Studies on the lenticel development, surface microflora and infection by common scab (Streptomyces scabies) of potato tubers growing in wet and dry soils

Abstract

S U M M A R YThe mechanisms of control of potato common scab (Streptomyces scabies) by irrigation were investigated in 5 years by studying the growth and surface microflora of young potato tubers developing in wet or dry soils. Direct examination of the tuber surface by light or scanning electron microscopy showed that the newly formed internodes near the apex, which carry stomata, had a very sparse microflora. In dry soil the older internodes, which carry lenticels at a susceptible stage, were increasingly colonised by actinomycete hyphae and discrete, although sometimes large, bacterial colonies. In wet soil, actinomycetes were rarely seen on tuber surfaces but bacteria were generally scattered over them, differences not always shown by isolation from periderm pieces onto water agar.When dry scab-infested soil was wetted, scabs did not subsequently develop on the two youngest tuber internodes (A-1, A-2), which may be an example of disease escape rather than inherent resistance of the stomata. The scab control achieved in wet soil was probably caused by some form of microbial antagonism, but whether through competition or antibiosis was not established.

Effect of chitosan and a biocontrol streptomycete on field and potato tuber bacterial communities

“…Common scab symptoms consist of superficial to deep corky lesions on the tubers. Methods used to control common scab include chemical treatments of seed potato tubers (Davis et al, 1976), irrigation (Adams and Lapwood, 1978), rotation strategies (Li et al, 1999), use of a tolerant cultivar (Bouchek-Mechiche et al, 2000), soil amendment with chitinous compounds (Vruggink, 1970;Beause´jour et al, 2003) and biological control with non-pathogenic streptomycetes (Liu et al, 1995;Ryan and Kinkel, 1997;Doumbou et al, 1998;Agbessi et al, 2003;Beause´jour et al, 2003). Recently, Beause´jour et al (2003) reported the use of a biological agent (Streptomyces melanosporofaciens Arcamone et al strain in combination with chitosan to control common scab.…”

Interactions and biocontrol of pathogenicStreptomycesstrains co-occurring in potato scab lesions

“…(Lapwood et al. 1973; Adams and Lapwood 1978) and chemical treatments (Davis et al. 1974; Loria 2001).…”

High soil moisture reduces common scab caused byStreptomyces turgidiscabiesandStreptomyces europaeiscabieiin potato

“…However, so far no methods alone seem effective and reliable for control of common scab in the field. The most widespread method is irrigation to reduce aerobic soil conditions during the early stages of tuber formation (Lapwood et al 1970;Adams & Lapwood 1978). Traditionally, the strategy for management of common scab in Norway has been to avoid liming before planting potatoes in order to maintain a low soil pH.…”