Studies on Sequential Parasitism by Orobanche and Cuscuta on Petunia hybrida

Parasitism by Cuscuta and Orobanche on Petunia hybrida resulted in decreased choline kinase activity and phospholipids in the host shoots. The Cuscuta-infected host roots suffered a decline in phospholipid concentration with no appreciable change in enzyme activity, whereas the roots of the Orobanche-infected plants exhibited a substantial increase in phospholipid concentration despite a marked lowering in enzymic activity. Superimposition of infection by Cuscuta on Orobanche-infected plants resulted in an increase in both enzyme activity and phospholipid in host shoots; the host roots recorded a decline in phospholipid, although enzyme activity was increased. As compared to the filaments infecting singly, Cuscuta, in sequential infection, registered an increase in phospholipid concomitant with a fall in enzyme activity, whereas the root parasite revealed a lowered enzyme activity and a slight decrease in phospholipid. It is hypothesized that a physiological response to infection by root parasite was an accumulation of phospholipids at the region under infection, and to that by shoot parasite was an uptake of phospholipids by the parasite from the host; this was effected not by de novo synthesis but rather by mobilization from distal regions.