Genetics of insect resistance and super-genes

A. C. Waiss et al. (J. Econ. Entomol. 72:256-258, 1979) reported that a flavone glycoside from corn silks of Zapalote Chico (ZC) had an antibiotic activity toward corn earworm, Heliothis zea (Boddie). Our source of resistance was ZC #2451, reported by B. R. Wiseman et al. (Environ. Entomol. 7:777-779, 1978) as restricting penetration in the silk channel. Sixteen translocations and one inversion marked by wx from the set listed in MNL 40:184-185, 1966, crossed and backcrossed once to IAC Maya latente before selfing, were used as markers. These markers were crossed to ZC. This cross was then "backcrossed" to IAC Maya wx (M wx) obtained by crossing and backcrossing thrice to IAC Maya, a commercial wx cultivar imported via Japan from South Africa. The Wx and wx segregates from the same ear, preferentially in the same reps, were planted in split-plot with five reps, late in the season to suffer heavier attack. The ears were harvested unhusked and a counting was done of the number of ears with and without exit holes of larvae. Table 1 presents data for totals only, and summarizes statistical analyses of the interactions. O. Ceska et al. (MNL 54:118-119, 1980) reported that in dried husks of a B Pl P-WW plants the flavone pathway was blocked by the P-WW allele. Since some of the markers had also P-WR segregating, a further decomposition of the sources of variation was possible since M wx and ZC are P-WW. This is presented in Table 2. With the exception of entry 15 the numbers differ from Table 1 because not all reps segregated for P-WW and P-WR.

In Table 1 the plus sign before X2 shows that there were significant differences in favor of ZC for T4-9(5657) at 4L.33 and for T6-9b at 6L.10; the minus sign before X2 indicated significant differences in favor of M wx for T4-9b at 4L.90 and for T3-9c at 3L.09. The significant interaction for reps in T3-9c suggests that the variety is segregating at this locus. In Table 2, using only the entries that segregated for P-WW and P-WR, appears an effect for ZC in T2-9b, 2S.18. Joining the three entries which did not have individual effect, there appears an effect for ZC in favor of P-WW, almost reaching the 5% level. The results suggest that the genetics of resistance follows the genes or super-genes responsible for sunlight-independent anthocyanin or anthocyanin-like (glycosides) including a specific factor, sm, controlling silk coloration. It seems that bm and bz are not involved.

For the factors of earworm resistance located in ZC we propose the symbols and indicate the probable regions as: Zer1 (Tu c2); Zer2 (Pl Bh sm); Zer3 (Br2); Zer4 (p). For M wx they should be: Mer1 (Tu c2); Mer2 (a3 a1).

The basic factors seem to be in chromosome 4 for both, in chromosome 6 for ZC, and in chromosome 3 for M wx. They are dominants or complementary dominants.

Table 1.

Table 2.

L. T. de Miranda, C. J. Rosseto, L. E. C. de Miranda, E. Sawazaki and N. C. Schmidt

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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