| Powdery mildew is one of the main serious disease in wheat production. Because of the single resistant source against this disease in many extended cultivars, the resistance degression is very fast by the occurrence of new races in this pathogen population. Therefore, to search the new resistant gene(s) is very urgent. It has been reported that there are a new recessive resistant gene(Pmx) located in 4D chromosome in a wheat cultivar u Zhuang 30?F). However, The expression frequency of this recessive genes rather low in conventional breeding. And it need many backcross and inbreed generations by turns for breeding a new variety with the recessive gene, which will expend lots of labor, material and need longer time. The molecular maker techniques developed in recent years can detect out some DNA segments which closely linked with this recessive gene, so that the resistant plants with this recessive gene can be selected out by detecting this molecular marker in laboratory. Using the selected plants as recur;ent parent, the efficiency of breeding will be increased obviously, which can save the time more than half and speed the breeding progress. In the present studies, the often used simple, rapid and lower cost molecular analysis method RAPD was used to scree~i the closely linking marker with the resistance gene(Pmx), so as to offer the theoretical grounds, for using the marker assistant selection in wheat disease resistant breeding. The experiment results showed: 1. The BSA (bulked segregent analysi method was used for screening the molecular markers. The materials used in the experiment were Fu Zhang 30? (resistant variety, F) and the non-resistant cultivars ongda 015?(N) and ing hua NO.1 ?J). The DNA from these cultivars was used as the template for RAPD analysis. Total 313 primers were selected out, in which 6 can derive special bands and another 6 can not from the resistant variety F. From non-resistant varieties N and 3, total 7 primers which can derive special bands were selected out. 2. The resistant cultivars F with the 6 primer derived special bands were crossed with the non-resistant parent N. Total 103 F-, plants from this cross were analyzed with RAPD method in laboratory, at the same time, the F, genetic segregation was studied by the statistical analysis of resistant and non-resistant plants from F-, in field. The results showed that only the special band (UBC4OS~28) derived by the primer UBC4O5 was linked closely with this resistant gene. By the detection of the segregation ratio in field, the frequency of crossing over is 13.6%, By analyzing of mapmarker 3.0 , the distance between them was 13 cM, LOD-7.3. 3 .The marker assistant selection was carried out among 66 F-, plants from the cross of inghua No. 1?X u Zhang? I he results showed that the selection efficiency was as high as 80.3%. The results of the present studies illustrated that using the molecular marker(UBC405628 )assistant selection, the recessive resistant gene(Pmx) will be used better and can speed the breeding progtss obviously, which are important significance in wheat powdery mildew resistance breeding theoretically and practically.
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