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  • Author or Editor: Tim Rinehart x
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Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Most cultivars in production belong to the species Hydrangea macrophylla but H. paniculata, H. arborescens, H. serrata, H. aspera, H. heteromalla, H. integrifolia, H. anomala, H. seemanii, and H. quercifolia are also commercially available. In addition to species diversity there is high intra-species variation, particularly in H. macrophylla, which includes mopheads, lacecaps, French, Japanese, dwarf, and variegated varieties. Relatively little is known about the genetic background or combinability of these plants. DNA sequence data, genome size, RAPD, AFLP, and ISSR markers have been used for taxonomic identification and to estimate diversity within the genus. All of these methods have limited usefulness in a large scale breeding program. We recently established microsatellite markers for Hydrangea and evaluated their utility for estimating species diversity and identifying cultivars within H. macrophylla and H. paniculata. We also verified an inter-specific cross between H. macrophylla and H. paniculata using these markers. Future research includes marker assisted breeding, particularly with respect to remontant flowering traits.

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Crapemyrtles (Lagerstroemia) are deciduous shrubs or trees with prolific summer flowers. Their popularity is due in large part to low maintenance requirements in sunny climates, wide range of growth habits, disease resistance, and bark characteristics, as well as having a long flowering period (up to 120 days). Once well-established, they are extremely tolerant to heat and drought. Lagerstroemia was first introduced to the southern U.S. from southeast Asia more than 150 years ago, and is comprised of at least 80 known species. Most modern cultivars are L. indica and L. fauriei hybrids. L. speciosa is a tropical crapemyrtle with very large flowers, but lacks cold hardiness. It is a vigorous plant, but only when grown in Hardiness zones 9 or 10. We recently established microsatellite markers for Lagerstroemia and evaluated their utility for verifying interspecific hybrids. Here we verify F1 hybrids between L. indica `Tonto', `Red River', and L. speciosa. We also genotyped two commercially available L. speciosa hybrids. Currently, we are using crapemyrtle SSRs for cultivar identification and germplasm conservation. Future research includes marker-assisted breeding to produce powdery mildew and flea beetle resistant cultivars, as well as improved growth habit and fall foliage color.

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Production of viable interspecific seedlings from a cross between Lagerstroemia indica L. ‘Tonto’ × L. speciosa (L.) Pers. was confirmed by comparison of morphological traits and genetic markers. Traits such as plant height and width showed marked variation within the seedling population whereas variation in other traits such as flower size and color was very limited. Seedlings were found to be functionally sterile as either male or female parents. Observed sterility prevents the maximum introgression of important complex traits such as cold hardiness by sib mating or backcrossing into clones derived from this parental combination. ‘Princess’ was confirmed to be a sterile hybrid of L. indica and L. speciosa whereas ‘Monia’ was indicated to have L. indica in its ancestry but not L. speciosa.

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Breeding of crapemyrtle (Lagerstroemia) in the United States has focused on developing hybrids between parents with disease or pest resistance and those with good floral characteristics. The objective of this work was to study the general and specific combining ability of several horticulturally important traits in crosses between pest-resistant parents and those with saturated flower colors. Ten crapemyrtle parents were tested in a factorial mating design including 25 of the 29 possible families. Analysis of variance revealed significant differences (P ≤ 0.05) for all traits for the general combining ability of parents. The cross between ‘Arapaho’ and ‘WHIT IV’ displayed the best specific combining ability for a desirable combination of height, leaf-out time, bloom time, and flower color based on current breeding objectives. Overall, this study revealed the importance of both additive and nonadditive genetic variability in crapemyrtle, suggesting that an integrated breeding strategy to capture both additive and dominance variance would be appropriate for producing new, improved crapemyrtle clones for the four traits evaluated.

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