Undifferentiated Region Research Articles

Resistance to the pea wilt organism (Fusarium orthoceras A. & W. var. pisi Lin.) was first noted by Linford (1928). Wade (1929) showed that resistance was inherited as a single dominant Mendelian character and that pea plants fall into two discontinuous resistant and susceptible classes. The symptoms of the disease have already been described fully by Linford (1928, I93ia). The organism invades susceptible plants through the undifferentiated region of the young rootlets. Cortical invasion is negligible except at this point of entry, for the parasite early establishes itself in the stelar region through which it advances upward, mainly in the xylem. The present paper is a report of studies carried out with the purpose of throwing some light upon the nature of the marked resistance to this parasite which occurs in many varieties and strains of the host. Resistant and susceptible strains of Alaska variety were used. As already shown in a previous paper (Walker, 1931), this variety contains certain stocks which are a mixed population of homozygous resistant and homozygous susceptible individuals. By single-plant selection from such stocks pure lines of resistant and susceptible populations have been secured. These were chosen for this comparative study because of their great similarity in all major characters except those of resistance and susceptibility to wilt.

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