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.

Colonization Dynamics and Spatial Progression of Verticillium dahliae in Individual Stems of Two Potato Cultivars with Differing Responses to Potato Early Dying

Potato early dying (PED), caused by Verticillium dahliae, is a chronic yield-limiting disease of potato (Solanum tuberosum). In this study, we describe the colonization dynamics of V. dahliae in two potato cultivars with varying responses to PED. We utilized a quantitative real-time polymerase chain reaction (Q-PCR) assay to assess the colonization and spatial progression of V. dahliae in cvs. Ranger Russet (moderately resistant) and Russet Norkotah (highly susceptible). Ninety plants per cultivar were inoculated with a conidial suspension in the greenhouse. Every 2 weeks until week 10, we collected basal samples from 15 plants, and repeatedly sampled the growing apices of another 15 plants. The mean infection coefficient (IC) values in the basal and apical samples were significantly lower in cv. Ranger Russet at all five sampling dates. The pathogen was detected in basal samples of both cultivars by week 2, and in apical samples of cv. Russet Norkotah at week 4 and of cv. Ranger Russet at week 6. Colonization of cv. Russet Norkotah consistently increased in apical and basal samples during the 10 weeks, while it plateaued after week 6 in cv. Ranger Russet. Differences in response to PED appear associated with the speed of colonization and the establishment of a higher population density by V. dahliae in the plant.

Multiplex Real-Time Quantitative PCR to Detect and Quantify Verticillium dahliae Colonization in Potato Lines that Differ in Response to Verticillium Wilt

Potato early dying (PED), also known as Verticillium wilt, caused by Verticillium dahliae, is a seasonal yield-limiting disease of potato worldwide, and PED-resistant cultivars currently represent only a small percentage of potato production. In this study, we developed a real-time quantitative polymerase chain reaction (Q-PCR) approach to detect and quantify V. dahliae. The efficiency of the designed primer pair VertBt-F/VertBt-R, derived from the sequence of the β-tubulin gene, was greater than 95% in monoplex Q-PCR and duplex (using Plexor technology) procedures with primers PotAct-F/PotAct-R, obtained from the sequence of the actin gene, designed for potato. As few as 148 fg of V. dahliae DNA were detected and quantified, which is equivalent to five nuclei. Q-PCR detected V. dahliae in naturally infected air-dried potato stems and fresh stems of inoculated plants. Spearman correlations indicated a high correlation (upward of 80%) between V. dahliae quantifications using Q-PCR and the currently used plating assays. Moreover, Q-PCR substantially reduced the variability compared with that observed in the plating assay, and allowed for the detection of V. dahliae in 10% of stem samples found to be pathogen free on the culture medium. The described Q-PCR approach should provide breeders with a more sensitive and less variable alternative to time-consuming plating assays to distinguish response of breeding lines to colonization by V. dahliae.

Molecular Characterization of Vegetative Compatibility Group 4A and 4B Isolates of Verticillium dahliae Associated with Potato Early Dying

Forty isolates of Verticillium dahliae, collected from potato seed tubers and potato plants from various regions in North America and previously assigned to vegetative compatibility groups (VCGs) 4A or 4B, were characterized using molecular markers. The VCG 4A isolates were previously shown to be a highly virulent pathotype of potato and to interact synergistically with the root-lesion nematode Pratylenchus penetrans to cause potato early dying. All but one of the VCG 4A isolates characterized in this study lacked the subspecies-specific repetitive DNA sequence E18 and could be differentiated from the remaining isolates by restriction fragment length polymorphisms (RFLPs) in the nuclear rDNA and Trp1 loci. The E18 RFLP patterns of several VCG 4B isolates from Maine and New York were highly similar to those of VCG 4B isolates previously collected from potato and tomato fields in Ontario. The data presented here suggest that the molecular markers will be useful for the detection and classification of isolates of V. dahliae associated with potato early dying.