Evaluation location: Nebraska, United States
Sugar beet cultivars were seeded (5 seeds per pot) into 0.5 l pots using a custom soil mixture of 25% sand, 25% clay, and 50% peat moss. Upon emergence, plants were thinned to 1 plant per pot and maintained in a climate-controlled greenhouse at 24-30ºC with supplemental light set at 10 hr:14 hr (light:dark) cycle. Following three weeks of growth, two 10-ml holes (1.27 cm in diameter) were formed in the soil using a round-bottom centrifuge tube. Cells were then be capped with a natural cork stopper. Beets were grown for two more weeks to allow for sufficient root mass to invade soil cells. Five sugar beet root aphids were placed in each cell (10 aphids per pot or plant), and the corks replaced to enclose the aphids. Aphids were allowed to multiply for three weeks and then be evaluated and sampled
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To determine resistance or susceptibility of individual plants, root aphids were evaluated by visual rating (Fig. 1). The root aphid infestation were evaluated by removing the soil/root-ball from the pot and breaking open the ball so that both root cells are visible. The extent to which the aphids were present in the cells is the basis of the visual rating system, where 0 represents no aphids, 1 represents isolated aphids, 2 represents small colony, up to ¼ of cells, 3 represents cells ¼ to ½ full, 4 represents cells ½ to ¾ full, 5 represents cells ¾ full to full, and 6 represents cells excessively full. Plants with a root aphid rating of 0 or 1 are considered resistant and plants with a root aphid rating of 5 or 6 are considered susceptible. Ten plants per cultivar were evaluated. Susceptible check was HM3035RZ and had an average root aphid rating of 4.8 (19 plants). Resistant check was Monohikari-lot #8161 and had an average root aphid rating of 0.8 (19 plants).