Reaction to the potato leafroll virus (PLRV) in diploid potatoes

Summary Diploid parents with some resistance to PLRV, were intercrossed to give 3 families with 191 clones which were evaluated for reaction to PLRV and yielding ability. After inoculation with PLRV the clones could be separated into those: 1) resistant, 2) susceptible, 3) intolerant, reacting with low virus concentration, 4) tolerant and 5) intermediate in reaction. Both the ELISA test and the evaluation of external disease symptoms were necessary to separate the clones. No correlation was found between resistance to PLRV and tuber yielding ability.     

Potato leafroll virus and potato virus Y in seed potatoes used to plant the North Carolina crop

Incidence of potato leafroll virus (PLRV) and potato virus Y (PVY) was determined in seed potatoes (Solatium tuberosum) from Canada, Maine, Minnesota, New York, North Dakota, Nebraska, Pennsylvania, and Wisconsin used to plant the North Carolina crop in 1977, 1978 and 1979. Incidence of PLRV ranged from 0–5.2% (X = 0.57%) and for PVY from 0-5.6% (X = 0.62%) from all sources (112 seed lots). All PVY isolates (177) tested from potato caused a very mild veinbanding and mottling onNicotiana tabacum cultivars NC 95 and NC 2326. No serological difference was detected between these isolates and the common strain of PVY from tobacco in North Carolina. Essentially no spread of PVY occurred in three potato fields observed each year of the study.     

Electrotherapy and shoot tip culture eliminate potato virus X in potatoes

Potato stems infected with potato virus X (PVX) were exposed to either 5, 10, or 15 miliampers (mA), for 5 or 10 minutes, followed by immediate planting the axillary buds tipin vitro. Temperature increased from 4 to 10 C in the tissues during the exposure to the electricity. After a 60 days growing period, therapy efficiency (TE, TE = % plant regeneration X% virusfree resulting plants) was influenced by the severity of treatment, since organogenesis and virus elimination were both stimulated by the electricity. The highest TE values were obtained at 15 mA for 5 minutes. Under these conditions, 40% to 80% of the buds regenerated, and 60% to 100% of the regenerated plantlets tested virus negative.     

Environmental factors influencing aphid transmission of potato virus Y and potato leafroll virus

Summary The effect of temperature, relative humidity (RH) and light on aphid transmission of potato virus Y (PVY) and potato leafroll virus (PLRV) was studied using as vectorsMyzus persicae Sulz. andAphis gossypii Glov. Host susceptibility was enhanced by 48 h pre-inoculation exposure at 25°C and by 48 h post-inoculation exposure to 30°C. High RH (80%) in both pre- or postinoculation phases enhanced host susceptibility. Continuous fluorescent light (4000 lux) did not alter the rate of transmission of either virus. High RH (80–90%) and high temperature (25–30°C), when combined, increased virus transmission by 30–35%. Transmission rates were reduced by nearly 50% if RH was maintained at 50% in either of the two phases even if the temperature was 25 or 30°C. Both viruses were acquired by aphids earlier (13–20 days after inoculation) when the source plants were incubated at 25 or 30°C. Most virus was transmitted from plants inoculated with PVY 13 to 16 days and with PLRV 15 to 20 days previously. Transmission rates of PVY were enumerated from symptom expression on test plants and by Enzyme Linked Immunosorbent Assay (ELISA) whereas those of PLRV were enumerated from symptom expression alone.     

Field testing potatoes for resistance to leafroll and virus Y

A method of screening seedlings in a breeding program for resistance to leafroll and virus Y under field conditions is outlined. From the results, more meaningful decisions can be made as to the prospects of a particular seedling surviving under commercial conditions. In addition, parents for resistance to the two viruses can be identified.     

Heat inactivation of leafroll virus in potato tuber tissues

Heat inactivation of leafroll virus in tuber tissues of three potato varieties (Russet Burbank, Katahdin, and Mohawk) was studied. Russet Burbank did not tolerate high constant temperatures and a low proportion of tubers and eye-pieces survived the treatments. On the other hand, Russet Burbank eye-pieces survived, with few exceptions, treatment at 40 C for four hours alternating with room temperaure (16–20 C) for 20 hours daily for as long as eight weeks. Inactivation of the virus was complete after six weeks of this treatment. Results obtained with the Katahdin and Mohawk varieties in similar tests were variable, and this possibly may be attributed to the higher room temperature (25–30 C) prevailing during these experiments.     

Resistance of potato clones to the green peach aphid and potato leafroll virus

During 1980 and 1981 potato cultivars and breeding selections, including cultivated species and their hybrid derivatives, were evaluated for resistance to the green peach aphid (GPA),Myzus persicae (Sulzer), and to potato leafroll virus (PLRV). Criteria used were the number of aphids which colonized the clones in free choice field experiments and the number of plants derived from these experiments which showed symptoms of PLRV infection. Generally, greater resistance to GPA was found inSolarium tuberosum gp.andigena selections and hybrids than in gp.tuberosum cultivars. There were approximately fourfold differences in season-mean GPA levels among the clones tested each year. Forty-two families, representing a cross-section of the USDA breeding populations at the University of Idaho Research and Extension Center, Aberdeen, showed a similar range in colonization levels. Resistance to GPA colonization appeared to be more prevalent in gp.andigena, gp.phureja, and gp.stenotonum derivatives. There was a weak positive correlation (r² = .34, P = .01) between foliar total glycoalkaloids and season-mean GPA colonization levels for six clones representing the range of observed resistance to GPA. Resistance to GPA colonization was apparently not directly related to resistance to PLRV infection. Katahdin, for example, was relatively susceptible to GPA colonization but very resistant to PLRV infection whereas selection A69657-4 (gp.andigena) was among the most resistant to GPA colonization but among the more susceptible to PLRV infection. Breeding for resistance to GPA colonization therefore may not be as promising for PLRV control as developing PLRV resistant cultivars.     

Overwintering and monitoring of potato leafroll virus in some wild crucifers

A potato leafroll virus (PLRV) isolate has been successfully transmitted to and recovered from two wild crucifers,Sisymbrium altissimum L. (Jim Hill or tumble mustard) andCapsella. bursa-pastoris (L.) Medic. (shepherd’s purse) by the green peach aphid (GPA),Myzus persicae (Sulzer). Virus antigen in both plant species was found to be higher in root tissue than in foliar tissue, based on enzyme-linked immunosorbent assay (ELISA) determinations.C. bursa-pastoris was apparently a relatively poorer source of inoculum for the GPA thanS. altissimum. Using two geographically-separated biotypes ofC. bursa-pastoris, a Washington biotype was found to contain higher antigen titer in both leaf and root tissue than a California biotype, as determined by ELISA. Field studies demonstrated that both weed species can serve as overwintering sources of PLRV     

Comparison of three potato leafroll virus antisera and a single Beet western yellows virus antiserum for luteovirus detection in potato

Three potato leafroll virus (PLRV) antisera, representing European, British Columbian, and Californian isolates, performed similarly in detection of PLRV in ELISA tests of samples collected in three successive years at the Florida certification test plots and in tests of other samples collected in New York State. Although a range of absorbance values occurred, this was probably due to random variation in virus titers of samples rather than the occurrence of different virus strains or differential serological reactions by the antisera. Beet western yellows virus (BWYV) was detected in potato leafroll samples from nine states and provinces in North America. The BWYV-positive samples represented 40% in 1983 and 62.5% in 1984 of the total number of samples tested. These results confirm previous reports on the widespread occurrence of BWYV in potato with symptoms of leafroll.