Location: Plant Science Research
Project Number: 6070-21600-001-012-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2024
End Date: Sep 30, 2025
Objective:
Objective 1: Identify extreme heat-wave resilient soybean varieties.
Objective 2: Define morphological and physiological traits of heat-wave tolerance.
Objective 3: Develop screening strategies to help soybean breeding programs with generating extreme heat-wave resilient germplasm.
Approach:
1. Screen diverse germplasm for heat wave response
Temperature Gradient Greenhouse (TGG) reconfiguration
The current Temperature Gradient Greenhouse (TGG, size 30.5m x 6.1m) will be reconfigured to two sections: an unheated area and an extreme heat wave area (see below figure). Heating elements and heat distribution panels are indicated in red. The arrows indicate ventilation directions. Each circle indicates a plant. Space calculations show the reconfigured greenhouse has the capacity to grow approximately 250 individual plants, with space to expose 50 plants to “extreme heat wave” conditions for a specified period of time.
Extreme heat wave treatment and harvest
Plants will be grown in pots of well-drained commercial potting mix with slow-release fertilizer and frequent irrigation in the unheated area. Until flowering (R1) or pod-filling (R5) stage, plants will be moved to the extreme heat wave area to experience an extreme heat wave event (+8 °C) for 5 days. After the treatment, the plants will be returned to the unheated area for the remainder of the growing season.
Air temperature and relative humidity will be monitored continuously using sensors maintained at the top of the canopy at multiple locations within each treatment area.
Final yield harvest parameters will include pod number, seed number and size, branch numbers and harvest index. Genetic variation in pod number and seed number will be an indicator of stress effects on reproductive processes.
2. Characterize heat wave-resilient traits.
Assess the correlation of morphological and physiological response with heat wave resilience.
To evaluate plant physiological responses, the Li-6800 (LI-COR) portable photosynthesis system will be employed to measure gas exchange and photosynthesis rates, leaf temperature, chlorophyll fluorescence, water use efficiency (WUE), and vaper pressure deficit (VPD) during the daytime, while the same respiration indexes will be measured at night. Leaf thickness and chlorophyll content will be also measured using the MultispeQ device from PhotosynQ. For morphological assessments, wilting and sudden death syndrome rates will be evaluated during and after extreme heat wave treatments. Number and weight of flat and full pods as well as dry seeds will be measured at the final harvest. The final rating for heat-wave stress responses will be based on seed yield and harvest index.
3. Evaluate impact of heat wave on seed composition.
Seed protein and oil contents will also be measured using near-infrared reflectometry (AD7250, Perton) to determine the effects of elevated temperature during the growing season on seed composition.
The correlation between physiological, phenotypical, and seed composition parameters, as well as final yield, will be analyzed to define possible screening strategies and identify heat-wave tolerant parental genotypes to expedite the breeding process for heat-stress tolerance.
