S1 Progenies Research Articles

Forage yield potential of alfalfa plants of varying crown size from old stands

AbstractAlfalfa (lucerne) plants can persist from one growing season to the next because of their perennial crowns. Plants with large crowns often are selected for breeding purposes. The objective of this study was to determine the forage yield potential of plants with a full range of crown sizes sampled from old stands. This was accomplished by field evaluation of clones and S1 progenies derived from plants of different crown sizes obtained from a 1 m2 of 5‐year‐old stands of cultivars ‘Agate’ and ‘Magnum III’. Significant differences (P < 0.05) in dry forage yield (DFY) were found among entries in both tests. However, there was no consistent trend in DEY with respect to the crown size of the parental plants. Although the crown of space‐planted clones dug after 16 months showed a strong association (r > 0.7, P < 0.01) with DFY, the crown size of these clones was poorly correlated with the crown size of their parental plants. These results suggest that selections based on crown size from older stands may not lead to an improvement in either crown size or forage yield. Crown health will remain an important selection criterion when plants are sampled from old stands; crown size, however, may not be as important.

Inheritance and Linkage Relationships of Isozymes in Easter Cactus

Polyacrylamide gel electrophoresis was used to study inheritance and linkage of isozymes in Easter cactus (Hatiora species and interspecific hybrids). Five isozyme systems were analyzed: aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI). F1, F2, BC1, and S1 progeny were used for inheritance studies. Six polymorphic loci (Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2, and Tpi-2) were identified. Aat-1 and Pgm-1 were linked (recombination frequency = 26% ± 7%), but the other isozyme loci assorted independently. Aberrant segregation ratios were observed in at least one segregating family for all six isozyme loci. We hypothesize that segregation distortion was due to linkage between isozyme loci and other genes subject to pre- or postzygotic selection. The existence of five additional isozyme loci (Aat-2, Gpi-2, Mdh-2, Mdh-3, and Tpi-1) was inferred from segregation patterns and by comparison of isozyme profiles from phylloclades and pollen. These isozyme loci may prove useful for confirming hybridity in intra- and interspecific crosses, determining parentage of cultivars, and assessing genetic diversity in germplasm collections.

Response to divergent selection for early vigour in sunflower (Helianthus annuus L.)

Early vigour (EV), biomass at the first development stages, may be a positive trait to improve sunflower yield in water-limited environments. Field experiments were carried out from 1992 to 1995 to define an index to quantify EV in sunflower plants, evaluate the response to divergent selection for this trait, study EV ×environment interaction, estimate the heritability of EV, and study the association of EV with other traits. A sunflower population with a broad genetic base and 10 sunflower lines derived from it were used. Stem volume calculated from stem diameter and height measured approximately 425 degree-days after emergence was correlated with above-ground plant biomass at the same date. In 1992, divergent selection for high and low stem volume was carried out on this population and plants from every group were recombined independently, obtaining 2 new populations. Selection response, using these and the initial population, was studied in 1993. Ten S2 lines, 5 with high-EV derived from the high-EV population and 5 with low-EV derived from the low EV population, were sown in 1995 to study the EV ×environment interaction. Differences among lines with different EV were significant in all the environments studied. In 1993, a random sample from the initial population was selfed and broad sense heritability and heritability by parent-offspring regression were estimated. Heritability based on variance component estimates of S1 progeny means was 0·61. Realised heritability (± s.e.) from a divergent selection for high and low stem volume were 0·40±0·10 and 0·52±0·15, respectively. Heritability by parent-offspring regression was 0· 40± 0·10. These values and the high variability of stem volume observed in the new populations indicate that additional gain from selection should be possible.

The Development of Self‐Pollinated Inbred Lines of Meadowfoam by Direct Selection in Open‐Pollinated Populations

Limnanthes alba Benth. (meadowfoam) is an allogamous insectpollinated oilseed crop. Poor pollination and pollinator costs have purportedly limited the commercial production of this crop. Production costs can be reduced and seed yields might be increased by using self‐pollinated cultivars. Such cultivars have not been developed for this crop, however. Our objective was to develop self‐pollinated inbred lines by directly selecting for self‐pollination in open‐pollinated meadowfoam populations. A total of 520 S0 progeny from 26 L. alba accessions were screened for self‐pollination in the field under reduced pollinator loads. Sixteen L. alba var. versicolor S0 progeny produced seed in a high percentage of flowers, whereas the other 504 progeny produced seed in a small percentage of flowers. A total of 288 S0 progeny from six L. alba var. versicolor accessions were screened for seeds per plant in a pollinator‐free greenhouse. Forty‐nine of these progeny produced 5 to 48 seeds per plant by self‐pollination. S3 lines were developed by selecting for seeds per plant (in the absence of pollinators) among OMF‐63, OMF‐64, and OMF‐66 S0, S1, and S2 progeny using single‐seed descent. OMF‐63, OMF‐64, and OMF‐66 S3 and OMF‐64 S3 produced significantly more seeds per plant and seeds per flower by self‐pollination than Mermaid, an open‐pollinated L. alba var. alba cultivar. OMF‐63, OMF‐64, and OMF‐66 S3 produced 26.3 to 30.1 seeds per plant and 0.97 to 0.99 seeds per flower, whereas Mermaid produced 3.0 seeds per plant and 0.14 seeds per flower. OMF‐64 S5 lines produced 41.0 to 72.3 seeds per plant and 1.26 to 2.07 seeds per flower, whereas Mermaid produced 2.9 seeds per plant and 0.12 seeds per flower. These self‐pollinated inbred lines should be useful for developing elite self‐pollinated meadowfoam cultivars.

Genetic variation and response to selection for resistance to root‐knot nematodes in oil radish (Raphanus sativus ssp. oleiferus)

AbstractBased on a preliminary screening of a collection of cruciferous crops, such as oilseed rape (Brassica napus L. ssp. oleifera Metzg.), oil radish (Raphanus sativus L. ssp. oleiferus DC.), and yellow mustard (Sinapis alba L.), some plants within the oil radish varieties showed resistance to the root‐knot nematodes Meloidogyne hapla Chitwood and M. incognita (Kofoid & White) Chitwood. Resistance tests of S1 progeny of these selected genotypes revealed a quantitative nature of resistance to M. hapla. Only a few resistant individuals were found, but a significant effect of selection was observed. In contrast, the progenies of plants resistant to M. incognita showed a very low number of egg masses, suggesting that this resistance may be conferred by dominant major gene(s). The results indicate that resistance of oil radish to root‐knot nematodes may be effective and may thus provide new possibilities for the management of M. hapla and M. incognita.

Molecular Marker Analysis of the Approach to Homozygosity by Selfing in Diploid Alfalfa

Although inbreeding is used extensively in alfalfa breeding and genetics, the actual approach to homozygosity during inbreeding is unknown and may differ from that predicted by the inbreeding coefficient (F) because of the need to select for vigor and fertility when inbreeding. Observed and expected values of heterozygosity were compared by means of 40 co‐dominant RFLP loci for two inbred series each consisting of four independent lines derived by selfing two diploid alfalfa genotypes. Selfing was continued with selection for fertility until self‐sterility was reached at the S2, S3, or S4 generation. Additional S1 progenies were also evaluated to identify the heterozygons RFLP loci. The observed percentage heterozygosity, calculated as the percentage of the 40 RFLP loci still heterozygous in each plant, declined less than expected based on the inbreeding coefficient in each inbred series. The lowest observed percentage heterozygosity was 30% in one inbred series and 40% in the other inbred series despite expectations as low as 6%. Tests of genotype and allele ratios indicated that the deviations may be due to selection favoring hetcrozygotes. Our results show that inbreeding in diploid alfalfa proceeds more slowly than expected, based on F, and that inbreeding depression may limit the level of homozygosity obtainable.

Characterization of RNA-mediated resistance to tomato spotted wilt virus in transgenic tobacco plants expressing NS(M) gene sequences.

Transgenic Nicotiana tabacum plants expressing RNA sequences of the tomato spotted wilt virus NS(M) gene, which encodes the putative viral movement protein, were found to be highly resistant to infection with the virus. Expression of untranslatable as well as anti-sense RNA of the NS(M) gene resulted in resistance levels as high as those in plants expressing translatable RNA sequences. For all three types of transgenic plants resistance levels of up to 100% were reached in the S2 progeny. These results indicate that the resistance mediated by the NS(M) gene is accomplished by expression of transcripts rather than protein in transgenic plants, similar to previously observed N gene-mediated resistance. Protoplast inoculations revealed that resistant plants expressing NS(M) are, in contrast to N transgenic resistant plants, not resistant at the cellular level. This suggests the RNA-mediated resistance mechanism against TSWV targets viral mRNAs rather than the viral genome.

Somatic excision of the Ac transposable element in transgenic Arabidopsis thaliana after 5-azacytidine treatment.

We have introduced the maize Ac transposable element in Arabidopsis thaliana and found that after three selfing generations, the element is immobile and extensively methylated. Moreover, the nopaline synthase (nos) gene present on the same transferred T-DNA, was active early after transformation and regeneration, but inactive in most of the S1 progeny. We used 5-azacytidine (5AzaC) to determine whether a reduction in the methylation would affect both Ac transposition and expression of the nos gene. After treatment with 5AzaC doses from 0.3 mM to 1.0 mM, approximately 25% of the plants produced detectable amounts of nopaline, indicating that the nos gene was reactivated. Using the polymerase chain reaction (PCR) to detect the empty donor site left by Ac transposition, we demonstrated that 5AzaC also activates Ac excision in the transgenic plants. Approximately 13% of the 5AzaC treated plants (doses from 0.1 mM to 1.0 mM) were shown to have empty donor sites due to Ac excision. None of the plants cultivated in the absence of 5AzaC showed evidence for Ac transposition or reactivation of the nos gene. Further analysis using Southern blot indicate that some demethylation occurred in the genome of individual plants. These results may represent demethylation in few cells during development which may be sufficient to reactivate in these cells the expression of the nos and Ac transposase transgenes, the latter promoting Ac transposition in somatic cells.

Repeatability and heritability of divergent recombination frequencies in the Iowa Stiff Stalk Synthetic (Zea mays L.)

Variability in recombination frequency was reported in the Iowa Stiff Stalk Synthetic. The objectives of the present research were to verify the differences in recombination frequency among individuals in the Iowa Stiff Stalk Synthetic maize population and to determine if the recombination frequency differences persisted among the S1 progeny. Testcrosses to measure male recombination frequency on three chromosomes (4, su1-c2; 5, a2-bt1-pr1; 9, sh1-bz1-wx1) were repeated for eight S0 individuals. Recombination frequencies were repeatably divergent among those individuals which were selected based on high or low recombination frequencies on specific chromosomes. Individuals which had been selected for long and short total map distances across the three chromosome regions produced repeatably divergent recombination frequencies only at the su1-c2 region. The recombination frequencies of the S1 lines, derived from the S0 individuals which had the most divergent recombination frequencies on a single chromosome, were significantly different. The broadsense heritability estimates derived from the regression of six S1 lines on six S0 individuals ranged from 0.69 to 0.20 for the five chromosome regions. We conclude that genetic differences for recombination frequency exist in this population and that modification by selection should be possible.

Genetic Analysis for Stalk Lodging Resistance in Narrow‐Base Maize Synthetic Population ZPS14

Stalk lodging resistance and grain yield are the result of interactions of many traits expressed during maize (Zea mays L.) development. Determination of which traits influence stalk lodging resistance and grain yield might improve breeding program efficiency. The main objective of this study was to identify stalk traits that might relate to stalk lodging and grain yield, so that they can be selected as correlated traits for improving both grain yield and stalk quality. For this investigation, S1 progenies were randomly derived from the Yugoslavian maize synthetic population ZPS14. Correlations and path coefficient analysis showed stalk water content had the greatest impact on stalk lodging resistance and grain yield. Genotypic correlations (rg) revealed that stalk water content had a negative and significant influence on both percentage of lodged plants (rg = – 0.46*) and grain yield (rg = – 0.42*). Thus, improvement in grain yield and stalk lodging would be not expected from selection for stalk water content. However, a small number of S1 families with high stalk water content and above average grain yield were identified, suggesting some progress could be made in improving both traits simultaneously if the breeding population was large. A significant genotypic relationship was not found for grain yield and stalk lodging resistance (rg = 0.04). As shown by path analysis, direct effects of stalk lodging on grain yield were small and nonsignificant (P1.2 = 0.003). Breeding for better stalk quality, thus, will not affect future progress of selection for grain yield.

Identification of Cross‐Pollinated and Self‐Pollinated Progeny in Alfalfa through RAPD Nulliplex Loci Analysis

Alfalfa (Medicago saliva L.) is the most important forage crop in the world, but with current breeding practices improvements in yield potential have been limited during the last 40 yr. The development of hybrid alfalfa cultivars would likely improve forage yield potential, but an efficient method to estimate outcrossing rates would be needed to confirm percentage hybrid seed. The objective of this research was to demonstrate the applicability of a RAPD nulliplex analysis to estimate outcrossing/selfing rates in autotetraploid alfalfa. Marker selection is based on polymorphism between a seed parent and its bulk open‐pollination progeny. Polymorphic markers identify the seed parent as nulliplex (aaaa) for those particular loci, which allows the individual open‐pollinated progeny from that seed parent to be classified as F1 or S1 progeny based on the presence/absence of these markers. Two alfalfa genotypes served as seed parents in crossing studies which differed in pollination control and number of pollen parents. Random amplified polymorphic DNA (RAPD) nulliplex analysis was conducted on these two seed parents and their progeny. Controlled crossing and selfing provided independent control over S1s and F1s. Five polymorphic markers were identified for both seed parents and these markers were sufficient to identify S1 and F1 progeny. The percentage S1 seed was 7, 27, and 100% for crossing with emasculation, crossing without emasculation and self‐pollination, respectively. In conclusion, RAPD nulliplex loci analysis can provide accurate identification of F1 and S1 progeny and an estimation of outcrossing rates in autotetraploid alfalfa.

Persistance and Single‐Plant Productivity in Nondormant Alfalfa

Plant mortality is generally substantial in alfalfa (Medicago sativa L.) fields both at establishment and during the productive life of the stand. Most research has examined the effects of mortality on alfalfa yield per unit area. Consequences of mortality within a population on single*plant productivity have received relatively little attention. Understanding the basis for this mortality could affect management practices and the breeding and testing of alfalfa cultivars. The objective of this study was to describe agronomic, morphological, and physiological traits associated with persistence in nondormant alfalfa. This was accomplished by comparing two populations of S1 progenies derived from 60 surviving 6‐yr‐old plants from a commercial field of ‘CUF‐101’ (=field‐derived [FD] population) and 60 greenhouse‐grown CUF‐101 plants (=greenhouse‐derived [GHD] population) in field and greenhouse trials at Tucson, AZ. In a field trial, crown mortality, as measured by the percent live stems, did not differ significantly between the populations. Total forage yield, yield in winter and spring, and stem elongation rates were significantly greater in the GHD population. Root weight, total plant weight, root/shoot weight ratio, and concentration of total nonstructural carbohydrates in the root were significantly greater in the FD population in a greenhouse trial. Differences observed between the two populations are consistent with the elimination of presumably less competitive plants with smaller root systems and plants intolerant of grazing in the winter and early spring. This research suggests that mortality within stands of nondormant alfalfa is less likely for plants with larger roots and generally slower growth patterns that are typically associated with increased fall dormancy.

Genetic Variation within Maize Breeding Populations

Proper choice of germplasm determines the ultimate success of selection for genetic improvement. Germplasm included in maize (Zea mays L.) breeding has evolved from the original landrace cultivars to F2 populations of elite line crosses. Objectives of our study were to determine the mean and genetic variability (σ2G) of yield and other traits within three F2 populations (B73 × B84, B90 × Mo17, and B73 × Mo17), within three genetically narrow‐base synthetics (NBS) [BS14, Mol7‐Syn., and H73‐Syn.], and within three genetically broadbase synthetics (BBS) [BSll(FR)C9, BSCBI(R)C9, and BSSS(R)C9]. Fifty S1 progenies for each of the nine populations were evaluated at three locations for 2 yr. Differences among S1 progenies within each population were significant for most traits. Estimates of σ2G were determined from the S1 component of variance, and average estimates of σ2G for grain yield were similar for F2 and BBS populations, whereas the average estimate of σ2G for NBS populations was 40% smaller. Within population types, the related line cross (B73 × B84)F2 had 50% less σ2G for grain yield than the other two F2 populations. BS14, H73‐Syn., and BSCBI(R)C9 had smaller estimates of σ2G for grain yield than the other synthetic populations. Estimates of σ2G suggest selected F2 and BBS populations have greater potential for improved gains than the NBS populations. The related line (B73 × B84)F2 had 50% less 62G than either (B90 × Mo17)F2 or (B73 × Mo17)F2. (B90× Mo17)F2 and (B73 × Mo17)F2 had similar estimates of σ2G, although B90 and Mo17 are in the same heterotic group, whereas B73 and Mo17 are in different heterotic groups [Reid Yellow Dent (B73) and Lancaster Sure Crop (Mo17)]. Selection for improvement of yield would be more effective within the (B90 × Mo17)F2 than within (B73 × B84)F2 and more useful than within (B73 × Mo17)F2.

Transgenic fertile Scoparia dulcis L., a folk medicinal plant, conferred with a herbicide-resistant trait using an Ri binary vector

Transgenic herbicide-resistant Scoparia dulcis plants were obtained by using an Ri binary vector system. The chimeric bar gene encoding phosphinothricin acetyltransferase flanked by the promoter for cauliflower mosaic virus 35S RNA and the terminal sequence for nopaline synthase was introduced in the plant genome by Agrobacterium-mediated transformation by means of scratching young plants. Hairy roots resistant to bialaphos were selected and plantlets (R0) were regenerated. Progenies (S1) were obtained by self-fertilization. The transgenic state was confirmed by DNA-blot hybridization and assaying of neomycin phosphotransferase II. Expression of the bar gene in the transgenic R0 and S1 progenies was indicated by the activity of phosphinothricin acetyltransferase. Transgenic plants accumulated scopadulcic acid B, a specific secondary metabolite of S. dulcis, in amounts of 15-60% compared with that in normal plants. The transgenic plants and progenies showed resistant trait towards bialaphos and phosphinothricin. These results suggest that an Ri binary system is one of the useful tools for the transformation of medicinal plants for which a regeneration protocol has not been established.

Phenotypic recurrent selection in common bean (Phaseolus vulgaris L.) based on performance of S2 progenies

The effect of a recurrent selection procedure for improving seed yield per plant was evaluated in common bean. Progress was registered after three cycles of recurrent selection with S2 progeny evaluation performed on the grain yield/plant. Gain from selection was estimated by field testing 45 random S2 lines from each of the C0, C1 and C2 populations. Response to selection for seed yield/plant was 6 g from C0 to C1 and 4.4 g from C1 to C2. The seed yield improvement was due principally to an increase in pods/plant; little contribution was provided by the 1000-seed weight and seeds/pod traits. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Grain yield/plant is significantly correlated to pods/plant and seeds/pod traits in all cycles, indicating that plants with favourable combinations of these traits could be identified. The proposed recurrent selection procedure appears to be effective in improving the population and extracting superior genotypes for varietal development.

Recurrent selection for downy‐mildew resistance in pearl millet

AbstractOne population of pearl millet (Pennisetum glaucum (L.) R. Br.) highly susceptible to downy mildew (Sclerospora graminicola (Sacc.) Schroet.) was subjected to two cycles of recurrent selection for downy mildew resistance using a modified greenhouse screening method. The response to selection was evaluated under greenhouse and field conditions using 50 random S1 progenies and 50 random full‐sib progenies from each cycle bulk. Significant progress over cycles of selection was observed in all evaluation trials. These results demonstrated that, in a susceptible population, recurrent selection effectively increased the level of resistance to downy mildew. The modified greenhouse method for assessing resistance to downy mildew effectively differentiated genotypes and had the advantages of greater rapidity and suitability for use throughout the year, independent of season.A rapid decline of genotypic variance was observed in advanced cycles of selection, indicating that a small number of genes controls downy‐mildew resistance in this population. The comparison of genotypic and error variance components from S1 progenies and full‐sib progenies suggested that full‐sib progenies can be used successfully in recurrent selection for increased downy‐mildew resistance.

Occurrence and Physiological Breakdown of Self-incompatibility in Easter Cactus

The existence of self-incompatibility (SI) was demonstrated in `Britton' and `Rose' Easter cactus (Rhipsalidopsis). In a full diallel cross among five clones, 18 out of 20 outcrosses resulted in 68% to 100% fruit set, whereas reciprocal crosses between two of the clones and all five self-pollinations failed to set fruit. Pollen tube growth was greatly inhibited in styles of selfed pistils, but there was no evidence of pollen tube inhibition in compatibly crossed pistils. Easter cactus exhibited characteristics typically found in sporophytic SI systems (trinucleate pollen, papillate stigmas, and scant stigmatic exudate) together with those associated with gametophytic SI systems (stylar inhibition of pollen tube growth and absence of reciprocal differences in outcrosses). Additional experiments were performed to determine the effects of bud pollinations, growth regulators (BA, GA3, and NAAm), and high temperatures (0- to 48-h exposure at 40C) on the SI response. Heat treatments were more effective than either bud pollinations or growth regulators in overcoming SI, and yielded an average of 7.2 viable seeds per treated flower when plants were incubated for 12 h at 40C and selfed immediately after incubation. Isozyme analysis of the S0 parent and putative S1 progeny confirmed that selfing had occurred following heat treatments. Using S1 progeny in breeding programs may extend the flower color range and lead to a greater diversity in other plant characteristics than presently exists in cultivated germplasm. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine [benzyladenine (BA)], gibberellic acid (GA3), and α-naphthaleneacetamide (NAAm).

Rapid selection for serotonin-1A sensitivity in rats.

National Institutes of Health (NIH) heterogeneous stock (HS) rats were obtained and genetically selected for either larger (HI line) or smaller (LO line) hypothermic responses to the selective serotonin-1A (5-HT1A) agonist 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT). A randomly bred (RA) control line was also bred in parallel. There was a rapid response to selection, with HI and LO S1 progeny already showing significantly different hypothermic responses to DPAT. The data for the S3 progeny indicated that selection was proceeding in both directions, with the hypothermic responses of the LO line being about 0.5 degrees C less than that of the RA line (p < 0.01) and the hypothermic response of the HI line being about 0.7 degrees C greater (p < 0.01). The selected lines also differed in their hypothermic responses to the cholinergic agonist oxotremorine, but these differences did not change with further selection. These findings indicate that selection for 5-HT1A sensitivity may occur quite rapidly and that changes in muscarinic sensitivity do not parallel those changes in serotonergic sensitivity.

A Test of the ‘Tall‐Dwarf” Hypothesis in Pearl Millet, Pennisetum glaucum (L.) R. Br.

AbstractPositive height‐grain yield relationships exist for many cereals, but cannot be fully used in breeding because of lodging and harvestability problems in tall cultivars. Law et al. (1978) proposed a “tall‐dwarf” hypothesis for wheat, in which the positive effects of minor height genes could be exploited by selecting for them in a major dwarfing gene background. The applicability of this hypothesis to pearl millet was tested by crossing a set of dwarf S1 progenies (from a single population) which varied in height onto two male‐sterile lines. Mean (by S1 pollinator) hybrid grain yield was closely related to mean hybrid height (r2= 0.60) over a range of mean yields of 3.0–3.9 t ha−1 and a range of mean heights of 126–165 cm. The effect of height was expressed as an increase in grain number in one cross and as an increase in grain mass in the other, indicating the importance of background genetic effects on yield‐height relationships in dwarf hybrids. The concept of “tall‐dwarfs” appears to be applicable to pearl millet.

Relationship between transcript production and virus resistance in transgenic tobacco expressing the potato leafroll virus coat protein gene

The coat protein (CP) gene of potato leafroll luteovims (PLRV) was inserted into tobacco (Nicotiana tabacum) using disarmed Agrobacterium tumefaciens (LBA4404) containing a binary expression vector. PLRV CP gene transcript was detected in transgenic plants but its abundance differed between transformed lines. CP was not detected in virus-free transgenic plants. The segregation of kanamycin resistance in S1 seedling progenies (obtained by selfing transformed plants) indicated that multiple (up to five) integration events involving vector T-DNA had occurred in most transformants. However, the amount of detectable CP transcript was not related to the neomycin phosphotransferase II gene copy number. Multiplication of PLRV in mature transgenic plants was diminished by up to 6-fold; the greatest diminution was in those transformed lines in which most CP gene transcript was detected. However, S1 progeny seedlings of transgenic plants were no more resistant to infection, following inoculation with viruliferous aphids, than seedlings of non-transformed control plants.