Improvement of Resistance to Ear and Stalk Rots and Agronomic Traits in Tropical Maize Gene Pools

Abstract

Ear and stalk rots of maize (Zea mays L.) caused by Fusarium moniliforme (Sheldon) limit maize production in the lowland tropics. A modified ear‐to‐row (MER) selection scheme was used, with minor changes, to improve resistance to these diseases and five agronomic traits in eight tropical maize gene pools. Six pools were selected for stalk‐rot resistance (SRR) and two for ear‐rot resistance (ERR). Each pool included approximately 500 half‐sib (HS) families, and the selection intensity among and within families was adjusted so as to maintain this population size during each cycle of selection. Family selection was based on single‐row plots of 16 to 21 plants in one or two environments. Data on grain yield, plant and ear height, days to 50% silking (DS), lodging, disease and insect reaction, and plant and ear uniformity were recorded at appropriate stages of plant development. One cycle of selection was completed season−1. Selection for disease resistance was practiced under artificial inoculation. Averaged over pools, progress from selection (linear response) was 2.50** (significant at the 0.01 probability level), −0.15**, −0.35**, −1.66**, and −0.90% cycle−1** for yield, DS, plant height, SRR, and ERR, respectively. Yield improvement (linear response) averaged higher in pools selected for SRR (3.02% cycle−1**) than in those selected for ERR (1.38% cycle−1**). In the reduction of DS and plant height, however, greater progress was made in pools selected for ERR (−0.50** and −0.75% cycle−1**, respectively) than in those selected for SRR (−0.04** and −0.25% cycle−1**, respectively). Results indicate that the MER selection scheme employed by the International Maize and Wheat Improvement Center (CIMMYT) was effective in increasing grain yield, SRR, and ERR; and in reducing DS and plant height in maize.