Location of four new dominant mutants

Part of the study of a new set of EMS-induced mutations (MNL 57:30, 58:71) in 6418 M1 plants (about 5000 good ears) has been to describe dominants and locate them to chromosome. So far 55 have been assigned mutant numbers after proving heritable in outcrosses. Most are partial dominants. Many more await testing. Four have been located to chromosome using the waxy reciprocal translocation series (T wx linkage; Table 1).

Hsf*-1595 (hairy-sheath-frayed) first expresses as long hairs on leaf 4 or 5, especially along the margin. Sheaths and margins of upper leaves are densely pubescent, the leaves are narrower, and the sheaths bulge somewhat, in the manner of pubescent, high-altitude Mexican races. Plants are smaller and later. A very unusual feature is "fraying" of the leaf margin on some of the hairy-sheath plants. Enations of the margin can be up to 3 cm long and have the morphology of the sheath in miniature-curled lengthwise, shiny inside the curl, and a "ligule" between enation and blade, plus a cluster of hairs at the tip. "Fraying" is subject to modifiers. Ears are small with especially short husks, silking deep in the sheath. It is probably located on the long arm of chromosome 5. Its phenotype is quite different from Rgd2, also on chromosome 5, so we propose designating it Hsf1.

Hsf1-1603 (hairy-sheath-frayed) is very like Hsf1 but the incidence of "fraying" can be higher, and an odd expression distinguishes it. Two "coleoptile tubes" are often found across from the coleoptile. They may be very narrow and threadlike, have a small blade, or grow into tillers often nearly as large as the main stem. It also is located on chromosome 5, probably the long arm, and may be allelic to Hsf1.

Sdw*-1592 (semi-dwarf) plants are definitely not typical dwarfs. Height in the heterozygote is 2/3 of normal-internodes are shortened. Leaves are erect and short as are tassel branches, which can have barren tips. Ears are small. Wilting is frequent. It is probably on the long arm of chromosome 8; the data in Table 1 are skewed because intermediate forms, resulting from crowding, are not counted. Its proposed designation is Sdw1; its morphology is significantly different from Clt*-985.

Les*-2005 (lesion) is late-expressing starting as small yellowish spots and changing to small necroses 1-2 mm across. The homozygote has many more lesions than the heterozygote. It is probably on chromosome 9, possibly between wx1 and bk2.

Table 1. T wx linkage data for dominant mutants (only the significant linkages). 1:1 ratios are expected if unlinked to translocation.

Robert McK. Bird and M. G. Neuffer


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