2005 Volume 74 Issue 3 Pages 357-363
The α-amino nitrogen (A-N) contained in the roots and crowns of sugar beet is one of the harmful non-sugars that deteriorate the quality of sugar beet roots. This research was conducted to investigate the amount and distribution of the A-N and sucrose in the crown roots of the O-type (maintainer of male-sterile lines) sugar beets, which were suffered from root rot caused by artificial field inoculation with the fungus Rhizoctonia solani. The amount of A-N in all lines examined was increased by the infection with the fungus irrespective of the resistance to the disease. In the uninfected field, however, all the resistant lines contained a large amount of A-N, over 2 meq⁄100g, in the crown root than the susceptible one. On the other hand, the sucrose content of the crown roots was decreased by the infection with the fungus; the degree of decrease was less in resistant lines than in the susceptible ones. In the diseased plants, distribution pattern of A-N in the roots was different from that in healthy plants. The concentration of A-N was higher in the center of vascular bundles and lower in the epidermal region of the roots in the diseased plants. In conclusion, Rhizoctonia root rot deteriorated the quality of sugar beet root by decreasing the sucrose content and increasing the A-N amount of the roots. Although the A-N deteriorates the quality of sugar beet, O-type sugar beet that is resistant to Rhizoctonia root rot contained a large amount of A-N. This makes it difficult to breed high-quality sugar beets with high resistance to Rhizoctonia root rot.
