S-related protein can be recombined with self-compatibility in interspecific derivatives ofLycopersicon

Stylar proteins involved in the self-incompatible (SI) response ofLycopersicon hirsutum have been identified and mapped to the locus that controls SI (S locus).L. esculentum, a self-compatible (SC) species of cultivated tomato, does not display these proteins. Hybrids between SCL. esculentum and SIL. hirsutum are self-sterile despite these individuals bearing pollen containing theS allele ofL. esculentum. In progeny derived from backcrossing the hybrids toL. esculentum, there was a strong correlation between the presence of theS allele fromL. hirsutum and self-infertility. However, this relationship was uncoupled in a number of backcross (BC) progeny. The SI response appeared to be nonexistent in two self-fertile BC individuals that were heterozygous for theS allele ofL. hirsutum, based on Mendelian segregation of a tightly linked DNA marker,CD15, in selfed progeny. Among these progeny self-fertile individuals that were homozygous for theL. hirsutum allele of the linked marker were also determined to be homozygous for anS-related protein ofL. hirsutum through test crosses withL. esculentum. Therefore, plants were produced that were homozygous for a functionalS allele but were self-fertile. This result and other evidence suggest that theS-related proteins are not sufficient to elicit a self-incompatible response inL. esculentum and that there is a mutation(s) inL. esculentum somewhere other than theS locus that leads to self-compatibility.     

Pollen tube expression of pseudo-self-compatibility (PSC) inPetunia hybrida

Summary AnS _1.1 self-incompatible (SI) petunia plant which showed atypical seed set was found in an I₇ population. This plant showed a strong SI reaction when selfed but produced varying amounts of seed when used as the seed parent in crosses with unrelated individuals homozygous for the sameS allele. Reciprocal crosses yielded no seed indicating that the reaction was a stylar response. Self seed obtained by high temperature treatments produced 18 plants, all of which exhibited the parental characteristics, the ability to reject self pollen but accept, to varying degrees, pollen bearing the sameS allele from unrelated plants. Several petunias homozygous forS ₁, and exhibiting various levels of PSC as determined by self seed set, progeny tests and temperature treatments, were used as pollen parents. The mean seed set of these crosses produced a ranking of the pollen parents which reflected the PSC levels obtained by other methods. The behavior of the F₁ and F₂ populations suggests that the pollen discriminating ability may be a simply inherited, dominant character in these plants. The styles of these unusual petunias illustrate the participation of the pollen tube in determining PSC.Scientific Journal Series Paper Number 10.479 of the Minnesota Agricultural Experiment Station     

S-alleles are retained and expressed in a self-compatible cultivar of Petunia hybrida.

Summary We identified two S-allele-associated proteins (S-proteins) in a self-compatible cultivar of Petunia hybrida based on their segregation in F₁ hybrids between P. hybrida and its self-incompatible relative, Petunia inflata (with S₂S₂ genotype), and in selfed progeny of P. hybrida. These two S-proteins, designated S_x-protein (24 kDa) and S_o- protein (31 kDa), are pistil specific, and their expression follows a temporal and spatial pattern similar to that of S-proteins characterized in self-incompatible solanaceous species. Their amino-terminal sequences also share a high degree of similarity with those of solanaceous S-proteins. Selfing of P. hybrida yielded plants with S_oS_o, SxSo, and S_xS_x genotypes in an approximately 1:2:1 ratio, indicating that the S_x- and S_o-alleles, though expressed in the pistil, failed to elicit a self-incompatibility response. The S₂-allele of P. inflata is expressed in all the F₁ hybrids, rendering them capable of rejecting pollen bearing the S₂-allele. The S_o-allele is not functional in the F1 hybrids, because all the F₁ progeny with S₂S_o genotype are self-compatible. However, in F₁ hybrids with S₂S_x genotype, approximately half are self-incompatible and half are self-compatible, indicating that the function of the S_x-allele depends on the genetic background. These results strongly suggest that the presence of functional S-alleles alone is not sufficient for expression of a self-incompatibility phenotype, and reaffirm the multigenic nature of gametophytic self-incompatibility suggested by earlier genetic studies.     

Mapping quantitative trait loci controlling seed dormancy and heading date in rice, Oryza sativa L., using backcross inbred lines

 To detect quantitative trait loci (QTLs) controlling seed dormancy, 98 BC₁F₅ lines (backcross inbred lines) derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare were analyzed genetically. We used 245 RFLP markers to construct a framework linkage map. Five putative QTLs affecting seed dormancy were detected on chromosomes 3, 5, 7 (two regions) and 8, respectively. Phenotypic variations explained by each QTL ranged from 6.7% to 22.5% and the five putative QTLs explained about 48% of the total phenotypic variation in the BC₁F₅ lines. Except for those of the QTLs on chromosome 8, the Nipponbare alleles increased the germination rate. Five putative QTLs controlling heading date were detected on chromosomes 2, 3, 4, 6 and 7, respectively. The phenotypic variation explained by each QTL for heading date ranged from 5.7% to 23.4% and the five putative QTLs explained about 52% of the total phenotypic variation. The Nipponbare alleles increased the number of days to heading, except for those of two QTLs on chromosomes 2 and 3. The map location of a putative QTL for heading date coincided with that of a major QTL for seed dormancy on chromosome 3, although two major heading-date QTLs did not coincide with any seed dormancy QTLs detected in this study. Received: 10 October 1997 / Accepted: 12 January 1998     

Development of SCAR markers linked to self-incompatibility in <Emphasis Type="Italic">Brassica napus</Emphasis> L.

‘SI1300’ is a self-incompatible Brassica napus line generated by introgressing an S haplotype from B. rapa ‘Xishuibai’ into a rapeseed cultivar ‘Huayou No. 1’. Five S-locus specific primer pairs were employed to develop cleaved amplified polymorphic sequences (CAPS) markers linked the S haplotype of ‘SI1300’. Two segregating populations (F₂ and BC₁) from the cross between ‘SI1300’ and self-compatible European spring cultivar ‘Defender’, were generated to verify the molecular markers. CAPS analysis revealed no desirable polymorphism between self-incompatible and self-compatible plants. Twenty primer pairs were designed based on the homology-based candidate gene method, and six dominant sequence characterized amplified region (SCAR) markers linked with the S-locus were developed. Of the six markers, three were derived from the SRK and SP11 alleles of class II B. rapa S haplotypes and linked with S haplotype of ‘SI1300’. The other three markers were designed from the SLG-A10 and co-segregated with S haplotype of ‘Defender’. We successfully combined two pairs of them and characterized two multiplex PCR markers which could discriminate the homozygous and heterozygous genotypes. These markers were further validated in 24 F₃ and 22 BC₁F₂ lines of ‘SI1300 × Defender’ and another two segregating populations from the cross ‘SI1300 × Yu No. 9’. Nucleotide sequences of fragments linked with S-locus of ‘SI1300’ showed 99% identity to B. rapa class II S-60 haplotype, and fragments from ‘Defender’ were 97% and 94% identical to SLG and SRK of B. rapa class I S-47 haplotype, respectively. ‘SI1300’ was considered to carry two class II S haplotypes and the S haplotype on the A-genome derived from B. rapa ‘Xishuibai’ determines the SI phenotype, while ‘Defender’ carry a class I S haplotype derived from B. rapa and a class II S haplotype from B. oleracea. SCAR markers developed in this study will be helpful for improving SI lines and accelerating marker-assisted selection process in rapeseed SI hybrid breeding program.     

Effect of variation in self-incompatibility on pollen limitation and inbreeding depression in Flourensia cernua (Asteraceae) scrubs of contrasting density

Background and Aims

Selection may favour a partial or complete loss of self-incompatibility (SI) if it increases the reproductive output of individuals in the presence of low mate availability. The reproductive output of individuals varying in their strength of SI may also be affected by population density via its affect on the spatial structuring and number of S-alleles in populations. Modifiers increasing levels of self-compatibility can be selected when self-compatible individuals receive reproductive compensation by, for example, increasing seed set and/or when they become associated with high fitness genotypes.

Methods

The effect of variation in the strength of SI and scrub density (low versus high) on seed set, seed germination and inbreeding depression in seed germination (δ_germ) was investigated in the partially self-incompatible species Flourensia cernua by analysing data from self-, cross- and open-pollinated florets.

Key Results

Examination of 100 plants in both high and low scrub densities revealed that 51% of plants were strongly self-incompatible and 49 % varied from being self-incompatible to self-compatible. Seed set after hand cross-pollination was higher than after open-pollination for self-incompatible, partially self-incompatible and self-compatible plants but was uniformly low for strongly self-incompatible plants. Strongly self-incompatible and self-incompatible plants exhibited lower seed set, seed germination and multiplicative female fitness (floral display × seed set × seed germination) in open-pollinated florets compared with partially self-incompatible and self-compatible plants. Scrub density also had an effect on seed set and inbreeding depression: in low-density scrubs seed set was higher after open-pollination and δ_germ was lower.

Conclusions

These data suggest that (a) plants suffered outcross pollen limitation, (b) female fitness in partially self-incompatible and self-compatible plants is enhanced by increased mate-compatibility and (c) plants in low-density scrubs received higher quality pollen via open-pollination than plants in high-density scrubs.Key words: Flourensia cernua, population density, seed set, seed germination, female fitness, partial self-incompatibility, Mapimí Biosphere Reserve     

Mapping QTL controlling maize deep-seeding tolerance-related traits and confirmation of a major QTL for mesocotyl length

Deep-seeding tolerant seeds can emerge from deep soil where the moisture is suitable for seed germination. Breeding deep-seeding tolerant cultivars is becoming increasingly important in arid and semi-arid regions. To dissect the quantitative trait loci (QTL) controlling deep-seeding tolerance traits, we selected a tolerant maize inbred line 3681-4 and crossed it with the elite inbred line-X178 to generate an F₂ population and the derivative F_2:3 families. A molecular linkage map composed of 179 molecular markers was constructed, and 25 QTL were detected including 10 QTL for sowing at 10 cm depth and 15 QTL for sowing at 20 cm depth. The QTL analysis results confirmed that deep-seeding tolerance was mainly caused by mesocotyl elongation and also revealed considerable overlap among QTL for different traits. To confirm a major QTL on chromosome 10 for mesocotyl length measured at 20 cm depth, we selected and self-pollinated a BC₃F₂ plant that was heterozygous at the markers around the target QTL and homozygous at other QTL to generate a BC₃F₃ population. We found that this QTL explained more phenotypic variance in the BC₃F₃ population than that in the F₂ population, which laid the foundation for fine mapping and NIL (near-isogenic line) construction.     

Variability of the self-incompatibility reaction in Brassica oleracea L. with S 15 haplotype

Self-incompatibility (SI) is thought to have played a key role in the evolution of species as it promotes their outcrossing through the recognition and rejection of self-pollen grains. In most species, SI is under the control of a complex, multiallelic S-locus. The recognition system is associated with quantitative variations of the strength of the SI reaction; the origin of these variations is still not elucidated. To define the genetic regulations involved, we studied the variability of the SI response in homozygous S ₁₅ S ₁₅ plants in cauliflower. These plants were obtained from a self-progeny of a self-compatible (SC) plant heterozygous for S ₁₅ , which was generated after five selfing generations from one strongly self-incompatible initial plant. We found a continuous phenotypic variation for SI response in the offspring plants homozygous for the S ₁₅ haplotype, from the strict SI reaction to self-compatibility, with a great proportion of the plants being partially self-compatible (PSC). Decrease in SI levels was also observed during the life of the flower. The number of pollen tubes passing through the stigma barrier was higher when counted 3 or 5 days after pollination than one day after pollination. Analysis of the expression of the two key genes regulating self-pollen recognition in cauliflower, the S-locus receptor kinase (SRK) and S-locus cysteine-rich (SCR/SP11) genes, revealed that self-compatibility or PSC was associated with decreased SRK or SCR/SP11 expression. Our work shows the particularly high level of phenotypic plasticity of the SI response associated with certain S-haplotypes in cauliflower.     

Maternal environment affects the genetic basis of seed dormancy in Arabidopsis thaliana

The genetic basis of seed dormancy, a key life history trait important for adaptive evolution in plant populations, has yet been studied only using seeds produced under controlled conditions in greenhouse environments. However, dormancy is strongly affected by maternal environmental conditions, and interactions between seed genotype and maternal environment have been reported. Consequently, the genetic basis of dormancy of seeds produced under natural field conditions remains unclear. We examined the effect of maternal environment on the genetic architecture of seed dormancy using a recombinant inbred line (RIL) population derived from a cross between two locally adapted populations of Arabidopsis thaliana from Italy and Sweden. We mapped quantitative trait loci (QTL) for dormancy of seeds produced in the greenhouse and at the native field sites of the parental genotypes. The Italian genotype produced seeds with stronger dormancy at fruit maturation than did the Swedish genotype in all three environments, and the maternal field environments induced higher dormancy levels compared to the greenhouse environment in both genotypes. Across the three maternal environments, a total of nine dormancy QTL were detected, three of which were only detected among seeds matured in the field, and six of which showed significant QTL × maternal environment interactions. One QTL had a large effect on dormancy across all three environments and colocalized with the candidate gene DOG1. Our results demonstrate the importance of studying the genetic basis of putatively adaptive traits under relevant conditions.     

The self-compatibility mechanism in <Emphasis Type="Italic">Brassica napus</Emphasis> L. is applicable to F<Subscript>1</Subscript> hybrid breeding

Brassica napus, an allopolyploid species having the A genome of B. rapa and the C genome of B. oleracea, is self-compatible, although both B. rapa and B. oleracea are self-incompatible. We have previously reported that SP11/SCR alleles are not expressed in anthers, while SRK alleles are functional in the stigma in B. napus cv. ‘Westar’, which has BnS-1 similar to B. rapa S-47 and BnS-6 similar to B. oleracea S-15. This genotype is the most frequent S genotype in B. napus, and we hypothesized that the loss of the function of SP11 is the primary cause of the self-compatibility of ‘Westar’. To verify this hypothesis, we transformed ‘Westar’ plants with the SP11 allele of B. rapa S-47. All the transgenic plants and their progeny were completely self-incompatible, demonstrating self-compatibility to be due to the S haplotype having the non-functional SP11 allele in the A genome, which suppresses a functional recessive SP11 allele in the C genome. An artificially synthesized B. napus line having two recessive SP11 alleles was developed by interspecific hybridization between B. rapa and B. oleracea. This line was self-incompatible, but F₁ hybrids between this line and ‘Westar’ were self-compatible. These results suggest that the self-compatibility mechanism of ‘Westar’ is applicable to F₁ seed production in B. napus.     

Outcrossing rate and inbreeding depression in the perennial yellow bush lupine, Lupinus arboreus (Fabaceae)

Little is known about the breeding systems of perennial Lupinus species. We provide information about the breeding system of the perennial yellow bush lupine, Lupinus arboreus, specifically determining self-compatibility, outcrossing rate, and level of inbreeding depression. Flowers are self-compatible, but autonomous self-fertilization rarely occurs; thus selfed seed are a product of facilitated selfing. Based on four isozyme loci from 34 maternal progeny arrays of seeds we estimated an outcrossing rate of 0.78. However, when we accounted for differential maturation of selfed seeds, the outcrossing rate at fertilization was lower, ～0.64. Fitness and inbreeding depression of 11 selfed and outcrossed families were measured at four stages: seed maturation, seedling emergence, seedling survivorship, and growth at 12 wk. Cumulative inbreeding depression across all four life stages averaged 0.59, although variation existed between families for the magnitude of inbreeding depression. Inbreeding depression was not manifest uniformly across all four life stages. Outcrossed flowers produced twice as many seeds as selfed flowers, but the mean performance of selfed and outcrossed progeny was not different for emergence, seedling survivorship, and size at 12 wk. Counter to assumptions about this species, L. arboreus is both self-compatible and outcrosses ～78% of the time.     

RFLP mapping of QTLs conferring salt tolerance during the vegetative stage in tomato

 Quantitative trait loci (QTLs) contributing to salt tolerance during the vegetative stage in tomato were investigated using an interspecific backcross between a salt-sensitive Lycopersicon esculentum breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant Lycopersicon pimpinellifolium accession (LA722). One hundred and nineteen BC₁ individuals were genotyped for 151 RFLP markers and a linkage map was constructed. The parental lines and 119 BC₁S₁ families (self-pollinated progeny of the BC₁ individuals) were evaluated for salt tolerance in aerated saline-solution cultures with the salt concentration gradually raised to 700 mM NaCl+70 mM CaCl₂ (equivalent to an electrical conductivity of approximately 64 dS/m and a water potential of approximately −35.2 bars). The two parental lines were distinctly different in salt tolerance: 80% of the LA722 plants versus 25% of the NC84173 plants survived for at least 2 weeks after the final salt concentration was reached. The BC₁S₁ population exhibited a continuous variation, typical of quantitative traits, with the survival rate of the BC₁S₁ families ranging from 9% to 94% with a mean of 51%. Two QTL mapping techniques, interval mapping (using MAPMAKER/QTL) and single-marker analysis (using QGENE), were used to identify QTLs. The results of both methods were similar and five QTLs were identified on chromosomes 1 (two QTLs), 3, 5 and 9. Each QTL accounted for between 5.7% and 17.7%, with the combined effects (of all five QTLs) exceeding 46%, of the total phenotypic variation. All QTLs had the positive QTL alleles from the salt-tolerant parent. Across QTLs, the effects were mainly additive in nature. Digenic epistatic interactions were evident among several QTL-linked and QTL-unlinked markers. The overall results indicate that tomato salt tolerance during the vegetative stage could be improved by marker-assisted selection using interspecific variation. Received: 4 January 1999 / Accepted: 4 January 1999     

Fine linkage mapping enables dissection of closely linked quantitative trait loci for seed dormancy and heading in rice

Two quantitative trait loci (QTLs) for seed dormancy (tentatively designated Sdr1) and heading date (Hd8) have been mapped to approximately the same region on chromosome 3 by interval mapping of backcross inbred lines derived from crosses between the rice cultivars Nipponbare (japonica) and Kasalath (indica). To clarify whether Sdr1 and Hd8 could be dissected genetically, we carried out fine-scale mapping with an advanced backcross progeny. We selected a BC₄F₁ plant, in which a small chromosomal region including Sdr1 and Hd8, on the short arm of chromosome 3, remained heterozygous, whereas all the other chromosomal regions were homozygous for Nipponbare. Days-to-heading and seed germination rate in the BC₄F₂ plants showed continuous variation. Ten BC₄F₂ plants with recombination in the vicinity of Sdr1 and Hd8 were selected on the basis of the genotypes of the restriction fragment length polymorphism (RFLP) markers flanking both QTLs. Genotypes of those plants for Sdr1 and Hd8 were determined by advanced progeny testing of BC₄F₄ families. Sdr1 was mapped between the RFLP markers R10942 and C2045, and co-segregated with C1488. Hd8 was also mapped between C12534S and R10942. Six recombination events were detected between Sdr1 and Hd8. These results clearly demonstrate that Sdr1 and Hd8 were tightly linked. Nearly isogenic lines for Sdr1 and Hd8 were selected by marker-assisted selection.Communicated by D. Mackill     

RFLP mapping of QTLs conferring salt tolerance during germination in an interspecific cross of tomato

 Most cultivars of tomato (Lycopersicon esculentum) are sensitive to salinity during seed germination and at later stages. Genetic resources for salt tolerance have been identified within the related wild species of tomato. The purpose of the present study was to identify quantitative trait loci (QTLs) for salt tolerance during germination in an inbred backcross (BC₁S₁) population of an interspecific cross between a salt-sensitive tomato breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant Lycopersicon pimpinellifolium accession (LA722). Onehundred and nineteen BC₁ individuals were genotyped for 151 restriction fragment length polymorphism (RFLP) markers and a genetic linkage map was constructed. The parental lines and 119 BC₁S₁ families (self-pollinated progeny of 119 BC₁ individuals) were evaluated for germination at an intermediate salt-stress level (150 mM NaCl+15 mM CaCl₂, water potential approximately −850 kPa). Germination was scored visually as radicle protrusion at 8-h intervals for 28 consecutive days. Germination response was analyzed by survival analysis and the time to 25, 50, and 75% germination was determined. In addition, a germination index (GI) was calculated as the weighted mean of the time from imbibition to germination for each family/line. Interval mapping, single-marker analysis and distributional extreme analysis, were used to identify QTLs and the results of all three mapping methods were generally similar. Seven chromosomal locations with significant effects on salt tolerance were identified. The L. pimpinellifolium accession had favorable QTL alleles at six locations. The percentage of phenotypic variation explained (PVE) by individual QTLs ranged from 6.5 to 15.6%. Multilocus analysis indicated that the cumulative action of all significant QTLs accounted for 44.5% of the total phenotypic variance. A total of 12 pairwise epistatic interactions were identified, including four between QTL-linked and QTL-unlinked regions and eight between QTL-unlinked regions. Transgressive phenotypes were observed in the direction of salt sensitivity. The graphical genotyping indicated a high correspondence between the phenotypes of the extreme families and their QTL genotypes. The results indicate that tomato salt tolerance during germination can be improved by marker-assisted selection using interspecific variation. Received: 29 January 1998 / Accepted: 4 June 1998     

S allele discrimination in styles of Petunia hybrida bearing stylar-conditioned pseudo-self-compatibility

Summary A cross between a 0% pseudo-self-compatible (PSC) plant (S_3.3) and a 100% PSC plant (S_1.1) yielded an F₁ population which, when selfed, produced a high mean seed set which was not significantly different than that produced when the F₁ was backcross pollinated by the 100% PSC parent. Backcross pollinating the F₁ with the 0% PSC parent yielded no seed. No S_3.3 plants were recovered in the F₂ populations, indicating that pollen tubes containing the S₃ allele were inhibited during pollen tube growth of the selfed F₁ plants. Apparently stylar-conditioned PSC does not remove all discriminatory power from these petunia styles. Crossing the F₁ (S_1.3) with an self-incompatible (SI) plant (S_2.2) produced plants which were used for computation of a standard linkage test. An approximate map distance of 28 units was found between the S specificity locus and the major gene(s) which influenced its expression. Other generalized PSC modifying genes apparantly were not linked with the S locus.Scientific Journal Series Paper Number 10,606 of the Minnesota Agricultural Experiment Station     

Protein expression of a self-compatible allele from Lycopersicon peruvianum: introgression and behavior in a self-incompatible background

Lycopersicon peruvianum (wild tomato) is a gametophytic self-incompatible (SI) species. One natural population has been shown to harbor a self-compatible (SC) allele. A stylar protein associated with the self-compatibility allele has been elucidated using SDS-PAGE. The temporal and spatial expression of this protein is presented and compared with protein expression of two SI alleles. Hybrids containing the SC and SI alleles were used in a backcrossing program to introgress the SC allele into SI backgrounds in six independent lines. Controlled pollinations and SDS-PAGE were used to identify and select classes of progeny. After four backcross generations (approximately 97% recovery of the SI backgrounds) the SC allele still confers self-fertility in lines that contain this allele, providing evidence that the mutation to SC occurred at the S-locus and that the associated protein is likely responsible.     

A genetic model and molecular markers for wild oat (Avena fatua L.) seed dormancy

Seed dormancy allows weed seeds to persist in agricultural soils. Wild oat (Avena fatua L.) is a major weed of cereal grains and expresses a range of seed dormancy phenotypes. Genetic analysis of wild oat dormancy has been complicated by the difficulty of phenotypic classification in segregating populations. Therefore, little is known about the nature of the genes that regulate dormancy in wild oat. The objectives of our studies were to develop methods to classify the germination responses of segregating wild oat populations and to find molecular markers linked to quantitative trait loci (QTL) that regulate seed dormancy in wild oat. RAPD markers OPX-06 and OPT-04 explained 12.6% and 6.8% respectively, of the F₂ phenotypic variance. OPF-17 was not significant in a simple regression model, but it was linked in repulsion to OPT-04. A three-locus model of seed dormancy in wild oat is presented based on the 41-day germination profiles of F₁, F₂, F₃, BC₁P₁F₁, BC₁P₁F₂, and BC₁P₂F₁ generations, and the 113 day germination profile of 126 F₇ recombinant inbred lines. Loci G ₁ and G ₂ promote early germination, and the D locus promotes late germination. If at least one copy of the dominant G ₁ or G ₂ alleles are present regardless of the genotype at D locus, then the individual will be nondormant. If the genotype is g ₁ g ₁ g ₂ g ₂ D_, then the phenotype will be dormant. Received: 1 December 1998 / Accepted: 1 February 1999     

Marker-assisted introgression of blackmold resistance QTL alleles from wild Lycopersicon cheesmanii to cultivated tomato (L. esculentum) and evaluation of QTL phenotypic effects

Blackmold, caused by the fungus Alternaria alternata, is a major ripe fruit disease of processing tomatoes. Previously, we found blackmold resistance in a wild tomato (Lycopersicon cheesmanii) and quantitative trait loci (QTL) for resistance were mapped in an interspecific population. Five QTLs were selected for introgression from L. cheesmanii into cultivated tomato using marker-assisted selection (MAS). Restriction fragment length polymorphism and PCR-based markers flanking, and within, the chromosomal regions containing QTLs were used for MAS during backcross and selfing generations. BC₁ plants heterozygous at the QTLs, and subsequent BC₁S₁ and BC₁S₂ lines possessing different homozygous combinations of alleles at the target QTLs, were identified using DNA markers. Field experiments were conducted in 1998 (with 80 marker-selected BC₁S₂ lines) and 1999 (with 151 marker-selected BC₁S₂ and BC₁S₃ lines) at three California locations. Blackmold resistance was assessed during both years, and horticultural traits were evaluated in 1999. The BC₁S₂ and BC₁S₃ lines containing L. cheesmanii alleles at the QTLs were associated with a large genetic variance for resistance to blackmold and moderate heritability, suggesting that significant genetic gain may be achieved by selection in this genetic material. L. cheesmanii alleles at three of the five introgressed QTLs showed a significant, positive effect on blackmold resistance. A QTL on chromosome 2 had the largest positive effect on blackmold resistance, alone and in combination with other QTLs, and was also associated with earliness, a positive horticultural trait. The other four QTLs were associated primarily with negative horticultural traits. Fine mapping QTLs using near isogenic lines could help determine if such trait associations are due to linkage drag or pleiotropy.     

A self-compatible mutant S allele conferring a dominant negative effect on the functional S allele in Ipomoea trifida

A spontaneously occurring self-compatible mutant has been identified in Ipomoea trifida, a species possessing sporophytic self-incompatibility controlled by a single multiallelic S locus. Analysis of the segregation of compatibility/incompatibility phenotypes in selfed and crossed progenies of the self-compatible mutant plant indicated that the self-compatibility trait was caused by a mutation at the S locus; the mutated S allele was therefore designated Sc. RFLP analysis of progeny plants segregating for the Sc allele using the SSP gene (a gene linked closely to the S locus of I. trifida) as a probe confirmed that the mutation was present at the S locus. Self-incompatibility responses were examined in F₁ progenies obtained from crosses between the self-compatible mutant and self-incompatible plants homozygous for one of three S alleles, S ₁ , S ₃ and S ₂₂ , where the dominance relationship is S ₂₂ >S ₁ >S ₃ . All F₁ progeny plants from crosses with S ₂₂ and S ₁ homozygotes were self-incompatible and exhibited the respective phenotypes of each self-incompatible parent (either S ₂₂ or S ₁ ) in both stigma and pollen. However, of the F₁ progeny plants from the cross with the S ₃ homozygote, those carrying the genotype ScS ₃ were all self-compatible and cross-compatible as both female and male parents with the S ₃ homozygote. These results indicate that the dominance relationship between the four S alleles is: S ₂₂ >S ₁ >Sc>S ₃ and so reveal the unexpected finding that the mutated Sc allele is dominant over a functional S ₃ allele. A possible explanation for this observation is that the gene product encoded by the Sc allele confers a dominant negative effect on the S ₃ gene product. Received: 21 June 2000 / Accepted: 18 July 2000     

Genetic and QTL analyses of seed dormancy and preharvest sprouting resistance in the wheat germplasm CN10955

The inheritance and genetic linkage analysis for seed dormancy and preharvest sprouting (PHS) resistance were carried out in an F₈ recombinant inbred lines (RILs) derived from the cross between “CN19055” (white-grained, PHS-resistant) with locally adapted Australian cultivar “Annuello” (white-grained, PHS-susceptible). Seed dormancy was assessed as germination index (GI7) while assessment for preharvest sprouting resistance was based on whole head assay (sprouting index, SI) and visibly sprouted seeds (VI). Segregation analysis of the F₂, F₃ data from the glasshouse and the RIL population in 2004 and 2005 field data sets indicated that seed dormancy and PHS resistance in CN19055 is controlled by at least two genes. Heritabilities for GI7 and VI were high and moderate for SI. The most accurate method for assessing PHS resistance was achieved using VI and GI7 while SI exhibited large genotype by environment interaction. Two quantitative trait loci (QTLs) QPhs.dpivic.4A.1 and QPhs.dpivic.4A.2 were identified. On pooled data across four environments, the major QTL, QPhs.dpivic.4A.2, explained 45% of phenotypic variation for GI7, 43% for VI and 20% for SI, respectively. On the other hand, QPhs.dpivic.4A.1 which accounted for 31% of the phenotypic variation in GI7 in 2004 Horsham field trial, was not stable across environments. Physical mapping of two SSR markers, Xgwm937 and Xgwm894 linked to the major QTL for PHS resistance, using Chinese Spring deletions lines for chromosome 4AS and 4AL revealed that the markers were located in the deletion bins 4AL-12 and 4AL-13. The newly identified SSR markers (Xgwm937/Xgwm894) showed strong association with seed dormancy and PHS resistance in a range of wheat lines reputed to possess PHS resistance. The results suggest that Xgwm937/Xgwm894 could be used in marker-assisted selection (MAS) for incorporating preharvest sprouting resistance into elite wheat cultivars susceptible to PHS.