QTL Verification And Mapping For Resistance To Fusarium Verticillioides Ear Rot Based On Near Isogenic Lines In Maize

ABSTRACT:Maize ear rot is a disease caused by fungi. There are lots of pathogens which can cause ear rot. Fusarium verticillioides is predominant pathogens in China. After infecting corn, Fusarium verticillioides cause ear rot. Besides, pathogen products mycotoxins such as moniliformin and fumonisin while metabolism. Maize ear rot leads to loss of yield and quality. Fine mapping the disease-resistant QTL is one of the important aspects in breeding for disease resistance. But researchs on resistance gene on maize ear rot stay in the preliminary positioning stage now. No researcher verify the localizing QTL using near isogenic lines groups, and no one obtain gene related to maize ear rot. In this study, the inbred lin e BT-1(with high resistance to maize ear rot) and the inbred lines Xi502 (high sensitivity to maize ear rot), inbred lines N6(high sensitivity to maize ear rot).They were used to breeding near isogenic line groups. We select from two directions in two sets of populations. Finally, we obtain four near isogenic line groups respectively. QTL in bin 2.04-2.05 of chromosome 2 and bin 4.05-4.06 of chromosome 4 verified and localized based on the four groups. The main results are as follows:1. Investigating agronomic traits, growth period of near isogenic lines and their parent lines. The genetic backgrounds are also detected in SSR molecular markers. We obtain near-isogenic lines groups which are similar with recurrent parent on the agronomic traits and growth period traits. Detection on the recovery rate of genetic backgrounds found that the near isogenic lines with parental line Xi502 as recurrent parent, parental line BT-1 as nonrecurrent parent has a low recovery rate, about 80%. The recovery rates of the other three NILs reach more than 90%, even reach 95%.2. Investigate the resistance of the four near isogenic lines selected from combinations BT-1×Xi502 and BT-1×N6 under different infection time. With the change of infection time, the occour time and increasing of incidence are very different. The symptoms occur later in ear of BT-1, and no significant change in the incidence of disease with the infection time. The symptoms occur early in ear of Xi502. Then symptoms spread to the surrounding from the local, the incidence gradually increased. The symptoms also occur late in ear of N6, and onset of a large area, did not change significantly in the incidence along with the increase of the infection time. Investigation of near isogenic lines showed that the incidence rate are effected by both recurrent parent and non-recurrent parent.3. Near isogenic lines target QTL locus provide more effect than in the preliminary mapping groups. The chromosome segment 4.04-4.08 from BT-1 supply about 30% resistance to ear rot in positive near isogenic lines selected from BT-1 and Xi502,the chromosome segment 2.04-2.07 supply about 20% of the resistance. In reverse near isogenic lines, the segment 4.04-4.08 from Xi502 supply about 6-9% susceptibility to ear rot, the segment 2.04-2.07 supply about 3% of the resistance. The segment 4.04-4.08 of chromosome 4 from N6 supply 10-20% resistance to ear rot in reverse near isogenic lines selected from BT-1 and N6, the segment from BT-1 supply 45% resistance to ear rot in positive near isogenic lines selected from BT-1 and N6.4. A preliminary analysis of the interaction effect between QTL in chromosome 2 and chromosome 4. In the near isogenic lines with Xi502 as recurrent parent, QTL in chromosome 2 and chromosome 4 provide about 18% and 45% of the resistance, respectively, the two QTLs provide about 30% of the resistance, showing that QTL in chromosome 2 have a negative effect to QTL in chromosome4. In the near isogenic lines with the recurrent parent BT-1, QTL in chromosome 2 and chromosome 4 provide about 0% and 5.5% of the susceptibility, respectively. Two QTLs provide about 4% of the susceptibility. The result verifies that the QTL in chromosome 2 have a negative effect on QTL in chromosome 4. However, due to the small difference in the reverse near isogenic lines, it is hard to identify the result, besides the recurrent parent share low genetic background in these groups, the purification of the background need further research.5. Resistance analysis of the two groups to verify the QTL presence in chromosome 4 and chromosome 2. QTLs are mapped between marker BI and B3 in chromosome4 and using near isogenic lines. And QTLs are mapped between marker A1 and A3 in chromosome 2 as well. The results are similar to the previous research which provides a basis for fine mapping the gene of maize ear rot.