LOCATION OF B AND St IN PISUM

19 RESEARCH REPORTS

PNL Volume 11

1979

Lamm, R. L. Swedish University of Agricultural Sciences, Alnarp, Sweden

In PNL 9:26-27, 1977, 1 pointed out that further cytogenetica1 studies

of interchange trisomies would be desirable in order to establish the location

of B and St in Pisum. The results of such investigations are given below.

In a backcross made by E. Nilsson between 1.85 (Extra Rapid, T[3-5]b,

B St) and L48 (De Winton, N-type, b st) as the recurrent parent, he demonstrate.

strong linkage between the T-point and these genes (Lamm, Hereditas 34:280-288.

1948). In addition to 118 2n plants, Nilsson found 10 2n+l plants, 8 of the

genotype B st and 2 being b st. I have repeated this backcross and, besides

50 2n plants, I obtained 5 trisomies - 3 B st and 2 b St. One of the trisomic

B st plants, on selfing, produced a progeny of 15 2n plants, 13 being of the

genotype b st and 2 B st. The progeny also contained one 2n+l plant of the

genotype B st. With reference to Fig. la, 1 found that the extra chromosome

in the four B st plants was the short 5³ chromosome, whereas the two b St

plants contained the long 3⁵ chromosome.

PNL Volume 11 1979

RESEARCH REPORTS

In Fig. lb, the probable pachytene configuration is illustrated. It

should, however, be mentioned that chiasmata in the interstitial segment are

rare. The genetic results indicate that belongs to the short and St to

the long arm of chromosome 3.

In Fig. lb, the probable location of Gp is also indicated according to

my results given in PNL 9:26-27, 1977. However, according to my earlier

results (PNL 8:36-37, 1976) from crosses with L84 (T[l-5]a), Gp should rather

be localized in the place indicated by brackets in Fig. lb. While considering

this location as an alternative, it should be noted that trisomies never occur

as the result of numerical non-disjunction if there is a chiasma in the inter-

stitial segment (Sutton, J. Genet. 38:459-476, 1939).

In order to obtain further information concerning the location of B,

St, and Gp, L83 has been crossed with a line of N-type recessive for those

particular genes, but it will take some time to obtain results from backcrosses

and from the progenies of 2n+l plants. Until more facts are available, I

tentatively propose that B be localized in the short and St in the long arm

of chromosome 3, and Gp in the long arm of chromosome 5.

Fig. la. Illustration of the Fig. 1b. Probable pairing at pachytene in

reciprocal translocation giving the translocation heterozygote oi crosses

rise to the T(3-5) structure between L83 and lines ot the normal struc-

of L83. ural type with a tentative location of B,

St, and Gp.