DISTRIBUTION, HOST-RANGE AND BIOMASS OF 2 SPECIES OF CISTANCHE AND OROBANCHE CERNUA PARASITIZING THE ROOTS OF SOME EGYPTIAN XEROPHYTES

This study involves three species of the family Orobanchaceae: Cistanc he phelypaea, C. tubulosa and Orobanche cernua. These species are obli gate perennial root parasites. They may occur together infecting hosts growing in the following phytogeographical regions: (1) along the Med iterranean coastal belt in deep oolitic limestone sand dunes and in lo amy salt affected ground; (2) southern Sinai; and (3) south-eastern Eg ypt in Gebel Elba. In the Galalah and the Arabian desert regions, the parasite-host associations grow in silt terraces and runnels of the ma in wadis. The three root parasites were recorded to infect 16 differen t host species belonging to eight families from the Dicotyledoneae. Pa tterns of host specialisation occur in both Cistanche species where ab out 50% of their hosts belong to the Chenopodiaceae, while O. cernua e xhibits a wider host range since it infects desert perennials and some cultivated crop plants. Compared to non-infected plants, it is appare nt that Hammada elegans and Anabasis articulata Meg., which are hosts of C. phelypaea and C. tubulosa, respectively, were particularly sensi tive to infection. The reduction in fresh and dry mass of such hosts w as much higher than found in other hosts of Cistanche or O. cernua. Th e water content and succulence ratios of the parasitic species were si gnificantly higher than their hosts and comparable non-infected specie s. The specificity of the parasites towards succulent hosts was higher in both robust species of Cistanche than in the less robust species O . cernua. (C) 1996 Academic Press Limited