[Show abstract][Hide abstract] ABSTRACT: Survival of Ralstonia solanacearum race 3 biovar 2 (phylotype II sequevar 1) in Egyptian soils and compost was studied under laboratory and field conditions.
Survival of the pathogen under laboratory conditions varied with temperature, water potential and soil type, with temperature
being the major determinant of survival of the pathogen. The effects of temperature and moisture content were variable between
different experiments, but survival was generally longer at 15°C than at 4, 28 and 35°C respectively. Survival was also longer
when moisture levels were constant compared with varying moisture levels at all temperatures. In experiments to compare the
effects of progressive drying in sandy and clay soils there was a difference in survival times between the two soil types.
In sandy soils, the pathogen died out more rapidly when soil was allowed to dry out than in controls where the soil was kept
at constant water potential. In clay soils there was little difference between the two treatments, possibly due to the formation
of a hard impermeable outer layer during the drying process, which retarded water loss from within. Survival in mature composts
at 15°C was of the same order of magnitude as in soils but shorter at 28°C, possibly owing to increased biological activity
at this temperature, or a resumption of the composting process, with concomitant higher temperatures within the compost itself.
The maximum survival time recorded over all soil types and conditions during in vitro studies was around 200days. In field studies, the maximum survival time in both bare sand and clay was around 85days at
depths up to 50cm. The survival time was reduced in field experiments carried out in summer to less than 40days and in one
study when the ground was flooded for rice cultivation, the bacterium could not be detected 14days after flooding. The maximum
survival time of R. solanacearum in infected plant material or in infested soil samples incorporated into compost heaps was less than 2weeks. At the culmination
of field soil and compost experiments, no infection was detected in tomato seedlings up to 10weeks after transplanting into
the same soils or composts under glasshouse conditions at a temperature of 25°C.
No preview · Article · Oct 2011 · European Journal of Plant Pathology
[Show abstract][Hide abstract] ABSTRACT: Surveys over three seasons of irrigation, drainage and artesian well water throughout the major potato-growing areas of Egypt
indicated that Ralstonia solanacearum bv. 2 race 3 (phylotype II sequevar 1), cause of potato brown rot, was limited to the canals of the traditional potato-growing
areas in the Nile Delta region, with positive findings more commonly associated with the network of smaller irrigation canals
flowing through potato-growing areas. Pathogen populations in the canals of the Delta (~100–200cful−1) were generally variable throughout the year with presence linked to potato cultivation in the immediate area. The pathogen
was not detected in irrigation or drainage water associated with potato cultivation in the newly reclaimed desert areas (designated
as Pest-Free Areas, PFAs) or in the main branches of the Nile upstream from these areas. In vitro studies showed that temperature and microbial activity were the main factors affecting survival of the pathogen in canal
water. In experiments at temperatures of 4, 15, 28 and 35°C, survival was longest at 15°C and shortest at 35°C. Survival at
4 and 28°C tended to be intermediate between these extremes as was survival when the bacterium was grown at fluctuating temperatures.
Aeration, solarisation and pH variation between 4 and 9 appeared to have little effect on survival. Survival in autoclaved
or filter-sterilised canal water was longer than in untreated water irrespective of other factors with survival times exceeding
300days at 15°C in some experiments. Evidence is presented indicating that survival in water-saturated sediment may be longer
than in the overlying water suggesting that sediment may provide a protective niche for the pathogen in some circumstances.
The maximum survival time in non-sterile Egyptian canal water at high inoculum pressure was estimated to be up to 300days
at optimum temperature for survival (15–30°C) suggesting the potential for long-distance spread in Egyptian surface waters
from sources of contamination.
No preview · Article · Dec 2009 · European Journal of Plant Pathology