seed. Gene flow can enhance the genetic diversity of plant populations and may therefore increase the popu-The extent of pollen-mediated gene flow (PMGF) in wheat (Tritilation's ability to respond to changing stressors in the cum spp. L.) as a function of distance from a pollinator source has been measured in recent field studies. Wheat is primarily self-pollinated; environment. In plants, pollen dispersal is the primary however, some cross-pollination can occur depending on biological, mode of gene flow among populations and occasionally agronomic, and environmental factors. The complexity of these interbetween populations of different species (Levin and actions restricts attempts to develop a workable mechanistic model; Kerster, 1974). Although PMGF is not unique to transtherefore, we pursued an entirely empirical modeling approach. We

Herbicide tolerant crops provide farmers access to a new weed control option of nonselective herbicide such as Roundup1 A wheat transgenic event 33391 was produced via Agrobacterium‐mediated transformation of a donor cultivar Bobwhite wheat (Triticum aestivum L.) and was identified as a commercial candidate to develop Roundup Ready wheat2 The objective of this study was to assess field efficacy of the transgenic event in spring wheat production regions in North America. Transgenic event 33391 was tested in field trials at 14 locations in 1999, 13 locations in 2000, and 14 locations in 2001. All trials were split‐plot designs with multiple rates of Roundup treatment. No vegetative or reproductive damage was observed with the application of 4 L ha−1 Roundup at the 3‐ to 5‐leaf stages. No yield reduction was observed with Roundup treatment. The transgenic event with or without Roundup application yielded as high as the nontransgenic Bobwhite. These results indicate that the wheat transgenic event 33391 has at least 2× tolerance to the nonselective herbicide Roundup.

Anther-culture response was examined among three spring wheat (Triticum aestivum L.) cultivars to evaluate the genetic component of response and to determine whether androgenetic performance could be improved by selection. The three lines, the three possible F1's among the three lines, their F2's, and the backcrosses to the parents were evaluated for callus production and regeneration capacity. Significant variation was observed among the generations of the three crosses for callus formation. Genetic variation for regenerability was nonsignificant. Callus production was negatively correlated (-0.24) with regeneration capacity. The random variation in the study was too great to determine whether major-gene differences for antherculture response exist among the three lines by examining population distributions. When the material was evaluated for quantitative gene effects, the estimates for the additive gene effects were generally greater than the estimates for the dominance gene effects for callus formation. Only the Pavon x Chris cross, however, exhibited a significant narrow sense heritability estimate for callusing response (0.94). Due to the large component of random variation and the varying selection potential among crosses for androgenetic performance, improving anther-culture response in wheat by selection could prove difficult unless the anther-culture process itself selects for response traits at the gametic level.

An Agrobacterium-mediated transformation system with glyphosate selection has been developed for the large-scale production of transgenic plants. The system uses 4-day precultured immature embryos as explants. A total of 30 vectors containing the 5-enol-pyruvylshikimate-3-phosphate synthase gene from Agrobacterium strain CP4 (aroA:CP4), which confers resistance to glyphosate, were introduced into wheat using this system. The aroA:CP4 gene served two roles in this study-selectable marker and gene of interest. More than 3,000 transgenic events were produced with an average transformation efficiency of 4.4%. The entire process from isolation of immature embryos to production of transgenic plantlets was 50-80 days. Transgenic events were evaluated over several generations based on genetic, agronomic and molecular criteria. Forty-six percent of the transgenic events fit a 3:1 segregation ratio. Molecular analysis confirmed that four of six lead transgenic events selected from Agrobacterium transformation contained a single insert and a single copy of the transgene. Stable expression of theAROA:CP4 gene was confirmed by ELISA through nine generations. A comparison of Agrobacterium-mediated transformation to a particle bombardment system demonstrated that the Agrobacterium system is reproducible, has a higher transformation efficiency with glyphosate selection and produces higher quality transgenic events in wheat. One of the lead events from this study, no. 33391, has been identified as a Roundup Ready wheat commercial candidate.

1988. Chromosome doubling and aneuploidy in anther-derived plants from two winter wheat lines. Genome, 30: 177 -181. Anther-derived, doubled haploid populations were obtained from two hard red winter wheats, 'Centurk' and NB88. Spontaneous doubling frequency, efficiency of colchicine treatment, and vernalization requirement were evaluated within each population. In cytological evaluation among the regenerates, haploids, diploids, haploid aneuploids, and diploid aneuploids were observed. Most regenerates were either haploid or diploid. The frequency of anthers producing at least one haploid, diploid, or aneuploid was the same for both genotypes. The regenerates from the same anther had the same ploidy level 83 % of the time, suggesting the callus was usually derived from one microspore. Over 60% of the anthers produced at least one diploid plant. The high frequency of spontaneous doubling suggests that chromosome doubling by colchicine treatment could be eliminated. Ninety-eight percent of the colchicine-treated 'Centurk' plants produced seed, while only 43% of the NB88 colchicine-treated plants produced seed. Anther culture did not replace the vernalization requirement. Vernalization was required for uniform flowering. Results indicate that it is feasible to use 'Centurk', NB88, and other genotypes with high callus induction, plantlet regeneration, and colchicine response to efficiently produce doubled haploids. ., et MASCIA, P. N. 1988. Chromosome doubling and aneuploidy in anther-derived plants from two winter wheat lines. Genome, 30 : 177-181. Des populations d'haploi'des doublCes dCrivCes de cultures d'anthkres ont CtC obtenues de blCs durs d'hiver rouges, soit les blCs 'Centurk' et NB88. La frkquence des doublements spontanCs, l'efficacitk des traitements a la colchicine et les exigences de vernalisation ont CtC CvaluCes pour chaque population. Les Cvaluations cytologiques chez les plantules rCgCnCrCes ont permis de dCceler des haploi'des, des diploi'des, des haploi'des aneuploi'des et des diploi'des aneuploi'des. La majorit6 des plantes rCgCnCrCes furent haploi'des ou diploi'des. La frkquence des anthkres qui ont produit au moins une haploi'de, une diploi'de ou une aneup!oi'de fut la meme pour les deux genotypes. Dans 83 % du temps, les plantules rCgCnCrCes d'une meme anthkre ont prCsent6 les memes niveaux de ploi'die, ce qui suggkre que les cals Ctaient gCnCralement dCrivCs d'une androspore. Au dela de 60% des anthkres ont produit au moins une plante diploi'de. La frkquence ClevCe des doublements spontanCs suggkre que le doublement des chromosomes par colchicine pourrait etre CliminC. Chez les plantes 'Centurk' traitCes a la colchicine, 98% ont produit des grains alors que chez les plantes issues de NB88, seulement 43% des plantes ainsi traitCes ont produit des grains. La culture d'anthkres n'a pas remplacC les exigences de vernalisation; celle-ci fut requise pour assurer une floraison uniforme. Les rksultats indiquent que le recours a 'Centurk'. NB88 et autres gCnotypes a pourcentages ClevCs d'induction d...