利用60Co-γ-射线处理小麦-簇毛麦6V单体添加系花粉，并给中国春授粉，在一个M1单株减数分裂中期Ⅰ检测到一个由2条小麦-簇毛麦易位染色体和一条完整小麦染色体构成的三价体，说明参与易位的2个小麦片段均来自同一条小麦染色体，推测两条易位染色体由相互易位产生。将其中涉及外源大片段的易位染色体称为外源大片段易位（large alien segment translocation, LAST），涉及外源小片段的称为外源小片段易位(small alien segment translocation, SAST)。对后代中两个易位染色体均纯合的植株（LAST’’+SAST’’, 2n = 44）进行顺次C-分带和GISH研究，结果表明外源大片段易位染色体为T7BS-6VS•6VL，外源小片段易位染色体为T6VS-7BS•7BL，易位断点分别位于7B染色体短臂约FL0.60处及6V染色体短臂约FL0.70处。在M2代群体中检测到7种染色体组成类型，比例为3(LAST’’+SAST’’)∶20(LAST’+SAST’)∶2(LAST’’+SAST’)∶1(LAST’+SAST’’)∶1LAST’∶2SAST’∶22(0型)，其中外源大片段和外源小片段易位染色体往往相伴出现。抗病鉴定结果显示抗白粉病基因位于外源大片段易位染色体T7BS-6VS•6VL上。对LAST’+SAST’型（2n = 43）M2代单株花粉母细胞减数分裂的GISH研究结果显示，88.5%的后期Ｉ或末期Ｉ细胞中出现T6VS-7BS•7BL和T7BS-6VS•6VL的共分离。此外，在个别后期Ｉ细胞中观察到外源大片段易位染色体T7BS-6VS•6VL发生落后和着丝粒断裂现象，并在LAST’型单株（2n =42）的自交后代中筛选到一个通过着丝粒断裂-融合产生的外源小片段插入易位T7BL•6VS-7BS，这为利用外源大片段易位进一步创制携带抗病基因的小片段插入易位提供了新的思路。还分别获得了T7BS-6VS•6VL和T6VS-7BS•7BL的纯合易位系。
The short arm of Haynaldia villosa chromosome 6V confers Pm21 that conditions immunity from or high resistance to almost all known powdery mildew races. In the middle of the 1990s, Cytogenetic Institute, Nanjing Agricultural University (CINAU) has obtained the T6VS•6AL translocation line by which some wheat cultivars with high yield and powdery mildew resistance have been developed. However, this translocation obviously has a large amount of redundant alien genes. To develop terminal and/or intercalary translocations with as short as possible alien chromosomal segments conferring Pm21 is more important in wheat breeding. In addition, the more translocations with different breakpoint positions at the length of 6VS are, the higher resolution of physical mapping of Pm21 is. In this research, our objective is to induce new translocations involving H. villosa chromosome 6V through pollen irradiation. Pollen of Triticum aestivum-Haynaldia villosa 6V monosomic addition lines (2n = 43), treated with 1 000 rad 60Co-γ-rays, was pollinated to T. aestivum cv. ‘Chinese Spring’. Pollen mother cells (PMCs) of M1 plants at meiotic metaphase Ⅰ were used for GISH analysis. A trivalent observed was formed by two T. aestivum-H. villosa translocation chromosomes and a wheat chromosome in a M1 plant, indicating that the translocation chromosomes might be resulted from a reciprocal translocation event. The translocation involving the large alien segment was called ‘large alien segment translocation’ (LAST) while the translocation involving the small alien segment was called ‘small alien segment translocation’ (SAST). Sequential C-banding and GISH technique were used to identify a homozygous M2 plant (LAST’’+SAST’’, 2n = 44). The results showed that the reciprocal translocation involved T. aestivum chromosome 7B and H. villosa chromosome 6V with the translocation breakpoints at about FL0.60 of 7BS and about FL0.70 of 6VS, respectively. The LAST chromosome was identified as T7BS-6VS•6VL while the SAST chromosome was identified as T6VS-7BS•7BL. Seven chromosome constitution types were observed in the M2 population with the ratio of 3(LAST’’+SAST’’):20(LAST’+SAST’):2(LAST’’+SAST’):1(LAST’+SAST’’):1LAST’:2SAST’:22(none alien). The LAST chromosome occurred accompanied by the SAST chromosome at most times. Resistance analysis showed that the plant with a single LAST chromosome was resistant to powdery mildew. Then, Pm21 was located at the proximal region of FL0.70 of 6VS. Meiotic analysis of M2 plants with the genome of 20ⅡW+Ⅰ7B+ⅠT7BS-6VS•6VL+ⅠT6VS-7BS•7BL (2n = 43) showed that T7BS-6VS•6VL and T6VS-7BS•7BL co-segregated at meiotic anaphase Ⅰ or telophase Ⅰ in 88.5% of PMCs. The LAST chromosome T7BS-6VS•6VL stayed late or centric-misdivided in several PMCs at anaphase Ⅰ. An intercalary translocation, T7BL•6VS-7BS, arising from the centric breakage-fusion of 7B and T7BS-6VS•6VL, was then detected in a progeny of a plant with the genome of 20ⅡW+Ⅰ7B+ⅠT7BS-6VS•6VL. It provided a new strategy for inducing intercalary translocations with alien chromosomal segments conferring resistance genes. Homozygous T7BS-6VS•6VL and T6VS-7BS•7BL translocation lines were obtained in M3 generation.
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