Ramón A. Arancibia

The Role of Aphid Abundance, Species Diversity, and Virus Titer in the Spread of Sweetpotato Potyviruses in Louisiana and Mississippi

Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG), and Sweet potato virus 2 (SPV2) are sweetpotato (Ipomoea batatas) potyviruses nonpersistently transmitted by aphids. Our objective was to determine how aphid abundance, aphid species diversity, and virus titers relate to the spread of SPFMV, SPVG, and SPV2 in Louisiana and Mississippi sweetpotato fields. The most abundant aphid species were Aphis gossypii, Myzus persicae, Rhopalosiphum padi, and Therioaphis trifolii. Aphids were captured during the entire crop cycle but virus infection of sentinel plants occurred mainly during the months of June to August. SPFMV was more commonly detected than SPVG or SPV2 in sentinel plants. Virus titers for SPFMV were higher in samples beginning in late June. Because significant aphid populations were present during April to June when virus titers were low in sweetpotato and there was very little virus infection of sentinel plants, low virus titers may have limited aphid acquisition and transmission opportunities. This is the first study to comprehensively examine aphid transmission of potyviruses in sweetpotato crops in the United States and includes the first report of R. maidis and R. padi as vectors of SPFMV, though they were less efficient than A. gossypii or M. persicae.

Development of a Mechanical Undercutting System to Minimize Sweetpotato Skinning during Harvest

Abstract. Sweetpotatoes have been an important high-value crop in Mississippi and future growth is expected. Industry growth has created the need for a continuous supply of sweetpotatoes throughout the year. Therefore, managing the harvest process and postharvest storage environment is critical to maintaining a year-round supply of quality sweetpotato roots. This has been a challenge in Mississippi and growers have been experiencing post-harvest losses due to excessive root shrinkage (weight loss) and bacterial and fungal rots. Studies indicate that 20% to 25% of sweetpotatoes are lost to moisture loss and decay during postharvest storage. This is directly related to skinning at harvest procedures that cause cuts and abrasions (skinning) to the delicate skin of the sweetpotato root is. These wounds provide a way-of-entry for diseases to infect the root, as well as moisture loss that results in root shrinkage. De-vining sweetpotatoes prior to harvest is a commonly used method to halt root growth and to begin toughening the skin. This method is viable for producers using manually-assisted harvesting for the fresh market. Producers using bulk harvesting prefer to leave vines on to reduce the amount of foreign material going into storage. A new method of halting plant growth and allowing the root to cure in the ground prior to harvest is needed. The objective of this study was to design and test a mechanical root pruning blade to halt plant growth and initiate skin set prior to harvest of sweetpotatoes and to quantify the effects of undercutting sweetpotatoes on skin strength relative to de-vining. It was hypothesized that cutting the deep root of the sweetpotato plant would allow this process to begin. Therefore, two different undercutting implements were designed and fabricated. One was assembled from currently available off-the-shelf components and the other was a modified commercially available sweetpotato digger. These implements were tested in experimental plots and the skin strength was directly measured. Root skin strength was measured at three days and six days after treatment. There was a significant rainfall event on the fifth day after treatment, meaning that no comparison between the time periods can be made. One of the tested varieties responded to undercutting. Results indicated that at three days after treatment, undercutting had no significant effect on skin strength for both vine conditions (vine-on and de-vined). At six days after treatment, undercutting with the newly developed implement significantly increased skin strength for roots in which the vine had been left on. There was no difference between using the modified digger and no treatment. Additionally, there was no treatment effect on roots which were de-vined. These results indicate that in a bulk harvesting system, undercutting with the new implement will increase skin strength after the roots have cured in the ground.