| Effects of nitrous acid on germinating seeds of Triticum
monococcum (negative results)
T. FUJII National Institute of Genetics, Misima, Japan OESTERGREN (1957) and NYGREN (1955) obtained polyploids in Phalaris, Crepis and Melandrium by treatment with nitrous acid. Recently, KIHARA and TSUNEWAKI (1960) obtained tetra- and aneuploids in Emmer wheat in the same way. This method was applied by the present author to germinating seeds of Triticum monococcum L, var. flavescens KOERN. 60 seeds for each lot were soaked in water at room temperature. Germinating seeds were picked up 24 and 48 hours after the start of the experiment and were treated with nitrous acid for 8, 16 and 24 hours, each treatment at the pressure of 3 and 5 atmospheres. (Viable seeds showed a developing embryo after 24 hour treatment which was not observed in dead seeds.) Details of treatments and growth behaviour are shown in Table 1. Nitrous acid treatment apparently does not affect either germination or survival rates and seedling length or the number of offshoots. Induction of polyploidy was examined by the observation of chromosomes at MI with smear technique. All spikes, except two, had seven bivalents like those of the control lots. Thus tetraploids or any kinds of chromosome irregularities were not obtained. One plant in each of the lots subjected to 6 atm. for 24 hours and 3 atm. for 8 hours was haploid but this was not due to the effect of nitrous acid because sporadical appearance of haploids is known in T. monococcum. According to the results of KIHARA and TSUNEWAKI, nitrous acid treatment is very efficient when it is given 24 hours after pollination, when the first meiotic division is taking place. Treatments for 10 hours or longer produced tetra and hypotetraploids in about 70 per cent or more of the treated plants. Their number was increased to 98 per cent by treatment at 6 atm. pressure for 15 hours. But on the basis of my cytological observation the upper confidence limit on the proportion of induced polyploids at the 95 per cent level was calculated as 0.8 per cent. Nitrous acid did not produce polyploidy when it was applied to germinating seeds for up to 24 hours at pressures of 3 and 6 atms. But polyploid plants may be produced by subjecting germinating seeds or some other growing stage to more intensive treatment. Corrections: Instead of "nitrous acid" read "nitrous oxide". |