IMPACT OF DROUGHT STRESS AND TEMPERATURE ON THE PARASITIC WEEDS STRIGA-HERMONTHICA AND ALECTRA-VOGELII IN THEIR EARLY GROWTH-STAGES

The effect of simulated drought on the germination of Striga hermonthi ca and Alectra vogelii was studied in growth cabinets. Drought stress was applied either during the preconditioning of the seeds or at the t ime of application of the germination stimulant. The response of these weeds to a range of alternating day/night temperatures during germina tion and their attachment to the host plant was also investigated usin g root chambers. During the preconditioning period S. hermonthica was not sensitive to variation in osmotic potential between 0 and -1.5 MPa but A. vogelii required longer preconditioning periods at -1.2 and -1 .5 MPa. The germination of both parasites was significantly reduced by increasing the osmotic potential of the stimulant. Optimum day/night temperatures for germination and attachment of S. hermonthica were 30/ 20-degrees and 35/25-degrees-C, and of A. vogelii 25/15-degrees and 30 /20-degrees-C. Deviation in temperature from the optimum significantly reduced the germination and attachment of both parasites. The results show that S. hermonthica is more adaptive to adverse climatic conditi ons of increased osmotic potential and extreme temperatures than A. vo gelii.