|Mojtahedi, H - WSU IAREC, PROSSER WA|
|Santo, G - WSU IAREC, PROSSER WA|
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 1999
Publication Date: October 3, 1999
Citation: BROWN, C.R., MOJTAHEDI, H., SANTO, G.S. GENETIC ANALYSIS OF RESISTANCE TO MELOIDOGYNE CHITWOODI INTROGRESSED FROM SOLANUM HOUGASII IN CULTIVATED POTATO. JOURNAL OF NEMATOLOGY. 31:264-271. 1999. Interpretive Summary: It costs about 2,400 dollars per acre to grow potatoes in the Columbia Basin. About 300 dollars of this are spent to apply strong pesticidal chemicals to the soil. These chemicals are called soil fumigants. They are designed to reduce or eliminate soil-borne pathogens or pests such as nematodes. Nematodes are microscopic worms that cause damage to plant roots and to the actual potatoes developing in the soil. The Columbia root-knot nematode invades potato roots and reproduces, releasing eggs into the soil. When the eggs hatch the young nematodes invade the tubers, resulting in blemishes and deformation of the tuber surface. The deformation looks like a bumpy surface. The blemishes and the bumps become more severe the longer the potatoes are kept sitting in the soil or in the potato storage. If a grower has severe root-knot damage in a lot of potatoes he/she will try to get that lot processed right away before the damage gets worse. The processor or fresh packer might also refuse to buy the potatoes if the damage is severe. In Washington State 20 million dollars are spent to prevent 40 million dollars of damage on potatoes just from root-knot alone. This research reports the discovery of resistance to root-knot nematode in a wild species of potato from Mexico. The research tells us that there are separate genes controlling two different races of this nematode. The process of breeding the resistance into cultivated potatoes has begun with the steps reported int this paper. The type of resistance has been characterized partially. The nematode is unable to establish a successful feeding zone inside the root. This prevents reproduction and there are very few eggs available to provide young nematodes that can invade the tubers. We can
Technical Abstract: An accession of Solanum hougasii, a wild tuber-bearing potato species native to Mexico, was found to be resistant to races 1 and 2 of Meloidogyne chitwoodi. A resistant selection was selfed and the progeny possessed the same combined resistance uniformly. A selected resistant seedling from the selfed progeny was crossed to cultivated tetraploid potato (S. tuberosum) to form an F1 hybrid, and was backcrossed to cultivated tetraploid potato to form a BC1 population in which resistance to the two races segregated. Progeny of the BC1 were tested in inoculation experiments with four replicates for each progeny genotype for each race of nematode. Resistance was evaluated on the basis of extracted egg counts from the entire root system of pot-grown plants. Considering resistance to each race separately, for race 1, nonhost (Rf ? 0.1) status was exhibited by approximately half of the BC1. About one- third of the progeny showed non-host status to race 2. Egg production among progeny that showed non-host status for both races was higher with race 2 than with race 1. Analysis of co-segregation established that genetic control for the two races appears to be independently segregating. Although genes for resistance to race 1 derived from S. bulbocastanum and S. fendleri were previously described, this report is the first analysis showing independent genetic control in Solanum spp. for resistance to race 2 of M. chitwoodi only.