In an ongoing project with Michael Freeling to recover new transposon-induced mutants, a novel ear phenotype was found in a Mu-containing family. The mutation is recessive and is now in its third generation of crosses. The ear begins development as an unbranched structure, but subsequently the apex divides to form first and second order branches (Fig. 1). The resulting ears are small, rounded and hollow with a proliferation of silks. The ears can be pollinated (though it is difficult to keep them shootbagged) and kernels form on the outer and inner surfaces of the ear. Segregating within the mutant-ear population is an unbranched tassel phenotype. Three of 7 branched-ear individuals had unbranched tassels out of 60 total, whereas there were no unbranched tassels on plants with unbranched ears
The only description in the literature, to our knowledge, that resembles this ear phenotype is club (N.H. Nickerson and E.E. Dale, Ann. Mo. Bot. Gard. 47:227,1955). Club is described as "apparently caused by one or more incomplete divisions of the growing point when the ear is partly formed, followed by simultaneous development of each new point into a more or less independent ear tip". However, while the tassel of club is described as exceedingly thick due to shortened internodes, the tassel of this new mutant is of normal thickness. J.H. Kempton (U.S. Dept. Agr. Bull. 97, 1921) describes a number of branched ear abnormalities, including one entitled "bearsfoot". Our interpretation of Kempton's figures is that the branching in these various abnormal ears occurs at the base of the ear rather than at later occurring divisions of the apex.
Figure 1. Section through mutant ear.
Sarah Hake and Bruce Veit
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