by W. Garrett Owen
Ornamental sweetpotato intumescence: a physiological disorder
by W. Garrett Owen (Michigan State University) - wgowen@msu.edu
During a recent greenhouse visit, I inspected a crop of dark purple ornamental sweetpotato (Ipomoea batatas) plants. The matured leaves were exhibiting abnormal growth on the upper surface (Fig. 1). The growth ranged from sporadic green bumps to translucent or white lesions to black out-growths (Fig. 2).
Figure 1. Mature leaves of sweetpotato vines exhibiting abnormal, translucent out-growths on the upper leaf surface.
Figure 2. Abnormal growth on the upper leaf ranged from sporadic green bumps to translucent or white lesions to black out-growths.
At closer examination, the small green bumps were rising between the veins of the leaf and along the mid-rib. Though the green bumps were intermittent, I noticed a pattern among the leaves. I found some leaves to only exhibit small green bumps, while others, the green bumps were starting to enlarge and extrude out from the leaf surface, turning translucent (Fig. 3). The enlarged translucent lesions appeared white due to the intensity of out-growth (Fig. 4) that were present along or on the mid-rib and most of the growth occurring at the leaf base (Fig. 5).
Figure 3. Small green bumps protrude out from the leaf surface, turning translucent or white along the mid-rib.
Figure 4. Microscope view of enlarged translucent lesions present along the mid-rib of an ornamental sweetpotato leaf.
In some instances, I found the out-growth to be black (Fig. 6). While the majority of the abnormal out-growth occurred on the upper leaf surface, I did find some growth arising from the leaf petiole. The abnormal growth is a physiological disorder termed, intumescence, however other common and interchangeable names include: excrescences, neoplasms, galls, genetic tumors, lesions, enations, and oedemata.
Figure 5. Enlarged translucent lesions appear white due to the intensity of outgrowth that are present along or on the mid-rib and with most of the growth occurring at the leaf base.
Figure 6. Translucent out-growth turn black and become dry.
Causative factors
Intumescence development on leaves and petioles can have an impact on the aesthetic value of ornamental crops. You may be wondering, “What causes this physiological disorder?” The causative factor related to intumescence development is rather vague. Many have proposed intumescence development to be a result of air contamination, carbohydrate balance, chemical application, excess water, genetics, hormones and hormone concentration, humidity, light quality and quantity (intensity), and temperature. To date, there is no cure for intumescence development on ornamental sweetpotato. The best method to avoid intumescence development on ornamental sweetpotato crops would be to select cultivars that are less susceptible. Trials conducted at Kansas State University determined which ornamental sweetpotato cultivars were the least and most susceptible to intumescence development (Table 1). For more information, watch the two e-GRO webinars: Blisters, Bumps and Lesions: The Physiological Disorders of Intumescence and Edema (Link to Part 1) and (Link to Part 2).
Table 1 (click here to enlarge). List of ornamental sweetpotato (Ipomoea batatas) cultivars screened in a trial conducted at Kansas State University (Craver et al., 2014).
Literature cited
Craver, J. K., C.T. Miller, M.G. Cruz, K.A. Williams. 2014. Intumescences: Further Investigations into an Elusive Physiological Disorder. Greenhouse Production News. 24(9):32-40.
Source: e-GRO