Convergent improvement with four inbred lines of corn

It was possible by convergent improvement to make a marked improvement in the recovered lines in vigor, in resistance to smut and lodging, and in soundness of the ear in those instances where the original lines were lacking in these characters. The majority of the recovered lines yielded significantly higher in crosses to the recurrent parent than the original recurrent parent. It seems that a portion of the genotype of the non-recurrent parent was retained with ease by selection in the backcross progenies in 2- and 3-year backcrosses and in the one 4-year backcross. Some recovered lines yielded as well as the original F1 cross when tested in crosses with the non-recurrent parent. It seems that a number of the lines in these backcrosses had recovered sufficient amounts of the recurrent parent genotype to combine well with the nonrecurrent parent. No relationship was found between the performance of the recovered lines when crossed to the recurrent parent and their performance when crossed to the non-recurrent parent. In this study there was no apparent difference in the performance of the recovered lines from 2-year, 3-year, and in the one instance the 4-year backcrosses. From their appearance the recovered lines seemed to approach the appearance of the recurrent parent rather rapidly. It appears that two or three generations of backcrossing are enough to recover a sufficient amount of the genotype of the recurrent parent. One group of 4-year backcrosses used in this study did not seem different from the 2- and 3-year backcrosses in that same line. It was possible to obtain single crosses between recovered lines which yielded significantly higher than the original F1 cross. The chances of obtaining high-yielding crosses was greatest when the recovered parental lines had been high or intermediate in combining ability as measured by their yield in crosses to the non-recurrent parent.