Plant-Fungal Symbioses: Climate Change, Applications for Plant Production, and Farmer Education

Abstract

Climate change is associated with increasing challenges for the wild and agricultural ecosystemson which humans depend. In our most diverse forests and in agricultural lands, rising temperatures, shifts in precipitation regimes, and growing pressure from pathogens and pests represent major challenges that will impact the supply of food, fuel, fiber, and ecosystem services worldwide. Although the effects of climate change on plant communities have been studied previously, their particular effects on plant-microbe symbionts are less understood. Plant symbioses with microbes, especially microscopic fungi, are vital for plant resilience, productivity, and survival in all ecosystems. In my dissertation I examine how climate change impacts aspects of plant-fungal associations, with a focus on two main environments: wild tropical forests, which are storehouses of biodiversity; and agricultural systems, the immediate sources of the plant products we need for human use. Specifically, my work focuses on understanding (1) how hurricane disturbances affect the diversity and composition of fungal symbionts associated with roots and leaves of tropical forest trees, with a focus on Puerto Rico; (2) how fungal symbionts can protect cultivated plants against heat stress and disease under a rapidly warming climate, with a focus on Lactuca sativa, an important crop in Arizona; and (3) how gaps in knowledge about plant pathogens merit attention in areas where tropical and agricultural environments meet, and climate change is felt in all sectors, as in the island of Puerto Rico. In quantifying effects of hurricane damage on fungal symbionts of tropical trees, I used a combination of fieldwork, next-generation sequencing, and statistical approaches to study fungal endophytes (fungi that live within healthy plant tissues without causing disease). I found a significant relationship between foliar endophyte richness and hurricane damage, with evidence that severe damage to forests is associated with decreases in symbiont biodiversity. To understand how such symbionts can impact plant health I transitioned to an economically important cultivated crop. I selected endophytic fungi isolated from Lactuca serriola (prickly lettuce), a weed that grows in hot locations and shows no signs of disease. I then used a series of in vitro and greenhouse experiments to evaluate whether these endophytes could colonize and impact the health of cultivated lettuce (Lactuca sativa) in response to heat stress and disease caused by a pathogen (Fusarium oxysporum f. sp. lactucae, FOL). Bioassay results showed inhibition of FOL by all of the focal endophytes and indicated that they were non-pathogenic to L. sativa. One endophyte enhanced stress-tolerance in L. sativa and significantly reduced disease severity of FOL. This endophyte represents an important focus for future research, as it may have important crop-improvement capacity for cultivated lettuce in our rapidly changing world. Finally, based on my growing interest in Extension and growing threats to agriculture in Puerto Rico due to increases in hurricane activity and pest pressure, I assessed the needs and knowledge of Puerto Rican farmers regarding the control and management of pests and pathogens in the field, with the goal of customizing educational workshops that fit the needs of farmers in the island. With Institutional Review Board approval, my study employed a questionnaire to improve understanding of the main problems faced on farms in Puerto Rico. I developed a plant pathology lesson plan that introduces basic concepts in plant pathology and disease management. This enhances Puerto Rican farmers’ knowledge and adaptive capacity, increases accessible education to underrepresented farming communities, and provides extension educators and interested institutions with open access to educational materials – all increasingly important in a world marked by climate change.