LINKAGE RELATIONS OF creep ON CHROMOSOME 5

PNL Volume 14

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RESEARCH REPORTS 41

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

Plants of the EMS-induced mutant creep (1) grow prostrate along the

ground. This distinctive behavior establishes creep as a worthy

seedling marker as well as a candidate for physiological studies. The

type of line for this mutant, WL 5859, is tall (Le.) and lacks an-

thocyanin pigmentation (a), the mutant having been induced in the

variety 'Torstag'. I crossed WL 5859 with one of my own le A lines

preparatory to attempting linkage studies. The A line had speckled

seeds but it was unknown at the time whether its genotype was F, Fs,

F fs, or f Fs.

As expected, the F1's of the initial cross were wild type with

respect to height, flower color, and habit, i.e. Le/-.A/-.Creep/-. The

F1 's also had speckled seed. The of a small field population grown

in 1980 and scored for Creep-creep and for speckled vs. non-speckled

seed showed the segregation pattern indicated in Table 1. This F2 also

segregated for A-a but the .a/a plants were not included in the summary.

It is clear that only one of the polymeric genes for seed speckling

segregated, but it still was unknown whether the segregating locus in

question was F or Fs. However, since the Creep A parent was either F or

Fs but not both, it is evident from the results that the creep a parent

was homozygous recessive for both f and fs. Therefore, the segregation

data in Table 1 suggest the possibility of linkage between creep and f

on chromosome 3 or fs. on chromosome 5.

F3 plants were grown from F2 segregants with the genotype

A, creep, f., f.s. To test whether creep was linked with £ on chromosome

3 or with Fs on chromosome 5, the creep F3 plants were crossed recipro-

cally with each of two marker lines. The first marker line carried

st-b-chi-6. (f being closely linked with st). This first marker line had

speckled seeds, resulting from the presence of Fs alone, i.e. it was

known to be f. Fs. Reciprocal crosses were also made between the creep

F3 line and a ce (A) line, .ce residing near fs. on chromosome 5. The ce

line had colorless seeds (f, fs). The relevant genic makeup of the two

crosses was as follows:

PNL Volume 14

1982

RESEARCH REPORTS

All F1's from the crosses involving the chromosome 3 markers had

speckled seeds, whereas all F1's from the ce. crosses had colorless

seeds, and all F1's from both crosses had a normal (Creep/-) growth

habit. The F1's from both series of crosses were scored in the field in

1981 (Table 2).

Direct and indirect evidence from both crosses show that creep is

situated in chromosome 5. One piece of direct evidence comes from the

cross involving The calculated estimate of linkage between creep

and was 17.9 ± 5.6 (Table 2). Additional direct evidence came from

the cross involving the st parental line. Since the st line carried Fs

(but not F), the line provided a chromosome 5 marker as well as the

chromosome 3 markers. The Fs-creep linkage estimate was 15.7 ± 1.6.

The st. line also provided corroborating negative evidence inasmuch

as st shown to be independent not only of creep but also of Fs.

Moreover, the st-b-chi-6 parent was heterozygous for Cr (Cr/cr). so some

of the data could be used in a three-point analysis involving cr, creep.

and fs. Although the data are meager, there is evidence of repulsion

phase linkage between creep and cr. in this cross.

The data are considered insufficient to establish gene order be-

cause these crosses did not allow a direct test of linkage intensity

between ce. and fs. But the recovery of ce-creep-fs segregants in

provided the genotype for three-point coupling phase crosses now in

progress.

1. Sidorova, K. K. 1975. PNL 7:57-58.