Hydraulic Conductance in Susceptible versus Tolerant Peach Seedlings Infected with Leucostoma persoonii

Abstract

Eight open-pollinated peach families [Prunus persica (L.) Batsch] were selected from a germplasm collection that was screened for tolerance to Leucostoma persoonii (Nits.) Höhn. [imperfect state, .Leucocytospora leucostoma (Pers.) Höhn] following field inoculation. The eight peach families were either susceptible or tolerant to L. persoonii infection based on canker length measurements. Three open-pollinated seedlings per family were chosen for evaluation. Following artificial inoculation, measurements of hydraulic conductance per pressure gradient (Kh) were made on 2-year-old branch segments from the 24 seedlings, and safranin dye was used to mark the conductive xylem pathways. For the peach families tolerant to L. persoonii, the specific Kh of the canker branch segments was greater than that for the most susceptible peach families. The inoculated branch segments from the tolerant peach families maintained ≈15% to 30% of the water transport of control segments. Safranin dye movement indicated that the sapwood in inoculated branch segments of seedlings from the susceptible peach families was almost completely blocked. Isolation experiments indicated deeper penetration of the fungus into the xylem of seedlings of susceptible than tolerant families. Xylem dysfunction appears to be correlated with a reduction in Kh, and the seedlings in the tolerant peach families are better able to maintain water transport through the stem segment invaded by the fungus.