The relation of plant colors to total dry weight in maize.

A number of years ago Brink (Jour. Amer. Soc. Agron. 26: 697-703, 1934) reported the relative yielding capacity of four different anthocyanin plant-color types, namely, purple A B Pl, sun red A B pl, dilute purple A b Pl, and dilute sun red A b pl. The stocks were so bred that all four classes occurred with approximately equal numbers in each of the 11 families involved in the test and so that the residual genotypes of the four color classes were approximately the same. Somewhat more than 3500 plants were observed and yields were reported as average dry weight of ears per plant in pounds as follows: Purple .433, sun red .569, dilute purple .561, dilute sun red .511. Thus dilute sun red, the prevailing color type of the country, yielded significantly more than purple and both sun red and dilute purple significantly more than dilute sun red.

The writer has made similar tests, using total dry weight of plant as the criterion of yield. The genes b and pl were derived from two dilute sun red (A b pl) inbred dent lines and their dominant alleles from several genetic stocks, including purple A B Pl, brown a B Pl, and reddish brown a^p B Pl. Each of these genetic stocks was crossed with each dilute sun red inbred and purple plants of the resulting progenies were backcrossed from one to three times with the same or the alternate inbred. Some of the cultures, therefore, were little if any more vigorous than the inbred lines and some showed marked heterosis. The four color types of any one culture, howeve, were comparable and occurred in approximately equal nunbers, In table 1 are shown the average dry weights per plant in grams for the several color types of each of 14 cultures.

Table I

In addition to backcrossing heterozygous purple plants of table 1, certain sun red and dilute purple plants were backcrossed with one or other of the same dilute sun red inbreds. Results are shown in table 2.

Table 2

From the results presented in table 1, it is obvious that purple plants were not appreciably less in dry weight than sun red and dilute purple plants. The dilute sun red plants were lowest in dry weight but not markedly less than the other three color types. The results given in table 2 were similar to those of table 1. In one lot of cultures, dilute sun red plants were slightly less in weight than sun red ones. In the second lot of cultures, dilute sun red again was less in weight than dilute purple; and the difference here is greater than in the other tests.

On the whole and in so far as the results here reported are concerned, it can be said that in segregating cultures, dilute sun red plants were slightly less in total dry weight than were plants of the other color types. Whether or not the fact has any significance, it should be remembered that, in all these tests, comparisons have been made between homozygous dilute sun red and heterozygous purple, sun red, and dilute purple.

Among genes other than B and Pl that are related to plant colors of maize, the A a pair is of fundamental importance. In most instances, only in the presence of dominant A do anthocyanin pigments develop. Where A results in purple or red, its recessive alleles usually give brown or have no appreciable effect on color. Accordingly several tests have been made of the possible influence of A and of some of its alleles on dry weight of plant. Certain colorless (green) types were crossed with the two dilute sun red inbreds used in the tests noted above. The F₁ plants were backcrossed to the colorless parent. Three sets of cultures were grown from the following crosses: (a B pl x A b pl) x a B pl, (a b Pl x A b l) x a b Pl, and (a b pl x A b pl) x a b pl. In each set of cultures, two color types were represented. The results are given in table 3.

The records of table 3 reveal small but not consistent differences in total dry weight of plant between colored and colorless individuals of the several cultures. In averages of mean dry weights, sun red plants were about five per cent lighter than the corresponding colorless ones, while dilute purple and dilute sun red plants were heavier than their colorless sibs by six and three per cent, respectively. With the genotypic backgrounds here involved, there was relatively little effect of A and of its recessive allele a on total dry weight of plant.

There remains to be considered a possible difference between the influence of A and of sone of its recessive alleles when the background genotype contains both dominant B and dominant Pl. In one lot of tests purple A B Pl was crossed with brown a B Pl and backcrossed once with the same brown. The results are recorded in the first section of table 4. Another allele of A, namely, a^p, gives a reddish brown plant when in combination with B and Pl. Reddish brown was crossed with one of the two dilute sun inbreds ond the purple plants, resulting were backcrossed once or twice with the same reddish brovm. Recessive a2 with B and Pl gives brown plant color. This brown was crossed vith reddish brown and the resulting purple F₁ plants were backcrossed vith reddish brown. The genotypes concerned here are as follows: (A a2 B Pl x a^p A2 B Pl) x a^p A2 B Pl. All these progenies, segregating purple and reddish brown, are recorded in the second section of table 4.

Table 3

Table 4

Brown plants of the genotype A a2 B Pl were crossed with one of the dilute sun red inbreds, with purple, and with reddish brown. In all instances the resulting F₁ purple plants were backcrossed with A a2 B Pl. Here then the brown plant color is conditioned not by an allele of A but by an allele of A2. The cultures irivolving A2 and a2 are listed in the third section of table 4.

Cultures segregating for purple and brown plant color, as shown in table 4, whether the brown color is conditioned by a, or its allele a^p, or by a gene of a different chromosome a2, all exhibit consistent results. The averages of the mean dry weights are greater in each of the three lots of cultures by from 15 to 26 per cent for the purple than for the brown plants. Moreover in each of the 28 cultures of table 4 without a single exception, the purple plants are heavier than the brown ones.

Since for one of the genes conditioning brown plant color, namely, a, no consistent effect on weight was found when A and a were combined with B pl, b Pl, and b pl (table 3), it seems reasonable to assume that the lighter weight of brown plants conditioned by a, a^p, or a2 in contrast with purple plants conditioned by the dominant alleles of these genes, results from some deleterious effect of the brown pigments in the physiology of the plant, rather than from a direct effect of the recessive genes or of growth factors closely linked with them.

R. A. Emerson