Occurrence and Distribution of Potato Pests and Diseases in Kenya

Potato plays an important role in food security in Kenya but yields are low (<10 t/ha), and this is partly attributed to the lack of healthy planting material. This study is the first wide-scale survey to determine the occurrence and distribution of common potato pests and diseases in Kenyan seed (certified and quality declared) and ware crops. Potato crops growing on 101 farms in 21 districts were examined. Approximately 36% of plants in farmers’ fields sampled both during the long rains (main potato-growing season) and short rains seasons displayed virus-like disease symptoms. Six viruses (potato leafroll virus (PLRV), Potato virus A (PVA), potato virus M (PVM), potato virus S (PVS), potato virus X (PVX), and potato virus Y (PVY)) were detected using double antibody sandwich enzyme-linked immunosorbent assay in potato samples. Sequencing of polymerase chain reaction products from PVY-infected plants revealed the presence of recombinant strains of PVY (NTN and Wilga). Four aphid species, Macrosiphum euphorbiae, Aphis gossypii, Myzus persicae, and Aphis fabae, colonized potato in all districts, occurring in greater numbers west of the Great Rift Valley than to the east. There was a positive correlation between virus incidence and aphid numbers in the long rains (main) potato-growing season. PLRV, PVM, PVS, PVX, and PVY were detected in solanaceous weeds. Ralstonia solanacearum was detected in soils from 13 farms in 8 of the 18 districts surveyed. Approximately 38% of soil samples were infested with Meloidogyne spp. Phytophthora infestans isolates belonging to the US 1 and 2_A1 genotypes were identified. Although many economically important diseases are present in Kenya, the lower aphid incidence in districts east of the Great Rift Valley may indicate that these districts are more suitable for seed potato production.     

Volunteer potatoes as a source of potato leafroll virus and potato virus X

Volunteer potatoes were investigated as infection sources for potato leafroll virus (PLRV) and potato virus X (PVX) in a high elevation seed potato growing area of eastern Idaho. Population densities ofMyzus persicae were assessed. Percentage of PLRV and PVX infection of the volunteers and seed potato crops was determined, as well as density of volunteers and certain parameters of volunteer growth and reproduction. Volunteers apparently harbored no more PLRV than the potato crop from which they originated. But they were found to be an important reservoir of PVX with the infection increasing as much as 12.43% in one year. No aphids capable of transmitting PLRV were found although one species that can transmit potato virus Y was recorded. The mean density of volunteers varied from 0 to 84,880 stems/ha. The number of tubers remaining in the field after harvest and winter weather conditions appeared to be the only factors affecting volunteer density. Volunteer plants arising from seed pieces at an average depth of 6.1 cm were found to set an average of 2.1 new tubers per plant at an average depth of 4.0 cm. These results suggest that volunteer potatoes are a significant source of PVX infection in subsequent seed potato crops.     

Genetic Resistances to Potato Leafroll Virus, Potato Virus Y, and Green Peach Aphid in Progeny ofSolanum etuberosum

Increasing prevalence of potato leafroll virus (PLRV) and potato virus Y (PVY) has been reported in seed and commercial potato production, resulting in the rejection of potatoes for certification and processing. Host plant resistance to PLRV and PVY and their primary vector, green peach aphid,Myzus persicae, could limit the spread of these viruses. Host plant resistance to PLRV, PVY, and green peach aphid has been identified in non-tuber-bearingSolanum etuberosum (PI 245939) and in its backcross 2 (BC₂) progeny. Resistance to green peach aphid involved a reduction in fecundity and adult aphid size. In addition, one BC₂ individual was identified as possessing a genetic factor that was detrimental to nymph survival. PVY resistance was identified in all five BC₂ progenies evaluated in a field screening under intense virus pressure. PLRV resistance was identified in two of the five BC₂ progeny. This resistance was stable in field and cage evaluations with large populations of viruliferous aphids. Based on the segregation of virus resistances in the BC₂ , PVY and PLRV resistances appear to result from the action of independent genetic mechanisms that reduce the levels of primary and secondary virus infection. Two BC₂ individuals, Etb 6-21-3 and Etb 6-21-5 were identified as having multiple resistances to PLRV, PVY, and green peach aphid derived fromS. etuberosum. This germplasm could prove useful to potato breeders in the development of virus-resistant cultivars.     

Potato Plants Grown from Minitubers are Delayed in Maturity and Lower in Yield,but are not at a Higher Risk of <Emphasis Type="Italic">Potato virus Y</Emphasis> Infection than Plants Grown from Conventional Seed

Potato virus Y (PVY) is the most important virus in North American seed potato (Solanum tuberosum L.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type.     

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.     

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.     

Occurrence of Viruses Affecting Potato Crops in Khartoum State-Sudan

The incidence of Alfalfa mosaic virus (AMV), Potato leafroll virus (PLRV), and Potato virus Y (PVY) in potato crops derived from various types of seed potatoes was assessed visually and confirmed by direct tissue blot immunoassay, over two winter growing seasons (1999/2000, 2000/2001) at three locations, Elnaiya, Elshehinab, and Shambat in Khartoum State, the main potato growing region in Sudan. Virus infection was most prevalent in 2000/2001. In general, crops grown directly from imported certified seed potatoes and from “improved seed”, produced in Sudan from imported basic seed, showed the lowest levels of PLRV and PVY compared with crops grown from Sudanese farm saved seed. For AMV, however, only crops grown directly from imported certified seed potatoes had low levels of AMV. Crop location also affected virus incidence, although this varied with year. For AMV, levels were similar at all locations in 1999/2000, but were greatest at Elnaiya in 2000/2001. For PVY, levels were greatest at Elnaiya in 1999/2000 and Shambat in 2000/2001. For PLRV, no symptoms were observed in 1999/2000 and virus levels were similar for all locations in 2000/2001. This study reports for the first time the occurrence of AMV in potatoes grown in Sudan.     

Enzyme-linked immunosorbent assay (ELISA) for the detection of potato leafroll virus and potato virus Y in potato tubers after artificial break of dormancy

Summary Conditions necessary for the detection of potato leafroll virus (PLRV) and potato virus Y (PVY) in tubers from primary and secondary infected plants were investigated. Tubers were analysed before and after breaking dormancy by rindite treatment. PLRV was reliably detected indormant tubers whereas PVY was readily detected only when tubers had been rindite-treated and held for two to three weeks at 22°C and high humidity in the dark. PLRV occurred in higher concentration at the heel end than at the rose end of infected tubers and the concentration remained nearly unchanged during the experimental period of 35 days, whereas PVY was found to be more concentrated at the rose end and was rapidly accumulating in the tubers after the break of dormancy. In dormant tubers PVY concentration dropped during storage at 22°C. The use of ELISA for tuber indexing is discussed.     

Modification of serological techniques and their evaluation for detection of potato viruses in seed certification related activities

Development of alternative serological techniques to ELISA for detection of potato viruses offers advantages for monitoring virus incidence and for seed potato certification systems. Several trials showed that multiplex tissue print immunoassay (TPIA) and dot blot immunoassay (DBIA) might represent fast, practical, and sensitive alternatives for the detection of: Potato leaf roll virus (PLRV), Potato virus S (PVS), Potato virus X (PVX) and Potato virus Y (PVY), from green and/or tuber tissues. In TPIA, the specific precipitation patterns in infected tissues of leaf petioles or stem cross sections, observed with each virus, allowed identification of the specific virus or mixed infections in a single multiplex assay. For detection of PVY in green tissues, DBIA was shown to be over 50 times more sensitive than ELISA. TPIA and ELISA from the tuber stem end or from eyes might be used for rapid detection of PVY and PVS in seed potato tubers without prior germination. PVS was evenly distributed in potato tuber tissue, while PVY was localized in the vascular tissue beneath the epidermis, with irregular distribution along the periphery of the potato tuber. For laboratories in developing countries lacking time and facilities for tests based on tuber germination, monitoring for PVS and PVY using TPIA in tuber tissue may be a suitable alternative to ELISA.     

Cryotherapy of Potato Shoot Tips for Efficient Elimination of Potato Leafroll Virus (PLRV) and Potato Virus Y (PVY)

Viral diseases constitute a major constraint to high yield and high quality production of potato. Potato leafroll virus (PLRV) and Potato virus Y (PVY) are among the most damaging potato viruses and are prevalent in most potato growing areas. In the present study, attempts were made to eliminate PLRV and PVY by three cryogenic protocols, i.e., encapsulation-dehydration, encapsulation-vitrification and droplet. Results showed that both PLRV and PVY could be efficiently eliminated by cryogenic treatments with 83–86% and 91–95% of frequencies of virus-free plantlets obtained for the former and latter, respectively. Frequencies of virus-free plantlets produced by cryogenic treatments were higher than those by meristem culture (56% for PLRV and 62% for PVY) and thermotherapy (50% for PLRV and 65% for PVY), and similar to those by thermotherapy followed by meristem culture (90% for PLRV and 93% for PVY). Survival (75–85%) and regrowth (83–89%) from cryo-treated shoot tips were higher than those from meristem culture (50–55%) and thermotherapy followed by meristem culture (40–50%), but similar to those from thermotherapy (80–87%). The morphology of the plantlets regenerated from cryo-treated shoot tips was similar to that of non-treated plantlets. Thus, cryotherapy would provide an alternative method for efficient elimination of potato viruses, and can be simultaneously used for long-term storage of potato germplasm and for production of virus-free plants.     

The infection pressure of potato leafroll virus and potato virus Y in relation to aphid populations in Cyprus

Summary The infection pressure of two viruses, potato leafroll (PLRV) and potato virus Y (PVY), both common in seed potatoes grown in Cyprus, was determined in three experiments in 1982–83. Virus-free bait plants, of potato and four other species, were exposed weekly to field infection during the growing season (March–June), and then returned to an aphid-free glasshouse for symptom expression. Only tobacco plants produced clear symptoms enabling reliable assessment of PVY infection pressure. When assessed with ELISA or by tuber indexing, the potato plants were efficient baits for both viruses whose infection period commenced at emergence (mid March to early April) and ended within 6–7 weeks. The seasonal trend of aphid populations, determined with Moericke traps or 100-leaf counts, correspond to that of virus spread. Correlation and regression analysis of aphid and virus data implicated the alate form ofMyzus persicae as the principal vector of both viruses.     

Solanum demissum P.I. 230579, a True seed diagnostic host for potato virus Y

Seedlings ofSolarium demissum P.I. 230579 in the 5-to 10-leaf stage growing under 18-hour days and at 20 to 24°C developed dark, irregular, slightly elongated local lesions 3 to 5 days following inoculation with any one of three strains of potato virus Y (PVY). Local lesions did not develop after similar inoculations with any one of two or more strains each of potato viruses A, M, S, X, or spindle tuber and a single strain each of potato calico and potato yellow dwarf. Inoculations from diseased specimens infected with PVY plus potato viruses A, M, S, and X, singly or in some combinations did not affect the efficiency of P.I. 230579 in detecting PVY in the mixed infections. Plants of P.I. 230579 developed significant numbers of local lesions from PVY inoculations at temperatures from 16 to 27°C and at inoculum dilutions through 1:100. Excised individual leaves of P.I. 230579 can be used to detect PVY. Leaves of plants exposed to air pollutants are unsuitable for assay purposes.S. demissum P.I. 230579 is homozygous for the local reaction to isolates of PVY and is a valuable aid for indexing aphid or mechanically inoculated potato clones or seedlings for resistance to the virus. It is a superior diagnostic host for differentiating PVY from other viruses commonly found in potatoes in the United States.     

Population Growth of Myzus persicae on Potato Plants Infected with Different Strains and Variants of Potato virus Y

Potato virus Y (PVY) is one of the most economically important viruses affecting the potato crop. Several strains of the virus, including PVY^O, PVY^N, recombinant isolates; PVY^N:O (PVY ^N-Wi) and PVY^NTN and several variants of PVY^O have been reported from North American potato-production areas. The green peach aphid, Myzus persicae Sulzer, is a colonizer of potatoes and is considered the most important vector of PVY. The objective of this study was to measure the population growth of M. persicae on potato plants infected with different strains and genetic variants of PVY. The initial population of ten winged adults of M. persicae was allowed to develop on a potted plant for 12 days. Results clearly indicated that infections by different strains and genetic variants of PVY did not influence the population growth of M. persicae on potato plants during this period.     

Attempts to extend seed potato production in Israel to new areas at high altitudes

Summary Attempts were made to grow seed potatoes in the Gilboa mountains and central Golan Heights both at ca 500 m altitude. The activity of winged aphids was low between May and September, the period suitable for growing seed potatoes. Potato virus X (PVX) and potato virus Y (PVY) were rare. The highest incidence of potato leaf roll (PLRV) was 17% at Gilboa and 5% at Nov (central Golan). In both areas, spindle sprout was a severe problem in progeny tubers and it was associated with a purple top syndrome, probably caused by a mycoplasma, that appeared during growth. Activity of the probable vector, the leafhopperHyalesthes obsoletus, ceases in the Golan after June. Delaying planting until the end of May or later reduced the incidence of purple top and spindle sprout to nil. Both were reduced by Temik treatment and by covering the plots with netting but not by treatments with Rogor and Croneton. All three chemicals reduced PLRV incidence. Therefore, delayed plantings and insecticides may reduce purple top, spindle sprout and PLRV. This work was partly supported by funds of BARD 339-80.     

湖南省马铃薯主产区马铃薯病毒种类及流行分析

马铃薯是世界第四大粮食作物,其病毒病危害严重。2010年对湖南马铃薯主产区采集的66个病毒标样进行了RT-PCR检测,结果表明,检测出的马铃薯病毒有马铃薯Y病毒(PVY)、马铃薯卷叶病毒(PLRV)、马铃薯X病毒(PVX)、马铃薯S病毒(PVS)、马铃薯A病毒(PVA)和马铃薯纺锤块茎类病毒(PSTVd)。其中PVS的检出率最高,为54.5%,其次是PVX,检出率为45.5%,PVY的检出率为39.4%,PSTVd和PVA的检出率均为21.2%,PLRV的检出率为18.2%。2~4种病毒的复合侵染现象较为普遍。PVY中重组型PVY占85.7%。     

The effect of metribuzin interaction with potato viruses X and Y on potato foliage,yield and grade

Foliar treatment of potato (Solanum tuberosum L.) with metribuzin at 0.57–1.0 lb/A caused a necrotic reaction in leaflets of plants infected with potato virus Y (PVY), but not in plants infected with potato virus X (PVX) or potato leafroll virus. Necrosis symptoms resulting from metribuzin-PVY interaction were distinct from symptoms of either PVY infection or of metribuzin injury. This reaction was similar in the Russet Burbank, Lemhi Russet, and Pioneer cultivars. Russet Burbank infected with PVY and PVX, alone or in combination, was treated with metribuzin to study herbicidevirus interaction effects on yield. Secondary PVY infection alone caused a 57% yield reduction, and when combined with PVX caused a 71% yield reduction. Although leaflet necrosis was induced by the metribuzin-PVY combination, there was no significant yield interaction. Results suggest that post-emergence application of metribuzin can be used as an aid for detecting and removing potato virus Y infected plants from potato seed fields     

Seed Potato Production in Poland

The aim of this research was to analyze the regional distribution and quality of potato seed production in Poland from 2007 to 2011. The research was based on 10,559 tuber samples taken for the official post-harvest inspection assessment of seed potato lots. A very detailed map of seed plantation locations in Poland was created at the municipality level. The greatest concentration of seed production was from the northern and southern parts of Pomorskie Province, where many seed potatoes were cultivated, and in the north of the Zachodniopomorskie Province, around the towns of Koszalin and Ko?obrzeg. In both provinces, cultivars which were highly susceptible to PVY were cultivated on nearly half of the area. Over time a clear increase in the production of elite material and a decrease in those certified as the lowest category, CB, were observed. The quality of seed potato material was poorest following the harvest in 2008, because of high levels of virus infection; 30 % of the seed lots were not certified. Potato leaf roll virus (PLRV) was recorded occasionally and it is at present of no economic importance in Poland. The role of potato virus Y (PVY), increased, probably because of the growth in the share of foreign cultivars (mainly Dutch) which are more susceptible to PVY. There were also changes in the populations of PVY strains. The share of Polish cultivars in potato seed production decreased to 36.3 % in 2012.     

马铃薯病毒外壳蛋白融合基因转化马铃薯及其抗病性分析

将多种病毒的有效核酸片断拼接成融合基因转入马铃薯可获得多抗马铃薯材料。针对马铃薯生产中分布广泛、危害严重并经常混合感染的马铃薯X病毒(PVX)、马铃薯Y病毒(PVY)、马铃薯卷叶病毒(PLRV)和马铃薯S病毒(PVS),开展了利用基因工程方法获得兼抗4种马铃薯病毒转基因马铃薯材料的研究。试验在前期获得含4种马铃薯病毒外壳蛋白基因片段的质粒pART27-XSYV-rh的基础上,通过根癌农杆菌(Agrobacterium tumefaciens)介导转化马铃薯(Solanum tuberosum)品种‘陇薯3号’,PCR扩增和PCR-Southern杂交证明,4价融合基因已整合到马铃薯基因组中。qRT-PCR分析表明,该融合基因在转基因植株中能正常表达。3株转基因植株的抗病性鉴定结果表明,2株对4种病毒同时具有抗性;1株对PLRV侵染表现阳性,对另外3种病毒同时具有抗性。