Of the many hundreds of maize lines tested for resistance to maize chlorotic dwarf virus (MCDV), all have shown at least some plants with the vein clearing symptom associated with susceptibility to MCDV. Zea diploperennis was found to be resistant to MCDV by L. R. Nault, D. T. Gordon, V. D. Damsteegt and H. H. Iltis (Plant Disease 66, in press). Crosses of Z. diploperennis as the pollen parent and maize were made to transfer resistance to the latter. F1 x maize seedlings were exposed to leafhopper, Graminella nigrifrons viruliferous with MCDV. Following a virus acquisition access period (AAP) of 48 hours, leafhoppers were allowed to feed on test seedlings for 48 hours. After 14 days seedlings were examined for vein clearing symptoms. Leaf samples were taken from symptomless plants to test for virus by enzyme linked immunosorbent assay (ELISA). ELISA is generally more sensitive and accurate than symptoms in tests for virus. Of the 107 BC1 plants, 22 appeared resistant to MCDV. This is not a significant deviation from a 3:1 ratio (X2 = 1.125, P = 0.30-0.20).
Plants with negative reactions in ELISA were transplanted to the greenhouse and used to pollinate other maize plants or selfed. The second generation backcross (BC2) or selfed seedlings were exposed to viruliferous leafhoppers. Symptomless seedlings were assayed by ELISA and those that reacted negatively for MCDV were transplanted to the 1981 field or greenhouse-sunyard. The transplants were again inoculated with MCDV as older plants (some were tasseling) to insure that these plant populations did not include "virus escapes." Leafhoppers were caged in groups of approximately 10 on the youngest leaf for a period of 48 hours following a 48-hour AAP. After 14-21 days plants were again tested for MCDV by ELISA. The following results were recorded:
These results indicate that resistance to MCDV in Zea diploperennis is controlled by two dominant complementary genes.
W. R. Findley, L. R. Nault, W. E. Styer and D. T. Gordon
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