Selection for Sucrose Yield in Stressed Sugarbeet Seedlings
Progress in improving sucrose yield in sugarbeet (Beta vulgaris L.) has been slow, due to large environmental variation associated with root yield and a negative correlation between root yield and sucrose concentration. Appropriate stress applied on segregating populations could increase performance differences among genotypes and increase the genetic variance. Stress that forces defoliated plants to grow new leaves from their stored root reserves logically ought to select for increased photosynthate storage and, therefore, increased sucrose yield. Stress was imposed in greenhouse tests by trimming the leaves from 3- to 4-wk-old sugarbeet seedlings and covering them with black plastic, thereby forcing the plants to grow new leaves from their stored root reserves. When this stress was imposed on seedlings of a series of cultivars varying in root yield and sucrose potential, those cultivars with the highest potential sucrose yield had the greatest survival rate (fewest plants dying). The correlations between percent survival after stress and total sucrose yield were 0.96 and 0.90 for field and greenhouse replicated trials, respectively. Open-pollinated seed increases of the surviving plants in two heterogeneous populations resulted in increases in field root yield, sucrose concentration and total sucrose yield. These increases, although in a favorable direction, were not always at the desired probability of significance. Data combined over 2 years of testing gave significant increases in total sucrose yield for the two new stress selection populations over their parents at the 0.07 and 0.14 probability levels. This method shows promise as a quick, inexpensive technique for improving both root yield and sucrose concentration.
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