There is a significant and apparent dieback of Malosma laurina in the Santa Monica Mountains, some which is found near Pepperdine University. Other areas near Pepperdine show a flourishing growth of M. laurina and our objective was to determine why this difference in M. laurina health exists. We initially hypothesized that in addition to water stress, the unhealthy M. laurina was effected by a pathogen. Under further inspection, the unhealthy plants contained hyphae in some of their xylem vessels, while the healthy ones did not. We sought to determine whether the existence of hyphae in the unhealthy plant’s xylem affected its ability to transport water by measuring the conductance (Kh) of both sick and healthy M. laurina. We created an apparatus that measured water flow through a stem when a known hydrostatic pressure was applied. We also used a vacuum to remove embolism from the stem samples to determine whether the decrease in conductance could be attributed to embolism due to cavitation, or xylem obstruction due to hyphae. Our results showed that the conductance, both pre vacuum and post vacuum, was significantly higher in the healthy M. laurina than in the unhealthy M. laurina. This fact, along with the non significant percent embolism values between the healthy and unhealthy plants demonstrates that there is another factor causing decreased xylem flow in the unhealthy M. laurina samples other than embolism due to cavitation. This conclusion supports our hypothesis that a fungus is involved in the apparent M. laurina dieback.
Palmeri, Gabriella N.; Olsen, Braden S.; Sauer, Kaitlyn E.; and Davis, Stephen D., "Possible Fungal Infection Leading to Malosma laurina Dieback" (2015). Pepperdine University, Featured Research. Paper 206.