaparro
Phytophthora capsici causes seedling death, crown and root rot, fruit rot, and foliar blight on squash and pumpkins (Cucurbita spp. L.). A total of 119 C. moschata accessions, from 39 geographic locations throughout the world, and a highly susceptible butternut squash cultivar, Butterbush, were inoculated with a suspension of three highly virulent P. capsici isolates from Florida to identify resistance to crown rot. Mean disease rating (DR) of the C. moschata collection ranged from 1.4 to 5 (0 to 5 scale with 0 resistant and 5 susceptible). Potential resistant and tolerant individuals were identified in the C. moschata collection. A set of 18 PIs from the original screen were rescreened for crown rot resistance. This rescreen produced similar results as the original screen (r = 0.55, P = 0.01). The accessions PI 176531, PI 458740, PI 442266, PI 442262, and PI 634693 were identified with lowest rates of crown infection with a mean DR less than 1.0 and/or individuals with DR = 0. Further selections from these accessions could be made to develop Cucurbita breeding lines and cultivars with resistance to crown rot caused by P. capsici.
Les D. Padley Jr, Eileen A. Kabelka, Pamela D. Roberts, and Ronald French
Phytophthora capsici causes several disease syndromes on Cucurbita pepo L. (squash, pumpkin, and gourd), including crown rot, foliar blight, and fruit rot, which can lead up to 100% crop loss. Currently, there are no C. pepo cultivars resistant or tolerant to this pathogen, which can aid in disease management strategies. The objective of this study was to evaluate a select group of C. pepo accessions for resistance to the crown rot syndrome of P. capsici. One hundred fifteen C. pepo accessions, from 24 countries, were evaluated for their disease response to inoculation with a suspension of three highly virulent P. capsici isolates from Florida. Replications of each accession, including susceptible controls, were planted in the greenhouse using a randomized complete block design. At the second to third true leaf stage, each seedling was inoculated at their crown with a 5-mL P. capsici suspension of 2 × 104 zoospores/mL. Fourteen days after inoculation, the plants were visually rated on a scale ranging from 0 (no symptoms) to 5 (plant death). Mean disease rating scores (DRS) and sds were calculated for each accession and ranged from 1.3 to 5.0 and 0 to 2.0, respectively. Eight accessions with the lowest mean DRS were rescreened. Results paralleled those of the initial study with one accession, PI 181761, exhibiting the lowest mean DRS at 0.5. Further screening and selection of accessions from the C. pepo germplasm collection should aid in the development of breeding lines and cultivars with resistance to crown rot caused by P. capsici.