PRIMARY HAUSTORIAL DEVELOPMENT OF STRIGA-ASIATICA ON HOST AND NONHOSTSPECIES

Initial interactions of Striga asiatica with a susceptible host and no nhost plants were examined by histological methods. Haustorial develop ment was initiated when radicles of S. asiatica were placed in contact with host or nonhost roots. Reorganization of the S. asiatica root ap ical meristem was rapid and involved the formation of a distal group o f cells that penetrated the host or nonhost root. Penetration of the e pidermis of the host (sorghum) roots and advance into the cortex occur red within 24 to 48 h of inoculation. Penetration of the endodermis by the developing endophyte was delayed for 72 to 96 h after initial con tact. However, upon penetration vascular continuity was established be tween parasite and host. In contrast, interactions with nonhosts provi ded evidence of active resistance mechanisms. Penetration of lettuce, marigold, and cowpea roots by S. asiatica was most frequently arrested in the cortex, and endophytic cells were necrotic 72 h after inoculat ion. Some species-specific differences were observed in the reactions of nonhosts to penetration, although in their general nature the inter actions with S. asiatica were similar.