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Khalil R. Jahed and Peter M. Hirst

seed set), and the other fuses with the two polar nuclei to produce the endosperm. Pollen source and temperature have a tremendous influence on the rate of pollen tube growth. Jackson (2003) and Petropoulou and Alston (1998) proposed that the

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Chao Gao, Deyi Yuan, Ya Yang, Bifang Wang, Dongming Liu and Feng Zou

= 400 μm. CC = canal cell; Co = cortex; En = endodermis; Ep = epidermis; Ov = ovule; Pa = papilla; PT = pollen tube; TT = transmitting tissue; VB = vascular bundle. Therefore, in this study, we explored the processes of pollen tube growth and

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Candace N. DeLong, Keith S. Yoder, Leon Combs, Richard E. Veilleux and Gregory M. Peck

Apple pollination occurs when pollen is transferred, often by an insect vector, from the anthers of one blossom to the stigma of another. After pollen grains are deposited, they are rehydrated by stigmatic secretions, and pollen tube growth begins

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Thomas M. Kon, James R. Schupp, Keith S. Yoder, Leon D. Combs and Melanie A. Schupp

( Byers, 2003 ). An inherent challenge with blossom thinning is the short period of time that growers have to apply treatments over large acreage ( Moran and Southwick, 2000 ). Models have been developed to estimate the rate of pollen tube growth in apple

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Keith Yoder, Rongcai Yuan, Leon Combs, Ross Byers, Jim McFerson and Tory Schmidt

and fertilization through damaging the anthers, stigma, and style of flowers or inhibiting pollen tube growth in the style of flowers and are applied when some, but not all, flowers are fertilized ( Fallahi and Willemsen, 2002 ; Greene, 2002

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Nachida Ben-Njima

Group-author : R. Socias i Company

Pollen tube growth was studied in 10 almond [Prunus amygdalus Batsch, syn. P. dulcis (Mill.) D.A. Webb] selections of the Zaragoza breeding program, whose main objective is the development of self-compatible cultivars. Self-compatibility was evident in eight of the selections, as indicated by the fact that pollen tube growth was similar following self- and cross-pollination. In the other two selections, pollen tube growth differed following self- and cross-pollination, one showing self-incompatibility and the other an irregular progression of crossed pollen tubes. The importance of the style in sustaining pollen tube growth was evident, and pollen tube growth was influenced by style type.

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Levava Roiz, Uzi Ozeri, Raphael Goren and Oded Shoseyov

Aspergillus niger B-1 (CMI CC 324626) extracellular RNase (RNase B1) was purified to homogeneity. It was found to contain two isoforms of 32- and 40-kDa glycoproteins, sharing a 29-kDa protein moiety. Optimal RNase activity was observed at 60 °C and pH 3.5. In `Almog' peach [Prunus persica (L.) Batsch (Peach Group) `Almog'] and `Murcott' tangerine (Citrus reticulata Blanco `Murcott') the enzyme inhibited pollen germination and pollen tube growth in vitro as well as in vivo. In field experiments, spray application of the RNase caused a reduction in `Fantasia' nectarine [Prunus persica (L.) Batsch (Nectarine Group) `Fantasia'] fruit set and interfered with embryo development. The biological effect of the RNase may be of horticultural value, due to its potential to control fertilization.

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Anson E. Thompson, David A. Dierig and Jon P. Rebman

Vernonia galamensis (Cass.) Less. (Asteraceae) constitutes a species complex of six subspecies, one of which contains four varieties. Crossing barriers between the subspecies and varieties are being examined. In the analysis of microspore mother cells, no differences in chromosome number (n=9) were found, and meiosis appeared to be normal within and between subspecies. However, an extended delay in time was observed in all subspecies in which chromosomes remained condensed during the post-meiotic tetrad stage. No apparent effect on pollen formation or pollen tube growth was observed from this unusual phenomenon. Self and reciprocal intraspecific crosses are being made, and pollen tube growth into the ovules assessed by fluorescent microscopy. These techniques are being used to characterize self-incompatibility within subspecies and varieties, and to determine the possible barriers to pollen tube growth and autofertility.

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Patricio A. Brevis, D. Scott NeSmith and Hazel Wetzstein

Effective pollination period (EPP) is the number of days during which pollination is effective to produce a fruit. The EPP is determined by ovule longevity, pollen tube growth rate and length of stigmatic receptivity. The objectives of this research were to establish the EPP of rabbiteye blueberry and to further the understanding of its limiting parameters. The experiments were conducted in growth chambers using blueberry plants of the cultivars Brightwell and Tifblue. Emasculated flowers were hand-pollinated at 0, 2, 4, 6, and 8 days after anthesis (DAA). Ripe fruit were harvested to record percentage fruit set. Stigmatic receptivity was evaluated as the number of germinated tetrads on the stigma 24 hours after pollination. Under day/night temperatures of 23/10 °C, the EPP was 7 days. Stigmatic receptivity was lowest on the day of anthesis and increased as flowers aged. Stigmatic receptivity was not positively correlated to fruit set, therefore, this parameter was not the most limiting factor of the EPP. Observations of pistils pollinated 3 DAA indicated that the fastest growing pollen tubes reached the bottom of the style 2 to 3 days after pollination. Self-pollination resulted in normal pollen tube growth in the style and inside the ovary. Self-pollen tubes were seen penetrating the micropile.

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Sierd Zijlstra, Coen Purimahua and Pim Lindhout

Crossing barriers between white- and purple-flowered species were examined. Four accessions of Capsicum annuum and three of C. pubescens were reciprocally crossed with one to four accessions of C. baccatum, C. cardenasii, C. chacoense, C. chinense, C. eximium, C. frutescens, C. galapagoense, and C. praetermissum. Capsicum chacoense is the only white-flowered species that inhibits C. annuum pollen tube growth but allows C. pubescens pollen tube penetration into the egg cell. Capsicum cardenasii and C. eximium exhibit similar crossabilities with C. annuum and C. pubescens: pollen tubes of C. cardenasii and of C. eximium can penetrate the egg cells of C. annuum but not vice versa, and pollen tubes of C. pubescens can penetrate the egg cells of C. cardenasii and of C. eximium but not vice versa.