Ann. Rep. Am. Breeders’
Association 7&8:188-199 (1912)
PRELIMINARY NOTES ON PEPPER HYBRIDSa
Herbert J. Webber
Ithaca, New York
No. 21 Department of Plant
Breeding, Cornell University, Ithaca, N.Y.
In the summer of 1908 a number of races of peppers were grown in the plant breeding gardens at Cornell primarily to observe the varieties and become familiar with the characters presented in order to determine whether this group of plants furnish a favorable field for inheritance studies. Other work prevented the extensive study contemplated, but a few hybrids were made which have since been grown. The second generation of these hybrids produced in the summer of 1910 has given some points of interest and has demonstrated that this is a fertile field of study. It is thought that the notes here presented may be of some interest and may serve in some measure to direct attention more forcibly to the study of what may be termed body characters, such as branching, form of plant, etc.
The races used in the experiments were the commercial sorts known under the names New Celestial, Red Chili, Golden Dawn, Sweet Upright, Dwarf Bell, and Large Bell. The seed used was purchased directly from a seedsman and was supposed to be true to type. In careful experiments it is of course important that seed of known purity be used. The only assurance that the races used in these experiments were pure is found in the fact that the varieties as grown, from 20 to 30 plants of each, were apparently pure so far as could be judged by observation. The attempt was made to obtain inbred seed from each plant used as a parent in order to test its purity, but in the Golden Dawn, one of the parents most used, all of the inbred capsules failed to mature seeds. Inbred seed from plants of Red Chili, New Celestial, Dwarf Bell, and Large Bell used in the experiments in the summer of 1909 produced plants apparently true to type, showing no visible breaking up, and the parent plants were thus judged to be pure in these cases.
In one case, however, a plant of New Celestial, in the course of the experiments, has been shown to have been heterozygous with reference to at least two allelomorphic pairs, namely, sweet and pungent flavor and the green or yellow coloration of the young fruit.
The analysis of the characters considered in these hybrids is as yet, by no means complete and only by the study of a more extensive series of hybrids can final conclusions and deductions be reached. Such a careful series of experiment on a more extensive scale is now being conducted. The one point that has been most forcibly emphasized in the writer's study of this group is the necessity of a more careful study of individuals than is usually made. In the study of the characters of branching it is necessary to study each individual so carefully that one comes to recognize the individual as we do our human acquaintances by the peculiarities of "facial expression."
Only two series of hybrids will be considered in this paper. These will serve to bring out the characters which it is desired to discuss at this time.
NEW CELESTIAL, FEMALE x GOLDEN DAWN, MALE
These races are markedly different in a number of characters. The following are the characters studied which appear from the results to be allelomorphic:
|New Celestial (female)||Golden Dawn (male)|
|Young fruits||Chlorophyll-less (yellow)||With chlorophyll (green)|
|Mature fruits||Bright red
Blunt (bull nose type)
Aside from the above, which are believed to represent contrasted pairs of characters, several other characters have been studied which show segregation in more or less definite proportions.
F1 GENERATION HYBRIDS
The first-generation hybrids, of which about 100 plants were grown, were remarkably uniform in character, the variations being no more than would be expected as fluctuations in the various characters in a pure race. The type of branching was in general intermediate between the two parents, but this character will require further study in the light of hints on the analysis of branching characters obtained in the study of F2 hybrids. The size of leaves and fruit was also about intermediate between the two parents. As would be expected, all of the plants had red fruits, this character of the maternal parent being dominant over the yellow of the paternal parent. The peduncles were in all cases recurved, this paternal character being dominant. The character of the apex, blunt or lobed as contrasted with pointed, was rather variable, being in general intermediate. The young fruits were green, from the presence of chlorophyll as in the male parent.
The pungency was not tested in all of the hybrids, but this appeared to be a dominant character, marked pungency being found in all plants tested except in one series. In this exceptional case, Series 542a, from one hybrid capsule, of those tested 4 were pungent and 6 sweet. Selfed seed from each of the 6 sweet plants in Fs gave only sweet plants, while selfed seed of the 4 pungent plants in each case gave both pungent and sweet offspring, showing clearly that the mother parent of this cross was heterozygous with reference to this character though it was in other characters apparently of true New Celestial type.
F2 GENERATION HYBRIDS
The F2 generation plants were all grown from selfed seed. In many of the characters studied it was found impossible to group the plants as representing positively one or the other of the characters. They were thus grouped in five classes in such instances, the character as appearing in the male and the female representing the two extremes, with one intermediate class and two gonioclinic classes, representing a greater tendency toward the female on the one hand and toward the male on the other. About 200 hybrids of this combination were grown, but different numbers appear in the case of almost every character studied, owing to unripeness of certain plants at time the notes were taken, injury of plant, or failure to include the character in the observations made. This difference in number in different classes in no way affects the conclusions, though in all cases the numbers are too small.
Leaf size.—In this parental combination the leaves of the female parent, New Celestial, are considerably smaller than those of the male, Golden Dawn. F2 hybrids apparently show various gradations of size between the parents. In a general grading of size of leaves the following numbers were obtained in the groups as indicated above: (1) Like mother parent, 4; (2) with decided resemblance to mother, 2; (3) intermediate, 31; (4) with decided resemblance to father, 13; (5) like father parent, 28.
Apparently the father dominates in determining the general size of leaf, but there are many gradations between the two types. The preliminary study indicates that size of leaf here is dependent upon more than one and probably on several factors, the determination of which will require careful statistical study of at least length and breadth in a considerable number of hybrids.
Size of fruit.-—In size of fruits the two parents are markedly distinct, those of the mother parent being small in comparison with those of the father. The F2 hybrids have in general rather large fruits showing a dominating influence of the Golden Dawn. There are, however, many gradations between the two parental sizes. The general sizes were classified as follows: (1) Small like mother, 3; (2) with decided resemblance to mother, 1; (3) intermediate, 50; (4) with decided resemblance to father, 14; (5) resembling father, 30. Here as in leaf size there is a segregation, but size of fruit is evidently not a unit character, and more careful analysis is necessary to determine whether the inheritance can be explained by Mendelian formulas. In neither leaf size nor fruit size, where we would probably expect to have length and breadth or diameter as at least two distinct allelomorphs controlling general size, does there seem to be an approach to the well known 9:3:3:1 formula.
Fruit color.—The segregation of color in F2 hybrids is almost absolute; 151 had red fruits and 46 yellow fruits, while 3 were recorded as of intermediate color, being orange-red. Color segregates, therefore, as would be expected in Mendelian proportions. Of the number here concerned, 200, the expected proportion would be 150 red and 50 yellow. If the three orange-red fruits could be classed with the yellows, the expectation would be almost completely realized.
Position of fruit..—With reference to position of fruit, 31 had erect and 48 recurved peduncles. In general the segregation in this character is complete and plainly recognizable, but 5 plants were recorded as intermediate or doubtful. Here the numbers differ greatly from the expected ratio, 21 to 63, and, even assuming that the 5 doubtful plants belonged in the dominant class, the ratio would still be markedly different from the expectation.
Flavor.—In flavor there are apparently different degrees of pungency, but wherever there was noticeable pungency they were recorded as pungent. Of those on which flavor records were made, 33 were pungent and 10 sweet, which is as near the Mendelian proportion as could be expected. The segregation in this character is very distinct.
Color of young fruit..—In the New Celestial the ovary from the bud to the time of ripening remains yellowish in color, developing no chlorophyll, while in the Golden Dawn the ovary and young fruits up to the time of ripening are green, containing abundant chlorophyll in three or more outer layers of cells. This difference of color apparently depends entirely on the presence or absence of chlorophyll. The F2 hybrids gave 42 green to 13 yellow, which is almost exactly the Mendelian expectation.
Apex of fruit.—While the apex of the fruit in the New Celestial is pointed and in the Golden Dawn blunt, this character does not appear to segregate in definite proportions. The following are the recorded proportions: pointed like female, 2; mainly pointed like female, 20; about intermediate between pointed and blunt, 14; mainly blunt like male, 25; blunt like male, 27. It is interesting to note that if we take the first two classes as representing the pointed-fruit parent and the last three classes as representing the blunt-fruited parent we have a proportion of 22 to 66, which would be an exact Mendelian ratio if the blunt apex were a dominant character. In the Ft hybrids the records were: pointed like female, 0; mainly pointed like female, 3; intermediate, 10; mainly blunt like male, 4; blunt like male, 0. It would seem from the F1 plants therefore that the heterozygous of these characters is in general an intermediate fluctuating more strongly in certain plants toward one or the other parental type. It would not be admissible, therefore, to consider blunt point as dominant.
Our five classes of F2 hybrids, namely 2-20-14-25-27, would not seem to fall into a Mendelian segregation scheme unless we were to consider the first two classes as pointed, the third and fourth classes as representing the heterozygote plants with reference to this character, and the last class as representing the pure blunt-pointed character. This would give us a formula of 22:39:27, which would be as near as we should expect to the Mendelian formula with so small a number. This character, while markedly distinct in the two parents, in the hybrids seems to be mixed frequently on the same plant and difficult to segregate. I am inclined to believe that the plants which are difficult to throw into one or the other of the parental types represent the heterozygous form of these characters.
Form of branching.—The next series of hybrids presents better opportunities to study branching, but the parents in this series differ in at least one or two characters which evidently segregate in the F2 generation. New Celestial has erect or ascending branches which are rather finer and more numerous than in Golden Dawn. The latter variety in comparison has horizontal or spreading branches which are rather coarser and fewer in number. Of these three character pairs, erect and horizontal segregate the most plainly. Of the F2 hybrids examined with reference to these characters, 15 had erect branches like the mother; 4, nearly like the mother; 7, intermediate; 3, nearly like father, and 28, like the father. The segregation into fine and coarse branches, placing the individuals in similar classes, gave 2-15-16-8-16. The branches were not sufficiently different in number to permit of segregation into classes. While the segregation classes as given above do not apparently conform to a Mendelian formula, the segregation clearly takes place, which is the most important point. The segregation of erect and horizontal branches, namely, 15-4-7-3-28, would suggest a dominance of the horizontal or spreading type. The segregation of fine and coarse branches, namely, 2-15-16-8-16, suggests a case where the heterozygote is intermediate between the two parental types. The purity of the parents with reference to characters of branching was not determined, and studies of carefully selected pure-bred parental types will have to be made to determine the numerical proportions of the different types.
|FIG. 1.||FIG. 3.|
|F1 HYBRIDS OF RED CHILI x
(All figures of same comparative size.)
|Fig. 1. Hybrid with erect, many and fine
branches, which may be taken as an extracted type of the maternal parent in
these characters and in size.
Fig. 3. Hybrid with erect, few and coarse branches. Like Fig. 2. except in erect branches. Note greater height.
|FIG. 2.||FIG. 4.|
|F2 HYBRIDS OF RED CHILI x GOLDEN DAWN
(All figures of same comparative size.)
|FIG. 2. Hybrid with horizontal, few and
course branches which may be taken as an extracted type of the paternal parent
in these characters and in size.
FIG. 4. Hybrid with horizontal, many and coarse branches.
|F1G. 5.||FIG. 6.|
|F2 HYBRIDS OF RED CHILI x GOLDEN DAWN.
(All figures of same comparative size).
|FIG. 5. Hybrid with horizontal, few and
fine branches, giving a dwarf much smaller than either parent.
FIG 6, Hybrid with horizontal, many and fine branches.
|FIG. 7.||FIG. 8.|
OF RED CHILI x GOLDEN DAWN.
(All figures of same comparative size).
|FIG. 7. Hybrid with horizontal, few and
fine branches. A dwarfish plant, may be heterozygote with reference to few and
FIG. 8. Hybrid with erect, many and coarse branches, giving a giant plant in comparison with the size of either of the parental types. (Compare with extracted parental types Fig. 1 and 2.)
RED CHILI (FEMALE) x GOLDEN DAWN (MALE)
The first-generation hybrids of this combination, as in the preceding case, are all very similar and little more variable than a pure race. The leaves and fruits, which in the parental types are markedly different in size, are in F1 plants about intermediate between the two parents. All had red, pungent, and pointed fruits like the Red Chili and mainly recurved peduncles like the Golden Dawn. There was some variation in this latter character in the F1 hybrids, which may indicate impurity in the parents used.
Leaf size.—The difference in leaf size is much more marked in this series than in the preceding, the leaves of the Red Chili being much smaller than those of the Golden Dawn. Here, as in the preceding series, the F2 hybrids show various gradations of size between the two parents. The following numbers were obtained in the 5 classes as indicated above: Like mother, 19; with decided resemblance to mother, 22; intermediate in size, 50; with decided resemblance to father, 6; like father, 2. Here, as in the preceding series, Mendelian segregation cannot now be determined.
Size of fruit.—The fruit sizes recorded in the 5 classes as above were 24-20-75-7-3. It is interesting to note that in size of fruit and size of leaf in this combination the largest number approach the female parent while in the preceding series, in which New Celestial was crossed with Golden Dawn, the same male parent being used, the largest number of individuals approach the male parent in size.
Fruit color.—The segregation of color is practically complete, the ratio being 186 red to 41 yellow, only one plant showing an intermediate orange-red color. The proportion of the recessive yellow, here only 18 per cent, is lower than should be expected, but this is probably due to the small number of individuals concerned, there being only 227.
Position of the fruit.—In some instances this character was difficult to determine. Graded in the 5 classes as heretofore, there were 68-5- 10-5-21. There were thus 21 with recurved to 68 with erect peduncles in the series as a whole, with 20 plants falling in the doubtful intermediate classes. This would indicate a dominance of the erect fruit or straight peduncle in comparison with the recurved peduncle, which would be the reverse of the preceding series. In the first-generation hybrids there was some variation in this character, and it seems probable that this character may have been impure in one of the parents.
Flavor.—By no means all of the hybrids were tested with reference to this character, but of the 27 tested, which were taken at random, 22 were pungent and 5 sweet, showing segregation in about the ratio we should expect. In both this series and the preceding there would seem to be a preponderance of the pungent individuals, but this probably may be assumed to be due to the small numbers examined in each case.
Apex of fruit.—In the character of the apex of the fruit in this combination we have in the female parent, Red Chili, a more pointed fruit than that of the New Celestial used in the preceding series, and the results of the F2 segregation are markedly different. Here, graded into our five classes we have 93 pointed like the female; 7 mainly pointed like female; 15 about intermediate; 4 mainly blunt like male; and 2 blunt like male. In comparing these five classes in the two series of hybrids we have the following:
Series 542, New Celestial pointed (female), 2-20-14-25-27, Golden Dawn (male) blunt.
Series 543, Red Chili pointed (female), 93-7-15-4-2, Golden Dawn (male) blunt.
It will be observed that the series are reversed in the grouping of the numbers toward one or the other parent. In Series 542 the blunt apex appears to dominate, while in Series 543 the pointed apex is certainly dominant at least in giving far the largest number of hybrids exhibiting the character plainly. In the discussion of Series 542 with reference to this character it was pointed out that probably the most feasible Mendelian interpretation is reached for the plants in that series by assuming a distinctive heterozygous form represented by classes 3 and 4, while classes 1 and 2 represented the pointed type; this would give a proportion of 22:39:27, which would suggest a Mendelian proportion. It is clear, however, that the 543 series cannot be so interpreted. Here we are led to assume that the pointed apex is a true dominant and that owing to the long slender fruit of the mother producing a much more slender-fruited hybrid the blunt apex is in some measure obscured and that probably all of the classes other than the first or pointed class are to be considered blunt-pointed. This would give us a ratio for Series 543 of 93 to 28, which is near enough, to the Mendelian formula for a character pair, where one character is dominant, to satisfy our expectations. Whether this is the true interpretation of the segregation can probably be determined from the study of F3 generation hybrids grown in the summer of 1911.
Form of branching.—The form of branching in this series furnishes a very interesting study. In general the branches of Red Chili are erect or ascending, while those of Golden Dawn are horizontal or spreading, and in Red Chili the branches are rather numerous and fine while those of Golden Dawn are few and coarse. It would seem that we have to deal here with at least three character pairs which seem to be primarily concerned in determining what we may term the body form of the plant, namely:
The F2 plants of this series, carefully examined and grouped into 5 classes as above with reference to these three allelomorphs, gave the following results:
The three intermediate classes in the above series, it will be understood, show groupings of plants that seem to be bent in their resemblance more or less markedly toward one or the other parental type of the character. While these proportions are difficult to bring into harmony with Mendelian formulas, the characters show distinct segregation.
The most interesting feature in connection with this series of hybrids is brought out in the recombination of these characters. Both parents are medium-sized types in the pepper group. Apparently, by transferring the character of fine and coarse branches, we create a giant or a dwarf. Hybrids having erect, many, and coarse branches are giants in comparison with the parents, while those having horizontal, few, and fine branches are dwarfs in comparison with the parental forms. Other combinations of the three characters give various forms intermediate in appearance, and without a very careful analysis the hybrids seem to form a graduated series between the parents except that some are smaller and others larger than either parent. It is thought that a more careful study of hybrids from parents known to be genotypic with reference to these three character pairs will enable the investigator to group the plants in accordance with their gametic composition.
In no case which has come under the writer's observation has a more striking instance appeared of the apparent origination of a new character by hybridization than is found in the giant and dwarf types of this series, and yet by an understanding of the recombination of the branching or body characters of the two parents we apparently arrive at a reasonable and easily comprehended explanation of the origin of the apparently new characters through the recombination of the hereditary units or genes of the parental types.