Resistance Quantitative Trait Loci qMi-C11 and qMi-C14 in cotton have different effects on the development of Meloidogyne incognita, the Southern root-knot nematode

Authors: DASILVA, MYCHELE - UNIVERSITY OF GEORGIA; Davis, Richard; KUMAR, PAWAN - UNIVERSITY OF GEORGIA; NICHOLS, ROBERT - COTTON, INC.; CHEE, PENG - UNIVERSITY OF GEORGIA

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2018
Publication Date: 5/1/2019
Citation: Dasilva, M.B., Davis, R.F., Kumar, P., Nichols, R.L., Chee, P.W. 2019. Resistance Quantitative Trait Loci qMi-C11 and qMi-C14 in cotton have different effects on the development of Meloidogyne incognita, the Southern root-knot nematode. Plant Disease. 103:853-858.
DOI: https://doi.org/10.1094/PDIS-06-18-1050-RE

Interpretive Summary: Quantitative trait loci (QTLs) are sections of DNA that contain genes of interest and can be identified with molecular markers. QTLs named qMi-C11 and qMi-C14 impart resistance to the cotton root-knot nematode, Meloidogyne incognita, in cotton. Breeders had previously backcrossed both QTLs into Coker 201 (susceptible) to create M-120 RNR (highly resistant), and we crossed Coker 201 and M-120 RNR to create genetically nearly identical lines with either qMi-C11 or qMi-C14. Previous work suggests different modes of action for qMi-C11 and qMi-C14 in suppressing the nematode. To document individual and combined effects of the QTLs on nematode development and reproduction, Coker 201 (neither QTL), M-120 RNR (both QTLs), CH11 isoline (qMi-C11), and CH14 isoline (qMi-C14) were inoculated with M. incognita. At 4, 8, 12, 16, 20, 25, and 30 days after inoculation (DAI), roots were stained to observe nematode developmental stages (J2, swollen J2, J3, J4, and female), and the number of galls was counted. At 20, 25, 30 and 40 DAI, M. incognita eggs were harvested and counted. Both QTLs were effective in reducing the number of females present at 30 DAI: 80% of the nematodes on Coker 201 were female compared to 50%, 40%, and 33% females on CH14, CH11, and M-120 RNR, respectively. Furthermore, a greater proportion of nematodes remained in the J2 stage in M-120 RNR (41%), CH11 (58%) and CH14 (27%) than in Coker 201 (9%). More nematodes progressed to the J3 or J4 stage on Coker 201 and CH14 than on CH11 or M-120 RNR. All of this shows that qMi-C11 affects development early in the nematode life cycle and qMi-C14 affects development later. Coker 201 and CH14 had more galls than M-120 RNR. Coker 201 had more eggs than the other genotypes at 30 DAI. This study confirms that qMi-C11 and qMi-C14 act at different times and have different effects on the development of M. incognita and therefore have different modes of action.

Technical Abstract: QTLs qMi-C11 and qMi-C14 impart resistance to Meloidogyne incognita in cotton. Breeders had previously backcrossed both QTLs into Coker 201 (susceptible) to create M-120 RNR (highly resistant), and we crossed Coker 201 and M-120 RNR to create isogenic lines with either qMi-C11 or qMi-C14. Previous work suggests different modes of action for qMi-C11 and qMi-C14. To document individual and combined effects of the QTLs on nematode development and reproduction, Coker 201 (neither QTL), M-120 RNR (both QTLs), CH11 isoline (qMi-C11), and CH14 isoline (qMi-C14) were inoculated with M. incognita. At 4, 8, 12, 16, 20, 25, and 30 days after inoculation (DAI), roots were stained to observe nematode developmental stages (J2, swollen J2, J3, J4, and female), and the number of galls was counted. At 20, 25, 30 and 40 DAI, M. incognita eggs were harvested and counted. At 30 DAI, 80% of the nematodes on Coker 201 were female compared to 50%, 40%, and 33% females on CH14, CH11, and M-120 RNR, respectively, and a greater proportion of nematodes remained in the J2 stage in M-120 RNR (41%), CH11 (58%) and CH14 (27%) than in Coker 201 (9%). More nematodes progressed to the J3 or J4 stage on Coker 201 and CH14 than on CH11 or M-120 RNR. Coker 201 and CH14 had more galls than M-120 RNR. Coker 201 had more eggs than the other genotypes at 30 DAI. This study confirms that qMi-C11 and qMi-C14 act at different times and have different effects on the development of M. incognita and therefore, have different modes of action.