Non-transgenic Cultivars Research Articles

Age‐specific bioassays and fecundity of Phthorimaea operculella (Lepidoptera: Gelechiidae) reared on cry1Ac ‐transgenic potato plants

SummaryVariation in the susceptibility of lepidopterous pest larvae of different ages to transgenic crops and the potential for survivors to reproduce could have important consequences for the development of resistance in such pests. Experiments were undertaken in the laboratory to determine if larvae of the potato tuber moth, Phthorimaea operculella, of different ages (0 (< 1 day old), 3, 5, 7 days) varied in their susceptibility to cry1Ac9–transgenic potato (Solanum tuberosum) foliage grown in the glasshouse or field. The survival and fecundity of larvae reared on transgenic tubers was also determined in the laboratory. There were no apparent differences in susceptibility of larvae of different ages to transgenic foliage. Larvae fed glasshouse or field‐grown non‐transgenic foliage had significantly larger relative growth indices and more larvae pupated, than those fed transgenic foliage, regardless of larval age. Eggs from a laboratory colony were placed on transgenic or non‐transgenic tubers to measure survival and fecundity. Between 6% and 15% of eggs placed on transgenic tubers developed into pupae for three of the four transgenic potato lines tested. On one transgenic line, only six adults emerged from 1300 eggs. In contrast, between 71% and 97% of the eggs placed on non‐transgenic tubers developed into pupae. Male and female pupae from transgenic lines weighed less than those from non‐transgenic lines. The fecundity of females from two of four transgenic lines was lower than from the non‐transgenic parent cultivar. Although larvae of different ages did not exhibit any overall age‐dependent pattern of increasing or decreasing susceptibility to transgenic foliage of glasshouse or field‐grown plants, the ability of larvae to survive and reproduce on transgenic tubers suggests this pest has the ability to evolve resistance to the transgenic plants used in the present study.

Field studies on the environmental fate of the Cry1Ab Bt‐toxin produced by transgenic maize (MON810) and its effect on bacterial communities in the maize rhizosphere

Field studies were done to assess how much of the transgenic, insecticidal protein, Cry1Ab, encoded by a truncated cry1Ab gene from Bacillus thuringiensis (Bt), was released from Bt-maize MON810 into soil and whether bacterial communities inhabiting the rhizosphere of MON810 maize were different from those of the rhizosphere of nontransgenic maize cultivars. Bacterial community structure was investigated by SSCP (single-strand conformation polymorphism) of PCR-amplified 16S rRNA genes from community DNA. Using an improved extraction and detection protocol based on a commercially available ELISA, it was possible to detect Cry1Ab protein extracted from soils to a threshold concentration of 0.07 ng/g soil. From 100 ng of purified Cry1Ab protein added per gram of soil, only an average of 37% was extractable. At both field sites investigated, the amount of Cry1Ab protein in bulk soil of MON810 field plots was always lower than in the rhizosphere, the latter ranging from 0.1 to 10 ng/g soil. Immunoreactive Cry1Ab protein was also detected at 0.21 ng/g bulk soil 7 months after harvesting, i.e. in April of the following year. At this time, however, higher values were found in residues of leaves (21 ng/g) and of roots (183 ng/g), the latter corresponding to 12% of the Cry1Ab protein present in intact roots. A sampling 2 months later indicated further degradation of the protein. Despite the detection of Cry1Ab protein in the rhizosphere of MON810 maize, the bacterial community structure was less affected by the Cry1Ab protein than by other environmental factors, i.e. the age of the plants or field heterogeneities. The persistence of Cry1Ab protein emphasizes the importance of considering post-harvest effects on nontarget organisms.

Field evaluation of potato plants transgenic for a cry1Ac gene conferring resistance to potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

Cry1Ac-transgenic potato plants derived from Russet Burbank and Red Rascal cultivars were evaluated in field trials at Lincoln, Canterbury, New Zealand. Foliage of transgenic plants had fewer potato tuber moth ( Phthorimaea operculella (Zeller)) mines, of which the majority were <200 mm 2, than the non-transgenic control plants. Of the 800 transgenic tubers examined 5 months after harvesting the first field trial (1999/2000), 0.5% had potato tuber moth mine damage compared with 9% of non-transgenic tubers. After the second field trial (2000/2001) 0.06% of 5307 transgenic tubers had mine damage compared with damage to 25% of non-transgenic tubers. Mined foliage was collected during the first field trial, resulting in a total of 45 larvae from transgenic foliage and 269 from non-transgenic foliage. Two pupae and nine parasitoids emerged from larvae collected from and reared on transgenic foliage. Between 86% and 88% (Red Rascal or Russet Burbank cultivar, respectively) of larvae collected and reared on non-transgenic foliage either pupated or were parasitised. In the second field trial, three of the four transgenic lines evaluated produced yields comparable with their non-transgenic parent cultivar. These results suggest transgenic potato plants resistant to potato tuber moth could augment integrated pest management programmes. However, the potential of the target pest to develop resistance to such plants and effects on non-target insects must be evaluated before such plants can be recommended for potato tuber moth management.

Efficacy of transgenic Bt cotton for resistance to the Asian corn borer (Lepidoptera: Crambidae)

Transgenic Bt cotton is expected to provide satisfactory control of several lepidopteran species in cotton. The Asian corn borer (ACB), Ostrinia furnacalis (Guenée), is an important component of the lepidopteran pest complex of cotton in China. Monsanto's transgenic Bt cotton NC 33B, expressing Cry1Ac protein, and a Chinese transgenic Bt cotton GK-2, expressing Cry1A protein, were evaluated for resistance to ACB during 2001–2002. Field trials were conducted with an artificial infestation of ACB at different cotton crop stages, which coincided with the generations of natural ACB occurrence. Damage ratings were significantly reduced in transgenic cotton cultivars both NC 33B and GK-2 compared with their parental non-transgenic Bt cotton cultivars DP5415 and Simian 3, and a major conventional cultivar Shiyuan 321, respectively. In addition, percentage of plants stem-bored and mean number of tunnels per plant were significantly higher on GK-2 than on NC 33B in the second generation. Laboratory bioassays were carried out by exposing neonates to plant tissues collected from the field during the season. Tissues assayed included the new leaves, floral buds, match-head squares, and white flowers, which are the tissues initially attacked by the neonates in the field. Low larval survival rates were observed on NC 33B and GK-2, contrasting greatly to the high number of survivors found on equivalent non-Bt cotton tissue isolated throughout the season. However, larval survival was higher on the tissues isolated from late-season Bt cotton plants than on early season. In addition, higher larval survival was observed on GK-2 than NC 33B in assays with the late season tissues. This may be associated with reduced levels of available toxin in plant tissues as they age. Both laboratory and field data indicated that NC 33B and GK-2 were highly resistant to ACB. The high level of efficacy for Bt cotton against ACB offers the potential for season-long control.

Nymphiposition and Population Growth of Rhoaplosiphum padi L. (Homoptera: Aphididae) on Conventional Wheat Cultivars and Transgenic Wheat Isolines

Nymphiposition and population growth of bird cherry-oat aphid, Rhoaplosiphum padi L. (Homoptera: Aphididae), were measured in four experiments with conventional, non-transgenic cultivars of wheat (Triticum aestivum L.) and in four separate experiments with isolines of ‘Prospect’ wheat containing the pin2 gene with promoter for potato proteinase inhibitor II. In two experiments with conventional wheat, population growth of R. padi was lower on cultivars ‘Sharp,’ ‘Marshall’ and ‘Ember’ compared to that on ‘Russ.’ Numbers of R. padi were intermediate on ‘2375’ and did not differ from that on other cultivars. In the third and fourth experiments, Sharp and Marshall had less R. padi than ‘Guard’ and ‘Prospect,’ whereas ‘Butte 86’ and ‘Ivan’ had intermediate numbers of R. padi that did not differ from that on other cultivars. Nymphiposition by alate R. padi did not differ among cultivars, indicating a lack of antixenosis. Transgenic isolines did not show resistance to R. padi. Two of three experiments showed no effect of isoline on nymphiposition by R. padi, and three of four experiments showed no effect of isoline on final numbers of R. padi. However, in one experiment, nymphiposition by R. padi was greater on some transgenic isolines than others and, after 13 d, some transgenic isolines had greater populations of R. padi. Mechanical wounding of transgenic plants had no effect on nymphiposition or final numbers of R. padi. Although wheat cultivars Sharp, Marshall and Ember show promise as sources of antibiosis resistance to R. padi, more research is needed to understand potential use of proteinase transgenes in wheat for cereal aphid management.

Effects of transgenic potatoes with an altered starch composition on the diversity of soil and rhizosphere bacteria and fungi

The aim of this study was to investigate potential effects on the composition of the bacterial and fungal diversity in rhizosphere and soil of a transgenic potato line (SIBU S1) which was modified in its starch composition by RNA anisensing, compared to the non-transgenic parental cultivar (SIBU) at the flowering stage in 2000. Furthermore a second non-transgenic cultivar (SOLANA) was included in the study. To avoid artefacts derived from cultivation depending approaches, molecular techniques based on 16S-(bacteria) and 18S-(fungi) rDNA respectively were used to describe the microbial community structure. Comparing 16S- and 18S-rDNA DGGE fingerprints from the different bulk soil samples, it could be shown that no significant differences between the two cultivars and the transgenic line were found. Similar results were obtained for the rhizosphere samples using the eubacterial, α-and β-proteobacterial and fungal specific primers with the exception of, the eubacterial DGGE patterns obtained for the rhizosphere of SOLANA. These patterns revealed that the relative abundance of one band was enhanced compared with the patterns of SIBU and SIBU S1 and the sequence of the differentiating band showed the highest similarity with Enterobacter amnigenus. When Pseudomonas specific primers were used, relevant differences were found between the rhizosphere patterns of the transgenic potato line (SIBU S1) and the parental cultivar (SIBU). However, clear effects of the cultivar SOLANA on the structure of the Pseudomonas community compared to SIBU were also detected.

Tolerance to Salt Stress of the Transgenic Tetrasomic Tetraploid Potato, Solanum tuberosum cv. Desiree Appears to be Induced by the DREB1A Gene and rd29A Promoter of Arabidopsis thaliana

Tetraploid potato cv. Desiree was transformed using an Arabidopsis thaliana stress-inducible promoter rd29A and the DREB1A gene, which confers multiple tolerances to abiotic stresses (e.g., dehydration and elevated soil salinity). Transformed Desiree lines showed a direct correlation between the DREB1A expression levels and the tolerance to salinity. By producing a filial progeny from the transgenic lines which was considered to harbor a single copy of the DREB1A gene, crossed with a non-transgenic cultivar, the genotype at the transgenic locus of these tetrasomic tetraploids was estimated by chi-square test, suggesting the existence of a Simplex mode. The results showed that low-copy heterozygous loci with the DREB1A gene could sustain the expression, and consequently confer a significant tolerance to salinity in tetrasomic tetraploid potatoes.

Biological response of rat fed diets with high tuber content of conventionally bred and transgenic potato resistant to necrotic strain of potato virus (PVY N) Part I. Chemical composition of tubers and nutritional value of diets

In experiments on rats, nutritional properties of a diet with high content (40%) of potato tubers obtained from conventional or genetically-modified potato were determined. The potato cultivar Irga was transformed with viral genome sequences in order to improve its resistance to a necrotic strain of potato virus Y (PVY N). Four lines of genetically-modified potato were compared with non-transgenic somaclone from cv. Irga and three conventional cultivars Irga, Maryna and Ania. Potato tubers were autoclaved, dried and introduced to the diets which contained similar amount of protein (levelled through small addition of casein), fat, minerals and vitamins. Genetic modification of potato had no effect on the chemical composition (e.g. crude protein, starch, dietary fibre content and amino acid composition of protein) and nutritional properties of tubers (diet intake, animal growth, protein utilisation). Higher differences between chemical composition (especially in crude protein and starch content) and biological response of rats were determined in the case of diets containing tubers from conventional potato cultivars Ania, Maryna and Irga. Obtained results indicate that transgenic potatoes with genetically improved resistance to PVY N are substantial and nutritional equivalence to the non-transgenic cultivar.

Ethylene-inducible Expression of ipt Gene Produces a Dramatic Increase in Fower Bud Count in Transgenic Plants

Cytokinins play an important role in regulating plant growth and development. The cytokinin gene, isopentenyl transferase (ipt), was placed under the control of the ACC oxidase promoter from the LEACO1 gene from Lycopersicon esculentum and introduced into Nicotiana tabacum (cv. Havana) and chrysanthemum (Dendranthema × grandiflorum `Iridon'). Transformants were confirmed by PCR reaction and Southern blot and analyzed for phenotypical changes under both greenhouse and growth chamber conditions. With both species, LEACO1-ipt transgenic plants displayed a wide range of vegetative and generative phenotypes. With plants growing in the vegetative state, some LEACO1-ipt transgenic lines appeared similar to the non-transgenic wild-type cultivars while other lines showed excessive lateral branch development and short internodes. With plants grown under generative conditions, several LEACO1-ipt transgenic lines showed a 2 to 10-fold increase in the number of flower buds relative to the wild-type cultivars. With chrysanthemum, dramatic increases in bud count were observed on transgenic lines that otherwise displayed a morphology similar to the non-transgenic lines. Analysis of ipt expression indicated a marked change in gene expression between the most extreme phenotypes observed in this study. LEACO1-ipt lines that express normal vegetative development but increased flower bud counts appear to have great potential for ornamental crop improvement.

Effect of genetic background on the target fatty acids of acyl‐ACP thioesterase transgenes in Brassica napus

AbstractAcyl‐acyl carrier protein (ACP) thioesterase (TE) is involved in the biosynthetic fatty acid pathway of plants. Conventional canola lines transformed individually with the bay‐TE (Uc FatB1), elm‐TE (Ua FatB1), nutmeg‐TE (Mf FatB1) or Cuphea‐TE transgene (Ch FatB1), produce seed oil with modified fatty acid compositions. This study assessed the effects of genetic background, cytoplasm, maternal parent, and interaction of different TE transgenes, on the target fatty acids using F1 seeds and double haploid (DH) lines. The F1 seeds were produced by crossing four TE transgenic parental lines and three non‐transgenic cultivars with distinct fatty acid compositions. The DH lines were developed from microspores of F1 plants. DH lines from different crosses showed that genetic background does not have an effect on the relative levels of the target fatty acids of the same TE, indicating the stability of the substrate specificity of the TE within canola. However, significant effects of genetic background on the content of the major target fatty acids, lauric acid (C12:0) or palmitic acid (C16:0) depending on the TE, were observed. Expression of the TE in low erucic acid (C22:1) genotypes resulted in higher target fatty acid levels than expression in high C22:1 genotypes. Reciprocal crosses showed maternal effects, but not cytoplasmic effects. In addition, co‐expression of two different TE transgenes in the same seeds was observed. These results indicate the importance of selection for appropriate genetic backgrounds in order to maximize the expression of the target fatty acids of TE transgenes, and also indicate potential uses of TE co‐expression in modifying canola seed oil.

Identification of geneticaly modified soybean seeds resistant to glyphosate

Advances in genetic engineering permit the modification of plants to be tolerant to certain herbicides that are usually not selective. For practical and commercial purposes, it is important to be able to detect the presence or absence of these traits in genotypes. The objective of this research was to develop a procedure for identifying genetically modified soybean (Glycine max L. Merr.) with resistance to the herbicide glyphosate. Two studies were conducted based on germination test. In the first study, soybean seeds were pre-imbibed in paper towel with the herbicide solutions, then transferred to moist paper towel for the germination test. In the second study, seeds were placed directly in herbicide solutions in plastic cups and tested for germination using the paper towel method. Eight soybean genotypes were compared: four Roundup Ready, that contained the gene resistant to the herbicide (G99-G725, Prichard RR, G99-G6682, and H7242 RR) and four non-transgenic parental cultivars (Boggs, Haskell, Benning, and Prichard). In the first study, the seeds were imbibed for 16 hours at 25°C in herbicide concentrations between 0.0 and 1.5% of the glyphosate active ingredient. In the second, seeds were subjected to concentrations between 0.0 and 0.48%, for one hour, at 30°C. The evaluation parameters were: germination, hypocotyl length, root length and total length of the seedlings. Both methods are efficient in identifying glyphosate-resistant soybean genotypes. It is possible to identify the genetically modified soybean genotypes after three days, by imbibing the seed in 0.12% herbicide solution, and after six days if the substrate is pre-imbibed in a 0.6% herbicide solution. The resistance trait was identified in all cultivars, independent of the initial physiological quality of the seed.

Stability of the Expression of Acyl‐ACP Thioesterase Transgenes in Oilseed Rape Doubled Haploid Lines

Transgene stability in doubled haploid (DH) lines is an important consideration for transgenic cultivar development programs. The objective of this study was to assess the expression stability of acyl‐acyl carrier protein (ACP) thioesterase (TE) transgenes in oilseed rape (Brassica napus L.) DH lines. The DH lines were developed from microspores of F1 plants from the crosses between transgenic parents carrying the bay‐TE (Uc FatB1), elm‐TE (Ua FatB1), nutmeg‐TE (Mf FatB1), or cuphea‐TE (Ch FatB1) transgenes and three nontransgenic cultivars having distinct seed oil fatty acid compositions. Of 333 DH1 plants developed from microspore‐derived embryos that had undergone selection for kanamycin resistance (the selectable marker) with bay‐TE F1 and cuphea‐TE F1 plants as the microspore donors, 20 plants did not show TE transgene expression. Polymerase chain reaction (PCR) and Southern blotting analyses confirmed that the absence of TE transgene expression in these 20 DH1 plants was due to escape of embryos from kanamycin selection or existence of an incomplete T‐DNA copy without the TE transgene. No DH1 plant with completely silenced TE transgenes was detected. Thirty of 34 transgenic DH lines showed a stable level of the target fatty acid, lauric acid (C12:0) for the bay‐TE and palmitic acid (C16:0) for the other three TE transgenes, over the two or three consecutive generations tested (DH2, DH3, and/or DH4 plants). Target fatty acids were significantly affected by temperature during seed development. DH lines carrying the elm‐TE or the cuphea‐TE transgene grown under high temperature conditions (25/20°C, day/night) during seed development showed higher levels of palmitic acid than under lower temperatures (20/15°C). These results support the application of the DH procedure in breeding programs for transgenic cultivars and indicate the important influence of environment.

Challenges in Testing Transgenic and Nontransgenic Cotton Cultivars

Cotton (Gossypium hirsutum L.) cultivars transgenically enhanced to impart herbicide resistance to either bromoxynil [3,5‐dibromo‐4‐hydroxybenzonitrile; BXN (Bayer Advanced, Peoria, IL)] or glyphosate [N‐(phosphonomethyl)‐glycine; Roundup Ready (Monsanto Co., St. Louis, MO)], and/or Bacillus thuringiensis var. kurstaki [Bt; Bollgard (Monsanto)] mediated resistance to certain lepidopteran insects were planted to 77% of the 2002 U.S. cotton hectarage, yet Official Cultivar Trial (OCT) protocols remain little changed since inception. The presence of transgenic, pest‐managing, and nontransgenic cultivars in OCTs poses challenges to provide unbiased cultivar performance because OCTs impose herbicide and insect management regimes appropriate for nontransgenic cultivars. Our objectives were to assess the merits of OCTs to test transgenic and nontransgenic cultivars and to recommend alternatives. Because OCTs levy common pest management on all cultivars, value‐added transgenic traits are not demonstrated, cultivar variation in their expression is not shown, and main effects and interaction of cultivar and pest management regime are confounded. Examples of pest management main effects that potentially affect cultivar ranks in OCTs include yield penalties imposed on herbicide‐resistant cultivars from routinely used, soil‐applied herbicides and yield advantages imparted to Bt cultivars from added insect control of OCT insecticide regimes. One recommendation to more comprehensively test cultivars is to augment OCTs with trials wherein the best performing transgenic and nontransgenic cultivars in OCTs are produced with their respective pest management programs. Such trials simultaneously evaluate cultivars and transgenic traits for yield, fiber quality, and economic returns. Still, bias imposed by nontransgenic pest management regimes in OCTs can only be quantified through trials levying transgenic and OCT‐type pest management treatments on transgenic cultivars.

Genetic Uniformity of the U.S. Upland Cotton Crop since the Introduction of Transgenic Cottons

Field genetic uniformity is the probability that any two plants selected at random within a region carry alleles that are identical by descent. Genetic uniformity of field crops can occur through breeding with genetically related backgrounds and grower choice of a few related cultivars among other factors. Transgenic cotton cultivars currently dominate the U.S. cottonseed market, comprising approximately 72% of the Year 2000 cotton hectares. All transgenic cotton cultivars were derived through backcross breeding with popular nontransgenic cultivars. The objective of this study was to apply pedigree analysis to estimate field genetic uniformity since transgenic cultivars were introduced into the U.S. cottonseed market in 1996. Coefficients of parentage and proportion of hectares planted to transgenic cultivars were employed to estimate field genetic uniformity for the southeastern, south-central, southwestern, and western production regions. Compared with field genetic uniformity estimated in the Year 1995 preceding introduction of transgenic cultivars, field genetic uniformity did change (0.18 vs. 0.13). The number of cultivars planted on the largest hectarage has not changed, but the percentage of the crop planted to a few cultivars has declined. The proportion of the hectarage planted to the most popular cultivar also has declined. Both of these factors affected field genetic uniformity resulting in a 28% reduction in uniformity across the USA.

Weed Management, Fiber Quality, and Net Returns in No-Tillage Transgenic and Nontransgenic Cotton (Gossypium hirsutum)1

Studies on weed management systems with bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton cultivars in a no-tillage environment were evaluated in North Carolina and Tennessee in 1997 and 1998. All weed management systems in nontransgenic and bromoxynil-resistant cotton controlled sicklepod 72 to 78%, whereas sicklepod was controlled at least 94% in glyphosate-resistant cotton. Entireleaf and pitted morningglory, smooth pigweed, and common cocklebur were controlled at least 92% with all management systems. Fiber quality was also measured in Tennessee. Micronaire and fiber strength ranged from 4.35 to 4.55 units and 28.6 to 30.1 g/tex, respectively, in bromoxynil-resistant and glyphosate-resistant cultivars that received postemergence over-the-top (POT) herbicides. Harvest trash content ranged from 0.80 to 1.15% in systems where POT and late postemergence–directed (LAYBY) herbicides were used and was 1.65% where multiple glyphosate applications were used with no LAYBY herbicides. Cotton lint yield and net returns were generally highest in systems that included bromoxynil or pyrithiobac POT followed by cyanazine plus MSMA LAYBY or multiple glyphosate treatments where no LAYBY herbicides were used.Nomenclature: Bromoxynil; cyanazine; glyphosate; MSMA; pyrithiobac; common cocklebur, Xanthium strumarium L. #3 XANST; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Stoneville BXN 47’, ‘Deltapine 5415RR’, ‘Paymaster 1220RR’.Additional index words: Color grade, extraneous material, fiber length, fiber strength, fiber uniformity, harvest trash, high-volume instrumentation, gin turn out, leaf grade, micronaire, staple length.Abbreviations: ASN, as needed; LAYBY, late postemergence–directed; fb; followed by; PDS, postemergence-directed spray; PRE, preemergence; POT, postemergence over-the-top.

Genetic Uniformity of the U.S. Upland Cotton Crop since the Introduction of Transgenic Cottons

Field genetic uniformity is the probability that any two plants selected at random within a region carry alleles that are identical by descent. Genetic uniformity of field crops can occur through breeding with genetically related backgrounds and grower choice of a few related cultivars among other factors. Transgenic cotton cultivars currently dominate the U.S. cottonseed market, comprising approximately 72% of the Year 2000 cotton hectares. All transgenic cotton cultivars were derived through backcross breeding with popular nontransgenic cultivars. The objective of this study was to apply pedigree analysis to estimate field genetic uniformity since transgenic cultivars were introduced into the U.S. cottonseed market in 1996. Coefficients of parentage and proportion of hectares planted to transgenic cultivars were employed to estimate field genetic uniformity for the southeastern, south-central, southwestern, and western production regions. Compared with field genetic uniformity estimated in the Year 1995 preceding introduction of transgenic cultivars, field genetic uniformity did change (0.18 vs. 0.13). The number of cultivars planted on the largest hectarage has not changed, but the percentage of the crop planted to a few cultivars has declined. The proportion of the hectarage planted to the most popular cultivar also has declined. Both of these factors affected field genetic uniformity resulting in a 28% reduction in uniformity across the USA.

Adaptation and Market Potential of Jack o' lantern and Miniature Pumpkin Cultivars in Eastern North Carolina

In 1998 and 1999, a total of 27 large-fruited and 15 miniature-fruited pumpkin (Cucurbita pepo) cultivars were evaluated for adaptation to eastern North Carolina grow- ing conditions. Test categories were yield (fruit number and weight); fruit characteristics (shape, rind and stem attributes); and susceptibility to edema (wart-like growths on fruit exterior), foliar diseases, preharvest and postharvest fruit decay, and viruses. Yields of large pumpkins ranged from over 3,200 fruit/acre (7,907 fruit/ha) for `SVT 4613367', `Autumn Gold', and `Gold Standard' to less than 1,000 fruit/acre (2,471 fruit/ha) for `Gold Rush' and `Progold 200'. For miniature pumpkins, over 33,000 fruit/acre (81,542 fruit/ha) were produced by `Touch of Autumn', `Lil' Pump- ke-mon', and `HMX 5682', whereas `Mystic' and `Progold 100' produced less than 7,000 fruit/acre (17,297 fruit/ha). `Gold Rush', `Howden', and `Progold 510' (large), and `EXT 4612297', `Lil' Goblin', and `Lil' Ironsides' (miniature) appeared the most susceptible to foliar diseases. Preharvest fruit decay ranged from 0% for `Howden' and `EXT 4612297' to over 20% for `Lil' Goblin', `Jumping Jack', `Peek-A-Boo', and `Tom Fox'. Virus incidence on fruit and foliage was low on virus-resistant cultivars ('SVT 4613367' and `EXT 4612297'), and ranged from 4% to 74% for nontransgenic cultivars. Virus incidence and/or severity on foliage and fruit were not related. `Early Autumn' (large) and `Touch of Autumn' (miniature) were the most prone to edema. `Aspen' and `Magic Lantern' (large) and `Baby Pam', `Lil' Goblin', and `Spooktacular' (miniature) were the most susceptible to postharvest fruit decay. Fruit characteristics are discussed in relation to marketability and possible consumer appeal to pumpkins.

Inheritance and Expression of Transgenes in Barley

Empirical assessments of transgene inheritance and phenotypic expression will assist in the development of efficient breeding strategies for transgenic germplasm, and guide research into the improvement of transformation techniques. The inheritance of a barley yellow dwarf virus (BYDV) coat protein gene and bar, and the expression of bar as measured by resistance to glufosinate‐ammonium damage, was studied in the T1 and T3 generations of barley (Hordeum vulgare L.) populations derived from seven independent transformation events. Most populations deviated from Mendelian inheritance patterns, and several showed evidence of transgene silencing. To further study transgene behavior, several transgenic lines were crossed to a diverse set of nontransgenic cultivars and breeding lines to produce single cross‐ and backcross‐derived populations. In these populations, the inheritance of glufosinate‐ammonium resistance generally fit Mendelian expectations for single, dominant loci. Quantitative measurements of glufosinate‐ammonium resistance showed heritable variability for glufosinate‐ammonium resistance both among and within individual transformation events, but no variability could be attributed to the different genetic backgrounds of the nontransgenic parents. It is concluded that, although transgenic parents such as these can be used in a breeding program, transformation systems that result in greater stability of transgene behavior are desirable.

Bacterial community composition in the rhizosphere of a transgenic, herbicide-resistant maize (Zea mays) and comparison to its non-transgenic cultivar Bosphore

Bacterial communities in rhizospheres of transgenic maize (Zea mays, with the pat-gene conferring resistance to the herbicide glufosinate; syn. l-phosphinothricin) were compared to its isogenic, non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40-60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR-SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to Proteobacteria, mainly of the alpha- and beta-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups: Cytophaga-Flavobacterium-Bacteroides, Chlamydiales-Verrucomicrobium, Planctomyces, Holophaga and to Gram-positive bacteria with a high G+C DNA content.

Bacterial community composition in the rhizosphere of a transgenic, herbicide-resistant maize ( Zea mays) and comparison to its non-transgenic cultivar Bosphore

Bacterial communities in rhizospheres of transgenic maize ( Zea mays, with the pat-gene conferring resistance to the herbicide glufosinate; syn. L-phosphinothricin) were compared to its isogenic, non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40–60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR–SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to Proteobacteria, mainly of the α- and β-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups: Cytophaga– Flavobacterium– Bacteroides, Chlamydiales– Verrucomicrobium, Planctomyces, Holophaga and to Gram-positive bacteria with a high G+C DNA content.