Inheritance of high palmitic acid content in the seed oil of sunflower mutant CAS-5

 Sunflower genotypes with increased levels of palmitic acid (C16 : 0) in the seed oil could be useful for food and industrial applications. The objective of the present study was to determine the inheritance of the high C16 : 0 content in the sunflower mutant line CAS-5 (>25% of the total oil fatty acids). This mutant was reciprocally crossed with the lines HA-89 (5.7% C16 : 0) and BSD-2-691 (5.4% C16 : 0), the latter being the parental line from which CAS-5 was isolated. No maternal effect for the C16 : 0 content was observed from the analysis of F₁ seeds in any of the crosses. The inheritance study of the C16 : 0 content in F₁, F₂ and BC₁F₁ seeds from the crosses of CAS-5 with its parental line BSD-2-691 indicated that the segregation fitted a model of two alleles at one locus with partial dominance for the low content. The analysis of the fatty acid composition in the F₂ populations from the crosses with HA-89 revealed a segregation fitting a ratio 19 : 38 : 7 for low (<7.5%), middle (7.5–15%), and high (>25%) C16 : 0 content, respectively. This segregation was explained on the basis of three loci (P1, P2, P3) each having two alleles showing partial dominance for low content. The genotypes with a high C16 : 0 content were homozygous for the recessive allele p1 and for at least one of the other two recessive alleles, p2 or p3. This model was further confirmed with the analysis of the F₃ and the BC₁F₁ generations. It was concluded that both the recessive alleles p2 and p3 were already present in the BSD-2-691 line, the allele p1 being the result of a mutation from P1. This genetic study will facilitate breeding strategies associated with the incorporation of the high C16 : 0 trait into agronomically acceptable sunflower hybrids. Received: 30 March 1998 / Accepted: 13 August 1998     

Epistatic interaction among loci controlling the palmitic and the stearic acid levels in the seed oil of sunflower

Two sunflower (Helianthus annuus L.) mutants with high concentrations of saturated fatty acids in their seed oil have been identified and studied extensively. The mutant line CAS-5 has high concentrations of palmitic acid (C16:0) (>25% compared with 7% in standard sunflower seed oil) and low-C18:0 values (3%). CAS-3 is characterized by its high levels of stearic acid (C18:0) (>22% compared with 4% in standard sunflower seed oil) and a low-C16:0 content (5%). CAS-5 also possesses elevated levels of palmitoleic acid (C16:1) (>5%), which is absent in standard sunflower seed oil. The objective of this study was to determine the relationships between the loci controlling the high-C16:0 and the high-C18:0 traits in these mutants. Plants of both mutants were reciprocally crossed. Gas chromatographic analyses of fatty acids from the seed oil of F₁, F₂, F₃ and the BC₁F₁ to CAS-5 generations indicated that the loci controlling the high-C16:0 trait exerted an epistatic effect over the loci responsible for the high-C18:0 character. As a result, the phenotypic combination containing both the high-C16:0 levels of CAS-5 and the high-C18:0 levels of CAS-3 was not possible. However, phenotypes with a saturated fatty acid content of 44% (34.5% C16:0+9.5% C18:0) were identified in the F₃ generation. These are the highest saturated (C16:0 and C18:0) levels reported so far in sunflower seed oil. When F₃ C16:0 segregating generations in both a high- and a low-C18:0 background were compared, the high-C16:1 levels were not expressed as expected in the high-C18:0 background (CAS-3 background). In this case, the C16:1 content decreased to values below 1.5%, compared with >5% in a low-C18:0 background. As the stearoyl-ACP desaturase has been reported to catalyze the desaturation from C16:0-ACP to C16:1-ACP, these results suggested that a decrease in its activity was involved in the accumulation of C18:0 in the high-C18:0 mutant CAS-3. Received: 10 March 1999 / Accepted: 16 June 1999     

Mapping minor QTL for increased stearic acid content in sunflower seed oil

Increased stearic acid (C18:0) content in the seed oil of sunflower would improve the oil quality for some edible uses. The sunflower line CAS-20 (C18:0 genotype Es1Es1es2es2), developed from the high C18:0 mutant line CAS-3 (C18:0 genotype es1es1es2es2; 25% C18:0), shows increased C18:0 levels in its seed oil (8.6%). The objective of this research was to map quantitative trait loci (QTL) conferring increased C18:0 content in CAS-20 in an F₂ mapping population developed from crosses between HA-89 (wild type Es1Es1Es2Es2; low C18:0) and CAS-20, which segregates independently of the macromutation Es1 controlling high C18:0 content in CAS-3. Seed oil fatty acid composition was measured in the F₂ population by gas-liquid chromatography. A genetic linkage map of 17 linkage groups (LGs) comprising 80 RFLP and 19 SSR marker loci from this population was used to identify QTL controlling fatty acid composition. Three QTL affecting C18:0 content were identified on LG3, LG11, and LG13, with all alleles for increased C18:0 content inherited from CAS-20. In total, these QTL explained 43.6% of the C18:0 phenotypic variation. Additionally, four candidate genes (two stearate desaturase genes, SAD6 and SAD17, and a FatA and a FatB thioesterase gene) were placed on the QTL map. On the basis of positional information, QTL on LG11 was suggested to be a SAD6 locus. The results presented show that increased C18:0 content in sunflower seed oil is not a simple trait, and the markers flanking these QTL constitute a powerful tool for plant breeding programs.     

Genetic control of high stearic acid content in seed oil of two soybean mutants

 Stearic acid is one of the two saturated fatty acids found in soybean [Glycine max (L.) Merr.] oil, with its content in the seed oil of commercial cultivars averaging 4.0%. Two mutants, KK-2 and M25 with two- and six-fold higher stearic acid contents in the seed oil than cv ‘Bay’, were identified after X-ray seed irradiation. Our objective was to determine the genetic control of high stearic acid content in these mutants. Reciprocal crosses were made between each mutant and ‘Bay’, and between the two mutants. No maternal effect for stearic acid content was observed from the analysis of F₁ seeds in any of the crosses. Low stearic acid content in ‘Bay’ was partially dominant to high stearic acid content in KK-2 and M25, and high stearic acid content in KK-2 was partially dominant to high stearic acid content in M25. Cytoplasmic effects were not observed, as demonstrated by the lack of reciprocal cross differences for stearic acid content in our analysis of F₂ seeds from F₁ plants. The stearic acid content in F₂ seeds of KK-2בBay’ and M25בBay’ crosses segregated into three phenotypic classes which satisfactorily fit a 1:2:1 ratio, indicating that high stearic acid content in KK-2 and M25 was controlled by recessive alleles at a single locus. The data for stearic acid content in F₂ seeds of the KK-2×M25 cross satisfactorily fit a 3:9:1:3 phenotypic ratio. The F₂ segregation ratio and the segregation of F₃ seeds from individual F₂ plants indicated that KK-2 and M25 have different alleles at different loci for stearic acid content. The alleles in KK-2 and M25 have been designated as st ₁ and st ₂, respectively. The stearic acid content (>30.0%) found in the st ₁ st ₁ st ₂ st ₂ genotype is the highest known to date in soybean, but it was not possible to develop the line with this genotype because the irregular seeds failed to grow into plants after germination. Therefore, tissue culture methods must be developed to perpetuate this genotype. Received: 28 March 1997 / Accepted: 18 April 1997     

Temperature effect on a high stearic acid sunflower mutant.

Vegetable oil with elevated saturated fatty acid content may be useful for producing solid fat without hydrogenation or transesterification. Under the nutritional point of view stearic acid is preferred to other saturated fatty acids because of its neutral effect on serum cholesterol lipoproteins. Selection of a very high stearic acid sunflower (Helianthus annuus L.) line (CAS-14), with up to a 37.3% of stearic acid in the seed oil, and the relationship between the expression of this character and the growth temperature are presented. The mutant was selected from the M(2) progeny of 3000 mutagenized seeds (4 mM sodium azide mutagenesis treatment) by analysing the fatty acid composition of half-seed by gas liquid chromatography. In order to genetically fix the mutant character, plants were grown at high day/night temperatures during seed formation. We found that temperatures higher than 30/20 degrees C are required for good expression of the phenotype, the maximum stearic acid content being obtained at 39/24 degrees C. This behaviour is totally opposed to that observed in normal and previously isolated high-stearic acid sunflower lines that contain more stearic acid at low temperature. Thus, a new type of temperature regulation on the stearate desaturation must occur. This line is the sunflower mutant with the highest stearic acid content reported so far.     

Genetic distance as a predictor of heterosis and hybrid performance within and between heterotic groups in sunflower

Heterosis is significant for seed yield and is one of the driving forces behind the hybrid seed industry in cultivated sunflower (Helianthus annuus L). Heterotic groups in sunflower, if any other than the female and male inbred-line groups exist, have not been well studied or described. The primary aims of this study were to assess the utility and validity of a series of proposed heterotic groups and estimate correlations between genetic distance, heterosis, and hybrid performance for seed yield in sunflower. Fortytwo female by male heterotic group (A × R) and 81 female by female heterotic group (A × B) single-cross hybrids were grown in Corvallis, Ore., and Casselton, N.D., in 1996 and 1997. Heterosis was significant for seed yield and plant height but not for seed oil concentration and days to flowering. Genetic distances were significantly correlated with hybrid seed yield when estimated from AFLP fingerprints (G _D) (r = 0.63 for A × R and 0.79 for A × B hybrids), but not from coancestries (G _C) (r = -0.02 for A × R and 0.54 for A × B hybrids). G _D (R ² = 0.4) was a poor predictor of hybrid seed yield. The proposed heterotic groups in sunflower seem to have utility, but do not seem to be as strongly differentiated as those in corn (Zea mays L.). The highest-yielding hybrids were from the B_C× R_B heterotic pattern; however, several B_C× B_C hybrids (within-group hybrids) were among the top-yielding hybrids. The outstanding performance of certain B_C× B_C hybrids casts some doubt on the validity of the B_C group. Substantial genetic diversity seems to be present within and between heterotic groups in sunflower. Received: 1 September 1998 / Accepted: 14 September 1999     

Increased pre-dispersal seed predation in sunflower crop-wild hybrids

The fitness of crop-wild hybrids can influence gene flow between crop and wild populations. Seed predation levels in crop-wild hybrid plants can be an important factor in determining plant fitness, especially in large-seeded crops such as sunflower. To determine patterns of pre-dispersal seed predation, seeds were collected from wild sunflowers (Helianthus annuus L.) and wild×crop F₁ hybrids at three experimental field sites in eastern Kansas. Seed heads were dissected and each seed was counted and scored for categories of seed damage by lepidopteran and coleopteran larvae. Hybrid seed heads showed significantly higher levels of insect-damaged seeds. The average hybrid plant had 36.5% of its seeds (or 45.1 seeds per plant) eaten by insect larvae while the average wild plant lost only 1.8% (or 95 seeds) to seed predators. Hybrid populations had higher levels of total insect damage even when date of flowering, flower head diameter, and the number of open heads within the study site were accounted for. These results suggest that the reduced fecundity of F₁ crop-wild sunflower hybrids demonstrated in other studies may be augmented by the increased seed predation in hybrid flower heads. Fecundity estimates of crop-wild hybrid and wild plants that disregard differential seed predation levels may not accurately reflect the actual relative contributions of hybrid and wild plants to future generations. Received: 21 December 1998 / Accepted: 8 July 1999     

Stearoyl-ACP and oleoyl-PC desaturase genes cosegregate with quantitative trait loci underlying high stearic and high oleic acid mutant phenotypes in sunflower

The genetic control of the synthesis of stearic acid (C18:0) and oleic acid (C18:1) in the seed oil of sunflower was studied through candidate-gene and QTL analysis. Two F₂ mapping populations were developed using the high C18:0 mutant CAS-3 crossed to either HA-89 (standard, high linoleic fatty acid profile), or HAOL-9 (high C18:1 version of HA-89). A stearoyl-ACP desaturase locus (SAD17A), and an oleoyl-PC de-saturase locus (OLD7) were found to cosegregate with the previously described Es1 and Ol genes controlling the high C18:0 and the high C18:1 traits, respectively. Using linkage maps constructed from AFLP and RFLP markers, these loci mapped to LG1 (SAD17A) and to LG14 (OLD7) and were found to underlie the major QTLs affecting the concentrations of C18:0 and C18:1, explaining around 80% and 56% of the phenotypic variance of these fatty acids, respectively. These QTLs pleiotropically affected the levels of other primary fatty acids in the seed storage lipids. A minor QTL affecting both C18:0 and C18:1 levels was identified on LG8 in the HAOL-9×CAS-3 F₂. This QTL showed a significant epistatic interaction for C18:1 with the QTL at the OLD7 locus, and was hypothesized to be a modifier of Ol. Two additional minor C18:0 QTLs were also detected on LG7 and LG3 in the HA-89×CAS-3 and the HAOL-9×CAS-3 F₂ populations, respectively. No association between a mapped FatB thioesterase locus and fatty acid concentration was found. These results provide strong support about the role of fatty acid desaturase genes in determining fatty acid composition in the seed oil of sunflower. Received: 7 December 2000 / Accepted: 21 May 2001     

Inheritance of high oleic acid content in the seed oil of soybean mutant M23

A mutant line, M23, of soybean [Glycine max (L.) Merr.] was found to have two fold increases in oleic acid content in the seed oil compared with the original variety, Bay. Our objective was to determine the inheritance of the high oleic acid content in this mutant. Reciprocal crosses were made between M23 and Bay. There were no maternal and cytoplasmic effects for oleic acid content. The F₁ seeds and F₁ plants were significantly different from either parents or the midparent value, indicating partial dominance of oleic acid content in these crosses. The oleic acid content segregated in the F₂ seeds and F₂ plants in a trimodal pattern with normal, intermediate and high classes, satisfactorily fitting a 121 ratio. The seeds of a backcross between M23 and F₁ segregated into intermediate and high classes in a ratio of 11. These results indicated that oleic acid content was controlled by two alleles at a single locus with a partial dominant effect. Thus, the allele in M23 was designated ol and the genotypes of M23 and Bay were determined to be olol and 0l0l, respectively. The oleic acid contents of the F₂ seeds and F₂ plants were inversely related with the linoleic acid content which segregated in a trimodal pattern with normal, intermediate and low classes in a 121 ratio. Thus, it was assumed that the low linoleic acid content in M23 was also controlled by the ol alleles. Because a diet with high oleic acid content reduces the content of low density lipoprotein cholesterol in blood plasma, the mutant allele, ol, would be useful in improving soybean cultivars for high oleic acid content.     

Genetic control of early events in protoplast division and regeneration pathways in sunflower

Experiments were conducted to identify the genetic factors controlling protoplast division and to determine eventual relations between genetic factors involving organogenesis, somatic embryogenesis and protoplast division in sunflower. The present study involved protoplast culture and two traits: total division per 100 protoplasts (TOTD) and asymmetric division per 100 protoplasts (ASYD) were scored in 52 recombinant inbred lines (RILs) from a cross between PAC-2 and RHA-266. Asymmetric division is an early event in the formation of embryoids from protoplasts. Analysis of variance indicated the existence of highly significant differences among parental genotypes and their RILs. Heritability for the two protoplast division parameters (TOTD and ASYD) was high (0.87 and 0.89, respectively) and genetic gain expressed as percentage of the best parent for 10% of the selected RILs was significant. Twelve putative loci associated with total division per 100 protoplasts were identified. Eleven QTLs were also detected for asymmetric division per 100 protoplasts. The QTLs present high significant LOD scores and sum to a high percentage of phenotypic variance. The percentage of phenotypic variation explained by each QTL ranged from 2% to 24%. Some segments of the linkage groups I, XV and XVII are likely to contain genes important for organogenesis, somatic embryogenesis and protoplast division, as clustering of QTLs for these characters were described. The QTLs identified in these three linkage groups should be involved in cell division and in early events associated with cell differenciation. Received: 15 December 1999 / Accepted: 30 December 1999     

Molecular analysis of the high stearic acid content in sunflower mutant CAS-14

Increasing the stearic acid content to improve sunflower (Helianthus annuus L.) oil quality is a desirable breeding objective for food-processing applications. CAS-14 is a sunflower mutant line with a high stearic acid content in its seed oil (>35% vs. <6% in currently grown sunflower hybrids), which is controlled by the Es3 gene. However, the expression of the high stearic acid character in CAS-14 is strongly influenced by temperature during seed maturation and it is not uniform along the seed. The objectives of this study were (1) to identify PCR-based molecular markers linked to the Es3 gene from CAS-14, (2) to map this gene on the sunflower genetic map, and (3) to characterize the interaction between CAS-14 and CAS-3, a sunflower high stearic acid (about 26%) mutant line with the Es1 and Es2 genes determining this trait. Two F₂ mapping populations were developed from crosses between CAS-14 and P21, a nuclear male sterile line with the Ms₁₁ gene controlling this character, and between CAS-14 and CAS-3. One hundred and thirty-three individuals from P21×CAS-14, and 164 individuals from CAS-3×CAS-14 were phenotyped in F₂ and F₃ seed generations for fatty acid composition using gas–liquid chromatography, and they were then genotyped with microsatellite [simple sequence repeat (SSR)] and insertion–deletion (INDEL) markers. Bulk segregant analysis in the P21×CAS-14 population identified two markers on LG 8 putatively linked to Es3. A large linkage group was identified using additional markers mapping to LG 8. Es3 mapped to the distal half of LG 8 and was flanked by the SSR markers ORS243 and ORS1161 at genetic distances of 0.5, and 3.9 cM, respectively. The Ms₁₁ gene was also mapped to LG 8 and genetic distance between this gene and Es3 was found to be 7.4 cM. In the CAS-3×CAS-14 population, two QTLs were identified on LG 1 and LG 8, which underlie the Es1 gene from CAS-3 and the Es3 gene from CAS-14, respectively. A significant epistatic interaction between these two QTLs was found. Results from this study provided a basis for determining CAS-14 efficient breeding strategies.     

Study of the variability and evolution of Orobanche cumana populations infesting sunflower in different European countries

 The parasitic plant Orobanche cumana Wallr. has become a limiting factor for sunflower crops in infested countries. Over the past few years the progression of this parasitic plant, its introduction into new countries, and the development of new and more virulent races have all been observed. Consequently, the survey and understanding of broomrape population evolution is now crucial for the establishment of efficient breeding programmes. With this in prospect, the genetic variability of O. cumana populations from infested European countries, Bulgaria, Romania, Turkey and Spain, was studied using RAPD markers. Eight populations with a total of 180 plants were analysed. Twenty three primers were used to obtain 133 reproducible bands which led to a binary matrix. This matrix was subjected to various complementary analyses including pairwise distances computed with the Nei and Li coefficient, AMOVA, Nei’s genetic diversity statistics, and an estimation of gene flow among populations with the infinite-island formula. The results gave consistent conclusions whatever the method used for data treatment. We show that this parasitic plant is probably self-pollinated, that there is little intra-population variability, and very little gene exchange appears to occur between different geographic regions. Populations were well structured and organized into two distinct groups (one group corresponding to the East European countries, Bulgaria, Romania and Turkey, and the other group corresponding to Spanish populations) and could have a monophyletic origin. These results are discussed in relation to the applied uses of RAPD markers in the determination of true O. cumana races instead of populations. Received: 20 December 1997 / Accepted: 4 February 1998     

Allozyme variation in domesticated annual sunflower and its wild relatives

 The annual sunflower (Helianthus annuus L.) is a morphologically and genetically variable species composed of wild, weedy, and domesticated forms that are used for ornament, oilseed, and edible seeds. In this study, we evaluated genetic variation in 146 germplasm accessions of wild and domesticated sunflowers using allozyme analysis. Results from this survey showed that wild sunflower exhibits geographically structured genetic variation, as samples from the Great Plains region of the central United States were genetically divergent from accessions from California and the southwestern United States. Sunflower populations from the Great Plains harbored greater allelic diversity than did wild sunflower from the western United States. Comparison of genetic variability in wild and domesticated sunflower by principal coordinate analysis showed these groups to be genetically divergent, in large part due to differences in the frequency of common alleles. Neighbor-Joining analyses of domesticated H. annuus, wild H. annuus and two closely related wild species (H. argophyllus T. & G. and H. petiolaris Nutt.) showed that domesticated sunflowers form a genetically coherent group and that wild sunflowers from the Great Plains may include the most likely progenitor of domesticated sunflowers. Received: 2 December 1996/Accepted: 4 April 1997     

AFLP mapping of QTLs for in vitro organogenesis traits using recombinant inbred lines in sunflower (Helianthus annuus L.)

Genetic control for two in vitro organogenesis traits, the number of shoots per explant plated (S/E) and the number of shoots per regenerating explant (S/RE), was investigated in 75 recombinant inbred lines (RILs) of sunflower and their two parents (PAC-2 and RHA-266). Genetic variability was observed among the 75 RILs for the organogenesis traits studied. Some RILs presented significant differences when compared with the best parental line (RHA-266). Genetic gain, in terms of the percentage of the best parent, for 32% of the selected RILs was significant. A set of 99RILs from the same cross including the 75 mentioned above was screened with 333 AFLP markers and a linkage map was constructed based on 264 linked loci. Six putative QTLs for the S/RE (tentatively named osr) and seven QTLs for the S/E (ose) trait were detected using composite interval mapping. For each trait, the QTLs explained 52% (ose) and 67% (osr) of the total phenotypic variance. These results suggested that additive gene effects predominate in explaining a large proportion of the observed genetic variation associated with regeneration ability. The coincidental location of QTLs for S/E and S/RE is discussed. Received: 20 September 1999 / Accepted: 16 May 2000     

Inheritance of low linolenic acid content of the seed oil of a mutant in Glycine max

Summary Linolenic acid content of the oil from F₁, F₂, and F₃ seeds was compared with the parental values from a cross between a soybean cultivar with high (7.0%) and a mutant line with low (3.4%) linolenate (183). Linolenic acid content of F₁ seeds was intermediate to that of selfed seeds from the two parents and values from reciprocal crosses were essentially the same. This demonstrated that in this cross, linolenic acid content of the oil was controlled by the embryo rather than by the maternal parent. The distribution of linolenic acid in F₂ seeds from F₁ plants was trimodal and extended across the range of parental values. High and low linolenate F₂ plants bred true for 183 content and the F₃ distribution of seeds from F₂ plants with intermediate levels of 183 was similar to the F₂ distribution. The data were consistent with a model for two alleles with additive effects at a single locus controlling percent linolenic acid in these progenies. The simply-inherited alleles for low linolenate could be readily transferred to agronomically superior soybean cultivars, which would improve the fatty acid composition of the oil.Cooperative Investigations of the Northern Regional Research Center, ARS, USDA, Peoria, Illinois and the Purdue Univ. Agric. Exp. Stn. Journal Paper No. 10,020 of the Purdue Univ. Agric. Exp. Stn.     

Occurrence of partial hybrids in wide crosses between sunflower ( Helianthus annuus) and perennial species H. mollisand H. orgyalis

Hybridisation between the annual diploid sunflower (Helianthus annuus) and the perennial diploid species Helianthus mollis and Helianthus orgyalis was obtained by means of a normal crossing procedure or embryo rescue. Hybridisation success was low. All plants examined cytologically appeared to be diploid. However, the phenotypes of these diploids were not intermediate between the parents and, despite great variation, they resembled the female parent-type predominantly. Thirty five percent of plants issued from sunflower pollinated with perennial Helianthus had a phenotype resembling the female sunflower parent. On average, only 5% of the minimum number of expected RAPD and RFLP bands from male parents were recovered in plants produced from mature seeds after pollination of sunflower by H. mollis. More hybrids were found among plants obtained from embryo rescue, with an average of 25% of the male parent bands recovered per plant. Analysis of individual plants indicated the occurrence of various levels of hybridisation. There was a significant positive correlation between the number of phenotype traits related to hybrid status and the number of bands derived from the male parent. A single hybrid plant might possibly represent the product of a ’normal’ hybridisation event. The mechanisms behind these unusual events and the consequences for the breeder are discussed. Received: 23 March 2001 / Accepted: 28 June 2001     

An insertion of oleate desaturase homologous sequence silences via siRNA the functional gene leading to high oleic acid content in sunflower seed oil

Classical sunflower varieties display a high linoleic acid content in their seeds [low oleic (LO) varieties] whereas genotypes carrying the Pervenets mutation display an increased oleic acid content of above 83% [high oleic (HO) varieties]. Despite the advantage in health terms of oleic acid, the nature of the mutation was still unknown. Previous work reported that HO genotypes carried a specific oleate desaturase (OD) allele. This enzyme catalyses the desaturation of oleic acid into linoleic acid. The present work demonstrates that this allele is organised in two parts: the first section present in both HO and LO genotypes carries a normal OD gene, the second section is specific to HO genotypes and carries OD duplications. The study of mRNA accumulation in LO and HO seeds revealed that the mutation is dominant and induces an OD mRNA down-regulation. Furthermore, OD small interfering RNA, characteristic of gene silencing, accumulated specifically in HO seeds. Considered together, these observations show that the mutation is associated with OD duplications leading to gene silencing of the OD gene and consequently, to oleic acid accumulation. This finding allowed the development of molecular markers characterising the mutation that can be used in breeding programmes to facilitate the selection of HO genotypes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Inheritance of reduced linolenic acid content in soybean seed oil

 Linolenic acid is the unstable component of soybean [Glycine max (L.) Merr.] oil that is responsible for the undesirable odors and flavors commonly associated with poor oil quality. Two mutants, M-5 and KL-8, have been identified that have lower linolenic acid levels in the seed oil than the ‘Bay’ cultivar. Our objective was to determine the relationships between the genetic systems controlling linolenic acid in these mutants. Reciprocal crosses were made between the mutants and ‘Bay’, and between the two mutants. No maternal effect for linolenic acid content was observed from the analysis of F₁ seeds in any of the crosses. The data for linolenic acid content in F₂ seeds of M-5בBay’ and KL-8בBay’ crosses satisfactorily fit a 1 : 2 : 1 and 3 : 1 ratio, respectively. For the M-5×KL-8 cross, segregation observed from the analysis of F₂ seeds for linolenic acid content satisfactorily fit a ratio of 3 more than either mutant: 12 within the range of the two mutants: 1 less than either mutant. The segregation ratio of F₂ seeds and the segregation of F₃ seeds from F₂ plants indicated that M-5 and KL-8 have alleles at different loci that control linolenic acid content. The allele in KL-8 has been designated as fanx (KL-8) to distinguish it from fan (M-5). The low linolenic acid segregates with the genotype fanfanfanxfanx provide additional germplasm to reduce the linolenic acid content from the seed oil of soybean. Received: 18 December 1995 / Accepted: 12 July 1996     

Herbivory and natural selection on flowering phenology in wild sunflower, Helianthus annuus

Plant fitness is strongly affected by flowering phenology, and there are several ecological factors that are thought to shape the distribution of flowering times. One relatively underexamined factor is the timing and intensity of attack by herbivores that feed on flowers or developing seeds. This study tests the hypothesis that herbivores that feed on developing seeds of wild sunflower, Helianthus annuus (Asteraceae), impose selection on flowering phenology. First, the study population was found to contain genetic variation for mean date of flowering, so this trait could evolve if natural selection were operating. Next, the phenological pattern of abundance of five seed-feeding herbivores was documented. Damage by three herbivores, Haplorhynchites aeneus (Cucurlionidae), the head-clipping weevil, Homoeosoma electellum (Lepidoptera: Pyralidae), the sunflower moth, and Suleima helianthana (Lepidoptera: Tortricidae), the sunflower bud moth, was highest early in the flowering season, and declined as the season progressed. Damage by one herbivore, the seed fly Gymnocarena diffusa (Diptera: Tephrididae), was lowest early in the flowering season and increased as the season progressed. Finally, damage by two seed weevils, Smicronyx fulvus and S. sordidus (Curculionidae), whose damage was not distinguished, was constant through the flowering period. Third, damage by Haplorhynchites, Homoeosoma, and Suleima was found to be detrimental to plant fitness, suggesting that plants that flower when these herbivores are not abundant should have higher fitness. Finally, two phenotypic selection analyses were performed. The first included damage by Homoeosoma and Suleima, as well as flowering date, leaf area, and inflorescence diameter, as characters predicting plant fitness. In this analysis directional selection was found to act to decrease damage by the two herbivores, but did not act on flowering date. The second selection analysis was identical except that damage by the two herbivores was not included. In this analysis significant directional selection was found to favor later-flowering plants. Comparison of these two analyses suggests that all selection on flowering phenology is attributable to damage by Homoeosoma and Suleima: plants that flower later avoid damage by these two herbivores. While other influences on flowering phenology, such as pollination, mate availability, and seasonality, have been well documented, this study is one of few to demonstrate natural selection on flowering phenology that is a direct consequence of insect attack. Received: 17 November 1998 / Accepted: 18 July 1999