Role of indole-3-acetic acid in gall formation in Phytophthora-infected stem of pigeonpea

High content of indole-3-acetic acid (IAA) was detected in tissue of galls formed on pigeonpea stem after infection with Phytophthora drechsleri f. sp . cajani. IAA was in trace in healthy tissues. The amount of IAA in gall ti ssues from naturally infected stems was more (27.3 mug/250 g). The galls fo rmed on naturally infected stem were bigger (8.8 x 4.7 cm) than the artific ially inoculated ones (4.9 x 2.8 cm). The galls were formed only on moderat ely resistant cultivars of pigeonpea. Plants of susceptible cultivars dried from the infection site due to necrosis of host tissues. Resistant cultiva rs showed neither galls nor rotting of stem. Inoculation of pure commercial IAA also induced galls on seems of pigeonpea.