Progress 09/01/06 to 08/31/08
Outputs
OUTPUTS: 1. Progeny of the Candidum x Ginerland population was clonally propagated, and tubers were produced for each progeny in the greenhouse. The tubers were inoculated with the most aggressive Fusarium isolate and incubated at 18C for 2 weeks. The level of resistance for each progeny was based on the area (square millimeters) of the rotted tissue around the inoculation site on each tuber half. The distribution of Fusarium tuber rot resistance in this population was bimodal, indicating that both major genes and minor modifying genes are involved in conferring caladium Fusarium tuber rot resistance. Transgressive segregants were common, but the great majority of them were highly susceptible (more susceptible than the susceptible parent Gingerland). The distribution of Pythium root rot resistance in the segregating population seems to support our previous suspicion that the trait is controlled by multiple loci with small effects. 2. Segregation data from 18 populations showed that a single locus with two alleles (S and s) was responsible for the presence or absence of leaf spots in caladium, and another single nuclear locus with two alleles (B and b) was responsible for the presence or absence of leaf blotching in caladium. The major cultivar Gingerland is heterozygous for the presence of leaf spots. Leaf spots were inherited independently from leaf shape, but closely linked with the color of the main leaf veins. The average recombination frequency between the leaf spot locus and the main vein color locus is 4.4%. Chi-square analysis of the joint segregation between leaf blotching and vein color (V) in five crosses showed that the blotching allele B is linked to the green vein allele Vg. Carolyn Whorton, White Christmas, and Florida Blizzard are heterozygous for leaf blotching, and their genotype for leaf blotching and vein color (Vr, Vw, and Vg for red, white, green veins) are Vrb//VgB, Vgb//VgB, and Vwb//VgB, respectively. Results obtained so far indicate that leaf spots and leaf blotching are independent from Fusarium tuber rot resistance and Pythium root rot resistance. 3. Nearly 1,300 advanced breeding lines were further screened for tuber characteristics (yield and branching habit, Dec. 2006 and 2007), container plant performance and quality (plant height and vigor, leaf number, color and brightness, etc; spring 2007 and 2008), and Fusarium tuber rot and Pythium root rot resistance. These screenings resulted in selection of six advanced breeding lines that have improved resistance to both Fusarium tuber rot and Pythium root rot and possess desirable growth habit, foliar and tuber characteristics. PARTICIPANTS: Zhanao Deng, Natalia Peres, Brent Harbaugh, F. Goktepe, Bates Sons & Daughters, Classic Caladiums, Happiness Farms TARGET AUDIENCES: Caladium growers, Greenhouse growers, Nurseries, Commercial landscapers, Home owners, Gardeners, aroid breeders, ornamental plant breeders, etc. Publications in scientific journals, trade magazines, and extension fact sheets; presentations at growers or professional meetings; field days; demonstration gardens, etc. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Caladium represents a group of ornamental and food aroid plants widely grown in the tropical and subtropical U.S. and in the Caribbean region. Fusarium tuber rot is one of the most destructive diseases of caladium. Understanding the mode of inheritance of Fusarium tuber rot resistance and foliar traits, particularly the genetic relationships between them, is very important for genetic improvement of caladium and other aroids. The finding that major genes are involved in Fusarium tuber rot resistance and their independence from leaf spots and leaf blotching will be very valuable to breeders in designing strategies for further improvement of caladium and other aroids for tuber rot resistance. In addition, leaf spots, leaf blotches, and vein colors represent the first linkage group of ornamental traits in caladium and possibly in other ornamental aroids.
Publications
- Deng, Z., F. Goktepe, and B.K. Harbaugh. 2008. Inheritance of leaf spots and their relationships with leaf shape and main vein color in caladium. Journal of the American Society for Horticultural Science. 133(1):78-83.
- Deng, Z., B.K. Harbaugh, and N.A. Peres. 2008. Improving caladium, gerbera, and lisianthus for better disease resistance and stress tolerance. HortScience. 43(4):1100-1101.
- Deng, Z., N.A. Peres, and B.K. Harbaugh. 2008. Super tubers - Researchers are evaluating and developing caladium cultivars with resistance to Fusarium tuber rot. Ornamental Outlook. 17(2):28-29.
- Deng, Z. and B.K. Harbaugh. 2008. Inheritance of leaf blotches, an important trait determining the ornamental value of caladium. HortScience. 43(4):1194-1195.
- Deng, Z., N.A. Peres, and B.K. Harbaugh. 2008. Improving disease resistance in caladium: progress and prospects. Book of abstracts of the ISHS (International Society for Horticultural Science) Xth International Symposium on Flower Bulbs and Herbaceous Perennials (20-24 April 2008, Lisse, the Netherlands). p. 11.
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Progress 09/01/06 to 08/31/07
Outputs
1. Determining the inheritance of Fusarium tuber rot resistance: Two populations were developed: one from Candidum x Gingerland, and the other from Red Frill x Candidum. Candidum was chosen because it was most resistant to Fusarium tuber rot and Pythium root rot among all commercial cultivars examined. Gingerland and Red Frill both were susceptible to the two diseases. Skew segregation was observed in the Red Frill x Candidum population for a number of foliar traits. Thus this population was excluded from further analysis. For the Candidum x Ginerland population, each of the 75 progeny was clonally propagated, and twenty to 50 #1 or larger (1.5 inch or larger in diameter) tubers were produced for each progeny in the greenhouse. Tubers were inoculated with the most aggressive Fusarium isolate and incubated at 18C for 2 weeks. The level of resistance for each progeny was assessed based on the area of the rotted tissue around the inoculation site on each tuber half. The
distribution of Fusarium tuber rot resistance in this population was bimodal, indicating that both major genes and minor modifying genes are involved in conferring caladium Fusarium tuber rot resistance. Transgressive segregants were common, but the great majority of them were highly susceptible (more susceptible than the susceptible parent Gingerland). 2. Determining the inheritance of foliar traits and their relationship with Fusarium tuber rot resistance: Segregation data from 18 populations showed that a single locus with two alleles was responsible for the presence or absence of leaf spots in caladium, with the presence allele (S) dominant over the absence allele (s). Gingerland is heterozygous for the presence of leaf spots. Leaf spots were inherited independently from leaf shape, but closely linked with the color of the main leaf veins. The recombination frequencies between the leaf spot locus and the main vein color locus were from 0.0% to 8.9%, depending one the cross or the
parental cultivars used, with an average recombination frequency of 4.4%. Results obtained so far indicate that leaf spots are independent also from Fusarium tuber rot resistance. Segregation data for plant height, leaf number, and leaf size are being collected, and data for tuber traits will be collected at the end of the 2007 growing season. These data are to be used to analyze the genetic relationship between Fusarium tuber rot resistance and foliar and tuber characteristics. 3. Developing elite disease-resistant breeding lines: Previously nearly 1,300 advanced breeding lines were identified through three screening schemes. These breeding lines were further screened for tuber characteristics (yield and branching habit, Dec. 2006), container plant performance and quality (plant height and vigor, leaf number, color and brightness, etc; spring 2007), and Fusarium tuber rot resistance (early summer 2007). These screenings resulted in selection of 126 breeding lines that possessed
Fusarium tuber rot resistance. These lines are being tested in replicated field trials for plant, foliar, and tuber characteristics.
Impacts
The finding that major genes are involved in Fusarium tuber rot resistance and their independence from leaf spots (and potentially other foliar traits) will be very valuable to breeders in designing strategies for further improvement of caladium and other aroids for tuber rot resistance and foliar traits. Leaf spots and vein colors represent the first linkage group of ornamental traits in caladium and possibly in other ornamental aroids. The identification of advanced resistant breeding lines will speed up development of new resistant cultivars, which will help field and greenhouse growers control caladium tuber rot, produce better ornamental plants, and reduce costs and labor associated with pesticide applications.
Publications
- Deng, Z., F. Goktepe, and B.K. Harbaugh. 2007. Inheritance of leaf spots and their genetic relationship with leaf shape and vein color in caladium. HortScience. 42(4):971.
- Deng, Z. J. Hu, F. Goktepe, and B.K. Harbaugh. 2007. Assessment of genetic diversity and relationships among caladium cultivars and species using molecular markers. Journal of the American Society for Horticultural Science. 132(2):219-229.
- Goktepe, F., T.E. Seijo, Z. Deng, B.K. Harbaugh, and N.A. Peres. 2007. Toward breeding for resistance to fusarium tuber rot in caladium: inoculation technique and sources of resistance. HortScience 42(5):1135-1139.
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