KERNEL PATTERN IN VARIEGATED PERICARP MAIZE AND THE FREQUENCY OF SELF‐COLORED OFFSPRING

Abstract

VARIEGATED PERICARP of the so-called calico type, as Emerson (1914, 1917) showed, is due to a gene, pvv (variegated pericarp, variegated cob), which mutates frequently in somatic tissue to an alternative stable form, PRR (red pericarp, red cob), conditioning uniformly distributed red pigment, or self color. The pattern on a variegated kernel (or ear) is determined by (1) the number of pvv to pRR mutations which occur and (2) the amount of pericarp tissue developing subsequently from each primary mutant cell. The most frequent separately recognizable elements entering into the generalized variegated phenotype are very narrow stripes orientated on the kernel polar-wise with reference to the point of silk attachment. These numerous, small, colored areas are referable to mutations which took place relatively late in development. Usually fewer than five per cent of the kernels bearing fine strines exclusively will give rise to plants with uniformly selfcolored rather than varieg,ated ears. Mutations occurring earlier in ontogeny result in correspondingly larger pigmented areas. The latter varv from merely prominent stripes of varying breadth and location on a single kernel to an entire self-colored kernel or a group of kernels which occasionally involves the whole ear. Areas of light pigmentation at the silk attachments distinguish these self-red ears from those due to previous germinal mutations. Plants grown from kernels showing these more conspicuous mutations often bear self-colored ears. The frequency of occurrence of such offspring, however, is correlated with both the size and the position of the pigmented area on the parent kernel. The present paper embodies an analysis of the rela.ionship between these two factors in the kernel pattern and the occurrence of offspring, with selfcolored pericarp. Inheritance of a given somatic mutation which affects merely a part of a kernel requires that the mutated sector include the archesporial cell. Only the mutations which occur prior to the differentiation of this cell, therefore, may be transmitted to the next generation. The earlier in the formation of the spikelet a mutation takes place, the larger will be the amount of pericarp tissue ultimately affected and the higher the likelihood that the megaspore will be included in the mutant sector. Hence, a positive relationship is to be expected between size of the pericarp stripe and the frequency of associated embryos of the mutant genotype.