| I. RESEARCH NOTES Analysis of cross-pollination in durum wheat A. BOZZINI, F. D'AMATO, L. M. MONTI and G. T. SCARASCIA MUGNOZZA Laboratorio per le Applicazioni in Agricoltura, C. N . E. N., Roma and Istituto di Genetica della Universita, Pisa, Italy In order to test the frequency of outcrossing in durum wheat plants raised from both irradiated and unirradiated seeds, four trials were conducted during two years in the experimental fields of the "Comitato Nazionale per l'Energia Nucleare" at the Casaccia (Roma, Italy). Two recessive clorina (yellow green) mutants of "Cappelli" were used as genetic markers (R4/172 and R4/188). Each of the four trials consisted of three plots, in each of which seeds of chlorina and of the mother line Cappelli (green) were sown in 21 alternate rows (150 seeds per row) in such a way as to have every one of the chlorina rows flanked, on both sides, by Cappelli rows. For one of the three plots, unirradiated chlorina seeds were used; for the remaining two, chlorina seeds irradiated with 9 Kr and 18 Kr of X-rays respectively were sown. The seeds were irradiated at 250 KV, 15 mA, 1425 r/min after being equilibrated at 9 % water content. All chlorina plants in each plot were harvested separately and their spikes were analyzed in the greenhouse for occurence of green seedling, assumedly resulting from cross-pollination with Cappelli. Outcrossing frequency was calculated on both a spike and a seedling basis. In unirradiated materials in the four trials the frequency of spikes with outcrossing events was between 4.96 % and 28.89 %, and the frequency of green seedlings between 1.8 %. and 17.6 %. (outcrossing). An increase over control in the frequency of outcross seedlings was ascertained in the material irradiated with 18 Kr of X-rays, whilst no difference was ascertained between the control and the 9 Kr series. The frequency of outcrossing events in the central portion of each plot was found to be higher than in the peripheral portion, probably because of higher pollen concentration in the center of the plot. Moreover, increase in outcrossing frequency in irradiated material apparently resulted from the reduction in spike fertility induced by irradiation: in the 18 Kr series, the frequency of spikes showing a spike fertility lower than 50 % was 18.18 as opposed to 8.26 % in the control. Reversion of chlorina to green in the two mutants used is rather low, as ascertained by an analysis of chlorina spikes prevented from undergoing cross pollination by bagging. If it is assumed that the frequency of cross-pollination between chlorina plants (which cannot be determined with the present experimental design) is either identical or comparable to that of the outcrossings chlorina x green, the real outcrossing figures in our material are twice or nearly twice those reported. That outcrossing in durum wheat is of normal occurence in the environmental conditions of the Casaccia experimental fields is shown by the cases of cross-pollinations found in our collection of induced mutants. In a total of 223 true-breeding M3 mutant progenies, 34 (15.2%) showed evidence of outcrossing, the frequency of individuals derived from cross-pollination being 9.62 %. It is concluded that careful control of pollination in Triticum durum is necessary both in pure line maintenance and in experiments with mutagenic agents. A detailed paper on the subject will be published in "Genetica Agraria", Pavia. |