Pratylenchus penetrans and the potato early dying disease.

Pratylenchus penetrans is a cosmopolitan species reported from 69 countries representing every continent except Antarctica. P. penetrans has a wide host range including potato and is found throughout the potato growing region of the northern USA. Most potato fields are infested with the fungus Verticillium dahliae as well as root lesion nematodes, and a disease interaction between the two has been demonstrated for multiple soil types, potato cultivars and production regions. The significance of the interaction between P. penetrans and V. dahliae is that it is synergistic rather than additive. This chapter discusses the economic importance, distribution, symptoms of damage, biology and life cycle, recommended integrated nematode management and management optimization of P. penetrans. Future research requirements are also mentioned.

Assessment of Resistance in Potato Cultivars to Verticillium Wilt Caused by Verticillium dahliae and Verticillium nonalfalfae

Verticillium wilt caused by Verticillium spp., also called potato early dying disease, is one of the most serious soilborne diseases affecting potato production in China. The disease has been expanding into most potato production areas over the past few years. Information on host resistance against Verticillium wilt among the potato cultivars in China is scarce, but it is critical for sustainable management of the disease. This study, therefore, evaluated 30 commercially popular potato cultivars against Verticillium dahliae strain Vdp83 and Verticillium nonalfalfae strain Vnp24, two well-characterized strains causing Verticillium wilt of potato in China. Both strains were isolated from diseased potato plants, and they were previously proven to be highly virulent. Ten plants of each cultivar were inoculated with the V. dahliae strain and incubated on greenhouse benches. Symptoms were rated at weekly intervals, and the relative area under the disease progress curve was calculated. The experiment was repeated once, and nonparametric analysis was used to calculate the relative marginal effects and the corresponding confidence intervals. Five resistant cultivars and four susceptible cultivars identified from the analyses were then challenged with the V. nonalfalfae strain. Cultivar responses to V. nonalfalfae were like those exhibited against V. dahliae, except for one cultivar. This study showed that resistance among potato cultivars exists in China against Verticillium spp. and that the resistance to V. dahliae identified in potato is also effective against the other Verticillium species that cause Verticillium wilt with a few exceptions. Cultivars identified as resistant to Verticillium wilt can be deployed to manage the disease until the breeding programs develop new cultivars with resistance from the sources identified in this study.

Multiple Disease Resistance in Interspecific Hybrids of Potato

Wild species of Solanum are excellent sources of disease resistance genes that may be incorporated into S. tuberosum through breeding. This study was initiated to determine whether multiple forms of disease resistance could be identified in interspecific Solanum hybrids. Thirty-two clones were evaluated for resistance to soft rot, common scab, black scurf, Verticillium wilt, and early blight. Most of the clones originated from populations that were not initially selected for disease resistance traits. Comparisons with the cultivars Atlantic, Russet Norkotah, and Russet Burbank indicated that all clones were more resistant than at least one cultivar for at least one disease resistance trait. Clone C545, which exhibited improved resistance to soft rot, scab, pitted scab, early dying disease, and early blight, appears to be an especially valuable source of disease resistance. The use of interspecific hybridization at the diploid level, combined with sexual polyploidization to return to the tetraploid level, provides a method to introduce multiple forms of disease resistance into advanced clones.

Effect of Compost Amendment or Straw Mulch on Potato Early Dying Disease

Single potato plants (Solanum tuberosum) cv. Superior were grown in field microplots to evaluate the effects of spent mushroom compost or straw mulch on early dying of potato caused by Verticillium dahliae and/or Pratylenchus penetrans. Prior to planting, soil was fumigated, placed in field microplots, and then infested with pathogens. Area under the senescence progress curve (AUSPC) was greater for plots infested with V. dahliae and/or P. penetrans than for noninfested plots. Plants grown in soil infested with both pathogens developed symptoms earlier than plants grown in soil infested with a single pathogen. Both V. dahliae and P. penetrans reduced yields; the combination of pathogens reduced marketable tuber yields by 22 to 44% (A- and B-sized tubers). Although the total number of tubers of all sizes was not affected by cultural or pathogen treatments, the addition of compost increased marketable tuber weight and decreased AUSPC. Soil amendment with spent mushroom compost may be a means of reducing the effects of potato early dying and increasing tuber yield when one or both pathogens are present.