BREEDING MAIZE LINES FOR COMPLETE AND PARTIAL RESISTANCE TO MAIZE STREAK VIRUS (MSV)

S-1 to S-5 inbred lines, derived from a maize population bred for its overall resistance to three tropical viruses, were screened for resist ance to maize streak virus (MSV) by artificial plant infection using v iruliferous leafhoppers. Symptoms were rated and intra-line frequency distributions studied for all pedigree inbred lines. Mortality due to MSV was very low among these inbreds. Symptoms appeared later, develop ed slower and were less severe than in the susceptible control hybrid. Results of a study of 500 S-1 and 93 S-2 lines suggested that resista nce is under genetic control via a system involving loci with major ge nes (with dominance for resistance) controlling high to complete resis tance, associated with a genetic system involving loci with minor gene s controlling partial resistance. Lines expressing complete resistance to MSV were developed from 5 cycles of inbreeding and selection. The relevance of such complete and partial resistance is discussed.