Resistance mechanism in rice to the midge Orseolia oryzae (Diptera: Cecidomyiidae)

The midge Orseolia oryzae (Wood-Mason) (Diptera: Cecidomyiidae) is a major and endemic pest throughout Asia. The pest is difficult to manage in view of a mixture of biotypes co-occurring in the same location and showing variable response to cultivated rice, Oryza sativa L., varieties and differentials. To develop an understanding of the resistance mechanism(s), studies were initiated during wet 2005 and 2006 in Coastal Karnataka. Antibiosis was the predominant resistance category. The maggots survived but as first instar only on all the resistant genotypes. On susceptible genotypes, larvae reached second instar at 7 d after release, third instar at 14 d after release, and pupal stage at 18 d after adult release. However, in certain resistant genotypes, maggot mortality was evident in the absence of the susceptible plant silver shoot condition. In all resistant genotypes, distinct antibiosis was observed at 14 d after adult release. Antixenosis was evident in few genotypes. So, the midge resistance in rice is manifested as a mixture of antixenosis and antibiosis. Estimation of biochemical constituents in rice shoot apices of selected resistant genotypes revealed higher levels of total phenols and total free amino acids compared with susceptible genotypes. But, the amount of total sugars, reducing sugars, crude proteins, and amino acids were not related to resistance. Biochemical profiles in relation to midge infestation showed increased phenol and decreased proline and indole acetic acid content in the growing apical meristem of resistant genotypes compared with susceptible genotypes.