Role of Pratylenchus penetrans in the potato early dying disease of Russet Burbank potato

The interaction of Pratylenchus penetrans and Verticillium dahliae for symptom expression of potato early dying and yield and quality of tubers of Russet Burbank potato was evaluated in microplots and field plots. Soil was fumigated with metham sodium before being infested with varying population levels of the nematode and/or fungus. In the microplot study, low and high initial populations of P. penetrans (about 25 and 75/100 cm3 of soil) or V. dahliae (about 3 and 9 colony-forming units/g of dry soil) had no effect on number and fresh weight of tubers compared to the control. Combined infestations of both organisms reduced yields up to 20% but did not affect number of tubers compared to the control. Dry matter content of tubers was reduced by V. dahliae compared to the control regardless of presence or absence of the nematode. Foliar symptoms of potato early dying were caused by V. dahliae alone, but were more severe when nematodes were also present with V. dahliae. Estimates of percent defoliation at weekly intervals beginning 13 wk after planting until harvest were consistent with rating of symptoms at 13 wk after planting. In field experiments, initial populations of P. penetrans ranging from eight to 44 nematodes/100 cm3 of soil did not affect yield or quality of tubers compared to the control. Initial populations of V. dahliae alone reduced yield one year but not another. Regardless of the effect of the fungus alone, the combination of V. dahliae and P. penetrans reduced yield by as much as 36% and also reduced specific gravity compared to the control. The population dynamics of P. penetrans was not consistent among years of experiments; populations of this nematode were either decreased or not affected by V. dahliae