The Genetic Variation And Improved Effects For Recurrent Parent Of The Backcross Later Generations Selected By Different Directions

In this study, two typical materials which have difference in the donor parents were selected out from the generations of BC2F2 using R08 as the recurrent parent, and the similary of the seed shape and color with R08 was considered as the selected stardard. One of the materials whose donor is CN962 had the similar characters in seed shape and color with R08 and was named A material, the other whose donor is 8065 differed in seed shape and color with R08 and was named B material.79 lines (BC2F4) were obtained using self-crossing them twice respectively, and the group comprising the lines which came from the A material is called A group, and the group containing the lines which came from the B material is called B group. Then the A, B group were classified into four second classified groups which named Rl, NRl and R2, NR2 by the same standard, six lines were selected randomly in each of them adding the line R08 as the tested group, and those lines which have crossed with R08 to develop general outstanding combinations(18-599, ES40, RP128,975-12, SCML-103,06KS-44) were served as the testing lines to develop 150 combinations as the analyzable materials through incomplete diallel cross. The genetic variation and improved effects for recurrent parent R08 of the backcross later generations selected by two different directions were analyzed by germination rate, resistance to northern leaf blight, combining ability and SSR molecular markers of these lines. The main results were summarized as follows:1. The results of germination rate and resistance to northern leaf blight of the backcross later generations by two different select directions showed that the 26 out of 79 improved lines was higher or significantly higher than R08 in germination rate, and that 29 lines of these lines were high-resistant to northern leaf blight, and that significant differences of germination rate, resistance to northern leaf blight in the lines of these generations selected by two different directions were observed. The synthetical analysis of these backcross later generations suggested that the lines selected by the standard that the seed shape and color are not similar to the R08 were better than the ones selected by the standard that the seed shape and color are similar to the R08 in above mentioned traits.2. The results of general combining ability (GCA) of these backcross later generations showed that, except ear length, plant height and ear height, the GCA of most yield traits in the majority of improved lines traits were no decrease compared with R08 in general, and that the GCA of ear row number,100-kernel weight and sterile length(whose improve standard is decrease to R08) were improved to R08. And there was a significant difference in influence for GCA of R08 in the lines of these generations. The synthetical analysis of them indicated that the lines selected by the standard that the seed shape and color are not similar to the R08 improved a little more traits. The most traits(three traits) were improved by X59 in the group of NR2. The retrogression of GCA of part of traits of some lines may be relevant to the cause that the test to GCA which is dominated by additive genetic effect has be take in so later generations that some lines which have inferior GCA have be retain.3. The results of 150 crosses SCA showed that the great majority of the lines of the backcross later generations have no significant difference to categories CK. Only the SCA of RP128×X50(the combination from the line in NR2 group) was significantly higher than categories CK. The number of hybrid combinations with superiority over the categories CK 5% in yield/plant is 19, take 13.19% of all the combinations. And in the all, there were 5 lines in R1 group,4 ones in NR1 group,4 ones in R2 group,6 ones in NR2 group,9 ones in A group,10 ones in B group. The number of the lines of the backcross later generations selected by two different directions is balanceable on the whole, and the number in these lines selected by the standard that the seed shape and color are not similar to the R08 was a little more. Analysis of the 14 hybrids which were superiority over CK 15%, RP128 and 06KS44 had more possibility to obtain high field hybrids crossed with improved lines, and R1, NR1, R2, NR2, A and B group derived lines respectively appeared 3.3,3,5,6 and 8 times as the male parent. The results were basically the same with the ones in analysis of superiority over the categories CK. Only RP128×X50 (the combination from the line in NR2 group) has the largest advantage over the CK, which is 32.55%, this combination and its male parent X50 could have significant potentiality.4. The results of SSR mark analysis showed that 44 microsatellite (SSR) loci distributed on 10 chromosomes of maize. Detected in the 272 alleles, there were 123 alleles appearing in the backcross generations of individuals but lost in R08. The average value of the ratio of the lines whose genotypes is same with recurrent parent R08 in 79 lines of the backcross later generations detected by each pair of primers was 16.5%. The synthetical analysis of these generations indicated that the lines whose genotype is same with R08 in the lines selected by the standard that the seed shape and color are not similar to the R08 were a little more. The synthetical analysis to the Genetic similar factors in different groups also gave similar result, The genotype similar degree to R08's of the backcross later generation lines selected by the standard that the seed shape and color are not similar to the R08 is lower on the whole, whose variation range is also wider.5. Comprehensive analysis showed that there were some differences in the genetic variation and improved effects for recurrent parent of the backcross later generations selected by two different directions. In conclusion, during the process of backcross for improving maize inbred lines, the method that selecting the lines in different direction could heighten the improve efficiency.