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Terri Woods Starman, Xiangrong Duan, and Shane Abbitt

DNA amplification fingerprinting (DAF) was used to evaluate the genetic relationships among 11 cultivars of poinsettia (Euphorbia pulcherrima Willd.). Amplification was with 10 octamer oligonucleotide primers that generated 336 DNA bands. Thirty-one percent of the bands were polymorphic and distinguished among cultivars. Genetic relationships were evaluated by cluster analysis, and the resulting dendrogram closely agreed with published cultivar relationships. Arbitrary signatures from amplification profiles (ASAP) were further used to characterize two cultivars, `Nutcracker Red' and `Peterstar Red', that were previously found to be genetically and morphologically similar, as well as five cultivars in the “Freedom” series. The DAF products generated with arbitrary octamer primers were reamplified with mini-hairpin decamer primers in these experiments. The ASAP profiles were complex and yielded a total of 231 bands, 38% of which were polymorphic and capable of distinguishing each Freedom cultivar. Five of the eight primer combinations distinguished `Nutcracker Red' from `Peterstar Red'. Thus, closely related cultivars of poinsettia can be separated using new and improved molecular fingerprinting protocols.

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Robert C. Ebel, Xiangrong Duan, and Robert M. Augé

Mycorrhizal colonization can alter stomatal behavior of host leaves before or during soil drying, but the mechanism of influence is not always clear. We examined the possibility that mycorrhizal symbiosis might result in either altered stomatal sensitivity to abscisic acid (ABA) moving from roots to shoots in xylem sap, or altered movement of ABA in xylem as a function of soil water content (θ). Mycorrhizal colonization of Vigna unguiculata did not change the relationship between stomatal conductance (g s) and xylem [ABA] during drying of whole root systems. Stomatal conductance was higher in mycorrhizal than in similarly sized and similarly nourished nonmycorrhizal plants when soil moisture was relatively high, perhaps related to lower xylem [ABA] in mycorrhizal plants at high soil θ. Neither g s nor xylem [ABA] was affected by mycorrhizae at low soil θ. Higher g s in mycorrhizal plants was evidently not related to a mycorrhizal effect on leaf water status, as neither g s/shoot Ψ nor shoot Ψ/soil θ relationships were altered by the symbiosis. Stomatal conductance was much more closely correlated with xylem [ABA] than with soil θ or shoot Ψ. Decreased xylem [ABA] may explain why mycorrhizal colonization sometimes increases g s of unstressed mycorrhizal plants in the absence of mycorrhizae-induced changes in host nutrition. This work was supported by USDA NRICGP grant 91-37100-6723 (R.M.A).

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Robert M. Augé, Xiangrong Duan, Jennifer L. Croker, Craig D. Green, and Will T. Witte

We compared the potential for foliar dehydration tolerance and maximum capacity for osmotic adjustment in twelve temperate, deciduous tree species, under standardized soil and atmospheric conditions. Dehydration tolerance was operationally defined as lethal leaf water potential (Ψ): the Ψ of the last remaining leaves surviving a continuous, lethal soil drying episode. Nyssa sylvatica and Liriodendron tulipifera were most sensitive to dehydration, having lethal leaf Ψ of –2.04 and –2.38 MPa, respectively. Chionanthus virginiana, Quercus prinus, Acer saccharum, and Quercus acutissima withstood the most dehydration, with leaves not dying until leaf psi dropped to –5.63 MPa or below. Lethal leaf Ψ (in MPa) of other, intermediate species were: Quercus rubra (–3.34), Oxydendrum arboreum (–3.98), Halesia carolina (–4.11), Acer rubrum (–4.43), Quercus alba (–4.60), and Cornus florida (–4.88). Decreasing lethal leaf Ψ was significantly correlated with increasing capacity for osmotic adjustment. Chionanthus virginiana and Q. acutissima showed the most osmotic adjustment during the lethal soil drying episode, with osmotic potential at full turgor declining by 1.73 and 1.44 MPa, respectively. Other species having declines in osmotic potential at full turgor exceeding 0.50 MPa were Q. prinus (0.89), A. saccharum (0.71), Q. alba (0.68), H. carolina (0.67), Q. rubra (0.60), and C. florida (0.52). Lethal leaf Ψ was loosely correlated with lethal soil water contents and not correlated with lethal leaf relative water content.