Guangyao Wang

Investigation of the Influence of Leaf Thickness on Canopy Reflectance and Physiological Traits in Upland and Pima Cotton Populations

Many systems for field-based, high-throughput phenotyping (FB-HTP) quantify and characterize the reflected radiation from the crop canopy to derive phenotypes, as well as infer plant function and health status. However, given the technologys nascent status, it remains unknown how biophysical and physiological properties of the plant canopy impact downstream interpretation and application of canopy reflectance data. In that light, we assessed relationships between leaf thickness and several canopy-associated traits, including normalized difference vegetation index (NDVI), which was collected via active reflectance sensors carried on a mobile FB-HTP system, carbon isotope discrimination (CID), and chlorophyll content. To investigate the relationships among traits, two distinct cotton populations, an upland (Gossypium hirsutum L.) recombinant inbred line (RIL) population of 95 lines and a Pima (G. barbadense L.) population composed of 25 diverse cultivars, were evaluated under contrasting irrigation regimes, water-limited (WL) and well-watered (WW) conditions, across 3 years. We detected four quantitative trait loci (QTL) and significant variation in both populations for leaf thickness among genotypes as well as high estimates of broad-sense heritability (on average, above 0.7 for both populations), indicating a strong genetic basis for leaf thickness. Strong phenotypic correlations (maximum r = −0.73) were observed between leaf thickness and NDVI in the Pima population, but not the RIL population. Additionally, estimated genotypic correlations within the RIL population for leaf thickness with CID, chlorophyll content, and nitrogen discrimination (r^gij = −0.32, 0.48, and 0.40, respectively) were all significant under WW but not WL conditions. Economically important fiber quality traits did not exhibit significant phenotypic or genotypic correlations with canopy traits. Overall, our results support considering variation in leaf thickness as a potential contributing factor to variation in NDVI or other canopy traits measured via proximal sensing, and as a trait that impacts fundamental physiological responses of plants.

Characterizing the Response of Irrigated Cotton to Hail Damage through Canopy Reflectance Measurements in Arizona

Cotton production in Arizona can experience hail damage in the summer in a time of very active growth. The current method of loss assessment is based on visual inspection that relies on the experience of the insurance adjuster. Through the use of sensor technology, the evaluation system can be greatly improved in the areas of spatial coverage and standardized analysis, with significant time and cost savings. This paper describes research carried out in central Arizona in irrigated cotton during the 2008 growing season. The goal of this project was to characterize through canopy reflectance measurements the crop response to hail damage simulated by manual branch removal. The treatments included a control and 25, 50, 75, and 100% removal of fruiting branches at three growth stages: 0, 14, and 28 days after flowering. The instrumentation included a 16-channel radiometer manufactured by CropScan programmed to scan in a range from 460 to 880 nm. After branch removal treatments, the canopy was scanned up to four times in a time period of 20 days. Preliminary results show that plants responded to the intensity of branch removal with different growth rates. Pending yield data will be added to the final analysis.