Claire Poore and Faculty Mentor: Ryan Stewart, Plant and Wildlife Sciences
Introduction
Agave and Yucca species are both cultural and economically important in the south western United States and Mexico. As desert plants, Agave and Yucca have adapted to hot and dry conditions and with increasing global temperatures, have the potential to fill even more important roles in modern agriculture1. The Navajo people place immense value on Yucca due to its source for food, twine, hair cleanser as well and its role in religious ceremonies. Agave has long been valued as a crop in Mexico and is used for food, fiber and beverages.
Fusarium oxysporum is a major plant disease and causes vascular wilt in Agave2. Climate changes and disease have reduced Agave production in Mexico for the past few decades3. Adaptive traits of Agave and Yucca have allowed them to thrive in desert communities; microbial communities of plants have been shown to play an important role for adaptive traits in desert plants.
Plant microbiomes play an important role in protecting plant from certain diseases and other threats4. Endophytes are microbial organisms that live inside of plants without causing disease and in many in cases bestow fitness enhancing characteristics on their hosts5. Previous studies have shown that inoculation of endophytes from related species can enhance disease resistance5. This study intends to show a transfer of disease resistance from Yucca to Agave using endophytes. Endophytes have also been shown to increase drought tolerance as well, however, due to sample availability we forwent that aspect of the study.
Methodology
Plant samples were collected, using permits, from the Utah-Arizona border in the Navajo nation. Two leaves from both the outer leaves and inner leaves of each Yucca plant sample were taken along with root samples from each plant. Species collected include, Y. baccata, Y. harrimaniae, and Y. angustissima.
Endophytes were isolated from plant material by cleaning and surface sterilizing the plant material in 70% ethanol solution for different time periods ranging from 1-3 minutes. The difference in time in solution allowed for the ethanol to penetrate through different layers of plant material. After being sterilized, plant material was placed on potato dextrose agar (PDA) and LB plates and allowed to grow for up to a week. Morphologically different colonies of bacteria and fungus were plated and isolated.
Antifungal properties were tested by dual culture plate assays. Mycelium of Fusarium oxysporum was combined with cooled liquid PDA and poured into plates. Candidate fungal and bacterial isolates were grown in liquid culture and were placed in ¼ inch plugs in Fusarium plates. Zone of inhibition was measured in contrast to a control of MiliQ water that had been UV sterilized.
Results
1 fungal and 1 bacterial isolate were identified as potential endophytes that inhibit growth of Fusarium oxysporum. Both isolates were found in root tissues of Yucca sampled; the fungal sample was isolated from Y. baccata and the bacterial sample was isolate from Y. harrimaniae.
Figure 1- Picture A: Control plates with Fusarium oxysporym. Picture B: Fungal isolate inhibition of Fusarium oxysporum
Discussion
Only Yucca samples were taken were taken due to the scarcity of Agave found outside of protected property which forced us to make an adjustment to our initial goals. DNA extractions and sequencing will be completed for the bacterial and fungal isolates that show potential to increase disease resistance. In vivo trials will also be conducted in the future by inoculating plant material with endophytes and Fusarium oxysporum to test if there is any increase in disease tolerance.
Conclusion
In the future traditional pesticides may take a backburner in pest control as synthetic pesticides are becoming less efficient due to gained resistance and public opinion turns against synthetic chemicals. Biocontrol agents are still a growing area of research and can take years to develop. Screening for antifungal properties of endophytic microbes is the first steps in identifying potential biocontrol agents.
Citations
1. Yang, X.H., et al., A roadmap for research on crassulacean acid metabolism (CAM) to enhance sustainable food and bioenergy production in a hotter, drier world. New Phytologist, 2015. 207(3): p. 491-504.
2. Avila-Miranda, M.E., et al., Vascular wilt caused by Fusaritum oxysporum in agave (Agave tequilana Weber var. azul). Journal of the Professional Association for Cactus Development, 2010. 12: p. 166-180.
3. Dalton, R., Saving the agave. Nature, 2005. 438(7071): p. 1070-1071.
4. Massimo, N.C., et al., Fungal Endophytes in Aboveground Tissues of Desert Plants: Infrequent in Culture, but Highly Diverse and Distinctive Symbionts. Microbial Ecology, 2015. 70(1): p. 61-76.
5. Mousa, W.K., et al., Bacterial endophytes from wild maize suppress Fusarium graminearum in modern maize and inhibit mycotoxin accumulation. Frontiers in Plant Science, 2015. 6: p. 19.