2.7.24
THE COMBINED EFFECT OF SOIL DISINFESTATION AND CROP ROTATION ON POTATO SCAB AND PEANUT POD WART DISEASES AND STREPTOMYCES POPULATION

G. KRITZMAN1, A. GAMLIELll2 and J. Katan3

1Department of Plant Pathology and 2Laboratory for Pest Management Research, ARO, Volcani Centre, Bet Dagan 50250 Israel; 3 Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Sciences, Rehovot 76100, Israel

Background and objectivesbr> Plant pathogenic Streptomyces species cause deep pitted scab in potatoes, and peanut pod wart In Israel. Since its first appearance it has caused severe damage and may be considered a major economic disease of potatoes and peanuts. This pathogen is seed transmitted and soil-borne [1]. It can survive in soil without a known susceptible host over for 10 ;years. The objectives of this study were to study the effect of crop rotation and combined disinfestation treatments on population dynamics of the pathogen and on disease incidence.

Materials and methods
Soil solarization alone (SH) or combined with reduced amounts of formalin (200 ;l/ha), SH combined with reduced dosage of methyl bromide (250 ;kg/ha) and SH combined with methyl bromide (400 ;kg/ha) were compared with an untreated control and with formalin alone (200 ;l/ha)[2]. Disinfestation treatments were assessed in intensive rotation of potato and peanut production compared with crop rotation with one of each, wheat, soybean or fallow field between crops. Streptomyces population were estimated to a depth of 60 ;cm at the end of disinfestation treatments and at the end of each crop. Disease incidence and severity were followed in each potato and peanut crop.

Results and conclusions
Solarization alone and combined soil disinfestation treatments effectively reduced the population of Streptomyces in the soil. Total Streptomyces population at the depth of 0-20 ;cm was reduced from about 20,000 ;CFU/g soil to less than 400 ;CFU/g soil. This reduction was correlated with incidence of potato scab in the first crop. The effect of crop rotation in disease control in the second crop was conspicuous, since disease symptoms were much more severe on peanut pods that were grown after potatoes than on those grown as second crop after wheat or soybean. Streptomyces populations rapidly increased in the potato-peanut rotation compared with a gradual increase in the plots where peanuts were grown after wheat or soybean. About 10% of the total population were pathogenic. The long-term effect of the SH alone or combined with formalin and methyl bromide was evident even after the fourth crop following single disinfestation treatment.

References
1. Grinstein A, Kritzman G, Riven Y, Peretz-Alon I, Bar Z, 1997. Crop Protection 16, 353-357.
2. Grinstein A, Kritzman G, Hetzroni A, Gamliel A, Mor M, Katan J, 1995. Crop Protection 14, 315-320.