Figure 1.
Virus symptoms on ‘Beauregard’ sweetpotato leaves the day before the first experiment was terminated.
All expanded leaves originating from nodes above the substrate surface are depicted with the bottom leaf in each column being the oldest and the top being the youngest. + N = nitrogen provided as KNO3, - N = no nitrogen provided. V0 = plants derived from non-inoculated, virus-tested plant stock; V1 = plants derived from V0 plant stock graft inoculated with the potyvirus complex (SPFMV, SPVG, SPVC, and SPV2); V2 = plants derived from plant stock infected with SPCSV. Potyvirus symptoms consist of purple ring spots (PRS, see arrow) and purple vein banding (PVB arrow). Sweet potato chlorotic stunt virus symptoms include deep interveinal purpling (IVP circle) that is distinguished from the natural purple cast (NPC circle) that develops on some sweetpotato leaves in that with IVP veins remain green, and the pigmentation is deeper.
Figure 2.
Virus symptom severity ratings of plants from the first (A) and second (B) experiments.
Virus symptom severity was assessed the day before each experiment was terminated by rating each leaf by visual estimation of the proportion of the leaf showing symptoms using a 0 to 3 scale in which: 0 = no symptoms, 1 = <1/3 of the leaf involved, 2 = 1/3–2/3 of leaf area involved, and 3 = >2/3 of the leaf involved. + N = nitrogen provided as KNO3, - N = no nitrogen provided. V0 = plants derived from non-inoculated, virus-tested plant stock; V1 = plants derived from V0 plant stock graft inoculated with the potyvirus complex (SPFMV, SPVG, SPVC, and SPV2); V2 = plants derived from plant stock infected with SPCSV. Severity ratings were transformed using log 10 and Fisher's LSD test at the 0.05 probability level was used to test for statistical significance. The data are expressed as means ± SE from non-transformed data.
Figure 3.
Representative adventitious roots from sweetpotato ‘Beauregard’ plants subjected to different virus treatments and grown with or without nitrogen.
+ N = nitrogen provided as KNO3, - N = no nitrogen provided. V0 = plants derived from non-inoculated, virus-tested plant stock; V1 = plants derived from V0 plant stock graft inoculated with the potyvirus complex (SPFMV, SPVG, SPVC, and SPV2); V2 = plants derived from plant stock infected with SPCSV. SR = localized swelling indicative of successful storage root initiation. Scale bar = 5 cm.
Figure 4.
Variation in adventitious root number (A), first order lateral root length (B), first order lateral root number (C), and lateral root density (D) in response to virus and nitrogen treatments at the onset of storage root initiation in ‘Beauregard’ sweetpotato.
+ N = nitrogen provided as KNO3, - N = no nitrogen provided. V0 = plants derived from non-inoculated, virus-tested plant stock; V1 = plants derived from V0 plant stock graft inoculated with the potyvirus complex (SPFMV, SPVG, SPVC, and SPV2); V2 = plants derived from plant stock infected with SPCSV. Root length and number were transformed using log 10 and square root transformation, respectively, and Fisher's LSD test at the 0.05 probability level was used to test for statistical significance. The data are expressed as means ± SE from non-transformed data.
Figure 5.
Variation in second order lateral root length (A) and number (B) in response to virus and nitrogen treatments at the onset of storage root initiation in ‘Beauregard’ sweetpotato.
Treatment legend: + N = nitrogen provided as KNO3, - N = no nitrogen provided. V0 = plants derived from non-inoculated, virus-tested plant stock; V1 = plants derived from V0 plant stock graft inoculated with the potyvirus complex (SPFMV, SPVG, SPVC, and SPV2); V2 = plants derived from plant stock infected with SPCSV. Root length and number were transformed using log 10 and square root transformation, respectively, and Fisher's LSD test at the 0.05 probability level was used to test for statistical significance. The data are expressed as means ± SE from non-transformed data.