ROLES OF OXALIC AND MALIC-ACIDS IN CHICKPEA TRICHOME EXUDATE IN HOST-PLANT RESISTANT TO HELICOVERPA-ARMIGERA

Effects of malic acid and oxalic acid on oviposition of Helicoverpa ar migera were investigated in a laboratory cage choice experiment. Malic acid stimulated oviposition at a concentration of 0.6 mu mol/cm(2) bu t inhibited it at 3.4 mu mol/cm(2). Oxalic acid showed neither stimula tion nor inhibition of oviposition at 0.25-1.7 mu mol/cm(2). Correlati ons between the amount of these acids in trichome exudate on leaf and pod surface and H. armigera populations and pod damage were investigat ed in a field experiment using 14 chickpea genotypes. Malic acid on th e leaves stimulated oviposition during the vegetative and flowering st ages, when its concentration was 0.1-0.7 mu mol/cm(2). Later, during t he podding stage there was no significant correlation between either e gg density or pod damage and malic acid levels. However, there was a s ignificant negative correlation between pod damage and oxalic acid lev els. Oxalic acid, which had been reported to have an antibiotic effect on H. armigera larvae, has an important role in resistance to this pe st in chickpea. The length of the podding period was also a factor inf luencing the extent of pod damage; a longer podding period resulted in prolonged exposure to H. armigera attack and more pod damage.