Alexandru BARBULESCU, Octavian COSMIN and Ioan SABAU
Research Institute for Cereals and Industrial Crops Fundulea
8264 Fundulea, District Calarasi, Romania

In Romania, the most important yield losses caused by the European Corn Borer are due to its stalk attack. This report is ongoing with research started at Fundulea in 1975 referring to the development of maize inbred lines resistant to the borer, also having satisfactory agronomic characters, stressing achievements obtained in the last experimental years.
After several previous cycles of crossing and screening for insect resistance, maize inbred lines with a pronounced resistance and increased agronomic characters have been obtained. By crossing these inbred lines with maize forms with acceptable levels of agronomic performance new hybrid combinations were achieved. From these, annually, over 700 lines were submitted to self-pollination under artificial infestation (10 plants for each line with 5-6 egg-masses per plant), retaining only lines showing reduced attack level and suitable agronomic traits. Some inbred lines showing representative attack values were infested with 20 egg-masses per plant. The attack score used the length of tunnels bored in stalks (cm), and the number of larvae per stalk, as counted in autumn by splitting plants.
It was found that after over 20 years of investigations on maize resistance to Ostrinia nubilalis inbred lines demonstrating constantly reduced attack by the borer have been obtained. Taking into account the data of the last three years of the experiment it is noticed that the attack produced by European Corn Borer was 14-fold lower, in maize resistant inbred lines as compared to that of highly susceptible lines. Some inbred lines showed a certain resistance degree even at a very severe attack. These lines showed a high combinative value and superior agronomic traits. By crossing some of these inbred lines, tolerant hybrids to the borer attack were achieved. Although one of these hybrids had a low level of borer attack, however Monsanto hybrid-Dekalb 512 Bt showed no damage caused by the borer.