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William A. Hoch, Geunhwa Jung, and Brent H. McCown

A significant pest affecting commonly planted Betula spp. is the birch leafminer (Fenusa pusilla Lepeletier), an insect that can be present in large populations in the landscape and can greatly reduce the vigor and ornamental value of these trees. Twenty-two interspecific crosses were performed between leafminer resistant and susceptible Betula species in an attempt to create the novel combination of ornamental white bark and significant leafminer resistance. Of the nine successful crosses, two produced resistant offspring. Progeny of the diploid × hexaploid cross B. turkestanica Litvin (2x) × B. alleghaniensis Britt. (6x) displayed a broad range of resistance levels, likely the result of segregating alleles contributed by the hexaploid parent. All crosses involving highly resistant individuals of B. costata Trautv. (2x) yielded leafminer susceptible progeny. These results suggest that the larval antibiosis demonstrated by B. alleghaniensis and B. costata is inherited as a recessive trait, and exhibits a gene dosage effect as evidenced by the B. turkestanica × B. alleghaniensis offspring. While most progeny of the B. populifolia Marsh (2x) × B. maximowicziana Regal (2x) cross were susceptible, a single resistant offspring, which was found to be triploid (3x), displayed a mechanism of resistance similar to that of a hypersensitive response. No strong intersectional barriers to hybridization were observed and all interploidy crosses were successful. The chromosome numbers of B. costata (2n = 2x = 28) and B. turkestanica (2n = 2x = 28) are reported here for the first time. The results of this study indicate that the potential exists for the development of insect resistant, ornamental white-barked birch clones through the implementation of a planned, systematic breeding program.

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Douglas C. Doehlert, Tsung Min Kuo, John A. Juvik, Eric P. Beers, and Stanley H. Duke

Metabolic characteristics of developing sugary-l maize (Zea mays L.) endosperms were investigated. In the later stages of development (>30 days postpollination), sugary-1 kernels maintained higher levels of many enzyme activities and retained more moisture than normal kernels. Higher enzyme activities were attributed to moisture retention and were not associated with any increase in dry weight accumulation. Of enzyme activities measured at 20 days postpollination, that of ADP-glucose pyrophosphorylase was higher in sugary-1 kernels than in normal, whereas total amylase, a-amylase, and pullulanase activities were lower. Experiments testing the effects of zero, one, two, and three doses of the sugary-1 gene in OH43 endosperms indicated that the sugary-1 phenotype was not expressed until three doses of the sugary-1 gene were present. Decreased activities of amylases, but not of pullulanase, were attributed to an interference in detection by phytoglycogen. Increased ADP-glucose pyrophosphorylase activity is attributed to a response by the maize endosperm cells to increased sucrose concentrations.

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Anne C. Kurilich, Shyh-Shyan Wang, and John A. Juvik

Inbreds IL451b sugary1 (su1) and IL678a su1 isogenic for the sugary enhancer1 (se1) gene mutation were used to analyze the relationship between se1 gene dosage and endosperm sugar content. Each line was self-pollinated and reciprocal crosses were made between the isolines of each genotype to produce se1 gene dosages of 0, 1, 2, and 3 in the triploid endosperm. Ears were harvested at 15, 18, 21, 24, 27, and 45 days after pollination (DAP). Whole kernels were freeze-dried, ground into powder, and stored at –80°C until subsequent chemical analyses. Sucrose, glucose and fructose were analyzed using high-pressure liquid chromatography (HPLC), the results of which indicated a significant increase in kernel sugar content when the se1 allele is homozygous.

\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[\begin{array}{lcl}&\underline{\mathrm{Sucrose\ content\ at}{\ }21{\ }\mathrm{DAP}(\%{\ }\mathrm{dry}{\ }\mathrm{wt})}&\\\underline{se1{\ }\mathrm{dose}}&\underline{\mathrm{IL}{\ }451\mathrm{b}}&\underline{\mathrm{IL}{\ }678\mathrm{a}}\\0&9.6&10.3\\1&8.0&10.7\\2&11.3&10.9\\3&15.8&12.2\end{array}\] \end{document}

Sucrose content at 21 DAP (typical maturity for harvesting) was observed to increase in the IL451b and IL678a backgrounds from zero to three doses of se1 by 65% and 18% respectively, indicating that this mutation varies in its expression in different genetic backgrounds. Associations between kernel phytoglycogen and starch content and se1 gene dosage are presented. The biochemical lesion associated with the se1 gene product is discussed.

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Manoel T. Souza Jr., Paula F. Tennant, and Dennis Gonsalves

Line 63-1 is a `Sunset'-derived transgenic papaya expressing the coat protein (CP) gene from a mild mutant of a Hawaiian isolate of Papaya ringspot virus (PRSV). Previous work showed that line 63-1 R1 plants exhibited a range of resistance to severe PRSV isolates from Hawaii (HA), Jamaica (JA), Thailand (TH), and Brazil (BR). Genetic and molecular data obtained in this study confirm that line 63-1 has two CP transgene insertion sites; segregation analysis shows that the CP and the npt II genes are present at both loci. To study the potential effect of gene dosage on resistance, various populations of R1, R2, and R3 seedlings were challenged by PRSV HA, BR, and TH. A R1 population obtained by self-pollination of line 63-1 hermaphrodite R0 plant exhibited resistance to all three isolates. The percentage of plants resistant to all three PRSV isolates increased in 63-1-derived populations as a result of recurrent selection. Additional genetic studies demonstrate that the number of resistant plants in a 63-1-derived population is directly correlated with the number of plants with multiple transgene copies. We conclude that transgene dosage plays a major role in affecting the resistance of 63-1 to PRSV isolates from various geographical locations.

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Jiangbo Dang, Tingrong Wu, Guolu Liang, Di Wu, Qiao He, and Qigao Guo

additive. Imbalanced gene expression usually occurs in aneuploid plants presumably due to the abnormal chromosome numbers ( Huettel et al., 2008 ). Such changes in gene dosage are likely to be associated with the specific phenotypes found in aneuploid

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Jin Wang, Yue Liu, Xueliang Chen, and Qiusheng Kong

). Furthermore, three functional models are used to describe the functions of the retained duplicated genes, including gene dosage, sub-functionalization, and neo-functionalization ( Flagel and Wendel, 2009 ). Gene dosage is one mechanism that affects the

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Mingxiu Liu, Peng Wang, Xu Wei, Qing Liu, Xiaolin Li, Guolu Liang, and Qigao Guo

not only the increase in gene dosage through the change in chromosome numbers but also the genetic background of the donor genotype. Nevertheless, through this work, we have been able to select triploid loquat plants with high accumulations of

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Shujun Zhou, Xin Tan, Liqin Fang, Jia Jian, Ping Xu, and Guoliang Yuan

, 2005 ; Carputo et al., 1999 ; Johnston and Hanneman, 1982 ; Johnston et al., 1980 ), the genome composition of the endosperm itself ( Dowrick and Brandram, 1970 ), and the effect of differential gene dosage (genome imprinting) ( Dikes and Comai, 2004

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Takashi Akagi, Yumi Takeda, Keizo Yonemori, Ayako Ikegami, Atsushi Kono, Masahiko Yamada, and Shinya Kanzaki

methodology of qPCR analysis for quantitative genotyping. Quantitative PCR to determine the gene or allele dosage was first used in the field of medicine ( Ochshorn et al., 2006 ; Zimmermann et al., 2002 ) because changes in gene dosage cause significant

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Guo-Gui Ning, Xue-Ping Shi, Hui-Rong Hu, Yan Yan, and Man-Zhu Bao

relationship between ploidy level and flower form. Because diploid, triploid, and tetraploid double flowers of petunia were found with no significant difference in petal number, we conclude that there is no gene dosage effect with regard to this trait