CHANGES IN MEANS AND VARIANCES OF QUANTITATIVE TRAITS IN BARLEY DUE TO RECURRENT IRRADIATION

Abstract

In order to generate genetic variability of quantitative traits in barley (Hordeum vulgare L.), seeds of cv. Puebla were irradiated with 60Co gamma rays from 1 to 64 kr during ten generations grown without human selection. To assess the effect of irradiation on means and variances of six quantitative traits, 84 M1 irradiated composites and the original variety were evaluated under a randomized block design with four replications at Chapingo, State of México. The experimental unit was a single row 2.0 m length, 0.30 m between rows and 0.10 m between plants; measurements were made an ten plants per plot. For plant height, stem number per plant, spikelet number per spike, spike length, spike volume and sterility percentage, phenotypic variances generally increased slowly at low recurrent irradiation dosages (1, 8, and 16 kr). At high dosages (48, 56 and 64 kr) the rate of increase of variance was higher than at low dosages until the fifth or sixth generation and it was very small or even negative afterwards. In general, means changed in a similar way as variances. The highest mean increases was observed in spikelet number per spike (11.3 %) and spike length (7.4 %), while the lowest increase occurred in spike volume (5.0 %) and plant height (2.6 %); for the stem number per plant there was a decrease in the mean. At increased dosages the higher increases in the means were found for percentage of sterility (126.0 %), spike let number per spike (12.4 %) and spike length (7.3 %).