Fertility, segregation at a herbicide-resistance locus, and genome structure in BC hybrids from two important weedy Amaranthus species

Field studies have established high potential for hybridization between two important and often coexisting weedy species, Amaranthus hybridus and Amaranthus tuberculatus. Prezygotic reproductive barriers between these species are believed to be limited to pollen competition and availability. A greenhouse study showed that a herbicide-resistance gene (ALS) from A. hybridus could be introgressed into an advanced A. tuberculatus background (BC2). However, evidence is lacking in support of such transfer in nature. Postzygotic reproductive barriers may minimize, if not preclude, natural introgression. Indeed, A. hybridus xA. tuberculatus hybrids are characterized by reduced fertility and even floral neuterism. The purpose of this study was to assess hybrid fertility in the BC1 generation and its relationship with genome structure and segregation at ALS. Fertility was assessed by measuring seed output and by pollen evaluation, and segregation at ALS was determined via a molecular marker system. The two parental species have the same ploidy (2n = 32) but differ in DNA content (2C) values, with A. tuberculatus chromosomes being on average 29% greater than those of A. hybridus. Given that most (98%) BC(1)s were homoploid, 2C values were used as indicators of relative genomic constitution. Fertility in the BC1 generation was greater than that of F1s, and 3% of BC1s had seed output similar to that of the parental species. Fertility in the BC1 did not correlate (in a strict way) with reconstitution of parental genomes. Hybrid sterility appeared to be controlled by relatively few loci. Heterozygosity at ALS was negatively correlated with fertility. Also, the A. tuberculatus ALS allele was not observed in the A. hybridus sexual condition, monoecism. Linkage of ALS to a locus associated (directly or via epistasis) with hybrid sterility may explain the fertility penalty observed with ALS introgression. Moreover, this linkage might explain why sequenced herbicide-resistance ALS alleles from sympatric A. tuberculatus and A. hybridus populations show independent evolution.     

Amplified fragment length polymorphism-based genetic relationships among weedy Amaranthus species

Weedy Amaranthus species frequently cause economically significant reductions in crop yields. Accurate identification of Amaranthus species is important for efficient weed control, but Amaranthus species can interbreed, which might cause difficulty when identifying hybrid-derived specimens. To determine which of several economically important weedy Amaranthus species are most genetically similar, and thus most likely to produce viable hybrids, we performed amplified fragment length polymorphism (AFLP)-based unweighted pair group method with arithmetic mean (UPGMA) analysis on 8 of these species, with 141 specimens representing 98 accessions. The analysis grouped the specimens into four principal clusters composed of Palmer amaranth (Amaranthus palmeri S. Wats.) and spiny amaranth (Amaranthus spinosus L.); Powell amaranth (Amaranthus powellii S. Wats.), redroot pigweed (Amaranthus retroflexus L.), and smooth pigweed (Amaranthus hybridus L.); waterhemp (Amaranthus tuberculatus (Moq.) Sauer) and sandhills amaranth (Amaranthus arenicola I.M. Johnst.); and tumble pigweed (Amaranthus albus L.). The cluster analysis provided evidence suggesting hybridization among Powell amaranth, redroot pigweed, and smooth pigweed. Further investigations using molecular analysis of the ribosomal internal transcribed spacer region from atypical plants supported this notion. Three species, Palmer amaranth, sandhills amaranth, and waterhemp, are dioecious; nevertheless, the Palmer amaranth and waterhemp-sandhills amaranth clusters were distinct from each other. The Palmer amaranth-spiny amaranth cluster included a cluster of Palmer amaranth and two clusters of spiny amaranth, a monoecious species. Thus the dioecious species Palmer amaranth and waterhemp may not necessarily hybridize with each other more readily than they would to one or more of the monoecious Amaranthus species.     

Transmission of herbicide resistance from a monoecious to a dioecious weedy Amaranthus species

The genus Amaranthus includes several important monoecious and dioecious weed species, and several populations of these species have developed resistance to herbicides. These species are closely related and two or more species often coexist in agricultural settings. Collectively, these attributes raise the concern that herbicide resistance might transfer from one weedy Amaranthus species to another. We performed research to determine if a dominant allele encoding a herbicide-insensitive form of acetolactate synthase (ALS) could be transferred from a monoecious species, A. hybridus, to a dioecious species, A. rudis. Numerous F₁ hybrids were obtained from controlled crosses in a greenhouse between A. rudis and herbicide-resistant A. hybridus, and most (85%) of these hybrids were herbicide-resistant. Molecular analysis of the ALS gene was used to verify that herbicide-resistant hybrids contained both an A. rudis and an A. hybridus ALS allele. Although hybrids had greatly reduced fertility, 42 BC₁ plants were obtained by backcrossing 33 hybrids with male A. rudis. Fertility was greatly restored in BC₁ progeny, and numerous BC₂ progeny were obtained from a second backcross to A. rudis. The herbicide-resistance allele from A. hybridus was transmitted to 50% of the BC₁ progeny. The resistance allele was subsequently transmitted to and conferred herbicide resistance in 39 of 110 plants analyzed from four BC₂ families. Parental species, hybrids, and BC₂ progeny were compared for 2C nuclear DNA contents. The mean hybrid 2C nuclear DNA content, 1.27 pg, was equal to the average between A. rudis and A. hybridus, which had 2C DNA contents of 1.42 and 1.12 pg, respectively. The mean 2C DNA content of BC₂ plants, 1.40 pg, was significantly (! < 0.01) less than that of the recurring A. rudis parent and indicated that BC₂ plants were not polyploid. This report demonstrates that herbicide resistance can be acquired by A. rudis through a hybridization event with A. hybridus.     

Biosystematics and agronomic potential of some weedy and cultivated amaranths

Summary Three weedy amaranths (Amarantkus hybridus, A. retroflexus and A. powellii) from nine California sites, three domesticated species (A. caudatus, A. hypochondriacus and A. cruentus) from the USDA plant inventory as well as other sources and a naturally-occurring crop-weed hybrid were studied for numerical taxonomy using morphological and allozyme variation data. The crop and weedy species groups were easily separated and the hybrid populations were found to be intermediate. Surprisingly, very little intraspecific variation was present. Crop, weed and hybrid amaranths were also compared for their yielding ability, harvest index, seed efficiency of grain production and protein, popping quality and other agronomic traits. Although field plot yields were similar among the three groups of species (700 Kg/ha seed without fertilizer treatment and water, ranging to 3000 Kg/ha with fertilizer applications of 170 Kg N/ha, and abundant water), the harvest index of the weedy group was much higher (25–40%) than the domesticated species (10–15%). The allocation of biomass to seed production is positively correlated with seed yield in the domesticated but not in the weedy types, whereas the percentages of biomass as stem material and as seeds are negatively correlated. Several weedy and crop characteristics together should provide the basis of new improved cultivars through genetic recombination and selection.     

Can hybridization cause local extinction: a case for demographic swamping of the Australian native Senecio pinnatifolius by the invasive Senecio madagascariensis?

Hybridization between native and invasive species can have several outcomes, including enhanced weediness in hybrid progeny, evolution of new hybrid lineages and decline of hybridizing species. Whether there is a decline of hybridizing species largely depends on the relative frequencies of parental taxa and the viability of hybrid progeny. Here, the individual- and population-level consequences of hybridization between the Australian native Senecio pinnatifolius and the exotic Senecio madagascariensis were investigated with amplified fragment length polymorphism (AFLP) markers, and this information was used to estimate the annual loss of viable seeds to hybridization. A high frequency (range 8.3-75.6%) of hybrids was detected in open pollinated seeds of both species, but mature hybrids were absent from sympatric populations. A hybridization advantage was observed for S. madagascariensis, where significantly more progeny than expected were sired based on proportional representation of the two species in sympatric populations. Calculations indicated that S. pinnatifolius would produce less viable seed than S. madagascariensis, if hybridization was frequency dependent and S. madagascariensis reached a frequency of between 10 and 60%. For this native-exotic species pair, prezygotic isolating barriers are weak, but low hybrid viability maintains a strong postzygotic barrier to introgression. As a result of asymmetric hybridization, S. pinnatifolius would appear to be under threat if S. madagascariensis increases numerically in areas of contact.     

Biorational management tactics to select against triazine-resistant Amaranthus hybridus: a field trial

1. The individual and joint effectiveness of two biorational tactics (crop interference and exploitation of negative cross-resistance to certain herbicides) in the management of triazine-resistant Amaranthus hybridus L. (smooth pigweed) were estimated. Biorational tactics exploit biological idiosyncracies of resistant (R) genotypes to maximize fitness cost(s) of resistance. We quantified selection against triazine resistance by relative performance comparisons between lines having comparable nuclear genomes but either resistant or susceptible cytoplasm. Increasing soybean density by reducing row spacing (from 76 cm to 25 cm) did not significantly increase the fitness cost of resistance.
2. Low doses of bentazon (100 and 300 g active ingredient ha^–1) did strongly increase the cost of resistance. Over 2 years, the mean relative performance of R genotypes in bentazon treatments was 0·40, compared to 0·60 in the absence of bentazon. Therefore, use of bentazon in soybean production has the potential to delay evolution of triazine resistance in maize–soybean rotations using triazines.
3. There was no consistent indication that increased soybean density and bentazon herbicide could act synergistically to increase costs of triazine resistance in Amaranthus hybridus . Nor were differences in response to biorational tactics evident between the two populations of origin (Maryland and Virginia, USA) from which experimental lines were derived.
4. Effects of the biorational tactics differed markedly between years, highlighting that resistance management depending primarily on these tactics would have widely variable results. Use of such tactics is likely to be most effective in the context of diversified weed management.     

微波法和超声波法提取绿穗苋多糖响应面优化研究

绿穗苋是一种药食兼用作物,其中多糖成份具有很高的药食价值。本研究以绿穗苋地上部分为材料,以微波和超声波两种方法对绿穗苋多糖进行提取,并通过响应面分析法对提取进行优化,确定最佳工艺,通过水提醇沉的方法得到绿穗苋粗多糖。综合比较两种提取工艺,提取效果最佳工艺为微波提取法。其条件为:提取时间41.42 min,提取功率211.65 W,料液比1:33.338 (g/mL),实际得率为13.25%。该研究结果促进绿穗苋资源的有效利用,为绿穗苋多糖的提取工艺及产品的开发利用提供理论依据。     

Transfer of glyphosate resistance: evidence of hybridization in Conyza (Asteraceae)

Transfer of herbicide resistance genes between crops and weeds is relatively well documented; however, far less information exists for weed-to-weed interactions. The hybridization between the weedy diploids Conyza canadensis (2n = 18) and C. ramosissima (2n = 18) was investigated by monitoring transmission of the allele conferring resistance to N-phosphonomethyl glycine (glyphosate). In a multivariate quantitative trait analysis, we described the phylogenic relationship of the plants, whereas we tested seed viability to assess potential postzygotic reproductive barriers (PZRB) thus affecting the potential establishment of hybrid populations in the wild. When inflorescences were allowed to interact freely, approximately 3% of C. ramosissima or C. canadensis ova were fertilized by pollen of the opposing species and produced viable seeds; >95% of the ova were fertilized under no-pollen competition conditions (emasculation). The interspecific Conyza hybrid ( ) demonstrated an intermediate phenotype between the parents but superior resistance to glyphosate compared to the resistant C. canadensis parent. Inheritance of glyphosate resistance in the selfed ( ) followed the partially dominant nuclear, single-gene model; backcrosses confirmed successful introgression of the resistance allele to either parent. Negligible PZRB were observed in the hybrid progenies, confirming fertility of the C. canadensis × C. ramosissima nothotaxa. The implications of introgressive hybridization for herbicide resistance management and taxonomy of Conyza are discussed.     

Genetic analyses of a hybrid cross between serotypes A and D strains of the human pathogenic fungus Cryptococcus neoformans

Cryptococcus neoformans has two varieties, var. grubii and var. neoformans, that correspond to serotypes A and D, respectively. Molecular phylogenetic analyses suggest that these two varieties have diverged from each other for approximately 18 million years. The discovery of pathogenic serotype AD hybrid strains in nature indicates that intervariety mating in C. neoformans occurs in the natural environment. However, little is known about the genetic consequences of hybridization in C. neoformans. Here, we analyzed a hybrid population of 163 progeny from a cross between strains of serotypes A (CDC15) and D (JEC20), using 114 codominant nuclear PCR-RFLP markers and 1 direct PCR marker. These markers were distributed on all 14 chromosomes of the sequenced strain JEC21 that was isogenic to one of the parents (JEC20) in our cross. Our analyses identified that of the 163 progeny, 5 were heterozygous at all 115 loci, 1 was completely homozygous and identical to one of the parents (CDC15), and the remaining 157 each contained at least 1 heterozygous locus. Because all 163 progeny inherited mitochondria from the MATa parent JEC20, none of the progeny had a genotype identical to either of the two parents or to a composite of the two parents. All 115 nuclear loci showed three different genotypes in the progeny population, consistent with Mendelian segregation during meiosis. While the linkage analysis showed independent reassortment among loci on different linkage groups, there were significant differences in recombination frequencies among chromosomes and among regions within certain chromosomes. Overall, the linkage-map length from this hybrid cross was much shorter and the recombination frequency much lower than those constructed using serotype D strains, consistent with suppressed recombination in the intervariety cross between strains of serotypes A and D. We discuss the implications of our results in our understanding of the speciation and evolution of the C. neoformans species complex.     

Herbicide resistant rice (Oryza sativa L.): Global implications for weedy rice and weed management*

Rice cultivars resistant to broad‐spectrum herbicides have been developed and their commercial release is imminent, especially for imidazolinone and glufosinate resistant varieties in the USA and Latin America. Glyphosate‐resistant rice should follow within a few years. Rice growers throughout the world could benefit from the introduction of herbicide‐resistant rice cultivars that would allow in‐crop, selective control of weedy Oryza species. Other perceived benefits are the possibility to control ‘hard‐to‐kill’ weed species and weed populations that have already evolved resistance to herbicides currently used in rice production, especially those of the Echinochloa species complex. Weed management could also be improved by more efficient post‐emergence control. Introduction of herbicide resistant rice could also bring areas heavily infested with weedy rice that have been abandoned back to rice production, allow longer term crop rotations, reduce consumption of fossil fuels, promote the replacement of traditional chemicals by more environmentally benign products, and provide more rice grain without adding new land to production. There are also concerns, however, about the impact of releasing herbicide‐resistant rice on weed problems. Of most concern is the possibility of rapid transfer of the resistance trait to compatible weedy Oryza species. Development of such herbicide resistant weedy rice populations would substantially limit the chemical weed management options for farmers. Herbicide‐resistant rice volunteers also could become problematic, and added selection pressure to weed populations could aggravate already serious weed resistance problems. Because of the risk of weedy Oryza species becoming resistant to broad‐spectrum herbicides, mitigating measures to prevent gene flow, eventually attainable by both conventional breeding and molecular genetics, have been proposed. With commercialisation of the first herbicide resistant varieties planned for 2001, these mitigating measures will not be available for use with this first generation of herbicide resistant rice products. Release of herbicide resistant rice should depend on a thorough risk assessment especially in areas infested with con‐specific weedy rice or intercrossing weedy Oryza species. Regulators will have to balance risks and benefits based on local needs and conditions before allowing commercialisation of herbicide‐resistant rice varieties. If accepted, these varieties should be considered as components of integrated weed management, and a rational herbicide use and weedy rice control should be promoted to prevent losing this novel tool.     

Spontaneous hybridization between maize and teosinte

The closest wild relatives of maize, Zea mays ssp. mays are various Zea taxa known as "teosinte." Hybrids between maize and the teosinte taxon, Zea mays ssp. mexicana, often occur when the 2 are sympatric in Mexico. Measuring the spontaneous hybridization rate of the 2 taxa would shed light on the mechanisms contributing to the evolution and persistence of these hybrid swarms. We conducted a series of field experiments in Riverside, CA, to measure the natural hybridization rates between maize and 2 teosinte taxa, Z. m. ssp. mexicana and Zea mays ssp. parviglumis. We planted teosinte within and near maize plantations. Hybrids were identified by progeny testing for a maize-specific herbicide resistance allele and a teosinte-specific allozyme allele. Hybridity was confirmed by growing putative hybrid progeny to maturity to evaluate whether they had the characteristic morphology of maize x teosinte hybrids. We found that maize and Z. m. ssp. mexicana naturally hybridize at a low rate (<1%), whereas Z. m. ssp. parviglumis hybridizes with the crop at a high rate (>50%).     

Genetic control of a cytochrome P450 metabolism-based herbicide resistance mechanism in Lolium rigidum

The dynamics of herbicide resistance evolution in plants are influenced by many factors, especially the biochemical and genetic basis of resistance. Herbicide resistance can be endowed by enhanced rates of herbicide metabolism because of the activity of cytochrome P450 enzymes, although in weedy plants the genetic control of cytochrome P450-endowed herbicide resistance is poorly understood. In this study we have examined the genetic control of P450 metabolism-based herbicide resistance in a well-characterized Lolium rigidum biotype. The phenotypic resistance segregation in herbicide resistant and susceptible parents, F1, F2 and backcross (BC) families was analyzed as plant survival following treatment with the chemically unrelated herbicides diclofop-methyl or chlorsulfuron. Dominance and nuclear gene inheritance was observed in F1 families when treated at the recommended field doses of both herbicides. The segregation values of P450 herbicide resistance phenotypic traits observed in F2 and BC families was consistent with resistance endowed by two additive genes in most cases. In obligate out-crossing species such as L. rigidum, herbicide selection can easily result in accumulation of resistance genes within individuals.     

Do escaped transgenes persist in nature? The case of an herbicide resistance transgene in a weedy Brassica rapa population

The existence of transgenic hybrids resulting from transgene escape from genetically modified (GM) crops to wild or weedy relatives is well documented but the fate of the transgene over time in recipient wild species populations is still relatively unknown. This is the first report of the persistence and apparent introgression, i.e. stable incorporation of genes from one differentiated gene pool into another, of an herbicide resistance transgene from Brassica napus into the gene pool of its weedy relative, Brassica rapa , monitored under natural commercial field conditions. Hybridization between glyphosate-resistant [herbicide resistance (HR)] B. napus and B. rapa was first observed at two Québec sites, Ste Agathe and St Henri, in 2001. B. rapa populations at these two locations were monitored in 2002, 2003 and 2005 for the presence of hybrids and transgene persistence. Hybrid numbers decreased over the 3-year period, from 85 out of ~200 plants surveyed in 2002 to only five out of 200 plants in 2005 (St Henri site). Most hybrids had the HR trait, reduced male fertility, intermediate genome structure, and presence of both species-specific amplified fragment length polymorphism markers. Both F₁ and backcross hybrid generations were detected. One introgressed individual, i.e. with the HR trait and diploid ploidy level of B. rapa, was observed in 2005. The latter had reduced pollen viability but produced ~480 seeds. Forty-eight of the 50 progeny grown from this plant were diploid with high pollen viability and 22 had the transgene (1:1 segregation). These observations confirm the persistence of the HR trait over time. Persistence occurred over a 6-year period, in the absence of herbicide selection pressure (with the exception of possible exposure to glyphosate in 2002), and in spite of the fitness cost associated with hybridization.     

Multifaceted,Cross-Generational Costs of Hybridization in Sibling Drosophila species

Maladaptive hybridization, as determined by the pattern and intensity of selection against hybrid individuals, is an important factor contributing to the evolution of prezygotic reproductive isolation. To identify the consequences of hybridization between Drosophila pseudoobscura and D. persimilis, we estimated multiple fitness components for F1 hybrids and backcross progeny and used these to compare the relative fitness of parental species and their hybrids across two generations. We document many sources of intrinsic (developmental) and extrinsic (ecological) selection that dramatically increase the fitness costs of hybridization beyond the well-documented F1 male sterility in this model system. Our results indicate that the cost of hybridization accrues over multiple generations and reinforcement in this system is driven by selection against hybridization above and beyond the cost of hybrid male sterility; we estimate a fitness loss of >95% relative to the parental species across two generations of hybridization. Our findings demonstrate the importance of estimating hybridization costs using multiple fitness measures from multiple generations in an ecologically relevant context; so doing can reveal intense postzygotic selection against hybridization and thus, an enhanced role for reinforcement in the evolution of populations and diversification of species.     

Costs of transgenic herbicide resistance introgressed from Brassica napus into weedy B. rapa

Wild relatives of genetically engineered crops can acquire transgenic traits such as herbicide resistance via spontaneous crop–wild hybridization. In agricultural weeds, resistance to herbicides is often a beneficial trait, but little is known about possible costs that could affect the persistence of this trait when herbicides are not used. We tested for costs associated with transgenic resistance to glufosinate when introgressed into weedy Brassica rapa . Crosses were made between transgenic B. napus and wild B. rapa from Denmark. F₁ progeny were backcrossed to B. rapa and BC₁ plants were selected for chromosome numbers similar to B. rapa . Further backcrossing resulted in a BC₂ generation that was hemizygous for herbicide resistance. We quantified the reproductive success of 457 BC₃ progeny representing six full-sib families raised in growth rooms (plants were pollinated by captive bumblebees). Pollen fertility and seed production of BC₃ plants were as great as those of B. rapa raised in the same growth rooms. Segregation for herbicide resistance in BC₃ plants was 1:1 overall, but the frequency of resistant progeny was lower than expected in one family and higher than expected in another. There were no significant differences between transgenic and nontransgenic plants in survival or the number of seeds per plant, indicating that costs associated with the transgene are probably negligible. Results from this growth-chamber study suggest that transgenic resistance to glufosinate is capable of introgressing into populations of B. rapa and persisting, even in the absence of selection due to herbicide application.     

Herbicide-tolerant corn by pollen selection

Summary Maize pollen was exposed to the herbicide Chlorsulfuron (CS), and segregation for tolerance was observed. The resulting plant generation exhibited significantly greater tolerance to CS than other (control) progeny. Since the increase in tolerance occurred after only one generation of pollen exposure, this result demonstrates that pollen selection can be used to develop herbicide-resistant crop species, even when the species are not amenable to cell culture. It also suggests a possible mechanism for the rapid evolution of herbicide tolerance in weeds.     

中国苋属nrDNA的ITS序列分析及其系统学意义

运用ＰＣＲ直接测序法,对苋属（Ａｍａｒａｎｒｈｕｓ Ｌ．）１５个种及外类群鸡冠花（Ｃｅｌｏｓｉａ ｃｒｉｓｔａｔａ Ｌ．）ｎｒＤＮＡ的ＩＴＳ区（包括ＩＴＳ－１,５．８５ｒＤＮＡ和ＩＴＳ－２）进行序列测定。结果表明苋属植物的ＩＴＳ序列总长度为６２９－６３２ｂｐ,长度变异仅发生在ＩＴＳ－１区（２５０－２５３ｂｐ）。采用ＰＡＵＰ软件进行系统发育分析表明：分布于中国的苋属植物可分为３组,即刺苋组（ｓｅｃｇ     

Self-compatibility and plant invasiveness: Comparing species in native and invasive ranges

A longstanding hypothesis (“Baker's rule”) is that plant invasiveness is facilitated by floral self compatibility rather than self incompatibility. Extending this idea, invasive species whose individuals vary in degree of self compatibility within the native range might be self compatible in invading or weedy populations, due to natural selection on the mating system. We compared mating system between native and invasive ranges for two major world invasives, one annual (Echium plantagineum) and one perennial (Solanum elaeagnifolium). For an additional annual species (Centaurea solstitialis) we compared non-weedy and weedy populations in the native range. No species was strongly spontaneously self pollinating, but the degree of self compatibility after hand pollination varied dramatically. Both annuals were self incompatible in native or non-weedy populations but self compatible in invasive or weedy ones; the reverse was true for the perennial. Individuals within populations of all three species also varied in their degree of self compatibility, suggesting a basis for natural selection, and populations of the same species sharing a status (native/non-weedy, invading/weedy) varied in average self compatibility. These results support the hypothesis that differential selection of progeny during invasion can result in self-compatible populations derived from ancestrally self-incompatible ones, but that this process may be less important in perennial species, which experience multiple opportunities for sexual reproduction. Overall, however, mating system may not operate alone and its contributions to invasiveness may be conditional on other attributes of a species including physiology, morphology, and life history.     

Experimental interspecific hybridization in fleas of the genus Nosopsyllus (Siphonaptera: Ceratophyllidae)]

Experimental interspecific hybridization between males and females of Nosopsyllus fasciatus and N. mokrzeckyi was carried out. Most abundant progeny was obtained after hybridization between N. fasciatus females and N. mokrzeckyi males. Hybrid descendants inherited, in general, the characters of the maternal species and in less number the paternal characters and those of both parents. The fecundity of hybrid progeny of N. fasciatus females and N. mokrzeckyi males in two generations was studied. A conclusion is made concerning close affinity of the species and their relative evolutionary youth.     

Hypothesis: Transgene establishment in wild relatives of wheat can be prevented by utilizing the Ph1 gene as a senso stricto chaperon to prevent homoeologous recombination

Durum and bread wheat need transgenic traits such as herbicide and disease resistance due to recent evolution of herbicide resistant grass weeds and an intractable new strain of stem rust. Transgenic wheat varieties have not been commercialized partly due to potential transgene movement to wild/weedy relatives, which occurs naturally to closely related Aegilops and other spp. Recombination does not occur in the F₁ hybrid between wheat and its relatives due to the presence of the Ph1 gene on wheat chromosome arm 5BL, which acts as a chaperone, preventing promiscuous homoeologous pairing to similar, but not homologous chromosomes of the wild/weedy species. Thus recombination must occur during backcrossing after the wheat Ph1 gene has been eliminated. Based on these findings, we speculate that Ph1 could be used to prevent gene introgression into weedy relatives. We propose two methods to prevent such transgene establishment: (1) link the transgene in proximity to the wheat Ph1 gene and (2) insert the transgene in tandem with the lethal barnase on any chromosome arm other than 5BL, and insert barstar, which suppresses barnase on chromosome arm 5BL in proximity to Ph1. The presence of Ph1 in backcross plants containing 5BL will prevent the homoeologous establishment of barnase coupled to the desired transgene in the wild population. 5BL itself will be eliminated during repeated backcrossing to the wild parent, and progeny bearing the desired transgene in tandem with barnase but without the Ph1-barstar complex will die.