Drought Conditions Differently Affect Starch Concentrations in the Stalks of Early and Moderate Maturing Louisiana Sugarcane Varieties

Abstract Sugarcane starch detrimentally affects the manufacture of raw sugar and its subsequent refining. Starch concentrations in field sugarcane have been steadily increasing over the past two decades in Louisiana (LA) and other regions due to (i) the rise in green cane (unburnt) harvesting, (ii) the introduction of new sugarcane varieties with higher starch concentrations, (iii) chemical ripening (depending on the sugarcane variety), and (iv) environmental conditions. Little is known about how abiotic environmental conditions affect starch concentrations in sugarcane. A large 2-year field study was conducted in 2022 and 2023 at the LSU AgCenter Sugar Research Station in St. Gabriel, LA, USA. Drought conditions occurred in 2023 with an average rainfall of 61 cm, which was much lower than the ~ 164 cm that occurred for the normal 2022 year. Field cane of 15 commercial and pre-commercial LA varieties was treated with Roundup PowerMax 3™ glyphosate ripener (365.4 mL/ha) and harvested 4, 6, 8, 10, and 12 weeks after treatment. The cane was hand-harvested and stripped of leaves, and the stalks shredded then analyzed with near-infrared spectroscopy for sucrose, moisture, purity, Brix, and fiber. Extracted juice was analyzed for total starch content using a microwave-assisted sonication method. Although the 2023 drought caused an average decrease of 1.5% moisture for all cane varieties, there was an average increase of 7.8% in sucrose content and 8.4% for theoretical recoverable sugar. The drought caused a marked increase in total starch concentration of 28.5% for all varieties. The maturity profile of the sugarcane played a strong role in the variety’s response to the drought stress, with early maturing varieties being more susceptible to the drought than mid-maturing varieties.