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Kimberly H. Krahl

A screening technique was developed for studying resistance to powdery mildew disease in 25 diverse Pulmonaria L. species and cultivars. Healthy Pulmonaria plants were inoculated by drawing naturally infected leaves of P. angustifolia `Blaues Meer' across the abaxial surface of three healthy, mature leaves per test plant. Inoculated leaves were rated for powdery mildew infection using a scale of 0-5, where 0 = no visible sign of infection, 1 = 1% to 20%; 2 = 20% to 40%; 3 = 40% to 60%; 4 = 60% to 80%; 5 = 80% to 100% of leaf surface covered with white mycelial growth. Each genotype was inoculated and evaluated four times. The data revealed a wide and continuous range of variability for powdery mildew disease incidence in the 25 lungwort genotypes that may be indicative of quantitative resistance. The majority of lungwort genotypes exhibited low levels of resistance to powdery mildew. Four cultivars (P. hybrid `Spilled Milk', P. hybrid `Excaliber', P. rubra `Redstart', and P. rubra `David Ward') and one selection (P. longifolia ssp. cevennensis) exhibited high levels of resistance to powdery mildew. Since Pulmonaria species intercross readily, these genotypes may be useful in the future development of new powdery mildew resistant Pulmonaria cultivars.

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Kimberly H. Krahl and William M. Randle

Ornamental plant breeding has focused almost exclusively on floral prolificacy rather than floral longevity. The importance of floral longevity is obvious in any ornamental crop grown primarily for floral display. This study was undertaken to determine the genetic basis of floral longevity in an important ornamental crop, petunia.

Four parental lines representing the extremes for floral longevity were used to generate 6 F1 families which were selfed to generate F2 families and backcrossed to create 12 backcross families. Generation means analysis was utilizied to determine estimates of additive. dominance, and epistatic genetic variance for floral longevity in petunia.

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Kimberly H. Krahl and William M. Randle

Botrytis diseases are the most common and among the most destructive diseases affecting greenhouse-grown crops. Presently a combination of cultural control and fungicidal sprays are used to control the disease. Increasing energy and labor costs plus evidence of resistance of B. cinerea strains to commonly used fungicides has made the disease more difficult to control. A source of genetic resistance would provide an additional powerful and stable tool to control the incidence of Botrytis disease.

In this study screening techniques for Botrytis resistance in petunia were developed and 40 petunia genotypes were screened for resistance to B. cinerea. A wide range of variability for resistance to B. cinerea was discovered in petunia. Results indicate the presence of useful quantitative-type resistance to B. cinerea in petunia.

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Kimberly H. Krahl and William M. Randle

Petunia hybrida Vilm. is one of the major bedding plants grown worldwide, and, like most bedding plants, is grown primarily for its seasonal floral display. While increased floral and reflowering capacity have been the focus of breeding programs for many ornamental species, floral longevity has received little direct attention. Increased floral longevity would enhance the value of any crop grown for floral effect. In this study, four parental genotypes (two with short flower life, two with long flower life) were crossed in a partial diallel mating design to create six F1 families. The F1 individuals were then selfed and backcrossed to the appropriate parents to create F2 and backcross families. Data from parental and F1 genotypes were analyzed to determine general and specific combining ability for floral longevity in petunia. Results indicated the presence of significant additive gene effects and nonsignificant nonadditive gene effects for floral longevity in this germplasm. However, aberrant F2 and backcross family means were observed in all families. For each family, F2 and backcross means were lower than expected given normal Mendelian segregation. Further experiments will be necessary to elucidate the causes for the deviate F2 and backcross family means before specific recommendations for selecting for increased floral longevity in petunia can be made.

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Kimberly H. Krahl and William M. Randle

Although Petunia hybrida Vilm., a major bedding plant, is susceptible to many diseases, no formal disease resistance studies have been conducted. Botrytis cinerea Pers. ex Fr. is a ubiquitous pathogen, causing great damage to greenhouse-grown ornamental crops, including petunia. In this study, a screening procedure for B. cinerea resistance in petunia was developed and 48 diverse petunia phenotypes were screened for resistance to B. cinerea in two seasons, spring and fall. The range of variability for resistance to B. cinerea in petunia was wide and continuous. Spearman's rank correlation coefficients between seasons were significant and moderate. While the majority of phenotypes displayed less than a 10% difference in mean percent infection in spring vs. fall seasons, several phenotypes displayed large differences that require further testing. One cultivar, `Pink Sensation Improved', exhibited low and consistent mean percent infection in both spring and fall and, therefore, may be a useful source of resistance to B. cinerea in petunia.