Environment of Origin and Domestication Affect Seed Germination, Root Morphology, and Response to Water Deficit in Chile Pepper (Capsicum annuum L.)
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Date
2022-03
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Abstract
Global climate change threatens agriculture by increasing precipitation variability and drought. To mitigate these risks, we can improve crop tolerance to abiotic stresses, such as soil water deficit, through genetic improvement utilizing unique sources of tolerance. Landraces, or traditional varieties from crop centers of origin, often have adaptations to their specific environments and the associated abiotic stresses. Chile pepper (Capsicum annuum L.) landraces grow across a wide range of environments in their native Mexico and provide a unique opportunity to study drought adaptation. Previous work suggests that chile landraces from Mexico have adaptations that contribute to water deficit tolerance, specifically in above-ground traits such as plant biomass and architecture. However, there is a lack of study on below ground adaptations to drought, likely due to the challenging nature of root experiments. Root traits, such as high root length or small diameter, play an important role in water deficit tolerance by improving the efficiency of water uptake.
In the present study, we explore seed germination, early-stage root growth and their responses to osmotic stress in a selection of chile pepper landraces from diverse environments of origin throughout Mexico. Additionally, we evaluate differences across levels of domestication by comparing wild-like landraces collected from forest environments alongside landraces collected from backyards. In the first experiment, seed from twelve accessions (individual landrace entries) were grown in a randomized complete block design in growth chambers. A water stress treatment was applied using polyethylene glycol (PEG) to simulate osmotic stress (two levels: untreated water and 20% PEG solution). Seed germination was monitored for 14 days, and germination percent reported. A second experiment studied the effect of greenhouse water deficit on nine of accessions grown in a randomized complete block design and subjected to well-watered and water deficit conditions (70 and 30% of field capacity, respectively). Five weeks after transplant, plants were destructively harvested, and soil was carefully cleaned from the root system. Roots were scanned using Winrhizo software (Regent Instruments Inc.) and total root length, average root diameter, root biomass, specific root length (SRL; total root length/root biomass), and root to shoot ratio are reported. All data were analyzed in R (v. 4.1.2), using linear mixed models and data was transformed as necessary.
Total root length was significantly reduced under water deficit (p < 0.05). A significant interaction was identified between accession and water treatment for germination percent (p < 0.05) and SRL (p < 0.1). Regression analysis with environmental parameters from the environment of origin indicate a significant relationship between germination percent, stress treatment, annual precipitation, and precipitation seasonality. Root diameter and weight also had significant relationships with stress treatment and total available soil water of the environment of origin. Finally, germination percent, root length, diameter, and SRL were all significantly lower in forest accessions, while root weight and root to shoot ratio were significantly higher.
Results provide evidence for drought adaptations in seed germination and root traits that could indicate tolerance to soil water deficit. For example, we observed a significant reduction in root diameter under water deficit in accession Ca0181, which originates from a low precipitation environment and could be exhibiting an adaptive response through improved water uptake efficiency often associated with a smaller root diameter. Significant relationships with environmental parameters such as annual precipitation, precipitation seasonality, and total available soil water provide evidence for environmental adaptations in seed germination and root traits. Additionally, root traits appear to be significantly influenced by domestication, despite water treatment. Smaller root diameter and high root to shoot ratios in forest accessions suggest possible adaptations that improve water uptake in less domesticated accessions. Chile root morphology and architecture is a relatively under studied subject. This work provides insight into chile root growth under water deficit and identifies accessions with possible tolerance. It also provides evidence for adaptations to drought suggesting that environmental parameters and level of domestication are effective ways of identifying tolerant germplasm. Results will be useful in continued studies on adaptations and may have direct implications in breeding for water deficit tolerance.
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Food, Agricultural, and Environmental Sciences (FAES): 3rd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
chile pepper, Capsicum, drought adaptation, water deficit tolerance, root morphology