Progress in screening for agronomically and botanically useful EMS-induced mutants

Early in 1981 EMS-treated pollen of Mo17 was used to pollinate 75 plants of the inbred A632. Many mutations and aberrations have resulted, among which some are quite novel. Phenotypic expression is being followed from kernel to harvested ear. Among the more interesting dominants are Tillered-1590, Golden-1585, Semidwarf-1592 and Hairy-sheath-frayed-1595, but many unusual phenotypes affecting most organs have been found. "Frayed" describes a leaf margin which has protrusions up to 1 cm long. A dominant very like Hsf*-1595 in the mature stage has just been found to have 1-2 odd little tubes exserted from the coleoptilar node, in one case developing into a tiller. Many of the sectored (MNL 57:30) and whole-plant dominant mutations noted in the M1 (1982) have been outcrossed to wx translocation stocks for location to chromosome arm.

Out of ca. 1140 M2 families examined last summer, over 270 had plants that differed significantly in time to pollination, plant or ear height, or other agronomically interesting characteristics. Outcrosses of these are being selfed, and next summer we will check the heritability of the traits and the form and relative yield of affected plants.

Segregation of mutants in the M2 does not fit standard genetic ratios because of the sectoring of M1 plants. It is not known if most EMS mutants are sectored in the M1, but, judging by the low proportions of many M2 mutant plants, many are. Some low ratios that were found were: bleached 2/38, virescent 5/37, rolled leaf 3/36. One family had 1 out of 17 plants from one side of the ear and 4 of 20 from the other side showing virescent (we had marked many ears above the midrib of the subtending leaf). Another case was 5/20 vs. 0/20 pale luteus. In plantings of 20 kernels we frequently found 1/20 white seedling, luteus, dwarf, etc. This explains why some mutants have not been seen until the M3 generation--rare M2 heterozygotes were selfed. Johri and Coe (MNL 55:31) found that ears generally do not sector cleanly into halves, as we have also observed, contributing to these low ratios.

Because of the many low ratios we cannot be sure that all variants noted are heritable. Ear variants were very common but one type was too frequent--small ears with large cupules, narrow shanks and short husks. Perhaps this was due to smut infestation in plants weakened by some mutation that had no direct effect on the ear. Among the more notable effects are few rows (8,10), many rows (18,20), short ears, short husks, fertile lower florets, long paleas, high cupule wings, secondary ears, branched silkless, large cupules, and many others. Unfortunately we could not self all plants in the field so many of these were found on plants that were open pollinated. It will take a while before we are sure these are heritable. Tassels also varied: male sterile, few branched, tiny anthers, awned paleas, barren branch tip, etc.

While placing the M1 ears in storage, a special effort was made to note any endosperm mutants that were readily distinguishable. Six mutants allelic to su1 were found, the number which one would predict by estimating one mutation per locus per 1000 M1 plants grown, using EMS treatment of pollen (Neuffer 1978, In D. B. Walden ed., Maize Breeding and Genetics).

Another subset out or ca. 4000 unexamined M2 families will be even more carefully examined next summer.

Robert McK. Bird and M. G. Neuffer

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

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