| Chromosome numbers in the A. smithii x T. aestivum 'Chinese
Spring' hybrid varied from 29 to 42 in root tip cells (Fig.
1a) and from 26 to 36 in pollen mother cells (PMC's). The A. smithii
x 'TAM 105' hybrid also showed range in chromosome variation, 34 to 36 in
root tips and 30 to 38 in PMC's. In both these hybrids, of the 33 PMC's
scored, 22 had fewer than 35 chromosomes (Table 1).
It seems likely that A. smithii chromosomes are preferentially eliminated
in these hybrids. Chromosomal instability was also present in the A.
smithii parent used to produce these hybrids. A. smithii showed
2n=28 (Fig. 1b) with a range of 2n=24 to 38. There
was very little pairing between A. smithii and wheat chromosomes
in A. smithii x wheat hybrids (Table 1.
Fig. 1c). Meiotic abnormalities, like anaphase bridges
(in 12 of 30 cells), laggards (in 17 of 19 cells) and quartets with micronuclei
(in 33 of 44 cells), were abundant. A. ciliare x T. aestivum 'Chinese Spring' hybrid had the expected chromosome number of 35. The chromosome pairing was 4.25 II and 0.11 III per cell and an average chiasma frequency of 4.9 (Table 2. Fig. 1d). Meiotic abnormalities, such as laggards (in 12 of 15 cells) and quartets with micronuclei (in 15 of 33 cells), were frequent. Attempts to obtain amphiploids by colchicine treatment (0.05% for 6 hrs) so far have been unsuccessful. However, backcross-1 seedlings from both A. smithii x wheat and A. ciliare x Wheat hybrids with wheat have been obtained. Eventually, we hope to obtain whent-Agropyron addition lines involving different A. smithii and A. ciliare chromosomes. Preliminary results indicate that A. ciliare is resistant to barley yellow dwarf virus (BYDV) and WSMV. Apart from cytogenetic analysis of Agropyron species genomes, obtaining BYDV and WSMV resistant germplasm is another major objective. Literature Cited ALONSO, L.C. and G. KIMBER 1980. A hybrid between diploid Agropyron junceum and Triticum aestivum. Cereal Res. Commun. 8: 355-358. BROWDER. L.E. 1980. A compendium of information about named genes for low reaction to Puccinia recondita. Crop Sci. 20: 775-779. CAUDERON, Y. 1979. Use of Agropyron species for wheat improvement. Proc. Conf. Broadening Genet. Base Crops, Wageningen, 1978. Pudoc, Wageningen 1979. pp. 175-186. CAUDERON, Y., B. SAIGNE and M. DAUGE 1973. The resistance to wheat rusts of Agropyron intermedium and its use in wheat improvement. Proc. 4th Int. Wheat Genet. Symp., Univ. Missouri, Columbia. pp. 401-407. DVORAK, J. 1980. Homoeology between Agropyron elongatum chromosomes and Triticum aestivum chrormosomes. Can. J. Genet. CytoL. 22: 237-259. KNOTT, D.R., J. DVORAK and J.S. NANDA 1977. The transfer to wheat and homoeology of an Agropyron elongatum chromosome carrying resistance to stem rust. Can. J. Genet. Cytol. 19: 75-79. MURASHIGE, T. and F. SKOOG 1962. A revised medium for rapid growth and bioassay with tobacco tissue culture. Physiol. Plant. 15: 473-497. PIENAAR, R. de V., H.S. ROUX, E.C. VERMEULEN and M.G. LOMBARD 1977. An intergeneric hybrid from the cross bread wheat (Triticum aestivum L. em. Thell. v. aestivum cv. Chinese Spring) x Coastal wheat grass (Agropyron distichum (Thumb.) Beauv.). Proc. 6th Congr. S. Agr. Genet. Soc. p. 76. SEARS, E.R. 1977. Analysis of wheat - Agropyron recombinant chromosomes. Proc. 8th Eucarpia Congr., Madrid, Spain. pp. 68-72. SMITH, E.L., A.M. SCHLEHUBER, H.C. YONG and L.H. EDWARDS 1968. Registration of Agent wheat. Crop Sci. 8: 511-512. |
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