Zhanao Deng and Natalia A. Peres
Zhanao Deng and Brent K. Harbaugh
Sarah M. Smith and Zhanao Deng
The genus Coreospsis is Florida’s state wildflower. One species, Coreopsis leavenworthii, is nearly endemic to Florida and is highly desirable for use in highway beautification. Maintaining genetic integrity is critical for C. leavenworthii producers, growers, and users. Coreopsis tinctoria is closely related to and shares similar habitats with C. leavenworthii in Florida. Previous studies indicated that the two species could hybridize and the F1 hybrids showed chromosomal aberrations and reduced pollen stainability. There has been strong concern that pollen-mediated gene flow from C. tinctoria could contaminate the gene pool and compromise the genetic integrity of C. leavenworthii. In the current study, hand pollination showed that C. leavenworthii and C. tinctoria were highly compatible. F1 hybrids were fertile and readily produced F2 and BC1 individuals. Inheritance studies indicated that the maroon spot on the ray flower is controlled by a single dominant allele and is homozygous in C. tinctoria. This spot serves as a reliable, easy-to-score morphological marker to detect pollen-mediated gene flow from C. tinctoria to C. leavenworthii. Following a discontinuous design, gene flow studies were conducted under field conditions in central Florida over 2 years. The highest rate of pollen-mediated gene flow from C. tinctoria to C. leavenworthii was 4.2% and occurred when the two species were grown 1.5 m apart. Gene flow from C. tinctoria to C. leavenworthii under field conditions followed a leptokurtic curve. Based on the obtained regression equation, separating the two species by 60 m or more could lower the pollen-mediated gene flow from C. tinctoria to minimal levels and protect the genetic integrity of C. leavenworthii.
S. Brooks Parrish and Zhanao Deng
Cultivated caladium (Caladium × hortulanum; 2n = 2x = 30) is an important ornamental aroid for the environmental horticulture industry. A better understanding of its genetic diversity is needed for continued improvement of caladium. The caladium germplasm maintained in the University of Florida’s caladium breeding program were surveyed for potential variation in chromosome number and nuclear DNA content to gain a better understanding of caladium genetic diversity at the cytogenetic level. For the first time caladium triploidy was discovered in two breeding lines, UF-15-414 and UF-4407 with 2n = 3x = 45 chromosomes and a nuclear DNA content of 13.86 pg·2C−1. In addition, a new chromosome number (2n = 2x = 34) was found in one cultivar, ‘White Wing’. Compared with their diploid parents or grandparents, the triploids showed a distinct, attractive leaf morphology with rounder and thicker leaves. The pollen stainability of UF-15-414 and UF-4407 was 63% and 73%, respectively, indicating potential male fertility, which was unexpected. Analysis of simple sequence repeat (SSR) marker banding patterns confirmed that UF-15-414 was a direct progeny of UF-4407 through hybridization with the diploid cultivar Aaron, whereas UF-4407 might result from fusion of an unreduced (female or male) gamete with a reduced gamete. Chromosome counting and SSR marker analysis of ‘White Wing’ and its progeny cultivars ‘White Wonder’ and ‘White Delight’ suggested that ‘White Wing’ possibly transmitted its 34 chromosomes to progeny during sexual reproduction. The discovery and characterization of these triploids revealed the occurrence of natural sexual polyploidization in caladium and indicated good potential for creating and selecting new triploids for future caladium breeding. The observed new chromosome number in ‘White Wing’ and its progeny cultivars implies that other chromosome variations may be present among cultivated caladiums. In summary, these results revealed two male-fertile triploid caladiums and a new chromosome number that can enrich the cytogenetic diversity in future caladium cultivar development.
David M. Czarnecki II and Zhanao Deng
Lantana camara is an important plant for the environmental horticultural industry, yet it can be invasive, cross-pollinating with native lantana and dispersing fruit (and seeds) to natural and agricultural lands. Identification and development of sterile cultivars is much needed to meet industry and consumer needs for noninvasive plant materials. Previously we evaluated the male fertility of 32 L. camara cultivars/breeding lines at five ploidy levels. This study was to assess their female fertility and understand the relationship between female fertility and ploidy level and the production of unreduced female gametes (UFGs) in L. camara. These cultivars/breeding lines significantly varied in percent fruiting plants (6.3% to 100.0%), percent fruiting peduncles (0.3% to 98.8%), fruit per peduncle (0.003 to 7.173), seed germination (0% to 57.1%), and female fertility index (0.003 to 2.998). Certain diploids (e.g., ‘Denholm White’) were highly female-sterile. Eleven of the 13 triploids evaluated were UFG-producing and rather fertile. The two non-UFG-producing triploids had the female fertility index of 0.005, thus most sterile. Tetraploids, especially those producing UFGs, were prolific fruit producers. These results show that ploidy level and UFG production play a significant role in determining fruit (seed) production capacity and female fertility of L. camara. None of the commercial triploid cultivars evaluated reached desirable levels of male and female sterility, indicating a strong need to develop new lantana cultivars that are male- and female-sterile. Our results suggest that production and selection of triploids can be effective to sterilize L. camara, but it is imperative to select diploids and tetraploids that do not produce UFGs as the breeding parents.
Zhe Cao, Zhanao Deng, and Mike Mclaughlin
The genus Caladium Vent. is a member of the family Araceae; some of its species are cultivated as ornamentals. The present study was conducted to determine the genome size, somatic chromosome number, and their variation within 63 accessions representing 10 species of Caladium. Caladium genome sizes estimated using propidium iodide staining and flow cytometry ranged from 2.98 pg/2C in Caladium lindenii Engl. to 9.89 pg/2C in Caladium ×hortulanum Birdsey ‘Chang Suek’. Two genome size groups (large and small) were evident among the 63 caladium accessions. The average genome size of 36 caladium accessions in the large genome size group was 9.29 pg/2C, roughly twice that of the 27 accessions in the small genome size group (4.50 pg/2C). Microscopic examination of squashed root tip cells revealed seven somatic chromosome numbers among 39 caladium accessions, including 2n = 18, 20, 24, 26, 30, 34, and 38, and provided the first chromosome counts for four caladium species new to Caladium. The results support the species status of C. marmoratum Mathieu ex K. Koch, C. picturatum K. Koch & C.D. Bouché, and C. steudneriifolium Engl. that were merged into C. bicolor (Aiton) Vent. previously and also support the species status of C. clavatum Hett., Bogner & J. Boos, and C. praetermissum Bogner & Hett., two species recently established in or transferred to Caladium. The results suggest that C. bicolor and C. schomburgkii Schott, not C. picturatum or C. marmoratum, are the chief parents of the fancy-leaved caladium (C. ×hortulanum). Four caladium cytotype groups (CCG-1 to -4) were identified in scatterplot of chromosome number vs. genome size. The genome size of C. bicolor, C. schomburgkii, and C. ×hortulanum in the CCG-4 is approximately twice that of C. humboldtii (Raf.) Schott and C. picturatum in the CCG-2, and the chromosome number of C. clavatum and C. marmoratum in the CCG-3 is close to twice that of C. humboldtii and C. picturatum in the CCG-2, both suggesting possible genome duplication or tetraploidization events in Caladium. However, the chromosome number of the CCG-4 species does not correspond to an expected 2n = 36 or 40, and the genome size of the CCG-3 species does not correspond to an expected 8.98 pg/2C. Conflicts between genome size and chromosome number indicate that genome duplication events were likely followed by chromosome fusions/losses in the formation of CCG-4 species and DNA losses likely followed tetraploidization in the formation of the CCG-3 species. The high level of cytological diversity found within Caladium affects germplasm collection and preservation efforts as well as breeding programs in the genus.
Zhanao Deng, Natalia A. Peres, and Johan Desaeger
Rosanna Freyre, Zhanao Deng, and Victor A. Zayas
S. Brooks Parrish, Renjuan Qian, and Zhanao Deng
Lantana species are an important component of the U.S. environmental horticulture industry. The most commonly produced and used species are L. camara and, on a smaller scale, L. montevidensis. Both were introduced to the United States from Central and/or South America. Lantana species native to the continental United States include L. canescens, L. depressa, L. involucrata, etc. and most of them have not been well exploited. This study was conducted to obtain information about somatic chromosome numbers, karyotypes, and genome size of these five species. Nuclear DNA content in these species ranged from 2.74 pg/2C (L. involucrata) to 6.29 pg/2C (L. depressa var. depressa). Four chromosome numbers were observed: 2n = 2x = 22 in L. camara ‘Lola’ and ‘Denholm White’, 2n = 4x = 44 in L. depressa var. depressa, 2n = 2x = 24 in L. canescens and L. involucrata, and 2n = 3x = 36 in L. montevidensis. Two basic chromosome numbers were observed: x = 11 in L. camara and L. depressa var. depressa, and x = 12 in L. canescens, L. involucrata, and L. montevidensis. Analysis of somatic metaphases resulted in formulas of 20m + 2sm for L. camara ‘Lola’ and ‘Denholm White’, 12m + 12sm for L. canescens, 44m for L. depressa var. depressa, 10m + 14sm for L. involucrata, and 32m + 4sm for L. montevidensis. Satellites were identified in all five species, but were associated with a different chromosome group in different species. L. depressa var. depressa had the longest total chromatin length (146.78 µm) with a range of 1.88 to 4.41 µm for individual chromosomes. The maximum arm ratio was observed in L. canescens, with a ratio of 2.5 in chromosome group 3. L. depressa var. depressa was the only species that had all of its centromeres located in the median region of the chromosome. The results show significant differences in nuclear DNA content, chromosome number, and karyotype among three native and two introduced lantana species and will help to identify, preserve, protect, and use native lantana species. The information will be helpful in assessing the ploidy levels in the genus by flow cytometry.
Zhanao Deng, Natalia A. Peres, and Johan Desaeger