| New types of Cs chlorosis found in hybrids between
the Emmer and the Timopheevi group of the tetraploid wheats Taihachi KAWAHARA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Muko, Kyoto Intra- and interspecific hybrids of wheat often show various types of hybrid weakness. Of these, necrosis and chlorosis are most commonly observed. In hybrids between the Emmer and the Timopheevi group, chlorosis is reported by TSUNEWAKI & HAMADA (1968) and by TSUNEWAKI & NAKAI (1973). It is caused by two complementary genes ; Cs1 carried by the Emmer group and Cs2 of the Timopheevi group. In the present study, a Cs1 tester strain was crossed to 11 strains of the Timopheevi wheats and three types of chlorosis differing with the time of appearance were recognized in the hybrids. Of these, two types were not described in the earlier reports. The results of crosses of ten strains of Triticum araraticum Jakubz. and one of T. timopheevi Zhuk. with a Cs1 tester strain of T. dicoccum Schubl. KU-123 are shown in Table 1. Hybrids were grouped into four types : 1) Normal. 2) Weakly chlorotic. Chlorosis began to appear in early tillering stage. Chlorotic plants tillered and headed normally but were less vigorous than normal ones with lower plant height and fewer tillers. 3) Moderately chlorotic. Chlorosis gegan to appear in early winter when the seedlings had 2 or 3 leaves. These plants showed stunted growth and mostly died in winter. Few survived plants were very weak and produced only a few tillers in spring. This would be the same type of chlorosis as that reported earlier. 4) Severely chlorotic. Most of the seedlings died without extending the leaves. Several plants produced 1 or 2 yellow leaves indicating chlorosis but they also died soon after. In order to study the genes responsible to chlorosis, four strains of the Timopheevi wheats were crossed with F1 hybrid between T. dicoccum KU-114(cs1) and KU-123. In these four hybrid combinations, segregation of normal and chlorotic plants fitted well to 1 : 1 ratio (Table 2). This confirmed that T. dicoccum KU-123 carries a single chlorosis gene which interacts with the gene of the Timopheevi wheats. Further, it may be assumed that the gene carried by the Timopheevi wheats consists of four alleles instead of the two reported earlier. |