Review of the sugar end disorder in potato (Solanum tuberosum, L.)

Processing quality has become increasingly important to the potato industry. A serious defect in product quality is the physiological disorder known as sugar ends, also referred to as dark ends, jelly ends, translucent ends, and/or glassy ends. Symptoms of the most common type of sugar end include relatively low starch and high sugar content in the basal end of the tuber. Tubers with the sugar end disorder produce French fries that are dark on one end, making the fries unacceptable to consumers. Sugar end potatoes cause time and profit losses at the processing plant and may require blending of loads to meet product specifications, along with the need to change processing protocols. Sugar end can be costly to growers if the tubers have insufficient quality and the crop is rejected for processing. Conditions conducive to the development of sugar ends include high soil temperatures, transitory soil moisture deficits, and insufficient or excess nitrogen fertilization. Tubers are most sensitive to these stresses during early bulking. Historically, several theories have been proposed concerning the mechanism of sugar end development. Research shows that stressed plants produce adequate amounts of assimilate to support continued tuber growth, but accumulate large amounts of sucrose in the basal tissues of the tuber immediately following stress. Accumulated evidence suggests that heat stress and water deficit induce changes in the activities of certain key carbohydrate metabolizing enzymes shifting the tuber from a starch synthesizing function to one of starch mobilization. Genetic resistance to sugar end development is known and the identified traits are highly heritable. This review summarizes sugar end investigations to-date, and presents a list of research-based crop management recommendations that assist potato producers in minimizing the potential for sugar end development in the field.