Effects of planting date and tobacco germplasm source on the occurrence of spotted wilt virus and on the abundance of thrips and tobacco aphids
Field experiments were conducted in Georgia during 1992 and 1993 to evaluate the impact of planting date and tobacco germplasm source on the abundance of thrips, primarily the tobacco thrips Frankliniella fusca (Hinds), and the tobacco aphid Myzus nicotianae Blackman, and on the incidence of tomato spotted wilt virus caused by thrips vectors. Twelve entries of flue-cured and burley tobacco, Nicotiana tabacum L., were planted in mid-April and early May, and they were monitored every 1-2 weeks for the presence of thrips and aphids and for the incidence of spotted wilt. Planting date had inconsistent effects on aphid population densities. More aphids were present in the late-planted tobacco in 1992 and in the early-planted tobacco in 1993. Cool weather in 1992 delayed the aphid population buildups until late in the season. Significant tobacco entry differences were observed. I-514, TI 1396, Polalta, NC 2326, and Kentucky 14 had the highest aphid population densities. Thrips populations were higher in the early-planted tobacco both seasons. K-326, TI 1396, and NC 2326 had higher thrips populations than the other entries. However, thrips population densities were not correlated with incidence of spotted wilt. Some entries with high incidences of spotted wilt (i.e., TI 1406, Tennessee 86, and Kentucky 14) had relatively low thrips populations. Conversely, the lines with suspected spotted wilt resistance (i.e., TI 1223, TI 1396, K-326, and Polalta) had lower incidence of spotted wilt, although thrips populations were relatively high. Planting date did not influence the incidence of spotted wilt among the 12 tobacco entries. Each tobacco entry had a spotted wilt incidence that was similar for both planting dates. There appears to be tobacco germplasm (l-35, TI 1223, TI 1396, TI 1586, and Polalta) that is resistant to tomato spotted wilt virus in the presence of known insect vectors.