A review of sweet potato scab and studies on Fusarium wilt of sweet potato (Ipomoea batatas (L.) Lam.) and approaches to its management

Tony-George Gunua (2010). A review of sweet potato scab and studies on Fusarium wilt of sweet potato (Ipomoea batatas (L.) Lam.) and approaches to its management MPhil Thesis, School of Agriculture and Food Sciences, The University of Queensland.

       
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Author Tony-George Gunua
Thesis Title A review of sweet potato scab and studies on Fusarium wilt of sweet potato (Ipomoea batatas (L.) Lam.) and approaches to its management
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2010-03
Thesis type MPhil Thesis
Supervisor Associate Professor Victor Galea
Professor Terry Price
Total pages 120
Total colour pages 11
Total black and white pages 109
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Stem or Fusarium wilt of sweet potato (Ipomoea batatas (L.) Lam. is an important disease caused by the fungus Fusarium oxysporum f. sp. batatas in cool temperate regions. Sweet potato farmers in Rockhampton have experienced tuber rots and stem wilts in the last two years. Laboratory procedures were followed to isolate causal pathogens from affected sweet potato tuber samples taken from Rockhampton, wilted stems from tissue cultured plants and wilted stem in glass house raised planst and test whether these rots and wilts were due to the infection by Fusarium oxysporum f. sp. batatas or other pathogens. Fusarium oxysporum, Alternaria alternata and Gibberella moniliformis (Fusarium verticillioides) were consistently isolated from affected tubers supplied by farmers, wilted tissue cultured plants and wilted plants grown in the glass house in Gatton. The Fusarium oxysporum and Alternaria alternata isolates were from sweet potato tubers and the Gibberella moniliformis (Fusarium verticillioides) isolates were from wilted stems from tissue cultered plants and plants raised in glass house. They were identified and given BRIP accession numbers. Fusarium oxysporium (BRIP 52431) denoted Foxy, Alternaria alternate (BRIP 52557) denoted Aa,. F. verticillioides isolates from tissue culture (BRIP 52428),denoted Fv1 and F. verticillioide from wilted stems in glass house (BRIP 52430) denoated as Fv2. The two F. verticillioides isolates Fv1 and Fv2 were more virulent in causing stem wilt than Fusarium oxysporium (Foxy) and Alternaria alternate (Aa) isolated from tubers. Inoculation with these isolates and pathogenicity studies on sweet potato cv. NG7570 in the glass house showed that inoculation of injured stems with agar culture blocks was the most effective method that incited wilt. A. alternata did not cause wilt so was excluded from further tests. Twelve (12) commercial cvs. of sweet potato showed varying degrees of tolerance when screened against the three Fusarium isolates under glasshouse conditions. The cultivars WSPF, Beauregard, L18 and NG7570 were the most susceptible while cv. L117 was highly tolerant, and the rest were moderately tolerant. Four fungicides (Chlorothalonil 720g/L a.i, carbendazim 500g/L a.i, mancozeb 750g/L a.i and zyban (Thiophanate-methyl and Mancozeb = 156g/kg-thiophanate –methyl a.i & 640g/kg mancozeb a.i) were compared for efficacy in total inhibition of fungal growth (EC100) in vitro against the three Fusarium isolates. These fungicide concentrations were then used as pre- and post-inoculation applications for control of wilt on sweet potato plants under glasshouse conditions. Carbendazim and zyban were effective both as curative and protectant fungicides whilst Chlorothalonil and mancozeb performed well as protectant fungicides. Sweet potato farmers can use all of these fungicides as protectants but only carbendazim and zyban as curative fungicides.
Keyword Sweet potato, sweet potato scab, Fusarium wilt management, chemical control
Additional Notes Colour pages - 6, 49, 55, 56, 57, 58, 59, 65, 68, 70, 71

 
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Created: Tue, 22 Mar 2011, 15:11:47 EST by Mr Tony-george Gunua on behalf of Library - Information Access Service