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Journal of Heredity 2007:98(4):356–359 doi:10.1093/jhered/esm046 Advance Access publication June 29, 2007 ª The American Genetic Association. 2007. All rights reserved. For permissions, please email: [email protected]. Genetic Control of Albinism in Pickerelweed (Pontederia cordata L.) LYN A. GETTYS AND DAVID S. WOFFORD Department of Agronomy Plant Genetics and Breeding, University of Florida IFAS, 304 Newell Hall, Box 110500, Gainesville, FL 32611-0500. Address correspondence to L. Gettys at UF/CAIP, 7922 NW 71 Street, Gainesville FL 32653, or e-mail: [email protected]. Pickerelweed (Pontederia cordata L.) is a diploid (2n 5 2x 5 16) perennial aquaphyte. Preliminary studies revealed that a group of nonalbino pickerelweed plants maintained for breeding and inheritance studies regularly produced albino seedlings. The objective of this experiment was to determine the number of loci, number of alleles, and gene action controlling albinism in pickerelweed. Five nonalbino parental lines were used in this experiment to create S1 and F1 populations. F2 populations were produced through self-pollination of F1 plants. Evaluation of S1, F1, and F2 generations allowed us to identify a single diallelic locus controlling albinism in these populations of pickerelweed, with albinism completely recessive to normal green leaf production. We propose that this locus be named albino with alleles A and a. Pickerelweed (Pontederia cordata L.) is a diploid (2n 5 2x 5 16) perennial aquaphyte found in marshes, swamps, streams, ditches, and shallow water along the margins of lakes and ponds (Godfrey and Wooten 1979; Bell and Taylor 1982; Tobe et al. 1998). The species is widely used as an ornamental in water gardens and as a native plant in wetland mitigation and restoration projects. Preliminary studies of pickerelweed revealed that albino seedlings were regularly produced by a group of normal (nonalbino) plants maintained for breeding and inheritance studies. Albino plants lack chlorophyll and are nonphotosynthetic; as a result, these plants are unable to generate the energy required to sustain life. Chlorophyll deficiencies may develop as a result of point mutations (Svab and Maglia 1986) or deletions (Day and Ellis 1984), but the impact on plant survival is the same—albinism is lethal in pickerelweed and other nonparasitic plant species. The phenomenon of albinism has intrigued researchers for years, and genetic control of the trait has been described in a number of species (see Börner and Sears 1986; Klekowski and Godfrey 1989). Albinism may be controlled by a single locus or by multiple loci, but this lethal trait is necessarily recessive to normal green leaf production. Single gene control of albinism has been described in a number of species, including maize (Shull 1915; Neuffer et al. 1997), soybean (Barwale and Widholm 1987), and Western 356 white pine (Bingham et al. 1972), whereas two or more loci control the trait in plantain–banana hybrids (Ortiz and Vuylsteke 1994), Solanum chacoense (Birhman et al. 1994), and groundnut (Coffelt and Hammons 1971, 1973; Dwivedi et al. 1984). There is no published information describing the genetic control of albinism in pickerelweed. The objective of this experiment was to determine the number of loci, number of alleles, and gene action controlling albinism in an experimental population of pickerelweed. Materials and Methods The plants used in this experiment were part of a population maintained for genetic and breeding studies at the University of Florida in Gainesville. All plants were grown in 1-l nursery containers filled with a commercially available potting mix amended with 10 g of controlled-release fertilizer per container. Plants were subirrigated and kept in a pollinator-free glasshouse with air temperature maintained at 27 C (day) and 16 C (night). Most plants produced more flowers when grown under long days; therefore, supplemental lighting was employed to artificially extend daylength to 16 h in this study. Five parent plants (coded WS, WM, BS, BM, and BL) were utilized in this experiment; all were nonalbino with normal green leaves. Parent WS was purchased from a commercial source, while the remaining parents were collected from natural populations throughout southern Florida. Each collected parent was selected from a different geographically isolated location so it is unlikely they share a common ancestor. Each parent was self-pollinated to create the S1 families WS 5, WM 5, BS 5, BM 5, and BL 5. Cross- and reciprocal pollinations were performed between parents to create the F1 families WS BM, WS BL, WM BS, WM BL, BS BM, BS BL, and BM BL. Representative nonalbino samples were selected from each F1 family and self-pollinated to generate F2 families. Cross- and reciprocal pollinations to create F1 families were performed between December 2001 and April 2002, while self-pollinations of parents and F1 plants (to produce S1 and F2 families, respectively) were conducted between January and June 2003. Brief Communications All flowers in each inflorescence were pollinated using the same pollen source. Anthers borne superior to stigmas were removed to facilitate access to the stigmatic surface and to prevent self-pollination when appropriate. Daily pollination data were recorded on jewelry tags placed on each inflorescence. Each completed inflorescence was enclosed in a small mesh bag and secured with a plastic-covered twist tie until fruits were ripe (usually 23–30 days after completion of pollinations). Fruits were air-dried for ;7 days and then dried floral tissue was removed from the enclosed seeds with a rubber-covered rub board. Seeds were germinated under ;5 cm of water in glass half-pint (250 ml) bottles, with additional water added as needed to maintain a constant depth. Germinated seeds were scored for leaf color (green or albino) several times each week, and germination conditions were maintained for a minimum of 8 weeks. Identification of seedlings expressing albinism was possible 2 or 3 days after radicle emergence, as leaves of albino seedlings were pure white with no traces of green (Figure 1). Affected seedlings were monitored for an additional 7–10 days after germination to ensure that the classification of albinism was accurate. Selected nonalbino F1 seedlings were transplanted into 612 cell packs filled with a commercially available potting mix and irrigated with an automatic mist system for 3–4 weeks until the seedlings were ;30 cm tall. These F1 seedlings were transplanted into 1-l nursery containers, sub-irrigated, and kept in a pollinator-free glasshouse under the conditions described above. Plants were grown to reproductive maturity and then self-pollinated to produce F2 seeds. No maternal effects were noted; therefore, data for each family were pooled within each cross/reciprocal set. Data from S1 and F1 families were used to develop a working model of genetic control of albinism in pickerelweed. Development of this model allowed the assignment of genotypes to parents; the model was then verified by analyses of F2 families. All data were analyzed using goodness-of-fit (chi-square or v2) tests with Yates’ correction for continuity (Steel et al. 1997). A test for heterogeneity of the data for F2 families from different crosses was performed to determine whether it was appropriate to pool data for all F2 progeny. Results and Discussion All S1 progeny in the families BS 5 and BM 5 had normal green leaves. The S1 family WS 5 produced 44 green and 22 albino seedlings, while WM 5 was composed of 50 green and 21 albino seedlings. The family BL 5 also segregated for albinism and had 77 green and 27 albino seedlings. The segregation patterns of the S1 families WS 5, WM 5, and BL 5 were not statistically different from a 3 green:1 albino ratio (P 5 0.1179, P 5 0.3730, and P 5 0.8208 for WS 5, WM 5, and BL 5, respectively). All F1 progeny in 5 of the families had normal green leaves, while progeny in the F1 families WS BL and WM BL segregated for albinism in patterns that were not statistically different from a 3 green:1 albino ratio (Table 1). The simplest model that would produce the seedling types recovered in these S1 and F1 families is a model with 2 alleles at Figure 1. Albino seedling of pickerelweed. one locus and green leaves completely dominant to albino leaves. Genotypes were assigned to all 5 parents using the proposed model and segregation of S1 and F1 progeny. The parents BS and BM were homozygous dominant (AA), while the parents WS, WM, and BL were heterozygous (Aa). Multiple nonalbino plants were randomly selected from each of the 7 F1 families and self-pollinated to create segregating and nonsegregating F2 populations. Six of the 7 F2 population ratios conformed to those expected under the proposed model, but populations from the family WS BL differed from the expected ratio (Table 2). The deviation in this single family is small (P 5 0.04) and is most likely due to sampling error, given the small number of F1 plants that were self-pollinated and the strong support for the model provided by the other families in this experiment. Chi-square analysis of segregating populations revealed that progeny in each population segregated in a manner that did not differ from the expected 3 green:1 albino ratio. Tests for heterogeneity among populations within each family were not significant, so intrafamily data were pooled. These pooled intrafamily F2 progeny segregated in a 3 green:1 albino ratio as expected (Table 1). Heterogeneity chi-square analysis performed on all segregating F2 populations was not significant (P 5 0.21), so all data for segregating F2 progeny were pooled. These pooled progeny segregated in a manner that was not significantly different from the expected 3 green:1 albino ratio (Table 1). Conclusions The results of this experiment suggest that albinism in these populations of pickerelweed is controlled by 2 alleles at one locus; gene action is completely dominant, with albinism recessive to production of normal green leaves. Our research with these populations of pickerelweed revealed that selfpollination of homozygous plants (genotype AA) produced only green-leaved offspring, whereas self-pollination of 357 Journal of Heredity 2007:98(4) Table 1. Classification of plants of pickerelweed in the F1 and F2 generations for green or albino leaf color. Cross- and reciprocal pollinations are pooled within each parental set and are listed by the cross (e.g., observations attributed to WS BM include data from WS BM and from BM WS). Chi-square values for segregating populations are based on a Mendelian 3:1 ratio No. of plants observed Expected ratio No. of plants expected Green Albino Green Albino v2 P Parents Generation Genotype Green Albino WS BM WS BM WS BM WS BL WS BL WS BL WM BS WM BS WM BS WM BL WM BL WM BL BS BM BS BM BS BL BS BL BS BL BM BL BM BL BM BL All seg. F2, families. F1 F2 F2 F1 F2 F2 F1 F2 F2 F1 F2 F2 F1 F2 F1 F2 F2 F1 F2 F2 Aa AA AA 5 Aa 5 Aa Aa AA 5 Aa 5 Aa AA AA 5 Aa 5 Aa Aa AA 5 Aa 5 AA AA AA 5 AA Aa AA 5 Aa 5 AA Aa AA 5 Aa 5 149 609 317 70 191 1165 125 795 533 65 445 1043 141 1152 84 917 542 109 598 598 0 0 128 22 0 399 0 0 159 28 0 368 0 0 0 0 167 0 0 217 — — 3 3 — 3 — — 3 3 — 3 — — — — 3 — — 3 — — 1 1 — 1 — — 1 1 — 11058.25 — — — — 1 — — 1 — — 333.75 69 — 1173 — — 519 69.75 — 352.75 — — — — 531.75 — — 611.25 — — 111.25 23 — 391 — — 173 23.25 — 0.88 — — — — 177.25 — — 203.75 — — 3.36 0.06 — 0.22 — — 1.51 1.29 — 0.37 — — — — 0.79 — — 1.15 — — 0.08 0.91 — 0.66 — — 0.24 0.31 — — — — — — 0.40 — — 0.28 F2 Aa 5 4198 1438 3 1 4227 1409 0.80 0.37 heterozygous plants (genotype Aa) resulted in green and albino progeny in a Mendelian 3:1 ratio. We propose that this locus controlling albinism in pickerelweed be named albino with alleles A and a. Single-gene control of albinism is not uncommon in the plant kingdom. Shull (1915) described similar genetic systems that control 2 types of albinism in maize—one producing pure white seedlings and the other resulting in yellowish white (chlorina) seedlings; both types of albinism are recessive, simply inherited, and controlled by a single diallelic locus. Neuffer et al. (1997) listed a multitude of other systems (e.g., the white, luteus, and chlorophyll loci) that condition albinism in maize in the same manner. Barwale and Widholm (1987) identified a chlorophyll deficiency in soybean that is controlled by a single recessive gene, while Bingham et al. (1972) reported that albinism in Western white pine is conditioned by a single recessive gene as well. Recessive lethal alleles are routinely maintained in heterozygous individuals within populations and typically have no deleterious effect on the fitness of heterozygous plants; however, it is unclear whether lethal recessive alleles provide any hidden benefit to populations. Table 2. Classification of segregating (S; F1 parent 5 Aa) and nonsegregating (NS; F1 parent 5 AA) F2 populations of pickerelweed derived from self-pollination of F1 plants. Cross- and reciprocal pollinations are pooled within each parental set and are listed by the cross (e.g., observations attributed to WS BM include data from WS BM and from BM WS) No. of F2 population No. of F2 population Observed Expected ratio Expected Parents Genotype S NS S NS S NS v2 P WS BM WS BL WM BS WM BL BS BM BS BL BM BL Aa AA Aa Aa Aa AA Aa Aa AA AA AA Aa AA Aa 10 22 9 17 0 5 11 10 3 6 7 12 7 9 1 2 1 2 — 1 1 1 1 1 1 — 1 1 10 16.67 7.5 16 — 6 10 10 8.33 7.5 8 — 6 10 0.00 4.20 0.27 0.05 — 0.08 0.05 0.99 0.04 0.61 0.83 — 0.77 0.82 358 Brief Communications Acknowledgments This research is presented by the senior author as partial fulfillment for the Doctor of Philosophy degree and was supported by the Florida Agricultural Experiment Station. Mention of a trademark or a proprietary product does not constitute a guarantee or warranty of the product by the Florida Agricultural Experiment Station and does not imply its approval to the exclusion of other products that may be suitable. We would like to thank David Sutton, Paul Pfahler, and Eric Ostmark for their contributions to this experiment. Dwivedi SL, Nigam SN, Pandey SK, Gibbons RW. 1984. Inheritance of albinism in certain interspecific and intersubspecific crosses in groundnut (Arachis hypogaea L.). Euphytica. 33:705–708. Godfrey RK, Wooten JW. 1979. Aquatic and wetland plants of southeastern United States: monocotyledons. Athens (GA): The University of Georgia Press. Klekowski EJ Jr, Godfrey PJ. 1989. Ageing and mutation in plants. Nature. 340:389–391. Neuffer MG, Coe EH, Wessler SR. 1997. Mutants of maize. Plainville (NY): Cold Spring Harbor Laboratory Press. References Barwale UB, Widholm JM. 1987. Somaclonal variation in plants regenerated from cultures of soybean. 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