Phytophthora root characterization in different phenological stages of soybean

Abstract

Phytophthora root and stem rot, caused by Phytophthora sojae Kaufm. & Gerd is considered one of the main diseases causing soybean (Glycine max (L.) Merril) losses. The objective was to verify the virulence patterns in differentiating lines of P. sojae for inoculations in different phenological stages, in seedlings and lateral branches of adult plants. Seventeen differentiating lines were used and five P. sojae pathotypes with distinct virulence patterns were sinoculated. Inoculations were performed 10 days after emergence (DAE) in seedlings hypocotyl, and 35 DAE were inoculated in lateral branches of adult plants. The experiments were conducted in a completely randomized design with two factors, these being 17 genotypes and 5 pathotypes, in 6 replications. Evaluations were performed 10 days after inoculation counting the number of dead seedlings/branches. P. sojae characterization were classified as resistant, the criterion was up to 15% of dead seedlings/branches, moderately resistant when they presented between 16 and 31% of dead seedlings/branches, and susceptible when they presented from 31% of dead seedlings/branches. Inoculation results in seedlings and in lateral branches of adult plants, allowed the characterization of the genotypes for the different P. sojae pathotypes, presenting the same resistance classification regardless of the phenological stage. Strong and positive correlations between the stages prove the efficiency of the different phonological stage during the inoculation. In addition, phenological stage of inoculation can be adjusted according to the availability of time, seeds, or plants in research projects and in breeding programs.