POD WART DISEASE OF PEANUTS

Peanut pod wart, a relatively new disease to peanut culture, was first reported in Israel in 1988 attacking peanut plants and causing dark w arts on the pod. The causal agents are various Streptomyces spp. Scann ing electron microscopy showed a significant difference between health y and diseased tissues of the exocarp and mesocarp layers of the pod; there were no effects on the endocarp layer. The mesocarp cells of inf ected tissue were smaller and more compressed than those of healthy ti ssue. In most cases two cells under the peak of the wart were extremel y large and the cells growing from them toward the surface were uneven , forming the shape of a fan. The pathogen could be isolated from the soil and rhizosphere, but in the pod it was found only in the warted t issue. The microorganisms isolated from the warts belong to different groups of Streptomyces spp.; subsequent pathogenicity tests proved the ir virulence to a limited host range. In potato, these isolates of Str eptomyces spp. caused deep pitted scab; in peanuts they caused warts. Peanut seeds which developed in infected pods were free of the pathoge n if the shell was undamaged. However, the pathogen is surface seedbor ne, and contaminated seeds during the mechanical cracking process.