Genetics of horizontal resistance to pests by glucosides and super-genes

Toxics in plants are usually alkaloids, glucosides, resins, and organic acids. Anthocyanins and flavones and related substances appear in glucoside form which is not toxic per se. Stimulated, the glucoside hydrolyzes, producing sugars and aglucones that are toxic. They are phytoalexins in the sense of Mueller. DIMBOA one aglucone confers resistance to Helminthosporium turcicum, Diplodia maydis, Gibberella zeae, Erwinia spp., Rhopalosiphum maydis, Ostrinia nubilalis, atrazine, etc.

Resistance in Zapalote Chico to Heliothis zea (corn earworm) is, at least in part, by antibiosis with maysin, a flavone glucoside. The authors (MNL 56:30-32) mapped, with the standard 9 wx translocations in IAC Maya latente, some effective factors for resistance to H. zea in Z. Chico and IAC Maya. (There is an error in Table 1, where the chi-square of wx T4-9b (4S.27; 9L.27) should read 11.46, with P < 0.01, instead of 1.116.) It was seen that resistance corresponded chiefly to super-genes and genes responsible for sunlight-independent synthesis of anthocyanins.

We did bibliographic research and analyzed 21 references in three groups. The first (Table 1), for lepidopterans, has 4 references for O. nubilalis and 3 for H. zea. The second has 4 for "stunt" (spiroplasma) and 1 with atrazine (Table 2). The third, for fungi, has 3 for H. turcicum, 2 for D. maydis, 3 for Ustilaqo zea and 1 for Puccinia sorghi (Table 3). References are listed at the bottom of the tables.

By the number of arms tested the expected frequency for random results was calculated and a X2 test of independence was applied. This was done for short arm, long arm, and one or another, by chromosome.

Our interpretation of how to classify the data is subject to criticism. However, we point out that A. C. Waiss et al. (Bull. Entomol. Soc. Am. 27:217-221, 1981) reported that the maysin content varies tremendously (up to 20-fold) within a corn line, and the cross between corn varieties regardless of maysin content often contained higher levels of maysin in the F1 than either of the parents. These observations can explain many non-repetitive results, and reinterpretations. G. E. Scott and C. O. Grogan (12) reported that only 8L was associated with resistance to atrazine, but applying a contingency X2 test to their data, which they did not apply, two more, 5L and 6L, were found. W. A. Russell and A. L. Hooker (21) did not consider 6L as associated, in part because it was not significant with 9c, but in combination with 4L, the X2 are three times greater than with any other arm combinations in their results, being, probably, complementary dominants.

We have probably misclassified some entries, but expect that this should not impair general conclusions, although the accuracy could be improved. In Tables 4 and 5 the statistical analyses are presented.

The mean X2 for lepidopterans was significantly greater than for fungi: X2 divided by X2 = F = 4.67 to 11.95 with P < 0.05 to P < 0.01. Four arms and 5 whole chromosomes were significant for insects, and only 1 arm and 1 chromosome for fungi. In total, for insects, 1S***, 1**, 4S**, 4L*** and 4*** were associated for resistance; 7L*, 7**, 9L*, 9** and 10* were not associated.

For "stunt" + atrazine (MDM+A), 6L** and 6** were associated with resistance and 9L and 9 tended not to be associated. For fungi, 6L* was associated and 10S* wasn't. For the total of the three groups there was association for 1S*, 4S*, 4L*, 4***, 6L** and 6*. There was no association for 9S*, 9**, 10S*, 10**. Only 3L and 2S, as expected, did not appear as significantly associated in any group or total.

The more probable cytogenetic locations of the resistance components to pests by glucosides are 6L, Dt2 Pl Bh sm (Dt2 is mutagenic of a to A, and Bh produces aleurone color even with c1 c1; 4L, Tu c2; 4S, Rp4; 3L, a3 a1; 2S, R2? rp7?; 1S, p. We reformulate our earlier suggestions in the sense that Zer1 should be in 4S around Rp4. There are clearly two effective factors with loose linkage in chromosome four. Other reformulation is that Zer3 could be nearer rp7 than to R2.

Resistance of plants to insects seems to depend much more on this system than resistance to diseases, that although present, appear blurred by other mechanisms.

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Luiz Torres de Miranda, Luiz Eugenio Coelho de Miranda, Eduardo Sawazaki and Nelson Cembranelli Schmidt


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