The biological mechanisms of resistance in selected lines of Nicotiana tabacum L. to Myzus nicotianae Blackman (Homoptera : Aphididae)

Since 1993, several aphid-resistant breeding lines of tobacco, Nicotiana tabacum L. have been developed at the Tobacco Experiment Station, Greeneville, TN. Crosses were developed between TI 1068, a resistant to the tobacco aphid, Myzus nicotianae Blackman, and ‘TN 86’ or ‘KY 17,’ two tobacco cultivars susceptible to the tobacco aphid. A research project was conducted to: 1) reevaluate levels of resistance of selected tobacco lines to the tobacco aphid, 2) determine the population growth parameters of the tobacco aphis that are affected by resistant tobacco, and 3) simulate aphid population growth on resistant and non-resistant tobacco using a computer-generated model. In 1996 & 1997, several entries were evaluated for aphid population growth in open field plots, greenhouse, and growth room. Field plots were allowed to become infested naturally by aphids. In greenhouse and growth experiments, adult aphids were placed individually onto each plant and allowed to colonize. Results indicated high resistance to the tobacco aphid on TI 1068 for a variety of experiments, compared to other resistant tobacco lines.

Initially 3 aphid-resistant tobacco entries (TI 1068, 301, 3001) were evaluated to determine their mechanisms of resistance. Four aphid growth parameters (life cycle, fecundity, reproductive longevity, survival) were investigated for their effects on aphid populations. Aphid development was significantly slower on leaf discs of TI 1068, 301, and 3001 than on TN leaf discs. Aphid development, fecundity, reproductive longevity, and survival did not differ significantly among all tobacco entries tested when reared on excised leaves from greenhouse-grown plants. Aphids reared on leaves excised from field-grown TI 1068 plants had a longer life cycle, lower reproductive rate, shorter reproductive longevity, and shorter survival time than aphids reared on the standard cultivar, TN 86.

A computer simulation, based on data from laboratory experiments,was developed to predict seasonal population development of tobacco aphids on TN 86 and TI 1068 aphid populations under field conditions, but in the absence of limiting factors such as weather, predators, disease, and parasitoids. It was estimated using this model that progeny from one aphid on TN 86 could exceed to 10,000,000 individuals within 40 days; whereas, less than 700 aphids would develop on TI 1068. Future work on the effects of weather, predators, diseases, and parasitoids on an aphid populations could prove useful in more accurately predicting aphid population growth in a typical tobacco field.