INCOMPATIBILITY OF CUSCUTA HAUSTORIA WITH THE RESISTANT HOSTS - IPOMOEA-BATATAS L AND LYCOPERSICON-ESCULENTUM MILL

Establishment of haustorial connections with the resistant host is qui te difficult. Host resistance to Cuscuta infection was considered at t wo levels: (i) at the surface of host and (ii) during the haustorial b ursting and its connection with the vascular bundles of the host. Feel ings of the two resistant hosts Ipomoea L. and Lycopersicon esculentum Mill. analysed were found to contain strong inhibitors of cell-wall d egrading enzymes (CWDE). The CWDE, i.e. cellulase (EC 3.2.1.4), polyga lacturonase (EC 3.2.1.15) and xylanase (EC 3.2.1.8), were studied in t he haustoria bearing region of Cuscuta and in different parts (peeling s, peeled and unpeeled) of the stem/petiole of resistant hosts. Feelin gs showed no detectable activity and the peeled portion showed high ac tivity, while unpeeled tissue occupied an intermediate position. Mixed enzyme preparations of the haustoria-bearing region of Cuscuta and th ose of different parts of the stem/petiole of resistant hosts indicate d chat the Feelings contained strong inhibitor(s) of CWDE of Cuscuta, providing a defence mechanism to the host against haustorial penetrati on. Although haustorial penetration in the peeled host tissue becomes comparatively easy, the haustorial bursting inside the host tissue and subsequent connection with the host vascular bundle is prevented. Thu s, the defence mechanism appears to be spread throughout the resistant host tissue.