Studies on Variegated Pericarp

1. The behavior of a variegated of a given origin recurrent matings to inbred

lines carrying either colorless pericarp, red cob (WR)¹ or colorless pericarp, white cob (WW) alleles.

In 1948 a single collection of pollen from a homozygous variegated pericarp plant, S1937‑10, was placed on the silks of several highly inbred field corn lines including W8, W22, W23, M14 (red cob); 40B, and 4Co63 (white cob). The S1937 stock had been inbred to a degree equivalent to three selfings. The immediate parent of S1937‑10 was a medium variegated plant heterozygous for colorless pericarp, white cob.

Each of the six resulting F₁ families grown in 1949 was relatively uniform in plant types expected, but contained three discrete classes of offspring with reference to pericarp type. Among the 304 F₁ plants from which ears were harvested 11% were light variegated, 72% were medium variegated, and 16% were red. The proportions in which the three kinds of plants occurred in each F₁ family were similar. Plant S1937‑10 had borne a light variegated ear, but it is assumed, on the basis of the progeny test, that the tassel was a chimera containing V^lt (light variegated². V_m (medium variegated), and R (red) tissue. Presumably the ear shoot belonged to the V^lt portion of the plant.

Numerous plants within each F₁ hybrid‑family were backcrosses in 1949 to the corresponding inbred line. Fifty families were grown fram these backcrosses in 1950, representing individual light variegated, medium variegated, and red ears, respectively, distributed over each of the six F₁ pedigrees.

Within sampling limits, one‑half the plants in each backcross family bore ears in 1950 with colorless pericarp, as predicted. The progenies from the red ears contained about equal numbers of red and colorless pericarp plants.

The 41 families segregating variegated pericarp were scored first for grade of variegation against a set of arbitrarily designated standard ears varying from class 1 (very few red stripes) to class 7 (very heavily striped). As the variegated ears were being worked over, however, it became apparent that the distribution within each family was not continuous but actually more or less sharply discontinuous in addition to the few red ears (ca. 6%) which occurred in these families, variegateds of two grades only, light and medium, appeared to be present. This was unmistakably true for the 22 backcross families involving inbreds W8, W22, and 4Co63. It probably held for the remaining groups (W23, 40B and M14) also, although the separation into the two classes of ears, light and medium variegated, within them was judged "clear‑cut" in 12 families, only "fairly certain" in six others, and "uncertain" in one. In the latter seven families the difficulty of classification usually involved the placement of only 1–4 ears. The general character of the results observed on classifying the material on the basis of the discontinuity in grade of variegation may be inferred from table 1 in which the distribution of offspring in the families involving inbred W8 are given.

¹ R. A. Emerson's simplified terminology for the P alleles is followed: VV = P^VV(variegated pericarp and cob); WR = P^WR (colorless pericarp, red cob); RR = P^RR (red pericarp, red cob).

² The terms "V_lt" and "V_m" are used in a phenotypic sense, and their employment is not intended to imply that these phenotypes are necessarily associated with corresponding alleles at the P locus.

Table 1

Distribution of progeny from light variegated and medium variegated
F₁ ears backcrossed to inbred W8.

Family	Parent ear (F1)	Number of Progeny				Per cent Vlt^1
		Vlt	Vm	Red	Colorless
6‑70	Vlt	21	27	3	65	41.2
‑71	"	25	22	1	48	52.1
‑72	"	51	44	3	90	52.0
‑73	"	38	48	3	96	42.7
‑74	Vm	7	160	8	161	4.0
‑75	"	9	141	9	124	5.7
‑76	"	7	161	7	161	4.0
‑77	"	2	134	5	131	1.4

¹ Based on variegated and red ears.

Four points are noteworthy from a survey of the data from all the backcross families: (1) both light and medium variegated parent ears give the same two classes of variegated offspring, but with different frequencies; (2) within the respective V_lt and V_m parent ear groups there is considerable regularity from family to family within three backcross groups (W8, W23, 4Co63) in the proportion of V_lt and V_m offspring. The W22 backcross families from V_lt (but not V_m) ears appear to be definitely irregular in this respect, and the families from the V_lt ears in the other two groups (40B, M14) are somewhat doubtful; (3) the frequency of V_lt offspring from V_lt parents is much higher than from V_m parents and vice versa (4) the same basic pattern of inheritance (with modifications superposed in some cases) appears to characterize each of the six backcross groups.