RESUMO
Because sweetpotato [Ipomoea batatas (L.) Lam.] stem cuttings regenerate very easily and quickly, a study of their early growth and development in microgravity could be useful to an understanding of morphological changes that might occur under such conditions for crops that are propagated vegetatively. An experiment was conducted aboard a U.S. Space Shuttle to investigate the impact of microgravity on root growth, distribution of amyloplasts in the root cells, and on the concentration of soluble sugars and starch in the stems of sweetpotatoes. Twelve stem cuttings of 'Whatley/Loretan' sweetpotato (5 cm long) with three to four nodes were grown in each of two plant growth units filled with a nutrient agarose medium impregnated with a half-strength Hoagland solution. One plant growth unit was flown on Space Shuttle Colombia for 5 days, whereas the other remained on the ground as a control. The cuttings were received within 2 h postflight and, along with ground controls, processed in approximately 45 min. Adventitious roots were counted, measured, and fixed for electron microscopy and stems frozen for starch and sugar assays. Air samples were collected from the headspace of each plant growth unit for postflight determination of carbon dioxide, oxygen, and ethylene levels. All stem cuttings produced adventitious roots and growth was quite vigorous in both ground-based and flight samples and, except for a slight browning of some root tips in the flight samples, all stem cuttings appeared normal. The roots on the flight cuttings tended to grow in random directions. Also, stem cuttings grown in microgravity had more roots and greater total root length than ground-based controls. Amyloplasts in root cap cells of ground-based controls were evenly sedimented toward one end compared with a more random distribution in the flight samples. The concentration of soluble sugars, glucose, fructose, and sucrose and total starch concentration were all substantially greater in the stems of flight samples than those found in the ground-based samples. Carbon dioxide levels were 50% greater and oxygen marginally lower in the flight plants, whereas ethylene levels were similar and averaged less than 10 nL.L (-1). Despite the greater accumulation of carbohydrates in the stems, and greater root growth in the flight cuttings, overall results showed minimal differences in cell development between space flight and ground-based tissues. This suggests that the space flight environment did not adversely impact sweetpotato metabolism and that vegetative cuttings should be an acceptable approach for propagating sweetpotato plants for space applications.
RESUMO
We assessed the risk associated with introduction of sweet potato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), from infested areas to noninfested areas via shipment of sweet potato, Ipomoea batatas (L.), roots within the southern United States. Our study quantifies the effectiveness of risk mitigation procedures of sweet potatoes before shipment in relation to introduction of the weevil. The risk assessment relied on literature and expert information to determine appropriate parameters. Using a computational model, Monte Carlo simulations were conducted to estimate the likelihood of introduction of sweet potato weevil. Risk management options were incorporated and the risk analyses were performed to assess how the risk could be reduced. The study found the risk of introduction of the weevil for both domestic shipment and imports of sweet potatoes into new areas within the southern United States to be low. Sensitivity analysis was performed to assess model stability and the impact of parameter changes. Based on the sensitivity analysis, the most critical input was the postharvest mitigation, followed by the number of weevils per ton of sweet potatoes. We concluded that maintaining mitigations with monitoring in conjunction with public education to stop illegal transport of sweet potatoes and alternate hosts would significantly reduce the risk of introduction.
