Potential efficacy of spider mite-resistant genes in maize testcrosses
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Tropically adapted maize (Zea mays L) germplasm resistant to spider mite species (Acari: Tetranychidae) may contribute to host plant-resistant hybrids for western Great Plains States where spider mite populations are an economic problem. This study evaluated (1) the efficacy of seven mite-resistant maize inbred lines as sources of resistance in testcrosses with B73 and Mo17 and (2) the agronomic performance of F1 hybrids. Mite-resistant lines (S1-S5, S7, and S9), susceptible check inbred lines (B73 and Mo17), testcrosses between resistant and susceptible lines, and susceptible test hybrids (B73Mo17 and Pioneer hybrid 34K77) were arranged in randomized complete block design with three replications at Halfway, TX in 1997, 1998, and 2002 and at Lubbock, TX in 2001 and 2002. Resistance was evaluated for differences in spider mite infestations and feeding damage following augmented infestations just prior to tassel. Weekly samples showed that mite infestations and damages among genotypes varied greatly across weeks and between locations and years. Total mite densities, total damage ratings, mite per damage ratios (M/D), and a seasonal damage ratio (SDR) were calculated from weekly samples. The combined analysis of variance showed that environment, entry, environment entry interaction was significant for total mite density. Environment and entries were significant for total damage ratings, M/D, and SDR. Testcrosses (S2B73, S3B73, S9B73, S1Mo17, S2Mo17, and S3Mo17, S4Mo17, S5Mo17, and S9Mo17) had significantly lower mite damage than the check hybrid, B73Mo17, at the P<0.05 level. Damage to testcrosses S1B73, S5B73, and S7Mo17 were significantly different (P<0.01) from the check hybrid, B73Mo17 and the testcross S7B73 had a highly significant reduction in damage (P<0.001). Broad-sense heritability estimates indicated a large portion of resistance for these selection criteria were associated to genetic factors. Resistant testcrosses provided greater protection from spider mite feeding than did check hybrids across all environments. 2004 Elsevier Ltd. All rights reserved.
