| Spider mites cause significant yield reductions in maize, Zea mays L., grown in the Great Plains States. Determining the genetic performance of mite-resistant inbred lines would be important to breeding programs developing resistant hybrids. A study was conducted in 1997, 1998, 2001 and 2002 to evaluate the efficacy of resistance and agronomic performance of testcrosses with B73 and Mo17. Resistant inbred lines (S1, S2, S3, S4, S5, S7, and S9), testcrosses, check inbred lines (B73 and Mo17), and check hybrids (B73 x Mo17 and Pioneer 34K77) were arranged in randomized block design with three replications. Analysis showed that environment, entry, environment x entry interaction was significant for mite density. Environment and entries were significant for damage ratings (DR) and mite per damage (M/D). Heritability estimates indicated resistance was associated with genetic factors. Testcrosses had less damage than check hybrids. Testcrosses (S1 x B73, S2 x B73, S5 x B73, S2 x Mo17, and S3 x Mo17) significantly reduced damage, and S7 x B73 and S7 x Mo17 had highly significant reductions in damage. All testcrosses, except S1 x Mo17, S5 x Mo17, and S9 x Mo17, had grain yields statistically similar to check hybrids.; A Griffing's Methods 2 Diallel mating design was used to evaluate range of resistance, combining ability and agronomic traits of resistant F 1 crosses. Analysis for DR was significant for environments, entry, and environment x entry interaction. Mite density and M/D was significant for entry x environment interaction. Seasonal damage ratios were significant for environment and entry, but not interactions. Heritability estimates showed that >90% of the damage was associated with genotypic effects. Crosses with S1, S2, and S9 supported more mites, but had higher M/D values than S3, S4, S5, and S7, indicating greater tolerance to mite feeding. Crosses between tolerant lines or tolerant x antiobitic lines resulted in better resistance than crosses between antibiotic lines. S1 and S2 had the highest general combining ability-for reduce damage. S1 x S4, S1 x S7, S3 x S5, and S4 x S7, were the best crosses for specific combining ability for resistance to spider mites. |
