II. 8. Hybrid growth retardation due to two dominant complementary genes in barley.
T. Fukuyama, The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Japan.
In the course of studies on interaction between the nucleus genes of H. vulgare and the cytoplasm of H. bulbosum, a specific F1 hybrid was found to exhibit a marked growth retardation as compared with many other F1's. The process of finding this event and result of genetic study are given below:
In 1977, a Japanese two-rowed cultivar, Shin Ebisu 16(SE 16) was crossed to a Turkey six-rowed one, T. 193. The resultant F1 plant was grown in the field next year, and records were taken for date of heading, number of tillers, culm and ear length, and number of triplets per spike. As apparent in Table 1, the F1 was markedly less in number of tillers than their parents. Moreover, it was intermediate between parents for lengths of culm and ear, although an F1 hybrid is well-known to exhibit heterosis and is generally longer in stem length than their parents. No difference was observed in date of heading and number of triplets between F1 and SE 16.
Along with the above experiment, a cross between an alloplasmic SE 16 with cytoplasm of H. bulbosum and T. 193 was made, and characters of the resultant F1 of (B)-F1 were compared with those of autoplasmic F1 [(V)-F1] stated above. As seen also in Table 1, (B)-F1 headed much later than and was markedly inferior to (V)-F1 as to number of tillers, lengths of culm and ear, and number of triplets. The result shows that the growth retardation of the hybrid is intensified by the interaction with the deleterious effects of bulbosum cytoplasm.
Next, the seeds, taken from auto- and allo-plasmic F1, were planted, and number of tillers and culm length of each of the F2 plants were measured. Fig. 1 shows frequency distribution of growth-indices estimated by use of discriminant function based on number of tillers and culm length. A clearcut bimodal distribution in both auto- and allo-plasmic groups indicates that they are classified into normal and retardant types. And a number of these two phenotypes thus classified were found to fit well to the calculated ones on a 9:7 segregation ratio (Table 2). It may be safe to conclude that the growth retardation expressed by the hybrid of SE 16 x T. 193 is controlled by two dominant complementary genes, which are tentatively designated as GrtS involved in SE 16 and GrtT in T. 193. It was also known that these two genes were independently inherited with Vv for six-rowed character.
