Potato virus Y: Contact Transmission, Stability, Inactivation, and Infection Sources

In glasshouse experiments, two isolates of Potato virus Y ‘O’ strain (PVYO) were transmitted from infected to healthy potato plants by direct contact when leaves were rubbed against each other, when cut surfaces of infected tubers were rubbed onto leaves, and to a limited extent, when blades contaminated with infective sap were used to cut healthy potato tubers. However, no tuber-to-tuber transmission occurred when blades were used to cut healthy tubers after cutting infected tubers. When leaf sap from potato plants infected with two PVYO isolates was kept at room temperature, it was highly infective for 6 to 7 h and remained infectious for up to 28 h. Also, when sap from infected leaves with one isolate was applied to five surfaces (cotton, hessian, metal, rubber vehicle tire, and wood) and left to dry for up to 24 h before each surface was rubbed onto healthy tobacco plants, PVYO remained infective for 24 h on tire and metal, 6 h on cotton and hessian, and 3 h on wood. The effectiveness of disinfectants at inactivating this isolate was evaluated by adding them to sap from infected leaves which was then rubbed onto healthy tobacco plants. None of the plants became infected when bleach (42 g/liter sodium hypochlorite, diluted 1:4) or Virkon-S (potassium peroxymonosulfate 50% wt/wt, diluted to 1%) was used. A trace of infection remained after using nonfat milk powder (20% wt/vol). PVY infection sources were studied in 2011–2012 in the main potato growing regions of southwest Australia. In tests on >17,000 potato leaf samples, PVY was detected at low levels in seed (4/155) and ware (6/51) crops. It was also detected in volunteer potatoes from a site with a previous history of PVY infection in a seed crop. None of the 15 weed species tested were PVY infected. Plants of Solanum nigrum were symptomlessly infected with PVYO after sap inoculation, and no seed transmission was detected (>2,500 seeds). This study demonstrates PVYO can be transmitted by contact and highlights the need to include removal of volunteer potatoes and other on-farm hygiene practices (decontaminating tools, machinery, clothing, etc.) in integrated disease management strategies for PVY in potato crops.

Survival and reproduction of Liberibacterinfected tomato potato psyllid reared under cold environmental conditions

The tomato potato psyllid (TPP Bactericera cockerelli) survives on volunteer potatoes growing in frostfree areas in winter in the Auckland region and therefore could transmit Candidatus Liberibacter solanacearum (Lso) to commercial crops The survival and oviposition of laboratoryreared Lsoinfected TPP were tested under four selected environmental conditions 1212 h lightdark at 10C; 1311 h lightdark at 12C; 1410 h lightdark at 14C; and 159 h lightdark at 16C on excised leaves from volunteer potatoes (grown in the field during winter) and tomato (grown in the glasshouse) One hundred pairs of adult TPP (10 pairs/leaf) were tested on either potato or tomato in each environmental condition for 7 days Survival of females on potato or tomato was not significantly different between photoperiod but remained unhatched in all tested temperatures Results revealed that Lsoinfected TPP could feed (as indicated by excretory droplets) oviposit and survive on volunteer potatoes in Auckland winterlike conditions and potentially transmit Lso to crops grown in these cooler months

Detection of Clavibacter michiganensis subsp. sepedonicus in daughter tubers of volunteer potato plants

Daughter tubers of volunteer potatoes were tested for their ability to maintain <I>Clavibacter michiganensis</I> subsp. <I>sepedonicus (Cms)</I>. In different areas of the CR, volunteer potatoes were searched for in crops grown in rotation with potatoes and where one or two years before <I>Cms</i> had been detected and identified in samples of harvested seed or commercial potatoes using the test scheme in accordance to EC Directive 93/85/EEC. During May and June of 2005 and 2006, emerging or emerged plants of volunteer potatoes were collected at nine locations of Bohemia and transplanted to the experimental field in the Diagnostic Service Laboratory at Šluknov-Kunratice in Northern Bohemia. The daughter tubers of these plants were harvested and stored at 6°C for 1 month and then at 22°C for 3 months for multiplication of <I>Cms</i> cells. Samples of the daughter tubers were divided into 215 partial samples and tested for the occurrence of <I>Cms</i> at five terms which differed in length of storage time. The DAS ELISA test was used to detect <I>Cms</i> in the tuber samples. <I>Cms</i> was detected in eight of the nine potato volunteer tuber samples from different locations. The presence of <I>Cms</i> in positively tested tuber samples was confirmed using a pathogenicity test on eggplants (<I>Solanum melongena</I>). The optimal time for the detection of the pathogen in the harvested daughter tubers was between 4 and 10 weeks of storage at 22°C.