PUTATIVE ROLE OF PHOTODIMERIZED PHENOLIC-ACIDS IN MAIZE RESISTANCE TO OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE)

Five genotypes of maize were grown under three light regimes in the field. Artificial infestation with European corn borer, Ostrinia nubilalis (Hubner), egg masses resulted in greater leaf feeding damage for plants grown under a UV absorbing plastic (UV-) than for the same genotypes grown under UV transmitting (UV+) plastic or in the open. Leaf bioassays performed on tissue from the three different light regimes showed similar trends. Foliar nitrogen content was reduced as much as 15% for UV- plants. 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one levels were consistently higher in UV- plants as were the levels of cell-wall-bound hydroxycinnamic acids (HCA). Light-activated dimers of HCA called truxillic and truxinic acids were lower in UV- plants. These results indicate that cell-wall-bound truxillic and truxinic acids are an additional resistance mechanism that provide an explanation for increased susceptibility of greenhouse grown plants to folivores.