Identification And Molecular Cytogenetics Of Wheat - Rye 1RS / 1BL Translocation Line And 4RS / 4DL New Translocation Line

Wheat (Triticum aestivum L., AABBDD,2n=6x=42), one of the three major grain crops in the world, is the most main food source and has a pivotal role in the production and development of agriculture. Due to the long-term directional selection, genetic diversity of wheat is gradually losing and its genetic variation is more and more narrow. Consequently, the ability of diseases resistance, insect resistance and stress resistance (drought, salinity) of wheat declined seriously. The relative species of wheat contain abundant excellent genetic resources and they have huge potential value for wheat genetic improvement. Transferring excellent exogenous genes into wheat cultivars through chromosomal translocation is an effective way for wheat genetic improvement. Therefore, creating wheat-alien translocation chromosomes becomes the objective of many wheat breeders. Rye{Secale cereale L.) is one of the most successful relative species in wheat improvement, and the 1RS/1BL translocation lines are the most typical representative. However, in past 30 years, most wheat cultivars containing the 1RS/1BL translocation chromosome have lost their disease resistance due to occurrence of new biotypes of the pathogens. Unfortunately, the frequency of 1BL.1RS translocation chromosome in recently released wheat cultivars has declined. So, creating new wheat-rye translocation is urgent.In present study, wheat lines 12-26 and 12-39 were derived from wide hybridization between wheat line A42912 and rye inbred lines R3 of Weining. These two wheat lines and their selfed progeny were analyzed by cytological methods including C-banding, genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH). Combined with agronomic traits, we screened new wheat-rye translocation lines. Meanwhile, we studied the variation of chromosomal structure during the process of rye exogenous chromatin transferring into wheat genetic background. The innovative results are as follows:1. From the selfed progeny of 12-39, a 1R monosomic addition line 12-39-5 was screened. Then,191 selfed progeny of 12-39-5 were analyzed and chromosomal translocations were observed in 11 progeny. The frequency of translocation accounts for about 5.7%. Translocations included wheat-rye chromosomal translocations and translocations between 1R chromosome arms of rye. The result confirms that 1R monosomic addition line can effectively induce chromosomal translocation in high frequency.2. Eight progeny of 12-26 were identified,12-26-1 contained a 1RS/1BL translocation chromosome (2n=42),12-26-2 contained a 4RS/4DL translocation chromosome(2n=42), 12-26-3,12-26-4,12-26-5,12-26-6 and 12-26-7 contained a 1RS/1BL and a 4RS/4DL translocation chromosomes (2n=42), meanwhile,12-26-8 contained no rye chromatin(2n=42). So far,4RS/4DL translocation chromosome has not been reported and it is a new wheat-rye translocation chromosome.3. The transmission of 1RS/1BL and 4RS/4DL translocation chromosomes in 12-26-1, 12-26-2,12-26-3,12-26-4 and 12-26-6 has been investigated. The transmission ratios of 1RS/1BL in the selfed progeny of 12-26-1,12-26-3,12-26-4 and 12-26-6 were 79.8%, 63.3%,82.4% and 67.3%, respectively. The transmission ratios of 4RS/4DL in the selfed progeny of 12-26-2、12-26-3、12-26-4 and 12-26-6 were 56.2%,55.9%,57.0% and 56.4%, respectively. All the transmission ratios of 1RS/1BL were higher than that of 4RS/4DL.This indicates that the compensation effect of IRS to IBS is strong while the compensation effect of 4RS to 4DS is poor. Besides, in the progeny of 12-26-1 (1RS/1BL heterozygous) and the progeny of 12-26-2 (4RS/4DL heterozygous), the proportion of plants that contained homozygous translocation, heterozygous translocation and no rye chromatin deviated from Mendel’s law of segregation. That is, the 1RS/1BL and 4RS/4DL chromosomes in this study did not conform to the separation ratio of 1:2:1. The result provides a new cognition for breeders in the process of screening homozygous translocation.4. Disease resistance and agronomic traits of 6 homozygous 4RS/4DL translocation lines derived from 12-26-2 were investigated. Wheat parent A42912 was highly sensitive to stripe rust while homozygous 4RS/4DL translocation lines were immune to stripe rust. It indicates that the 4RS chromosome arm possesses resistance gene to stripe rust. At present, resistance genes for stripe rust derived from rye include formally named gene Yr9 and temporarily named genes YrR212 and YrCN17. The three resistance genes are located on IRS chromosome arm. Therefore, it is concluded that the stripe rust resistance gene on 4RS is a new gene to stripe rust resistance and is useful for wheat breeding program. The results of agronomic traits assessment indicated that, homozygous 4RS/4DL translocation lines grew weakly:plant height about 50 cm, weak tillering, purple shell, long awn, small spike and poor fertility. According to previous research, we suspect that the reasons leading to poor agronomic traits of homozygous 4RS/4DL translocation lines mainly are the following two points:(1) the poor compensation effect of 4RS chromosome arm to 4DS chromosome arm, (2) associated with the genetic background of wheat parent A42912.5. A large number of chromosomal structure variation were observed in the progeny of 12-26-3,12-26-4 and 12-26-6 which contained 1RS/1BL and 4RS/4DL translocation chromosomes, such as chromosome breakage, variation of chromosome numbers, robertsonian translocation, dicentric chromosome, ring chromosome and other complex chromosomal structure variation. Wheat chromosomes involving the structural variation are 4A,5A,2B,3B,5B,6B,7B,1D,2D,3D,4D,6D,7D and parts of A genome which repetitive DNA sequence probes did not recognize. It suggests that 1RS/1BL and 4RS/4DL double translocation line is cytogenetically unstable and easily leads to chromosomal structure variation in the progeny. These results have not been reported in previous research.6. We found unequal chromosome division in somatic cells of the progeny of 1R monosomic addition line and 1RS/1BL and 4RS/4DL double translocation lines. Not only rye chromosomes but also wheat chromosomes were involved in unequal division. The result indicates that exogenous chromosome monosomic addition and translocation could induce unequal chromosome division in somatic cells. Unequal chromosome division induced by translocation has not been reported in previous research.