New generation maize inbred lines resistant to diplodia ear rot, caused by Stenocarpella maydis (Berk) Sutton

Abstract

In an attempt to obtain superior levels of resistance to Stenocarpella maydis ear rot, three elite maize inbred lines (DO620Y, E739 and B37) from different genetic backgrounds that had previously been shown to have useful levels of resistance were crossed in all combinations. Additionally, two susceptible experimental maize populations were crossed to a resistant experimental inbred line as donor parent. Progeny in each of the five populations was selfed and selected for resistance over five successive generations, following artificial inoculation of plants at the localities Potchefstroom, Cedara and Hazyview. The five populations progressed from the S1 during 1997/98 to the S5 during 2000/01. A progressive improvement in resistance occurred over seasons in all progenies. After three cycles of selection, approximately 50% of the selections showed less than 10% infected ears, with a total of 84 selections showing no infection. Selections displaying the lowest disease incidence at any one locality were not necessarily the most resistant at another locality, possibly owing to significant pathogen × environment interactions. It is therefore possible that resistance in new generation inbred lines may be more stable than in the donor parents. Using I137TN as tester, a number of resistant selections were identified during 2001/02 that had combining ability for yield that compared favourably with commercial standards.