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Apomixis is asexual reproduction through seed. Apomixis in the genus Pennisetum is of the gametophytic (aposporous) type. Genes for apomixis have been transferred from a wild apomictic species (P. squamulatum) to pearl millet (P. glaucum) by conventional breeding to produce an obligately apomictic backcross 3 (BC3) plant (Dujardin and Hanna, 1989, J. Genet. Breed. 43:145). Molecular markers based on restriction fragment length polymorphisms and random amplified polymorphic DNAs were identified in BC3 that were shared only with the apomictic parent. Segregation of these informative markers in a BC4 population indicated that three linkage groups from P. squamulatum were present in BC3 and that minimal recombination between these alien chromosomes and those of the recurrent parent occurred. Transmission of only one of the linkage groups was required for transfer of apomixis. Recombination is essential for genetic mapping, thus we are beginning to map the informative molecular markers in an F, interspecific cross between pearl millet and P. squamulatum, a population that segregates for apomictic and sexual reproduction.

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allowed for the confirmation that UF-15-414 and UF-4407 resulted from sexual hybridizations ( Table 4 ). UF-15-414 exhibited a different banding pattern than UF-4407 in all markers except CaM48 and CaM62, each varying by the gain or loss of one band. UF-15

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Anthers contain starch and neutral lipids, which have key roles in microspore ontogeny and gametophyte development. In this study, we observed the dynamic changes in starch and neutral lipids in the anther developmental processes of castor (Ricinus communis) by cytochemical methods. Starch grains and neutral lipids presented a regular dynamic distribution during anther development. In young anthers, some neutral lipids accumulated in sporogenous cells, whereas neutral lipids disappeared with microspore growth. At the late microspore stage, starch grains began to accumulate in microspores, and the starch content of bicellular pollen significantly increased after microspore mitosis. At anthesis, starch grains and neutral lipids accumulated in the mature pollen grains. Visible changes occurred in anther wall cells. The epidermis, middle layer, and tapetum were degenerated, and only a single layer of endothecium remained at anthesis. The dynamic variation of starch grains and neutral lipids in tapetal cells was consistent with the changes in microspores and pollen during anther development. All these findings demonstrated that tapetal cells directly interacted with the developing gametophytes. The tapetal cells play an important role in supplying nutritional substances for microspore absorption. Moreover, the endothecium protects the pollen and contributes to anther dehiscence. The results of this study provide a foundation for the further research on sexual reproduction in angiosperms.

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Cranberry (Vaccinium macrocarpon Ait.) has the opportunity to partition resources into sexual and/or asexual (stolons) modes of reproduction. Nitrogen status has been shown to impact the degree of stoloniferous growth. To determine whether there is a genotypic response to varying nitrogen levels, six hybrid and four native cultivars were treated with three annual rates of nitrogen fertilizer (17, 34, or 67 kg·ha-1) for 4 years. Fruit yield was determined each year and asexual vegetative growth (stolons) weight was removed and measured in all but the first year of the experiment. Cultivars exhibited different patterns of yield and stolon weight response over the three nitrogen rates. Not all cultivars exhibited significant yield decreases at the high N levels. Vegetative growth (stolon weight) generally increased with increasing N, however, not all cultivars responded similarly over three N rates. Partitioning between yield and stolon production favored fruit yield at the lower N rates in three of the four native cultivars studied (`Cropper', `Early Black', and `Howes'). Yield over N rates was more stable for four of the six hybrid cultivars, which may be the result of greater heterozygosity in hybrids than natives, and/or genetic gain from one breeding and selection cycle, offering increased tolerance to nitrogen stress. This study indicates that genetic variation exists for yield, yield stability, and stolon production relative to nitrogen level, and that genetic gain in cranberry is possible for these traits. Future studies involving cranberry physiology and nutrition should consider the genotypes used.

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Starfruit (Averrhoa carambola L.) is reproduced by seeds from `Criollo' cultivars. The replication of desirable agronomic traits is difficult when selected plants are from sexual reproduction. The heterogeneity of plants is observed as higher trees, irregular fresh fruit yield, variable fruit quality, differential insect pest and disease susceptibilities, and extended period for recovering the inversion. Vegetative propagation is an alternative for reducing the heterogeneity of starfruit trees. Four grafting methods for propagating starfruit in the coast of Colima, Mexico: splice-side graft, wedge graft, whip graft, and bud graft were evaluated. The experiment was carried out on the Tecoman campus of the Universidad de Colima. The ambient conditions were dry tropic (BS1). Seven-month-old rootstocks were obtained from Criollo seedlings, and the scion was obtained from a healthy 15-year-old `Miss' donor tree. The experiment was distributed under a completely randomized design. The splice-side graft had 70% success and was the best, bud graft had 40% success, wedge graft, had 5% success and whip graft 0% success, and was the least successful.

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Floral initiation signals the commencement of sexual reproduction in angiosperms. In many plant species this developmental phase is controlled by photoperiod. However, it may be regulated by other factors, such as plant age or specific temperature or irradiance requirements. Floral initiation occurs in Pelargonium ×domesticum (regal Pelargoniums) in response to exposure to cool (7–12°C) temperatures for about 4–6 weeks, or to cumulative irradiance at 18–23°C. Broad genetic variability exists so that floral initiation in some cultivars is almost completely controlled by temperature, while in others it is almost completely controlled by cumulative irradiance. Among the latter group of genotypes, genetic variability exists for the amount of irradiance required. The purpose of this study was to determine the precise irradiance requirements for nine commercially important cultivars. The cultivars varied significantly in their response to irradiance with respect to floral initiation. Low irradiance requiring genotypes developed visible (5 mm) buds with as little as 250 mol of total cumulative irradiance; floral initiation in these cultivars occurred with only 50 mol of irradiance. High irradiance requiring genotypes still had vegetative meristems after 300 mol of total cumulative irradiance. Further studies were conducted on `Majestic', chosen for its high irradiance requirement. The objective of this study was to determine whether cool temperatures (7–12°C) or heat stress (23–28°C) could replace the irradiance effect. The results indicated that neither of these environmental conditions could replace the effects of moderate temperature (18–23°C) and high cumulative irradiance in this cultivar.

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Coreopsis rosea is important as a landscape plant and is of some impor-tance for restoration of native species. In both situations it is important to understand the breeding system so that the pollination process may be controlled for optimal seed production. The study of the incompatibility system is important to seed production. In commercial crops, seeds may be products of open pollination or F1 hybrids. In the former, genetic variability exists. In conservation and recovery programs of local flora, seeds with genetic variability are desirable. In development of commercial crops, uniform seeds and plants are desirable. Regardless of whether seeds will ultimately be used for commercial crops or for species restoration, an understanding of self-incompatibility will allow the pollination process to be manipulated for optimal seed production. The purpose of this research was to investigate the sexual reproduction mode in Coreopsis rosea. The objectives were to determine whether Coreopsis rosea operates with a self-incompatibility system, and, if so, to discover whether it is a sporophytic or gametophytic mode. The sporophytic form of self-incompatibility has been found in other plants in the Asteraceae family, but no one has studied self-incompatibility in Coreopsis rosea. The purpose of this research was to identify the self-incompatibility system in Coreopsis rosea. A series of self- and cross-pollinations were made in situ, and in vivo pollinations were made and the pistils studied under the microscope. Results indicate that Coreopsis rosea is self-incompatible and operates under the sporophytic mode.

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Soursop (Annonamuricata L.) is reproduced by seeds from `Criollo' cultivars in Mexico. The replication of desirable agronomic traits is difficult when selected plants are from sexual reproduction. The heterogeneity of plants is observed as taller trees, irregular fresh fruit yield, variable fruit quality, different insect pests, disease susceptibilities, and lower number of plants per hectare. There is an extended time period for recovering investments and commericialization problems due to fruit quality and price. Vegetative propagation is an alternative for reducing the heterogeneity of soursop trees. Three grafting methods were evaluated for propagating soursop in the dry tropic region of Colima, Mexico: 1) splice side graft; 2) wedge graft; and 3) bud graft. The experiment was carried out on the Tecoman Campus of the Universidad de Colima. Rootstocks were from 8-month-old healthy plants, 1-m tall and 1-cm diameter, obtained from `Criollo' seedlings, and the scions were obtained from a healthy 10-year-old `Sin Fibra' donor tree. This donor tree was selected for its excellent agronomic traits and fruit yield. Vigorous and terminal scions were used, disinfected with fungicide, and used the same day of excision. The experiment was distributed under a completely randomized design. Splice side grafting had 67% success after 60 days, while wedge grafting and bud grafting had 0% success.

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increased with increasing N application ( Table 3 ). Table 2. Effects of nitrogen (N) treatments on the sexual reproduction of P. armeniacum . Table 3. Growth of seedlings developed from seeds of N-treated plants of P. armeniacum . The emergence and number

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reproduction of triploids crossing with diploid R. hirta plants in the vicinity. A second population of progeny ranged from 3 x to 3 x + 5 and most likely resulted from either apomixis or sexual reproduction among triploids resulting in aneuploids. There

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