Variation in the Breeding System of Prunella Vulgaris L
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HORTSCIENCE 46(5):688–692. 2011. logical research documented significant var- iation in plant-growth patterns and flowering phenology (Bocher, 1949; Nelson, 1967), typ- Variation in the Breeding System ically considered to be the result of plant adaptation to particular habitats or climatic of Prunella vulgaris L. conditions. Recent research has demonstrated 1 that there is significant variation in antiviral Luping Qu and Mark P. Widrlechner properties among different P. vulgaris acces- USDA-ARS, North Central Regional Plant Introduction Station, G212 sions cultivated under a common set of field Agronomy Hall, Iowa State University, Ames, IA 50011-1170 conditions (Brindley et al., 2009). Eleven such accessions were also shown to differ more Additional index words. floral morphology, in-bud pollen release, selfed-seed set, bud than 10-fold in their concentration of the autogamy bioactive compound, rosmarinic acid (Berhow Abstract. Prunella vulgaris (Lamiaceae), commonly known as selfheal, is a perennial herb et al., personal communication) in dried, with a long history of use in traditional medicine. Recent studies have found that P. aboveground parts collected at peak flower- vulgaris possesses anti-inflammatory, antiviral, and antibacterial properties, and it is ing. These results strongly suggest that there likely that this will lead to increased commercial demand for this species. To date, is substantial genetic variation among popula- research publications on P. vulgaris cultivation and genetics are scarce. Using accessions tions of this species, at least for phytochemical originally collected from different geographical regions, we investigated the breeding properties. This variation is likely to confer system of this species by observing variation in floral morphology, time of pollen release, differences in pharmacological efficacy. and selfed-seed set in bagged flowers and isolated plants. Two types of floral morphology, To date, research publications on Prunella one with exerted styles, extending past open corollas when viewed from above, and the cultivation and genetics are scarce. Other than other with shorter, inserted styles, were found among 30 accessions. Two accessions the Chinese germination studies cited pre- originally collected from Asia uniformly displayed exerted styles, and 27 accessions had viously, most recent research on P. vulgaris inserted styles. One accession from Oregon displayed variation in this trait among has focused on analyses of its chemical con- individual plants. Microscopic observation of seven accessions, including ones with both stituents and medicinal properties (e.g., Brindley exerted and inserted styles, revealed that they all release pollen to some degree before the et al., 2009; Han et al., 2009; Psotova´ et al., flowers open. Using bagged flowers, we found that selfed-seed set varied widely among 2003; Zhang et al., 2007). This species has eight accessions, ranging from 6% to 94%. However, bagging may underestimate seed set also been used as a model plant for ecological for some accessions. The two accessions with the lowest rates when using bagged flowers and evolutionary research through detailed increased in seed set by 350% and 158%, respectively, when we evaluated single, studies of traits such as seed size and degree unbagged plants in isolation cages. The accession with 6% selfed-seed set when bagged of clonal propagation and geographic analy- also had exerted styles. These findings suggest that mating systems in P. vulgaris may be ses of hybridity (Fritsche and Kaltz, 2000; in the process of evolutionary change and that understanding breeding-system variation Macek and Lepsˇ, 2003; Schmid, 1985; Winn, should be useful in developing efficient seed-regeneration protocols and breeding and 1985, 1987; Winn and Cross, 1993). Although selection strategies for this species. it has been stated that P. vulgaris is out- crossing, but self-compatible, and the pres- ence of ‘‘cleistogamy’’ in smaller-flowered plants has been noted (Nelson, 1964, 1967), Breeding systems play crucial roles in cleistogamy and in-bud pollination, mecha- we are aware of no in-depth investigations on the evolutionary dynamics of plant species nisms to ensure self-pollination, to mechanisms this subject. (Charlesworth, 2006), are critical in the de- that foster cross-pollination such as dioecy and Prunella vulgaris was recently incorpo- velopment of effective and efficient genetic self-incompatibility. However, many plant spe- rated into the medicinal plant germplasm improvement strategies (Charlesworth, 2006; cies vary between these two extremes in their collection conserved by the USDA-ARS North Poehlman, 1987), and should not be over- reproductive biology (Goodwillie et al., 2005). Central Regional Plant Introduction Station looked in ex situ germplasm conservation Prunella vulgaris L. (Lamiaceae), com- (NCRPIS, Ames, IA) and from 2007 to 2011 (Sackville Hamilton et al., 2003).Variation monly known as selfheal, is a low-growing has been one of three medicinal-plant gen- in plant sexual breeding systems ranges from perennial herb. Its dried inflorescences have a era being studied in Iowa by the Center for long history of use in traditional Chinese and Research on Botanical Dietary Supplements European medicine (Mattioli, 1586; Pinkas (2010). For the purpose of establishing effec- Received for publication 19 Nov. 2010. Accepted et al., 1994) as a remedy for sore throat, fever, tive and efficient seed regeneration methods for publication 24 Feb. 2011. and wounds. Recent studies have found that and to guide its future crop improvement for This journal paper of the Iowa Agriculture and Home this species has potential to become an eco- producers and end-users, we conducted a series Economics Experiment Station, Ames, Iowa, Project nomically important medicinal herb through of observations and experiments designed to No. 1018, was supported by Hatch Act and State of its anti-inflammatory, antiviral, and antibacte- elucidate its breeding system initiated when we Iowa funds, and the research described herein was rial activities (Brindley et al., 2009; Chiu et al., observed interesting variation in patterns of supported by Award Number P50AT004155 from 2004; Kageygama et al., 2000; Psotova´etal., floral morphology and senescence. the National Center for Complementary & Alterna- tive Medicine. 2003; Zhang et al., 2007). With the emergence The content is solely the responsibility of the authors of such information, it is likely that this will Materials and Methods and does not necessarily represent the official views lead to increased commercial demand for this of the National Center for Complementary & Alter- species. Several investigations of seed germi- Prunella vulgaris plants used in this inves- native Medicine or the National Institutes of Health. nation in P. vulgaris, its typical method of tigation were grown from seeds of accessions Mention of commercial brand names does not horticultural propagation, have recently been originally collected from different geographical constitute an endorsement of any product by the published in response to new interest in its regions (Table 1), except for Ames 29994 and U.S. Department of Agriculture or cooperating cultivation (Guo et al., 2009a, 2009b, 2009c; 29995, which were received as plants from agencies. Zhang et al., 2008, 2009). Therefore, stud- Quarryhill Botanical Garden, Glen Ellen, CA, We are grateful to Jianjun Chen, Roger Chetelat, Candice Gardner, John Nason, and anonymous re- ies to optimize commercial production and where they had been grown isolated from each viewers for their useful critiques of an earlier draft of initiate genetic improvement are likely to other because the original collections were this report. follow. made in China and Japan in 1990 and 1989, 1To whom reprint requests should be addressed; Prunella vulgaris is native to a large part respectively. Additional information about the e-mail [email protected]. of the Northern Hemisphere. Pioneering eco- origins of these accessions is available online 688 HORTSCIENCE VOL. 46(5) MAY 2011 Table 1. Flower morphology and seed set of different Prunella vulgaris accessions. Flower morphology Exerted Inserted No. of flowers No. of seeds set Proportion of Genotype Origin style style bagged and (unbagged)z bagged and (unbagged)z maximum seed set (%)y Ames 27748 Iowa ü Ames 28312 Iowa ü Ames 28314 Iowa ü Ames 28355 Iowa ü Ames 28356 Iowa ü Ames 28358 Iowa ü 332 1117 84 Ames 28359 Iowa ü Ames 28435 Iowa ü Ames 28959 Iowa ü Ames 29047x Oregon ü 599 1067 45 Ames 29048 Oregon ü Ames 29049x Oregon üü 212 260 31 Ames 29155 Rep. Georgia ü Ames 29156 Rep. Georgia ü 238 (108) 814 (360) 86 (83) Ames 29157x Rep. Georgia ü 415 (473) 1370 (1892) 83 (82) Ames 29158 Rep. Georgia ü Ames 29159 Rep. Georgia ü Ames 29160 Rep. Georgia ü Ames 29161 Rep. Georgia ü Ames 29162 Rep. Georgia ü Ames 29232x Oregon ü 446 554 31 Ames 29662 Missouri ü Ames 29663 Illinois ü Ames 29664 Illinois ü Ames 29994x Sichuan, China ü Ames 29995x Japan ü 198 49 6 PI 656839x Iowa ü PI 656840 Iowa ü 230 865 94 PI 656841 Iowa ü PI 656842 Missouri ü zSeed-set when plant populations were grown in isolation cages where cross-pollination was promoted by supplying honeybees. yMaximum seed-set for a single flower is four for Prunella vulgaris. xAccession evaluated for in-bud pollen release. through the Germplasm Resources Information conditions. All digital photographs were taken style without disturbing their positions. Dig- Network (GRIN) database at <http://www.ars-