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Materials and methods

T. aestivum L. cv. Chinese Spring (CS), the 41 disomic substitutions in which each of A and B genome chromosome pairs of Chinese Spring was replaced by a homoeologous pair from the E, genome of L. elongatum, and the seven disomic additions of single L. elongatum chromosome in Chinese Spring were kindly provided by Dr. J. Dvorak, University of California, Davis, CA, USA (Table 1). All the above additions and substitutions are in a uniform cv. Chinese Spring background. These substitutions, additions and Chinese Spring were used as female parent in crosses with rye, Secale cereale L. cv. Qinling (a Chinese landrace).

The crosses were made in the field condition in the 1996-1997 growing season. Crosses were made using two outermost florets. Emasculated spikes were bagged to avoid pollination with other plants. After 2-3 days, the stigmas of emasculated florets were pollinated with fresh pollen of rye, then bagged again.

Number of seed-set per spike was counted about 20 days after pollination. Crossability percentages were estimated as the ratio of the number of seed-set to number of florets pollinated. The crossability of a test line with rye was represented by the average percentage of seed set of all the spikes pollinated of that line. The crossability of each spike was converted to angle and the converted data were then subjected to analysis of variance.


Results and discussion

The crossability of the 41 disomic substitutions and the seven disomic additions were compared with that of control, disomic Chinese Spring (Table 1). Disomic substitutions DS4Ee(4A), DS4Ee(4B), DS4Ee(4D), DS5Ee(5B), DS6Ee(6B) and disomic addition DA4Ee, displayed a pronounced reduction in crossability percentages in comparison with that of control whereas the remaining 36 substitutions and six additions had no statistically significant difference from the control.

All the disomic substitutions and disomic addition of homoeologous 4, i.e. DS4Ee(4A), DS4Ee(4B), DS4Ee(4D) and DA4Ee, showed significantly lower crossability than control Chinese Spring. The results indicated that chromosome 4Ee in L. elongatum suppressed crossability of wheat with rye.

The substitution line DS5Ee (5B) showed significantly lower crossability than Chinese Spring, while DS5Ee(5D) and DA5Ee, showed similar crossability to Chinese Spring. DS6Ee(6A), DS6Ee(6D) and DA6Ee showed similar crossability to Chinese Spring, while DS6Ee(6B) showed significantly lower than Chinese Spring. Since only one of the substitution line DS5Ee(5B) or DS6Ee (6B) was involved in this experiment and showed reduction of crossability, it was not assured that the reduction was caused by the suppressing effect of chromosome 5Ee or 6Ee on crossability, respectively. The reduction of DS51Ee(5D) or DS6Ee(6D) could be also caused by technical error or other factors in the experiment, such as partial sterility associated with these substitution lines.

Though the effect of the gene Kr3 was very weak (Riley and Chapman 1967; Falk and Kasha 1983), crossability genes in wheat, Kr1, Kr2, Kr3 and Kr4 were located on chromosome 5B, 5A, 5D and 1A, respectively (Riley and Chapman 1967; Krolow 1970; Zheng et al. 1992). According to the results of this study, it was demonstrated that chromosomes 4Ee in L. elongatum involved in the crossability of wheat with rye. It was suggested that homoeologous chromosome distribution of crossability genes in L. elongatu m was different from that of wheat.


Acknowledgements

The authors are highly thankful to the National Science Foundation, and Science and Technology Committee of Sichuan Province, for their financial supports. We particularly thank Dr. J. Dvorak for providing the stocks used in this study and Ms. J.P. Shong, Ms. Y.Q. Chen and Ms. Y. Zhou for emasculation work.

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