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Richard A. Criley and Setapong Lekawatana

Although in florescences of H. chartacea `Sexy Pink' can be harvested year'round in Hawaii, flowering is heaviest during the summer while demand is higher during winter months. The research was directed at identifying influences affecting the timing and rate of flower development, Dissection of apices of pseudostems which began development during June-July showed reproductive development (3-6 cm) in Jan-Feb when @6 leaves had unfurled. Some pseudostems had aborted the growing point after initiation had occurred. Data from 141 flowering pseudostems over 2 years of sampling showed that approx. 46 weeks were required from shoot emergence to flowering. Seasonal variation existed for leaf number and developmental period. The paper will analyze the influence of temperature on these two components of flowering.

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Warner Orozco-Obando, Gwen N. Hirsch, and Hazel Y. Wetzstein

The general doctrine of flowering in Hydrangea macrophylla (Thunb.) Ser. is that floral induction occurs during the fall months with the flower appearing the following spring or summer. However, hydrangea cultivars differ widely in their relative abundance and duration of flower production. The objective of this study was to determine how developmental flowering patterns compared among different hydrangea genotypes. Flowering was characterized in 18 cultivars by assessing flower initiation in dormant buds of 1-year-old stems that received natural outdoor inductive conditions. Terminal and lateral buds were dissected and floral developmental stage categorized microscopically. In terminal buds, flower development was very consistent and occurred in 100% of buds for all cultivars except `Ayesha' (33%). In contrast, lateral buds showed a wide variation in flower induction among genotypes. `Ayesha', `Blushing Pink', `Freudenstein', and `Nigra' had 10% or fewer lateral buds with floral initials. `All Summer Beauty', `David Ramsey', `Masja', `Nightingale', and `Penny Mac' showed high levels of floral induction (>92%). Within a cultivar, flower development was more advanced in terminal than lateral buds. In several cultivars, a significant correlation between bud size (length) and floral stage was found. However, low r-square values indicated that flower stage was explained largely due to factors other than bud length. This study shows that floral induction patterns vary markedly among hydrangea cultivars and provides insight into why cultivars differ in the extent and reliability of seasonal blooming. Genotypes that possess floral primordia in lateral buds would be amenable to cultural practices that enhance lateral budbreak and recurrent blooming.

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Carolyn E. Lister, Jane E. Lancaster, and John R.L. Walker

Phenylalanine ammonia-lyase (PAL) activity was measured in a range of New Zealand-grown apple (Malus domestica Borkh.) cultivars at three stages of fruit development. Anthocyanin and total flavonoid levels were also measured (by HPLC) in the same fruit. There was wide variation in the level of PAL activity, anthocyanin and total flavonoid levels in different apple cultivars and at different stages of development. There was no apparent correlation between average PAL activity over the three developmental stages and final anthocyanin concentration (r = 0.34, P > 0.1), but there was significant correlation between average PAL activity over the three developmental stages and the final concentration of total flavonoids (r = 0.75, P < 0.02). An inhibitor, PAL-IS, was also assayed in the same fruit but no correlation was found between PAL-IS and final anthocyanin levels (r = -0.30, P > 0.1) or total flavonoid levels (r = 0.15, P > 0.1). These results suggest that PAL activity has an influence on total flavonoid levels in the fruit but that PAL-IS does not. Anthocyanin levels are likely controlled at a point in the flavonoid pathway other than PAL or PAL-IS.

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Darlene M. Lawson, Minou Hemmat, and Norman F. Weeden

Five morphological and developmental traits (branching habit, vegetative budbreak, reproductive budbreak, bloom time, and root suckering) were analyzed in a family obtained from the apple (Malus domestica Borkh) cross `Rome Beauty' × `White Angel'. The phenotypic variation in these traits was compared with a selected set of marker loci covering the known genome of each of the parents to locate genes with major effects on the traits. The contrasting branching habits of the two parents appeared to be controlled by at least two loci. One of these, Tb, governed the presence or absence of lateral branches, particularly on the lower half of shoots. The locus was heterozygous in `White Angel' and was mapped to a 5 CM interval on linkage group 6. At least one other locus conditioning spur-type branching appeared to be segregating, but the locus or loci could not be linked to segregating markers. The timing of initial vegetative growth was tightly associated with the chromosomal region in which the Tb gene is located and maybe a pleiotropic effect of this gene. Time of reproductive budbreak correlated with segregation at the isozyme marker, Prx-c, on linkage group 5. Variation in time of bloom and later stages in flower development appeared to be controlled by different genes not linked to Prx-c. The tendency to produce root suckers cosegregated with a marker on `White Angel' linkage group 1, suggesting control by a single locus, Rs. Data from a `Rome Beauty' x `Robusta 5' family provided additional information on the inheritance of these traits.

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ZhaoSen Xie, Charles F. Forney, WenPing Xu, and ShiPing Wang

organization based on source-sink relationship: New findings on developmental, biochemical and molecular responses to environment 263 280 Roubelakis-Angelakis K.A. Molecular biology & biotechnology of grapevine Kluwer Academic Publishers

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Zhi-li Suo, Wen-ying Li, Juan Yao, Hui-jin Zhang, Zhi-ming Zhang, and Di-xuan Zhao

Tree peony cultivars are usually classified according to flower characteristics (flower form and flower color) which are commonly affected by environmental influences and developmental levels. Judgment of flower forms may also depend on the observer. Precise and rapid cultivar identification methods are also required to manage cultivar collections as well as tree peony breeding programs. The objective of this paper is to analyze the discriminatory ability of leaf morphology and Intersimple sequence repeat (ISSR) marker systems for tree peony cultivars. As a result, although there exist large variations of leaf morphology of tree peony cultivars, the morphological characteristics of biternately compound leaves 3, 4, and 5 from the base of a shoot at the middle part of a plant are relatively stable with smaller variations within cultivars (2.7% to 27.1%, 16.8% on average) and with larger differentiations among cultivars (72.9% to 97.3%, 83.2% on average). Statistical and principal components analyses indicate that 12 leaf morphological characteristics are valuable for cultivar classification. ISSR markers present a precisely discriminatory power in tree peony cultivar classification without environmental influences. The cultivars with multiple flower forms, which makes it difficult to make judgment by means of a flower-form-based classification system, have been significantly characterized using leaf morphology or ISSR markers.

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Ryan J. Hayes*, Ed Ryder, and Bert Robinson

Big vein (BV) disease of lettuce is caused by soil borne fungal vectored viruses, and reduces marketability through head deformation. Tolerant cultivars reduce BV frequency, but no resistant cultivars exist. L. virosa L. is highly resistance. The objectives were to 1) determine if L. virosa P.I.s exhibit variation for resistance, and 2) determine if resistance is transferable to lettuce. Seedlings were inoculated with root macerate of BV infected plants, transplanted to BV infested soil, and greenhouse grown for 3 months. Twelve plants in each of 1,2, or 3 reps of Great Lakes 65 (GL65-susceptible), Pavane (Pav-tolerant), L. virosa (11 accessions), and BC1 F2 through F5 families of lettuce cultivars x L. virosa accession IVT280 were tested. The percentage of BV afflicted plants was recorded. In hybrid families, BV free plants from tolerant families were selected and advanced. No BV was found in L. virosa. Variation for tolerance was observed in BC1 F2 and F3 families; 33% had greater tolerance than Pav (17% afflicted). Additional tests identified 11 BC1 F3 families (14%) with greater tolerance than Pav (42% afflicted). Subsequent BC1 F4 and F5 generations however, were more susceptible than Pav. Lactuca virosa is highly resistant, but resistance did not transfer to hybrid progeny. Variation for tolerance was observed in BC1 F2 and F3 families, but later generations were susceptible. Interactions or linkage of genes for developmental processes and BV resistance may hinder introgression. Introgression will continue using congruity backcrossing and a greater diversity of L. virosa.

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Ana Fita, Belén Picó, and Fernando Nuez

Roots are critical for plants to withstand environmental abiotic and biotic stresses. Wild taxa are often used as source of variation for improving root systems, as they are adapted to more stressful soil environments than their cultivated relatives. We studied the genetics of traits related to root biomass, root length, and root architecture (considering the primary/secondary and the tertiary root levels) in melon (Cucumis melo L.) in a 2-year assay by examining the root systems of mature plants in 91 F3 families derived from the cross between a wild accession, Pat 81 [C. melo ssp. agrestis (Naud) Pangalo], and a cultivated accession, `Piel de sapo' (C. melo ssp. melo L.). Despite the difficulties of working with adult plants, we found that Pat 81 and `Piel de sapo' differ greatly in their mature root systems, which is in concordance with the results previously obtained with young roots. Pat 81 developed roots with less biomass than `Piel de sapo', but this wild accession had more favorable root length and architectural traits: a higher density of framework roots, more uniformly distributed along the soil profile, longer laterals with a higher density of branches, and a higher number of root orders. This root structure is linked to a deeper rooting ability and to the capacity of exploiting a larger soil volume. The genetic analysis indicated that length and architectural traits are more stable than biomass traits, both between years and between developmental stages. Moderate to low broad- and narrow-sense heritabilites were found for root length and architectural traits, with most of the observed variation due to additive effects. Our results suggest that Pat 81 could be used as donor of valuable genes for increasing root length and improving the root architecture of cultivated melons, producing melons potentially more tolerant to soil stresses. The lack of phenotypic and genetic correlations between length and architectural parameters and root biomass suggest that root structure can be successfully improved without increasing carbon expenditures.

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Joanne A. Labate, Larry D. Robertson, Angela M. Baldo, and Thomas Björkman

Broccoli (Brassica oleracea L. var. italica Plenck) and cauliflower (B. oleracea var. botrytis DC) are closely related botanical varieties. The underlying genetic bases of their phenotypic differences from each other are not well understood. A molecular genetic marker enabling B. oleracea germplasm curators and breeders to predict phenotype from seeds or seedlings would be a valuable tool. Mutant alleles at flower developmental pathway loci BoAP1-a, Bo-CAL-a, and glucosinolate biosynthetic pathway locus BoGSL-ELONG have been reported to be associated with a cauliflower phenotype. We surveyed mutant alleles at these three loci in a genetically diverse sample of broccoli and cauliflower accessions from the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Plant Genetic Resources Unit (PGRU) and the University of Warwick, Genetic Resources Unit of Warwick HRI (HRI). Phenotypic and genotypic data were collected for multiple plants per accession during two field seasons. Simple genetic models assuming dominance or codominance of alleles were analyzed. Goodness-of-fit tests rejected the null model that the mutant genotype was associated with a cauliflower phenotype. A correlation analysis showed that BoAP1-a and BoCAL-a alleles or loci were significantly correlated with phenotype but the fraction of variation explained was low, 4.4% to 6.3%. Adding BoGSL-ELONG to the analysis improved predictive power using the linear regression procedure, Maximum R-square Improvement (max R 2). In the best three-variable model, only 24.8% of observed phenotypic variation was explained. Because tested genetic models did not hold robustly for the surveyed accessions, it is likely that there are multiple genetic mechanisms that influence whether the phenotype is broccoli or cauliflower. Our results in commercial cultivars indicate that other genetic mechanisms are more important in determining the horticultural type than are BoAP1-a and BoCAL-a.

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James W. Olmstead, Amy F. Iezzoni, and Matthew D. Whiting

Although maximizing fruit size is critical for profitable sweet cherry (Prunusavium L.) production, little is known about the cellular differences among and between cultivars that contribute to fruit size differences. A wide range of fruit size exists among sweet cherries, and, due to cultural and environmental differences, significant variation exists among genetically identical fruit from the same cultivar. To determine the relative contributions of flesh cell number and cell size to final fruit size in sweet cherry, equatorial sections of three cultivars with a wide range in final average fruit size [`New York 54' (NY54; 1.4 g fresh weight, 11.8 mm diameter), `Emperor Francis' (EF; 6.1 g, 21.0 mm), and `Selah' (12.8 g, 25.5 mm)] were created from mature fruit. Cells intersecting a transverse line were counted and average cell length was calculated. The average cell numbers were significantly different (P ≤ 0.05) between `NY54', `EF', and `Selah' (26.7, 47.4, and 83.2, respectively), indicating that flesh cell number is the major contributor to differences in fruit size between cultivars. Flesh cell numbers of `NY54', `EF', and `Selah' were similar at bloom and increased rapidly for a short duration after fertilization, suggesting a key developmental period for fruit size differences. To determine the contribution of cell number differences to variation in fruit size within a cultivar, fruit from `Bing' and `Regina' trees exhibiting a range of size due to cultural and environmental differences were measured. In both cases, average cell number was not significantly different (P = 0.9, P = 0.3, respectively), while average cell size was (P ≤ 0.05), further indicating fruit flesh cell number is a genetically controlled trait.