Breeding for Resistance to the Sugarbeet Root Maggot

Thirty-six genetically diverse sugarbeet (Beta vulgaris L.) lines were evaluated to determine their potential resistance to the sugarbeet root maggot, Tetanops myopaeformis Roder. Significant and relatively consistent differences in maggot damage were noted over 3 years. Damage ratings of F, crosses of resistant x susceptible lines tended to be intermediate between those of the parents. Selection for high- and low-maggot damage showed a linear trend in increasing and decreasing maggot damage, respectively. The average decline in the low-damage selection was approximately 5% per cycle. After five cycles of selection, there was no change in the rate of decline, indicating that further selection progress can be made. A greenhouse test confirmed field designations of resistant and susceptible genotypes. A low-damage inbred had lower maggot survival, smaller maggot weight, lower damage ratings, and greater root weight than a susceptible line. Additional index words: Beta vulgaris L., Tetanops myopaeformis Roder, Breeding for insect resistance, Divergent selection, Mass selection. HE sugarbeet root maggot (SBRM), Tetanops myopaeformiss Roder is one of the most serious insect pests of sugarbeets in the western United States and Canada. Its distribution coincides, with few exceptions, with the major sugarbeet growing areas of the western United States and Canada. It has been reported from the states of California, Colorado, Idaho, Minnesota, Montana, Nebraska, New Mexico, North Dakota, Oregon, Utah, Washington, and Wyoming; and from Alberta, British Columbia, Manitoba, and Saskatchewan provinces of Canada (9). Approximately 38% of the U.S. sugarbeet acreage is subject to damage. We estimate the current average annual loss from SBRM to be about 2% of the yield, or 481,000 metric tons. The prime method of controlling this insect has been with chemical pesticides (3). However, these can be expensive, and there is the possibility that the insect could develop resistance to insecticides. Plant resistance to insects has been developed by breeding in many crops and is one of the most efficient and economical methods of control when available. In the United States, several reports indicate that differences exist among sugarbeet genotypes for damage caused by the sugarbeet root aphid, Pemphigus populivenae Fitch (1, 4, 5, 15, 16), the green peach aphid, Myzus persicae (Sulzer) (5, 13), the bean aphid, Aphis fabae Scopoli (12, 13), and spider mites Tetranychus spp (13). However, none of these have played an important role in sugarbeet breeding program in the United States. In England, considerable research on plant resistance in sugarbeets has been reported for the green peach aphid (6, 7, 8, 14) and