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Studies on common scab of potato


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Lacey, MJ 2000 , 'Studies on common scab of potato', PhD thesis, University of Tasmania.

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This thesis includes studies on: 1) characteristics of
streptomycete isolates from common scab lesions of potatoes collected
from across the Tasmanian potato cropping region; 2) scab
conduciveness of soils from that region and ; 3) effects of green manures
on common scab of potato.
Most of 94 streptomycete isolates fitted into four groups based
on morphological and physiological characteristics. Groups were:
Streptomyces scabies (25 stains); S. violaceusniger (11);
Streptosporangium spp. (3); and strains resembling Streptornyces
halstedii (29). Some of the remaining 26 ungrouped strains resembled
S. scabies. Most S. scabies strains could grow at pH 4.5.
Pathogenicity of strains was evaluated in four ways. In a
potato disk assay, all S. violaceusniger strains, S. scabies reference
pathogen strain #32 and five S. scabies-like ungrouped strains showed
clear signs of pathogenicity. Media from oatmeal-broth (OMB) cultures
of S. scabies and S. violaceusniger strains inhibited radish seedling
growth, while S. violaceusniger strains 54/3 and 75/1-1 killed seedlings.
Surface necrosis occurred within 24 hours of dipping potato minitubers
in media from OMB cultures of S. violaceusniger. Three S. scabies
strains (including #32) also produced darkening of lenticels, indicating
necrotising potential. S. violaceusniger strains produced nigericin while
strains 54/3 and 75/1-1 also produced geldanamycin, probably
accounting for their virulence in pathogenicity assays. Thaxtomin A
production by strain #32 was also confirmed.
Scab conduciveness of 36 Tasmanian potato cropping soils
was compared in a glasshouse trial. Linear regressions showed no
association between scab severity and any of 12 individual soil chemical
properties. However, scab was much less likely below a threshold pH or
when the concentration of exchangeable cations Ca', Mg' and K+
(considered together as milliequivalents) were below a threshold value.
In glasshouse studies, green manures did not increase scabbing
and in one pot trial a broad-bean manure reduced scab severity. Green manures were associated with increased cellulase activity and electrical
conductivity (EC) of soil in the absence of added fertiliser plus, in some
trials, increased tuber yields. Added streptomycete antagonists did not
noticeably effect scab severity.
In field trials at two sites, lupin or ryegrass green manures did
not effect scab severity, while increased scab with an oat manure at one
site was associated with increased soil EC. Increased scab with a canola
green manure, evaluated at only one site, was associated with reduced
soil microbial activity as assessed by FDA hydrolysis. At field sites,
green manures did not affect tuber yield, soil cellulase activity or pH.

Item Type: Thesis - PhD
Authors/Creators:Lacey, MJ
Keywords: Potatoes
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

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