Effects of soil pH and Pratylenchus penetrans on the mortality of 'Mazzard' cherry seedlings and their susceptibility to Pseudomonas syringae pv. syringae

The effects of 3.9-7.0 soil pH range and Pratylenchus penetras on the mortality of 1-year-old 'Mazzard' cherry rootstock seedlings and their susceptibility to Pseudomonas syringae pv. syringae were investigated in four greenhouse experiments over 34-146 days. Soil levels of P, K, Mg, and Ca decreased with decreasing pH, indicating that nutrient imbalance and deficiencies may be induced at low pH. Pseudomonas syringae pv. syringae infected the seedlings at all pH levels. However, shoot lesion lengths increased at pH below 5.5 compared with those at pH 7.0, suggesting that low soil pH is predisposing the seedlings to P, s. pv. syringae. Seedlings maintained at below soil pH 5.5 had decreased plant growth and increased seedling mortality. Pratylenchus penetrans population densities decreased with decreasing pll with or without significant decrease in plant growth, indicating a direct effect of pH on P. penetrans. Pratylenchus penetrans-infected plants, however, grew less than the controls in two experiments at 38 and 120 days after inoculation. There were few two-way interactions between the main effects, suggesting that soil pH is the dominant factor in the mortality of 'Mazzard' cherry rootstocks, and that the nematode feeding may not be related to the predisposition to P. s. pv. syringae.