Virus Movement from Infected Sweetpotato Vines to Roots and Reversion on Root Sprouts

in HortScience

Sweetpotato is usually propagated in Uganda by vine cuttings from mature crops, but sometimes sprouts from storage roots are used, especially in drought-prone areas. No information is available on whether the storage of roots of Ugandan cultivars are infected with the viruses and whether the sprouts on them express symptoms so that farmers can eliminate diseased ones. Information on root sprout reversion from virus infection is also lacking. The storage roots of five sweetpotato cultivars was sourced either by random selection of roots from already harvested roots or obtained from symptomless plants selected before harvest at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK), and the National Semi Arid Resources Research Institute (NaSARRI). Roots were also generated in a screenhouse after being inoculated with Sweet potato feathery mottle virus (SPFMV) and/or Sweet potato chlorotic stunt virus (SPCSV). More than 70% of sprouts from roots of all the cultivars selected after harvest at MUARIK and NaSARRI were infected with the viruses. For roots obtained from symptomless plants, 64% and 21% of the sprouted roots from MUARIK and NaSARRI were infected with the viruses, respectively. Most of the root samples from MUARIK had visible virus symptoms on sprouts and tested positive for both SPFMV and SPCSV, whereas those from NaSARRI did not show symptoms and were infected primarily with SPFMV. Plants graft-inoculated with either SPCSV or SPFMV alone produced both infected and noninfected roots, whereas all the root sprouts from dually infected plants showed virus symptoms. Reversion from virus infection was observed on root sprouts infected singly with SPFMV, whereas those infected with SPCSV showed recovery only, and none of the root sprouts infected by both viruses showed recovery. This study proves that roots are good reservoirs for viruses, and reversion occurs only when singly infected with SPFMV. Therefore, there is a need to establish seed channels in which seedstock is cleaned continuously and made available to farmers.

Contributor Notes

This research was supported by the International Potato Center (CIP) through the Sweetpotato Action for Security and Health in Africa (SASHA) project as part of the Consultative Group for International Agricultural Research (CGIAR) Research Program on Roots, Tubers and Bananas (RTB).

Corresponding author. E-mail: adikiniscovia@gmail.com.

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    Virus symptoms expressed on root sprouts from randomly selected roots and on I. setosa after graft inoculation of asymptomatic root sprouts. (A) Symptomatic root sprout of ‘NASPOT 1’ from Makerere University Agricultural Research Institute, Kabanyolo (MUARIK). (B) Symptomatic root sprout of ‘Dimbuka-Bukulula’ from MUARIK. (C) Symptomatic root sprout of ‘Ejumula’ from MUARIK. (D) Asymptomatic root sprout of ‘NASPOT 1’ from the National Semi Arid Resources Research Institute (NaSARRI). (E) Asymptomatic root sprout of ‘Dimbuka-Bukulula’ from NaSARRI. (F) Asymptomatic root sprout of ‘Ejumula’ from NaSARRI. (G) Vein clearing. (H) Vein banding/mottling. (I) Vein chlorosis.

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    Sweetpotato root sprout of ‘NASPOT 1’ showing deviation of leaf morphology from normal. (A) ‘NASPOT 1’ with interveinal chlorosis and distorted leaf shape. (B) Normal ‘NASPOT 1’ leaves.

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    Percentage of sweetpotato root sprouts expressing virus symptoms from roots derived from plants graft-inoculated with Sweetpotato feathery mottle virus (SPFMV), Sweetpotato chlorotic stunt virus (SPCSV), and their combination for the four different sweetpotato cultivars. SPVD, sweetpotato virus disease.

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    Progress in disease severity resulting from virus infection on root sprouts of four sweetpotato cultivars over time under screenhouse conditions. Ejum, ‘Ejumula’; Kab, ‘Kabode’; Dim, ‘Dimbuka-Bukulula’; NAS, ‘NASPOT 1’l SPFMV, plants inoculated with Sweetpotato feathery mottle virus; SPCSV, plants inoculated with Sweetpotato chlorotic stunt virus; SPFMV + SPCSV, plants inoculated by both SPFMV and SPCSV.

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    Virus symptoms on root sprout resulting from infection by Sweetpotato chlorotic stunt virus (SPCSV). (A) Leaf purpling on ‘Dimbuka-Bukulula’. (B) Chlorotic spots on ‘Ejumula’. (C) Leaf purpling on ‘NASPOT 1’. (D) Chlorotic spot on ‘Kabode’.

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    Symptom expression on root sprout resulting from dual infection by Sweetpotato feathery mottle virus (SPFMV) and Sweetpotato chlorotic stunt virus (SPCSV) (A) Symptoms on ‘Dimbuka-Bukulula’ (mottling vein clearing, and distorted leaf shape). (B) Symptoms on ‘Ejumula’ (mottling and vein clearing). (C) Symptoms on ‘NASPOT 1’ (vein clearing, mottling, and distorted leaf shape). (D) Symptom on ‘Kabode’ (vein clearing).

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