|I. Research Notes
Polyploids and aneuploids of Triticum dicoccum var. Khapli produced by N2O-treatment
H. KIHARA and K. TSUNEWAKI
National Institute of Genetics, Misima, Japan
Ostergren reported in 1954 that N2O treatment is effective for the production of polyploids in Crepis. NYGREN (1955) and OSTERGREN (1957) obtained by the same treatment good results in Melandrium and Phalaris, respectively.
The present authors (1960) applied Ostergren's method to an Emmer wheat, T. dicoccum var. Khapli and obtained polyploids and aneuploids from almost all florets treated under the optimum condition.
In this note, performance as to fertility and other characters of the first generation of N2O-treated Khapli and the chromosomal constitution of the offspring are reported.
First generation Plants in the first generation after N2O - treatment were checked as to their chromosome number in root-tip mitoses and were cultivated in the greenhouse. Their performance as to plant height, seed fertility and some other characters was recorded, as summarized in Table 1, in which the plants are grouped in respect to their chromosome number.
The monosomic plants were more slender and shorter than the disomics, and their seed-fertility was extremely low in comparison with that of the latter. A plant having a telocentric chromosome and one with mixed chromosome numbers (2n=27 and 29) showed also very low seed-fertility. A trisomic plant showed a weaker vigor than the disomics but its seed-fertility was normal and it produced many seeds. Two plants having extremely aberrant chromosome numbers (2n=31 and 2n=47) were very weak and did not bear any seed. A11 autotetraploids (2n =56) and hypotetraploids (2n=55 and 2n=54) had stiffer and thicker straw than the disomics and showed low fertility.
Offspring The chromosome number of the offspring was cytologically investigated in root-tip cells. The results of the investigation are summarized in Table 2.
In the control (Group 1) no aberrant offspring were found. Progenies of two monosomics consisted of 12 disomics and one trisomic but no monosomics were recovered. The trisomic seemed to be produced from an aberrant meiosis in the monosomic parent as is known in monosomics of common wheat. A plant, whose roots were a mosaic of mono-and trisomic cells, gave in its offspring four plants, one of which was monosomic. Since the seed-fertility of those monosomics including the mosaic plant was about 25%. the very low transmission rate of the monosomic condition in this Emmer variety was seemingly due to strong selection against chromosome-deficient gametes and/or zygotes.
The trisomic plant produced 17 descendants among which two trisomics were recovered. The transmission rate of the trisomic condition is also significantly lower than that known in common wheat.
These facts suggest that it will be very difficult to establish an aneuploid series in Emmer wheat and that both monosomic and trisomic analyses will mean hard work.
All tetra- and hypotetraploids produced offspring which were also tetra- or hypotetraploids (2n=51-61). In these groups, there was on the average a strict correlation between the chromosome number of the parents and that of the offspring. The 56-chromosome khapli, being fairly stable in respect to the chromosomal constitution of the offspring, can be used for further genetic investigations.