|Reciprocal intergeneric hybridizations between wheat
Gerhard ROBBELEN and Sumin SMUTKUPT1)
Section of Cytogenetics, Institute of Agronomy and Plant Breeding University of Gottingen, Germany
Since FIRBAS (1920), several authors have tried to hybridize rye female x wheat male. Because of the ambiguous results reported in the literature, the following study was initiated to investigate the difficulties in obtaining this hybrid. The wheat variety "Chinese Spring" (2n=42) and a family of the "Petkuser" spring rye (2n=14) were used for reciprocal crosses. The seed setting in the combination wheat female x rye male (haploid Triticale) was 61.0 per cent, but only 1.0 per cent in the reciprocal cross (haploid Secalotricum). Part of the difference in seed setting could be attributed to a relatively slow growth of the wheat pollen tubes in the styles of rye; the male gametes, therefore, failed to reach the embryo sac in time for fertilization.
In contrast to the early statement of TSCHERMAK (1933), the reciprocal haploid hybrids being composed of the same genomes (R and W) but different in cytoplasm [r or w] were not completely alike phenotypically. In addition, the haploid Secalotricum was not of "maternal" type as KARAPETIAN (1966) reported. Rather were both reciprocal hybrids intermediate. In particular, the haploid Secalotricum was about 10 days earlier in ear emergence and its straw was about 5 cm shorter than that of the corresponding Triticale plants. These characters clearly demonstrate a cytoplasmic, but not a maternal type of inheritance.
By treatment of seedlings with 0.1 per cent colchicine solution amphidiploids of the Secalotricum and Triticale hybrids were obtained. The amphidiploid Secalotricum turned out to have longer straw and ears than the corresponding Triticale. Two backcrosses of the reciprocal F1 haploids to the male parent were made (cf. figure on the cover i and its explanation on the cover iii). The percentage of seed setting was the following:
in the first backcross, [r] RW x WW=4.4% and [w]WR x RR=4.9%,
in the second backcross, [r] WWR x WW=18.3% and [w]RRW x RR=7.2%.,
These differences in seed setting reflected the influence of the relative number of univalent chromosomes during the foregoing meiosis.
In addition to the poor seed setting in these crosses many of the seeds obtained were shrivelled. But with the aid of embryo culture it was always possible to raise hybrid plants from such seeds. This showed that only the endosperm was degenerated. There were, however, drastic differences in the percentage of shrivelled seeds among various crosses (Table 1).
|1) Present address : Faculty of Agriculture, Chiengmai University, Chiengmai, Thailand|