Natural hybridization between wheat (Triticum aestivum L.) and its wild relatives Aegilops geniculata Roth and Aegilops triuncialis L.

BACKGROUND

Cultivated bread wheat (Triticum aestivum L.) spontaneously hybridizes with wild/weedy related Aegilops populations, but little is known about the actual rates at which this hybridization occurs under field conditions. It is very important to provide reliable empirical data on this phenomenon in order to assess the potential crop–wild introgression, especially in the context of conducting risk assessments for the commercialization of genetically modified (GM) wheat, as gene flow from wheat to Aegilops species could transfer into the wild species genes coding for traits such as resistance to herbicides, insects, diseases or environmental stresses.

RESULTS

The spontaneous hybridization rates between wheat and A. geniculata and A. triuncialis, which are very abundant in the Mediterranean area, have been estimated for the first time in the northern part of the Meseta Central, the great central plateau which includes the largest area of wheat cultivation in Spain. Hybridization rates averaged 0.12% and 0.008% for A. geniculata and A. triuncialis, respectively. Hybrids were found in 26% of A. geniculata and 5% of A. triuncialis populations, at rates that can be ≤3.6% for A. geniculata and 0.24% for A. triuncialis.

CONCLUSION

The detection of Aegilops spp.–wheat hybrids in Aegilops populations indicates that gene flow can occur, although wheat is considered a crop with a low-to-medium risk for transgene escape. These data on field hybridization rates are essential for GM wheat risk assessment purposes. © 2023 Society of Chemical Industry.     

节节麦pbf基因的克隆、序列分析及原核表达

醇溶蛋白盒结合因子(prolamin-box binding factor,PBF)通过调控籽粒蛋白的表达效率进而影响面粉的加工品质。为给深入研究小麦籽粒PBF对籽粒蛋白质表达调控的分子基础提供参考依据,进而为小麦面粉加工品质的改良提供候选基因资源,利用特异引物组合pbfF1/pbf R1分别从两份节节麦(AS90、AS2386)中克隆出pbf基因后进行序列分析,并进一步构建pbf基因的原核表达体系。结果表明,从两份节节麦中克隆得到了2个不同类型的pbf基因(GenBank登录号分别为KJ544771和KJ544772),其中来源于AS2386的KJ544772与来源于普通六倍体小麦的1个pbf基因序列完全相同。推导的氨基酸序列分析表明,KJ544771和KJ544772所编码的蛋白质均为弱碱性的亲水蛋白,具有典型的DOF蛋白结构域。与其他远缘物种来源的PBF比对结果表明,该类蛋白在NLS核心、DOF结构域及Ser铰链区相对保守,而在C-端调控区变异较大,说明PBF蛋白具有种属特异性。同时,系统演化树显示,来源于节节麦AS2386的pbf基因与迄今已知的全部普通小麦的pbf基因具有高度的相似性,因此推测该种类型的节节麦很可能参与了最初的普通六倍体小麦的形成。此外,本研究成功构建了pbf基因的原核表达体系,可为后续功能验证的开展奠定基础。     

节节麦不同生育期叶片蜡质组成和超微形态的变化

为了解节节麦(Aegilops tauschii Coss.)不同生育期叶片表皮蜡质组成及晶体形态的变化,对节节麦叶片蜡质进行提取,利用气相色谱-质谱(GC-MS)联用仪和气相色谱-火焰离子化检测仪(GC-FID)对蜡质进行了定性和定量分析,并采用扫描电镜(SEM)对叶片表面蜡质晶体形态进行了观察。结果表明,节节麦叶表皮蜡质经GC-MS分析,共鉴定出化合物21种,主要以初级醇为主(苗期、抽穗期和灌浆期相对含量分别为85%、84%和70%),并含有少量的烷烃、醛、酮和脂肪酸;随着节节麦的生长发育,蜡质总量不断积累,烷烃含量极显著地升高,其中以C29烷烃的增加最明显,而初级醇含量显著降低,其中C26醇的相对含量降低最明显(苗期、抽穗期和灌浆期相对含量分别为80%、76%和63%),其他各类化合物组分变化不大。经扫描电镜观察,节节麦叶片近轴和远轴面的蜡质晶体形态无明显差别,苗期均为片状,抽穗期大部分仍以片状形态存在,并且蜡质晶体的密集程度比苗期稀疏,灌浆期蜡质晶体的密集程度变得更加稀疏。这些变化可能与抽穗期、灌浆期烷烃含量的增加和初级醇含量的减少有关。     

节节麦防除药剂及其增效助剂筛选

为筛选能有效防除节节麦Aegilops tauschii的除草剂及助剂，通过室内盆栽法评价11种除草剂对节节麦的防除效果，分析比较15种不同助剂对其中2种除草剂甲基二磺隆和异丙隆的增效作用，并明确其最适配比。结果显示，在供试11种除草剂中，甲基二磺隆和异丙隆对节节麦具有较的好防除效果，当其施药量分别为13、1 000 g（a.i.）/hm²时，对节节麦的鲜重抑制率分别达68.40%和76.46%，其余9种除草剂的防除效果较差，鲜重抑制率在4.62%~35.95%之间；筛选到对甲基二磺隆有显著增效作用的2种助剂——乙基和甲基酯植物油、有机硅408，其最适用量分别为甲基二磺隆喷液量的0.5%和0.2%（体积比），增效分别为15.21%和26.52%；筛选到对异丙隆有显著增效作用的3种助剂——异十三醇聚氧乙烯醚、聚醚改性七甲基三硅氧烷、乙基和甲基酯植物油，其最适用量分别为异丙隆喷液量的0.1%、0.05%、0.25%（体积比），增效分别为26.24%、21.80%和25.99%。表明甲基二磺隆、异丙隆可用于防除节节麦，添加助剂可进一步提高其对节节麦的防除效果。     

Physiological Responses of Wheat (Triticum Aestivum L.) –Aegilops Sharonensis Introgression Lines to Excess Copper

Two wheat lines (TL3 and TL5) derived from selection for Cu tolerance among wheat – Aegilops sharonensis hybrids were compared when grown as hydroponics at zero (control), 10⁻⁶ and 10⁻⁵  m CuSO₄. The morphometric measurements showed that the line TL5 with a more inhibited root system under 10⁻⁶  m CuSO₄ had a less inhibited shoot growth under 10⁻⁵  m CuSO₄ as compared to TL3. The decreased maximum efficiency of photosystem II and the more pronounced trend towards increased catalase activity suggested that despite the better shoot growth, the leaves of TL5 were more functionally injured. The increased content of carotenoids at excess Cu and the higher peroxidase and catalase activities of TL3 in control plants might contribute to its better stress tolerance. While no significant changes in enzyme activities were found at 10⁻⁶  m Cu, at 10⁻⁵  m the activities tended to increase. Although the close values of free phenolics concentrations in control plants, at Cu excess their content was higher in TL5 compared to TL3. The free phenolics content in roots at 10⁻⁶  m Cu decreased, and although higher at 10⁻⁵  m Cu, it remained below the control in TL3, and above the control in TL5. From the obtained results TL3 emerged to be more tolerant to excess Cu than TL5.     

Tan-Spot Resistance Screening of Aegilops Species

Two hundred and twelve accessions of 8 diploid and 10 polyploid species of Aegilops were evaluated for resistance to tan-spot disease of wheat, caused by Pyrenophora tritici-repentis (Died.) Drechs., under greenhouse conditions. One or more accessions of Ae. bicornis, Ae. biuncialis, Ae. Crassa, Ae. columnaris, Ae. cylindrica, Ae. speltoides, Ae. squarrosa. Ae. triaristata. Ae. triuncialis, and Ae. Ovata showed resistance following a 24-hour post-inoculation wet period. With a 36-hour wet period, diploids became only slightly or moderately susceptible and resistant polyploids became susceptible. A 48-hour wet period resulted in still greater susceptibility of both diploid and polyploid species.     

Cytology and Fertility of Hybrids and Amphiploids between Aegilops caudata L. ×Triticum turgidum (L.) Thell

Interspecific hybrids and amphiploids between Aegilops caudata L. (2n = 2x = 14, CC) and Triticum turgidum (L.) Thell. conv. durum Desf M. K. (2n = 4x = 28, AABB) were produced. Such hybrids can be used to introduce desirable traits such as disease resistance into cultivated durum wheats. One of the durum parents was a ph I mutation of the cv. ‘Cappelli’ used for testing the possibility of direct introduction of alien variation into cultivated species. The amphiploids were obtained both through colchicine chromosome doubling and as natural non-reductional mciosis products. In both hybrids and amphiploids, meiotic pairing and fertility were studied. Hybrids showed varying degrees of pairing and, in addition to the one involving the ph 1 mutant, one high pairing hybrid was found (Ae. caudata× cv. ‘Capinera’). Cytological examination of microsporogenesis in amphiploids revealed a high frequency of bivalent formation. Fertility proved to be a very variable character since some of the amphiploids were almost completely sterile. The use of amphiploids in breeding programmes is discussed in relation to meiotic and fertility data.     

Utilization of deletions to localize a gene for resistance to the cereal cyst nematode, Heterodera avenue, on an Aegilops ventricosa chromosome

A previous RFLP analysis showed that the Aegilops ventricosa chromosome 6M^V which compensates for the absence of 6D in 6M^V (6D) wheat substitution lines was a 2/6 translocated chromosome, either 2S–6S.6L or 2S–6L.6S. The distal part of its long arm consists of a translocated segment belonging to homoeologous group 2. Chromosome 6M^V carries a gene(s) for resistance to cereal cyst nematode. In order to define the part of 6M^V (2S or 6S or 6L) involved in this resistance, addition lines with a 6M^V deleted either for its short arm or for the distal part of its long arm were evaluated. It was shown that the gene(s) is carried by the group 2 translocated segment. The hypothesis that the gene(s) could be allelic to Cre2, another gene conferring resistance to the nematode introduced into the wheat complement from Ae. ventricosa is discussed.     

Allozymes and growth habit of Aegilops tauschii: genetic control and linkage patterns

Aegilops tauschii line of spring type growth habit with theearliest heading among all the VIR world germplasm collection of thisspecies was crossed with three Ae. tauschii lines of winter type growthhabit with low, intermediate and the highest vernalization requirement. 12enzyme loci were involved in genetic analysis. The growth habit was foundto be encoded by single codominant major gene, Vrn-D2. Thefollowing linkages were found: Est5 – Nadhd2 in chromosome 3, Vrn-D2 – Aco2 – Cat2 and Pgm – Nadhd1 in chromosome 4, Est2 – Got2 in chromosome 6.     

Allelic variation of the HMW glutenin subunits in Aegilops tauschii accessions detected by sodium dodecyl sulphate (SDS-PAGE), acid polyacrylamide gel (A-PAGE) and capillary electrophoresis

Variability of high molecular weight glutenin subunits (HMW-GS) was studied in198 accessions of Ae. Tauschii (2n=2x=14, DD) by sodium dodecyl sulphate(SDS-PAGE) and acid polyacrylamide gel electrophoresis (A-PAGE) and capillary electrophoresis (CE). A high allelic variation of HMW-GS, including some novel x- and y-type subunits and variable subunit combinations were observed. One accession(TD159) showed a x-type null form. The results by A-PAGE analysis revealed that the subunits Dx5 ^t and Dy10 ^t encoded by Glu-D ^t 1 locus in Ae. tauschii were different in relative mobilities in comparison with the subunits Dx5 and Dy10 found in bread wheats, whereas they had the same mobilities, respectively, when separated by SDS-PAGE. The higher resolution of Ae. tauschii HMW-GS separated by CE method showed two clear peaks in accordance with x- and y-type subunits, respectively,except the accession TD151 which possessed only subunit Dy12.1^*t. The electro elution time of the x-type and y-type subunits were about 13–14 and 7–8minutes, respectively. Characterization of wheat HMW-GS was facilitated by using CE which provides high resolution and increases the speed of analysis in conjunction with the traditional gel electrophoretic methods. A total of 42HMW-GS alleles were identified, among which were several alleles not presently detected in bread wheats. Hence Ae. tauschii is potentially a valuable genetic resource for quality improvement of bread wheat. This revised version was published online in August 2006 with corrections to the Cover Date.