CÓRDOBA NATIONAL UNIVERSITY
College of Agriculture, P.O. Box 509, 5000 Córdoba, Argentina.
J.G. Astolfi, I. Robbiano, M.N. Casanova, G. Manera, and R.H. Maich.
Conducting a plant breeding program under rainfed conditions it is not a natural enterprise. Slow genetic progress is the result of the presence of 'G x E' interactions, grain-yield component compensation, and the enigmatic origin of drought tolerance. However, increasing breeder efficiency is necessary in order to satisfy the world's food requirements. With the objective to measure changes in agronomic characteristics after eight cycles of a recurrent selection program, 90 S1-derived families (10/cycle) and 10 commercial cultivars were grown under the rainfed conditions of the central semiarid region of Argentina. Taking into account the more progressed cycles of recurrent selection (C7 and C8), a significant increment of 17.9 % was observed for spike biomass (C7). Similarly, increases of 20.9 % (C7) and 18.6 % (C8) were measured for spike straw. Several workers have found positive associations between the number of grains and dry weight of spikes/m2 in response to the phenotypic variation in the absence of water or nutritional limitations. However, establishing a direct relationship between the tendency to increase spike dry weight and genetic progress for grain yield should be cautiously considered.
R. Argenti, V. Davidenco, A. Masgrau, and R.H. Maich.
Our objective was to evaluate the actual agronomic performance in bread wheat and hexaploid triticale (X Triticosecale) using a selection index constituted by eleven traits measured at the plot level. Two samples of 118 S0 hexaploid triticale and 111 S0 bread wheat progenies were sown under rainfed conditions. A disruptive selection intensity of 17 % (triticale) and 18 % (bread wheat) was applied in both directions on the frequency distributions for the selection index. The 40 S1 triticale families (20/group) and 40 S1 bread wheat families (20/group) were evaluated during 2005. Grain and biological yield (gr/m2), spikes (#/sq m), and harvest index (%) were measured. Differentials and responses to selection were estimated from the S0 progenies and S1-derived families, respectively. Significant differences (P < 0.05) between the higher and lower index group mean values were observed in both species for all the variables except harvest index. In addition, mean values corresponding to the higher group were greater than those observed in the lower one. Taking into account previous results (Cereal Res Commun: in press) where realized heritability estimates were approximately 6-7 % obtained under good environmental conditions, the estimates were higher despite the more severe conditions of cultivation.
S.P. Gil, M.E. Reyna, C.S. Perrone, M.M. Cerana, and R.H. Maich.
We currently are analyzing eight cycles of recurrent selection in bread wheat. The plants were grown in the semiarid conditions of the central region of Argentina at the Experimental Farm of the College of Agriculture in Córdoba (31^o^ 29'S and 64^o^ 00'W) during 2005. We compared the C0 (initial); C1, C2, C3, C4, C5, C6, and C7 (intermediates); and C8 (more advanced) cycles. The variables measured were spike length; spike internode length; and length, width, and area of flag leaves. Data were evaluated with ANOVA and Duncan's Multiple Range Test (P < 0.05).
The results indicated that the C8 spike length was higher than other cycles with the longest spike internodes. With respect to leaves, the more evolved cycle had shorter flag leaves but wider and higher areas, regardless of the degree of significance. The shortening of the flag leaves in the more advanced cycle was observed after studying the morphological changes after three and six cycles of recurrent selection. Perhaps this behavior could be related to the plant adapting to stress conditions.