Abstract
Potato early dying (PED) disease complex is often called the Verticillium wilt of potato and is considered one of the most economically devastating diseases of potato worldwide. The severity of the disease greatly increases with the association of the soil-borne pathogens Verticillium dahliae and V. albo-atrum and the root lesion nematode (Pratylenchus sp.). Recently, an increase in wilt disease symptoms and a sharp decline in marketable tuber yield were observed in New Brunswick (NB), Canada. A survey of 71 fields, along with eight fumigated and eight non-fumigated fields, was carried out to determine and quantify nematodes and Verticillium in the soil. Techniques used included plate counts for Verticillium (CFU/g soil), real-time qPCR (RT-qPCR) for V. dahliae (cell/g soil), and nematode identification and counts (# of nematodes/kg of soil). The survey results of the 71 fields revealed that 55 fields had Verticillium sp. ranging from 2 to 66 CFU/g of soil by the plate method, and 68 fields had high V. dahliae ranging from 261 to 27,471 cell/g of soil by RT-qPCR method. All fields had high numbers of root lesion nematodes ranging from 560 to 14,240 nematodes/kg of soil. There was an uneven distribution of PED incidence in potato fields at various locations of NB. Fumigation with Chloropicrin significantly reduced the numbers of root lesion nematodes by 34.1-99.0%, Verticillium sp. CFU/g of soil by 50-100%, and V. dahliae cell/g soil by 38-91% in the eight fumigated fields. The management of the PED complex with various disease management products under field conditions was also studied in a field plot trial setup. The nematicide Velum applied in-furrow at the recommended label rate decreased the numbers of root lesion nematodes by up to 66% compared to other products. The combination of both Velum + Aprovia and the application of ammonium-lignosulfonate significantly reduced V. dahliae by 190.55% and 274.24%, respectively, compared to other products. The fungicide Aprovia applied in-furrow at the recommended rate for the management of Verticillium wilt significantly reduced Verticillium sp. CFU/g of soil in treated soil by 73.3% compared to Velum, Mustgrow, Senator PSPT, Vapam, ammonium-lignosulfonate, Nimitz, and the untreated control. Disease management products increased potato marketable yield by 27.38-97.74%. The results of this study suggest that the root lesion nematode and V. dahliae have a ubiquitous distribution in the fields cultivated with potatoes in NB. The co-infection of potato by both V. dahliae and the root lesion nematode can greatly increase the severity of PED. Fumigation with Chloropicrin significantly reduced the levels of root lesion nematodes and Verticillium in all fumigated fields. Management practices of PED using the fungicide Aprovia, the nematicide Velum, and a combination of both Velum + Aprovia had the greatest effect in reducing the population density of the root lesion nematode and Verticillium dahliae in soils of commercial potato fields in New Brunswick.