Selection for yield increase in population and inbred lines of corn (Zea mays), resistent to common rust (Puccinia sorghi)

Abstract

Six inbred lines of corn resistant to Puccinia sorghi (Schw.), were introduced from the United States of America and crossed onto eight local lines and one single cross, also resistant, plus onto seven susceptible local lines. The resulting F₁s were the beginning of a population “Seleção Rp" aimed at a combination of good yielding capacity with the presence of a large number of genes for resistance likewise, the same F₁s were the beginning for isolation of inbred lines for hybrid production. Population "Seleção Rp", iniciated by seed mixture and open polination of the F₁s, was divided in two sub-populations - "Seleção Rp duro" (flint) and "Seleção Rp dentado" (dent) - within both of which individual selections were made. Individual selections, their best progenies, and "Seleção Rp duro" progregenies crossed with a bulk of "Seleção Rp dentado" progenies, were tested for yield. Yield increase after these three generations was 16.6% and genetic variability decreased from 34,3% to 9.8%. Yield reached 76.3% of the check variety, "Sintetico IPEACS". S₆ inbreds were crossed to the inbred 669/62 as tester. "Seleção Rp" after three generations of selection was crossed to "Composto duro" and "Composto dentado" from the ESALQ (Piracicaba). Yield trials were conducted in Paracambi (Rio de Janeiro) and Itabuna (Bahia). "Seleção Rp", in Paracambi, yielded only 45.2% of the best hybrid and in Itabuna, 29.7%. Its crosses to the flint and dent “Compostos" yielded nearly the same as the original "Compostos". In the two localities, the rank the treatments were nearly the same; the very same entries being in the first and two last ranks of classification.