Temperature effects on circumnutation, host location and host acquisition by the parasitic plant Cuscuta campestris (Convolvulaceae)

Background/Question/Methods

Parasitic plants—which survive by extracting resources from other plants—play important roles in shaping natural and agricultural communities. But despite their ecological and economic significance, key aspects of the ecology of parasitic plants remain poorly studied. A good deal of previous research has explored the mechanisms by which parasites exploit their hosts, but relatively little is known about how environmental factors influence the critical stages of parasite growth preceding host acquisition. Seedlings of parasites in the genus Cuscuta (commonly called dodder) actively “forage” for hosts via directed growth toward light and odor cues from nearby host plants. We examined how the foraging behavior and success of C. campestris, a serious agricultural pest of more than 25 crops in 55 countries, is influenced by variation in temperature. In a series of experiments using reach-in and walk-in growth chambers, we manipulated ambient temperatures (between 15 and 45°C) and documented the effects on seedling circumnutation patterns, rates of host location success and rates of host acquisition success. 

Results/Conclusions

At higher temperatures, the average period of circumnutation (time required for one complete rotation) of C. campestris seedlings was significantly reduced: the rate of rotation was nearly twice as fast at 25°C compared to seedlings at 19°C.  Furthermore, when the temperature treatment was switched partway through the experiment, seedlings reacted with an average period of circumnutation as predicted by the corresponding temperature treatment (i.e., faster rotation in warm temperatures and slower rotation in cool temperatures).  Location of tomato hosts by foraging C. campestris was not directly influenced by temperature, as successful host location was observed across multiple temperatures tested.  Successful host acquisition by the parasite (confirmed by the formation of either prehaustoria or mature haustoria) appears to degrade at temperatures above 35-37°C, depending on the presence of absence of early tactile cues from the host.  These results suggest realistic changes in temperature can be an important factor driving parasitism success of dodders.  Moreover, this work helps elucidate the reactions of this noxious weed to a changing environment.