Laboratory Report 07.30.19

Compiled by Ann Northrup, Plant Pathologist

No Surprise To Gardeners
One of the most recognized weeds in our gardens is believed to express autotomy—that is the sacrifice of a body part in order to survive. Microscopic examination of Oxalis pes-caprae reveals an area at the base of each leaf petiole where the cells are smaller, creating a distinct notch. The tensile strength of the structure at that point measures significantly lower than other points along the petioles. When a leaf is pulled, as might happen when disturbed by a hungry herbivore, or tugged on by an annoyed gardener, the petiole breaks easily at that weak point leaving the buried bulbs and the plant meristem intact, able to continue growing. The detached part, as an added bonus to the plant, the detached part remains viable.

Journal of the Royal Society Interface, 20 February 2019. https://doi.org/10.1098/rsif.2018.0737

 

This Plant Grows On It’s Own Terms
Quite unexpectedly, a rare Japanese orchid, Cyrtosia septentrionalis, was recently found growing in the woods at Longwood Gardens in Pennsylvania. More than one large clump was found, suggesting that the orchid has been in the garden for several years. Due to its stringent growing requirement as an obligate parasitic symbiont with the plant pathogenic fungus Armillaria, the orchid is considered impossible to cultivate. As for its presence in Pennsylvania, long-lived seeds of the orchid are suspected to have hitchhiked along with some other plant acquired from Japan by Longwood Gardens in the past. It just happened to find what it needed in its relationship with the local Armillaria population for its establishment at Longwood. Indeed, the flowering orchid was discovered near the experimental greenhouses where new plant acquisitions would be housed. Squirrels have been observed noshing on the fleshy fruits, and may have some part in the distribution of the orchid at Longwood. For a plant that was once thought impossible to grow, the concern now is that it might be invasive.

https://longwoodgardens.org/blog/2019-01-07/phantasm-forest

 

Termites Mediate the Effect of Drought in Rainforest
Scientists conclude an important message from the results of this study. Intact ecosystems, such as ones including termite colonies as in this study, have “insurance” of sorts against environmental stresses, such as drought. A test site was set up preserving termite colonies in some plots while suppressing termites in other plots during a severe drought in the rainforest of Borneo. Termites need moisture to live and will go to great depths to retrieve moist soil, bringing it closer to the surface. This activity by the termites in the undisturbed plots maintained the overall productivity and health of the forest, whereas the forest plots with suppressed termite activity suffered from the drought.

Science (2018). https://science.sciencemag.org/content/363/6423/174

 

Biological Control Of Invasive Weed Is Complicated
One of Britain’s most prolific introduced weed species, Himalayan balsam (Impatiens glandulifera), is being targeted for suppression management with the use of an extremely host-specific fungal parasite, a rust fungus from the plant’s native Himalayan habitat. As one might expect, there is more than one genotype of the balsam expressing varying degrees of susceptibility to the rust fungus, and more than one strain of the parasitic rust with varying degrees of virulence. Results of recent studies have shown that the composition of microbes harbored inside of the balsam, either as endophytes or mycorrhizae, or the absence of these microbes, also impacts the severity of the rust disease.

Royal Holloway, University of London, January 16, 2019, as reported through Phys.org