Impact of donor QTL on grain yield and gray leaf spot of four recombinant inbred lines of maize

Improved maize (Zea mays L.) hybrids must possess both high grain yield (GY) and disease resistance for commercial production. Four recombinant inbred lines (RILs) with resistance to a gray leaf spot (GLS, caused by Cercospora zeae-maydis Tehon & E. Y. Daniels) were developed from a cross between YML32 (resistant) and Q11 (susceptible). Three RILs (RL1_1, RL1_2, and RL2_1) contained a resistance-carrying DNA segment (RDNAS); the fourth RIL (RL2_2) did not possess RDNAS. Five testers (four RILs and Q11, male) were crossed with 13 maize lines (female) of three known heterotic groups and tested in 2016 (2016 experiment; results published in 2018). In the current study, we crossed the 21 lines (female, 13 previous lines plus eight new lines, 2018 experiment) with the same five testers (male). The objectives were (a) to determine if GY of the testcrosses, especially with RIL2_2, and GY heterosis were improved over the testcrosses with Q11, and (b) to compare the results of the 2018 and 2016 experiments to know if different years and/or additional maize lines affected GY. The GY of the crosses with the four RILs and the GY heterosis of testcrosses were improved over the crosses with Q11 in the 2018 experiment, mainly because of low GLS score. RIL2_2, lacking the RDNAS, possessed GLS resistance genes different from those in the three RDNAS-carrying RILs. We concluded that at least 20 lines representing different heterotic groups should be crossed with new RILs and that a second year of testing would be desirable to obtain reliable estimates of GY of the new RILs and to identify new high-yielding hybrids.