| Maize rough dwarf disease(MRDD) is a kind of virus disease widely distributed in the world. In recent years, maize rough dwarf disease made a great damage to the production in Huang-Huai-Hai region. The majority of elite inbred lines and hybrids sensitive to MRDD, so making full use of the existing resistant germplasm in maize to breed disease-resistant new varieties has been an important objective. A major resistance QTL(qMrdd1) locus located at 1.2-Mb region flanked by markers M103-4 and M105-3 on chromosome 8 was mapped by us. The qMrdd1 locus acted in a recessive manner to reduce the disease-severity index(DSI) by 24.2-39.3%. In this study, the effect of qMrdd1 gene was identificated, also we transfer the qMrdd1 from resistance inbred lines to susceptible the maize inbred lines by multi-generation backcrossing and marker-assisted selection, these work laid a preliminary foundation for cultivation of maize rough dwarf disease resistant varieties. The main results were as follows:We try to transfer the qMrdd1 from 1145, CL313, NT411, 5413, P138 and FCD0602 to susceptible maize inbred lines through multi-generation backcrossing and marker-assisted selection(MAS), the susceptible lines include D129, zheng58, chang7-2, LX9801, D202, 9058, etc, which acts as a receptor and the recurrent parent. In the process, only those plants of harbouring the qMrdd1 gene were accepted. There have been BC5F3 of homozygous resistant and BC6F2 of population.Though the foreground selection, BC3F3 group of homozygous resistant and susceptible, resistance parents and recurrent parents were identified for MRDD resistance under the four conditions in the field, also were inoculated in Institute of plant protection, Jiangsu Academy of Agricultural Sciences. Result shows that parents of resistance had extremely low incidence rate, while D129, Zheng-58, Chang7-2, LX9801, etc. had MRDD plants with different DSI. The homozygous qMrdd1 of BC3F2 selected by MAS showed better resistance to MRDD. It was concluded that the qMrdd1 gene was decreased the disease-severity index(DSI) by 5-54.8%.Fifty SSR markers coveraging 10 chromosomes were chosen for genome-wide background selection. In theory, the share of recurrent parent genome usually respective reaches 93.75% ? 96.88% ? 98.44% in plants after three ? four and five generation of backcrossing, but the average of recurrent parent genome content did not actually reach the theoretical value in the accepted plants. One explanation is that a small amount of plants in each backcross population was planted, leading to select a limited range of plants, and the linkage drag is very serious.In the backcross group of resistance NT411(donor parent) and susceptible NT409(recurrent parent), 7 heterozygous plants with resistance gene were selected by MAS for self-pollinated to develop B1, B2, B3, B4, B5, B6, B7. The two group resistance and susceptible near isogenic lines(R1, S1 and R2, S2) were crossed with A7110, Q319, CT03, chang7-2, 43684, 43683, 43946 inbred lines to obtain 13 groups hybrids. The hybrids and 7 segregation populations were planted to investigate agronomic characters without inoculation of the MRDD virus. The results showed that there were no significant difference in ear length, ear diameter, rows per ear, kernels per row, and many other agronomic traits of the various genotypes plants the same to 13 groups of hybrids. There were no indication that qMrdd1 is associated with adverse effects and it could be used to improve maize resistance of maize rough dwarf disease. |
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