INFLUENCE OF NON-ALLELIC INTERACTIONS ON THE PHENOTYPE OF na

PNL Volume 1M 1982 RESEARCH REPORTS 47

Marx, G. A. NYS Agricultural Experiment Station, Geneva, NY USA

A preliminary experiment was conducted to study the linkage rela-

tions and interactions of nana (na) and microdwarf (lm), two genes known

to reside in chromosome 6 (1,5,6). The na. parent derived from the na

mutant isolated at Geneva (2); it also carried other chromosome 6

markers, viz. Arg. Pl, and wlo. WL 1329, obtained from Dr. Blixt, was

used as a source of lm. In Blixt's inventory WL 1329, besiges being

identified as lm, is listed in the "genotype" category as cry^s , but in

the "origin" category as "microcryptodwarf". Unlike the na parent,

WL 1329 is arg pl and Wlo. Thus the known or presumed genotypes of the

two parents were:

The populations also segregated and were scored for genes which were

not relevant to the study, and, except to say that the genes segregated

according to expectation, they will not be considered further. Each of

two F₂ populations examined descended from an individual plant grown

in the field. The two parents, additional F1 plants, and F2 populations

then were planted at the same time and grown in the same glasshouse

where they were fully classified and measured for internode length.

Nodes to flower were also recorded. A four-point linkage analysis of

Arg-Pl-Wlo-Na was performed on the combined populations and is presented

in the following article. Arg or Pl are not immediately relevant to

this article.

All F1's were classified as dwarf. The individual and combined F₂

distributions (Table 1) reaffirm the known linkage between na. and wlo.

but the estimate of linkage intensity (10.8 ±_ 2.2) was somewhat higher

than other estimates (2,3). The distributions do, in fact, appear dis-

turbed, the Na wlo class being noticeably larger than the na Wlo class.

Despite this, segregations for either gene in the individual and com-

bined F2 populations were statistically not significantly different from

expected.

PNL Volume 14

1982

RESEARCH REPORTS

The data suggest that the numerical imbalance of phenotypes might be

explained by something other than chance or misclassification. Part B

of Table 1 gives the Joint distribution between the Wlo-wlo locus and a

phenotype designated "long". This designation is used to characterize

F2 segregants that resembled the internode length and total height of

plants of the WL 1329 parent. This, and the two other phenotypic

classes (dwarf and nana). were determined visually and by measurement

(Table 2). There were a total of 55 "long" plants in the combined F₂

populations, the number expeoted for a perfect 3:1. Thus "long" was in-

herited as a recessive character. Of the 55 "long" plants, 38 were

associated with Wlo and 17 with wlo. indicating that "long" and wlo were

independently inherited (linkage chi-square = 0.12^n.s.).

Now, (a) since .na. is known to be rather tightly linked with wlo (2),

and (b) since there were 17 "long" plants with wlo (too many to be con-

sidered as crossover products), it may be reasonable to suppose that the

17 "long" wlo plants carried na. but that the nana phenotype'was masked

by the "long" phenotype. Therefore, by subtracting 17 (the "long" wlo

segregants) from the Na wlo class in Table 1 A (21-17=4) and transfer-

ring them to the na wlo class (41 + 17 = 58), we are left with a

distribution which shows the expected balance among the phenotypes. The

adjusted distribution becomes 153:4:5:58 for the Na Wlo. Na wlo, na Wlo.

na wlo classes, respectively. This produces an estimated recombination

percentage of 4% between na and wlo. a figure which is consistent with

estimates obtained in other crosses (2,3). Of course, this Juggling of

the data would be highly inappropriate were it not for the known tight

linkage between na and wlo.

On the basis of these assumptions, i.e. that na is hypostatic to

"long" and that "long" is not linked with na, what then is the genie

basis for the phenotype designated "long"? Although parental line

WL 1329 is represented as carrying cry , its phenotype more closely

resembles cryptodwarf (la cry ) than it does "slender" (la cry ).

Moreover, the phenotype of the "long" F_ plants closely approximated the

phenotype of the parental WL 1329 plants (Table 2). There were no

slender segregants. It would seem therefore that WL 1329 is cry rather

than crv and that the genotype as given in Blixt's inventory is a

typographical error. Even so, the presence of cryptodwarfs in F₂ implies

that the na parent as well as WL 1329 were homozygous for la and that

the Cry-cry alleles segregated in F2.

Still, WL 1329 is described as "microcryptodwarf", not as crypto-

dwarf, so we have yet to account for the purported presence of lm. a

factor for internode shortening. But since the parental and F2 "long"

plants resemble each other and both resemble ordinary cryptodwarrs, then

it is appropriate to ask: where is lm? The F₂ populations give little

hint of a segregation for this gene. However, many or most "long"

plants had weak, thin stems and frequently the Initial shoot aborted at

emergence and was replaced by a second shoot. Since Lindqvist (1) found

1m to be closely linked with wlo. there should have been evidence of

repulsion phase linkage between wlo and la in the present crosses. None

was detected.

PNL Volume 14 1982

RESEARCH REPORTS 49

The conclusion that cryptodwarf is epistatic to na is consistent

with other observations which indicate that the na phenotype is subject

to modification by genes at other loci (2). If this hypothesis is cor-

rect, then the ascending order of height for na plants is assumed to be:

na La Cry, na La cry^c na La cry^s, na la Cry, na 1a cry^c , and

na la. cry^s. Presumably, the presence of na cannot be visually detected

in certain of the forgoing gene combinations. Since Wellensiek's na is

extremely short, possibly it is Le na La Cry. It cannot be excluded,

however, that Le itself shortens na. Obviously, the evidence developed

in this experiment is not in accord with the assumption that WL 1329

carries Lm. If its presence was obscured by gene interactions and hence

merely not detected, then perhaps a cross between WL 1329 and a known

cryptodwarf would reveal its presence. It would be important that the

two lines would have the same or similar flowering genotype since inter-

node length is influenced by time and node of flowering.

We are left with the interesting proposition that La is dominant to

le., that na is epistatic to Le and to le (4), but that na is hypostatic

to combinations of le, la, cry^c and crv^s . As such this scheme is rife

with implications in physiological genetics. For example, what is the

phenotype of plants with the genotype Le. na la cry^s ?

1. Lindqvist, K. 1951. Hereditas 37:389-420.

2. Marx, G. A. 1981. PNL 13:35-37.

3. Marx, G. A. 1982. PNL 14:50-52.

4. Murfet, I. C. 1978. PNL 10:54-55.

5. Rasmusson, J. 1938. Hereditas 24:231-257.

6. Wellensiek, S. J. 1972. PNL 4:60.