Mapping and characterization of a quantitative trait locus resistance to the brown planthopper in the rice variety IR64

Abstract

Background: Rice planthoppers (main brown planthopper, Nilaparvata lugens Stål; BPH) was one of substantial threats to Asia rice production as its serious destruction and difficulties in control under field conditions. Notably, host-plant resistance was proved to be one of the effective ways to manage the pest. And stronger virulence will probably emergence when continuous use of insecticides. Therefore, more resistance genes with different resistance mechanisms were needed to be detected and then applied in the rice breeding practice.

Results: Resistance genes in the rice variety IR64 were evaluated considering the seedling bulk test and seedling survival rate. As a result, a locus with a large LOD score of 7.23 was found between markers RM302 and YM35 on chromosome 1. The locus explained 36.9% of phenotypic variation and was tentatively denominated Bph37. Moreover, Bph1 was detected to be harbored by the markers RM28366 and RM463, and had the largest LOD score of 2.08, explaining 7.7% of phenotypic variance in the same mapping population. Finally, the preliminary-near-isogenic-lines (pre-NILs) carrying Bph37 exhibited significant tolerance to the insects. But no antibiotic or antixenotic effects were observed in the resistant plants when infested with the insects.

Conclusions: We mapped one major BPH resistance gene Bph37 in consideration of seedling survival rate and the resistance lines showed tolerance to BPH. The detected gene should be beneficial for understanding the resistance mechanism of rice to BPH and for insect-resistance rice breeding programs.

Keywords: Brown planthopper (Nilaparvata lugens Stål); Genetic mapping; Insect resistance mechanism; Preliminary-near-isogenic line (pre-NIL); Tolerance.

Fig. 1

Frequency distribution of the BPH resistance evaluation of F_2:3 lines derived from the cross KWQZ/IR64. a, Seedlings survival rate. Three-week-old seedlings were treated with five to six BPHs per plant for 20 days. The survival rates of the parents IR64 and KWQZ were 67 and 18%, respectively. A lower survival rate indicates more susceptible. b, BPH resistance scores. Three-leaf seedlings were treated with eight BPHs per plant for 9–10 days. The average resistance scores of the parents IR64 and KWQZ were 5.6 and 8.7, respectively. A lower score indicates higher resistance

Fig. 2

Location of the resistance genes on the linkage map of rice chromosomes constructed using an F₂ population derived from KWQZ/IR64. a, Bph37 on the chromosome 1. b, Bph1 on chromosome 12. Markers are presented along the X-axis with distances (in cM) as shown. LOD scores are presented on the Y-axis. EXP, phenotypic variance explained by the locus

Fig. 3

BPH resistance phenotype in pre-NIL with one or two genes and the parents (IR64 and KWQZ) measured by using the seedling bulk test. a. resistance scores, b. survival rates. Each bar represents the mean of nine replicates, error bars, SD. Different lowercase letters above bars indicate that the means (bar) are significantly different at P = 0.05. The survival rate was equal to the surviving plants divided by total plants of each line

Fig. 4

Plant tolerance of different genotypes to the BPH insects. Bars represent means of eight replicates. Error bars represent the SD. Different lowercase letters above bars indicate that the means (bar) are significantly different at P = 0.05. Tolerance effect was evaluated with TI = W_t/W_c × 100, W_t and W_c are the dry weight of the infested and control plants, respectively

Fig. 5

BPH host choice among the different genotype plants. Bars represent means of eight replicates. Error bars represent the SD

Fig. 6

BPH development on plants of different genotypes. a. Increase in BPH growth weight on resistant and susceptible plants, b. BPH honeydew excretion on resistant and susceptible plants. Bars represent means of eight replicates. Error bars represent the SD