Stage of development of leaf and tuber tissue of the potato plant influences the titer of potato virus M

The enzyme-linked immunosorbent assay (ELISA) was adapted for the detection of potato virus M (PVM). Detectability of PVM was influenced by the stage of plant growth and that of the plant part assayed. In young potato plants, one week prior to flowering, PVM titer was relatively high (0.77 A_405nm units) in the basal leaves and barely detectable (0.09 A_{405 nm} units) in the top leaves. In mature plants, two weeks prior to harvesting, top leaves contained more virus (0.34 A_{405 nm} units) than middle (0.24 A_405nm units) or basal leaves (0.15 A_{405 nm} units). In rapidly growing tubers PVM content was higher (1.57 A_{405 nm} units) than that in fully grown tubers (0.71 A_405nm units) whereas the virus was not detectable in the mother tuber four weeks following planting. PVM was reliably detected when disks from intact leaves were substituted for leaf extracts as the test sample     

Use of Biocontrol Organisms and Compost Amendments for Improved Control of Soilborne Diseases and Increased Potato Production

Soilborne potato diseases are persistent problems in potato production and alternative management practices are needed. In this research, biocontrol agents (Bacillus subtilis GB03 and Rhizoctonia solani hypovirulent isolate Rhs1A1) and compost amendments (from different source material), were evaluated alone and in combination, for their potential to reduce soilborne diseases and increase tuber yield over three field seasons in Maine. Both biocontrol organisms reduced multiple soilborne diseases, stem and stolon canker by 20–38 %, black scurf by 30–58 %, and common scab by 10–34 % relative to the nontreated control treatment, and the combination treatment of both biocontrol organisms together provided nominally better control than individual treatments. However, biocontrol treatments had no direct effect on tuber yield. Compost amendments from different sources all increased total and marketable tuber yield substantially (11–37 % and 17–51 %, respectively) relative to nontreated controls. However, except for some reduction of Rhizoctonia canker, compost amendments did not reduce soilborne diseases (black scurf and commons scab) in any year, and resulted in increased levels of common scab in some years (20–45 % increase). The combination compost-biocontrol treatment, although did not perform significantly better than individual component treatments, still provided indications of combined beneficial effects from both component treatments. This research demonstrated the usefulness of these approaches and combinations as additional options for reduction of soilborne diseases and increased tuber yield and can be implemented for enhanced sustainability and productivity in potato production systems.     

Effect of hypovirulent rhizoctonia solani on rhizoctonia disease,growth, and development of potato plants

Field experiments were conducted to determine whether a hypovirulent, anastomosis group (AG) 3 isolate (Rhs 1A1) of R. solani could control rhizoctonia disease of potato caused by a virulent AG-3 isolate (Rhs 27). A uniform amount of Rhs 1A1, Rhs 27, or both was applied to formaldehyde-disinfected potato seed tubers at planting. In plots inoculated with Rhs 1A1 and Rhs 27, the area of infected stem tissue was significantly (P = 0.05) reduced by 56% as compared with that of plots inoculated with Rhs 27 alone. The number of stolons per plant was decreased by isolate Rhs 27 to one-half that of the uninoculated control, but remained unchanged in plots treated with both Rhs 1A1 and Rhs 27. The type of inoculum did not affect the percentage of infected stems or stolons. Plants inoculated with Rhs 1A1 alone exhibited a significantly (P = 0.05) greater growth response, expressed as a 4-fold increase in the dry weight of stolons, a 1.7-fold increase in the dry weight of stems, and reached full bloom approximately one week earlier than their respective control. Tuber yield increases associated with Rhs 1Al-treated plots were not statistically significant. When untreated seed tubers bearing natural inoculum (sclerotia) of R. solani were used, Rhs 1A1 failed to reduce disease severity or sig-nificantly stimulate plant growth.