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.     

Production of seed potatoes in Cyprus: incidence and economic importance of virus diseases

Summary Since 1981 seed potatoes have been produced on a semi-commercial scale in Cyprus by single multiplication of imported class A stocks. The main virus in these locally produced seed potatoes was potato leaf roll virus (PLRV) which was detected in 369 of 658 seed crops examined, at an average incidence of ca 1.5% (range 0.1%–15%). Tuber infections were detected in 203 of 223 samples tested, at an average incidence of ca 6.8% (range 1–32%), indicating a considerable spread of the virus during local seed multiplication. Potato viruses Y, X and A, and alfalfa mosaic virus occurred at much lower incidence than PLRV. The effect of secondary PLRV infection on ware-potato yield was determined in the cultivars Spunta and Cara, each planted on two different dates. In all four cultivar-planting date combinations there was a very close negative correlation between yield and virus incidence. At 100% infection, losses in total yield varied from 46% (later planting of Cara) to 72% (earlier planting of Spunta). The threshold level of infection for significant losses was ca 10%.     

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.     

A comparison of some methods for detecting potato leaf roll virus in potato tubers in Israel

Summary The results obtained by four methods for detecting PLRV in potato tubers grown in Israel were compared with the results obtained by aphid transmission to test plants. The correlation coefficients for potatoes lifted in July (seed for autumn) and September (seed for spring) were: Igel-Lange test, 0.18 and 0.25; datura grafting with tuber sprouts, 0.71 and 0.63; aphid transmission from sprouts to test plants, 0.89 and 0.81; and visual assessment in the Florida test (for spring seed), Up-to-Date 0.58, Blanka 0.67 and Désirée 0.33. The Igel-Lange test proved unreliable; datura grafting is time consuming and PLRV symptoms were similar to reactions ofDatura stramonium to wounding and to stress. The results of the Florida test were somewhat variable and were obtained too late. The sprout test was deemed the most suitable as it is accurate and the results can be obtained within two months. Contribution No 156-E, 1979 series, Volcani Center.     

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.     

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.     

Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

Trials to grow certified seed potatoes in the Golan Heights

Summary A trial to grow seed potatoes in summer 1968 in the Golan Heights indicated that hardly any aphid transmission of potato virus Y (PVY) could be noticed. Normal plant growth and tuber formation were observed. The incidence of seed borne virus diseases in fields grown from local seed produced in the Golan Heights in 1970 was: PVY 0.1–0.3% in 2 out of 33 inspected fields, potato leaf roll virus (PLRV) 0.3–2% in 19 fields. In 1972 30 fields were inspected, PVY was observed in 3 fields at a level of 0.1–0.2% PLRV at a level of 1–4% in 28 fields. Alfalfa mosaic visus (AMV) and Stolbur were not observed. The result of post-harvest control in field plots planted with seed potatoes produced in the Golan Heights in 1969, 1970 and 1971 were: PVY very low infection, 0.2–0.7%, for the three years; PLRV, low percentage, 0.3–0.7%, in 1970 and 1971, while it increased in 1972 to 1.3–6%. AMV and Stolbur were not observed.

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Zusammenfassung Die Felder auf den Golan-H?hen liegen 900 m ü. M. Die Temperatur ist tiefer als in den Ostgalil?ischen Bergen w?hrend des Sommers. Am 20. Mai 1968 wurden irische Pflanzkartoffeln der SorteUp-to-Date (anerkannt in Klasse A) in Merom Golan ausgepflanzt. In den Jahren 1969–1971 wurden im Mai Basispflanzen und Pflanzgut der Klasse A der SorteUp-to-Date an zwei verschiedenen Orten, Meron Golan und Ein Zivan, angebaut (Tabelle 2). In den Ergebnissen der Feldbesichtigungen, die 1969–71 2–3 mal in Juni/Juli durchge führt wurden, widerspiegelte sich ein offensichtliches Fehlen der Virus-Vektoren. Es wurde kaum eine Uebertragung des Kartoffelvirus Y (PVY) durch Blattl?use festgestellt mit einer Ausn?hme, n?mlich im September 1970, als eine verbreitete PVY-Infektion beobachtet wurde. Diese Parzellen unterstanden dem Seed Inspection Service, und der Ertrag wurde als zertifiziertes Pflanzgut verwendet. In den Jahren 1971–1972 wurden Muster von 100–200 Knollen in Pflanzgutgr?sse (40–100 g) zu verschiedenen Erntedaten entnommen und zu Untersuchungszwecken in einem insektensicheren Glashaus ausgepflanzt. Der durchschnittliche Virusbefall betrug 1971: PVY 1,3–2,6%, Kartoffel-Blattrollvirus (PLRV) 1,5–5,3%, Luzerne-Mosaikvirus (AMV) 6–12%, Stolbur 0–2% (Tabelle 2); 1972: PVY 1,3–2,5%. PLRV 0,5–4,6%, Stolbur war nicht vorhanden, AMV 2,5–4% (Tabelle 3). Pflanzgutmuster von den Golan-H?hen wurden 1970–72 in Versuchsparzellen angebaut. Der Virusbefall war wie folgt: PVY 0–0,7%, PLRV 0,3–6%, AMV 0–1% und Stolbur 0–0,5% (Tabelle 1). Vom Ertrag im Jahre 1970 wurden die Knollen in Pflanzgutgr?sse 1971 auf verschiedenen Feldern angebaut. Gem?ss dem Seed Inspection Service betrugen die Viruskheiten im Mittel: PVY 0,1–0,3% nur in 2 von 33 besichtigten Feldern; PLRV 0,3–2% in 19 Feldern, w?hrend das Virus in den andern 14 besichtigten Feldern nicht festgestellt wurde. 1972 wurden 30 Felder besichtigt, deren Pflanzgut im Sommer 1971 auf den Golan-H?hen erzeugt wurde. Befall mit Viruskrankheiten: PVY 0,1–0,2% in drei Feldern und keine Spur von PVY in den andern Feldern; PLRV 1–4% in 28 Feldern, und nur in 2 Feldern wurde kein sekund?res PLRV entdeckt. Die PLRV-Infektion ist also zunehmend h?ufiger aufgetreten und der Prozentsatz war h?her. Gelbscheckigkeit oder Calico infolge AMV oder Stolbur wurden in diesen 1971–1972 besichtigten Feldern nicht beobachtet. Die Ursache für diesen bedeutend geringeren Virusbefall auf den Feldern und den Kontrollparzellen, verglichen mit den Laboruntersuchungen, liegt in der Tatsache, dass eine betr?chtliche Zahl der AMV-infizierten Knollen nicht keimten oder unter Feldbedingungen nicht aufgingen. Pflanzen von PVY-infizierten Knollen neigen dazu, so früh aufzulaufen wie Pflanzen von gesunden Knollen; sie werden von ihren kr?ftigeren Nachbarn gedeckt und k?nnen daher den Augen des Anerkennungsexperten entgehen. Beurteilung von Pflanzkartoffeln von den Golan-H?hen. Im Frühling 1971 wurden Pflanzkartoffeln der SorteUp-to-Date von den Golan-H?hen im Vergleich met irischenUp-to-Date an neun verschiedenen Orten angebaut. An einem Ort war der Ertrag gleich, an vier Orten war er geringer und an den andern vier Orten h?her (Tabelle 6); w?hrend 1972 der Ertrag des Pflanzgutes von den Golan-H?hen gr?sser war mit dem gleichen Prozentsatz von grossen Knollen (über 60 g) (Tabelle 5). Die Pflanzkartoffeln von den Golan-H?hen verhalten sich wie Pflanzgut jüngerer Anbaustufen in bezug auf Auflaufen, Stengelzahl (Tabelle 4), Blühen und Knollenbildung.

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Résumé Les hauteurs de Golan se trouvent à 900 m audessus du niveau de la mer. Durant l'été la température y est plus basse que dans les montagnes de l'est de la Galilée. Le 20 mai 1968, on a planté à Meron Golan des plants irlandais certifiés A de la variétéUp-to-Date. Au cours des années 1969–1971, on a planté en mai des plants de base et des plants de classe AUp-to-Date dans deux localités différentes: Meron Golan et Ein Zivan (tableau 2). L'absence saisonnière apparente de vecteurs se reflète dans les résultats d'inspection des champs, exécutées 2–3 fois en juin-juillet 1969–71, ce qui explique qu'on n'a pu obsevver réellement aucune transmission par aphides de virus Y (PVY) sauf une fois où l'on observé, en septembre 1970, une infection réalisée en cours de saison. Les parcelles étaient soumises au contr?le du Service d'inspection des plants, et la production utilisée comme plants de pomme de terre certifiés. Au cours des années 1971–72, on a planté, en vue de tests, des échantillons de 100–200 tubercules de calibre ‘plants” (40–100 g), dans un abri toilé à l'abri des pucerons, et récoltés à différentes dates. En 1971, on a observé les viroses suivantes: PVY 1,3–2,6%, enroulement (PLRV) 1,5–5,3%, alfalfa (AMV) 6–12%, stolbur 0–2% (tableau 2). En 1972, les manifestations de viroses ont été les suivantes: PVY 1,3–2,5%, PLRV 0,5–4,6%, le stolbur étant absent, AMV 2,5–4% (tableau 3). On a planté des échantillons de plants provenant des hauteurs de Golan dans des parcelles expérimentales au cours des années 1970 et 1971. On a noté les viroses suivantes: PVY 0–0,7%, PLRV 0,3–6%, AMV 0–1% et stolbur 0–0,5% (tableau 1). En 1971, on a planté dans différents champs des tubercules de calibre ‘plants’ provenant de la production totale de 1970, les moyennes des maladies virologiques, selon le service d'inspection des plants, furent les suivantes: PVY 0,1–0,3% dans deux champs seulement des 33 champs inspectés, PLRV 0,3–2% dans 19 champs tandis qu'on a identifié aucune virose dans les 14 champs restants. En 1972, on a inspecté trente champs plantés avec des plants produits sur les hauteurs de Golan au cours de l'été 1971. Les manifestations virologiques ont été les suivantes: PVY 0,1–2% dans trois champs et aucune trace de PVY dans les autres; PLRV 1–4% dans vingt-huit champs et aucune manifestation de PLRV issu des plants dans deux champs seulement. L'infection de PLRV est donc devenue plus fréquente et le pourcentage d'infections plus élevé. On n'a pas observé de ‘Yellow mosa?c’ ou ‘Calico’ d? au AMV, ni de stolbur dans ces champs inspectés en 1971–1972. La raison de l'incidence remarquablement basse de virus dans les champs et parcelles de contr?le, comparativement aux tests de laboratoire, tient au fait qu'un nombre considérable de tubercules infectés de AMV ne germent pas ou ne lèvent pas dans les conditions des champs. Les plantes provenant de tubercules infectés de PVY ont tendance à lever aussi t?t que les plantes saines mais sont recouvertes par les plantes voisines vigoureuses. Elles peuvent par conséquent échapper aux yeux des contr?leurs. Appréciation des plants de pomme de terre des hauteurs de Golan. Au printemps 1971, on a planté, dans neuf localités différentes, des plants provenant des hauteurs de Golan, en comparaison avec des plantsUp-to-Date de provenance irlandaise. Dans une localité, la production fut identique, dans quatre localités elle était inférieur et elle fut supérieure dans les quatre autres (tableau 6); par contre en 1972 la production des plants des hauteurs de Golan était plus élevée avec le même pourcentage de gros tubercules supérieurs à 60 g (tableau 5). Les plants des hauteurs de Golan se comportent comme des plants plus jeunes eu égard à la levée, le nombre de tiges (tableau 4), la floraison et la tubérisation.

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Part of this paper was read at a session of the Virology Section at the 5th Triennial Conference of the EAPR (Norwich, September 1972).     

Production of seed potatoes in Cyprus: the effects of roguing and planting date on the spread of potato leaf roll virus,tuber yield,and infestation by potato tuber moth

Summary Field experiments during 1984–6 tested the effects of planting date on the development of aphid infestations and the spread of potato leaf roll virus (PLRV) in rogued or unrogued plots of potatoes, cv. Spunta. Plantings were made each month from December to April, the customary time for planting being February. Aphid infestation in early-planted plots was severe throughout the growing season; plots planted in February were also severely infested early in the growing season but the populations later gradually declined to undetectable levels. Nevertheless, the incidence of PLRV in the latter plots was as high as in those planted in December-January. Late-planted crops escaped aphid infestation and PLRV infection, either in part (March planting) or completely (April planting). Such crops, however, were uneconomical due to poor yields and heavy losses from potato tuber moth infestation. Roguing significantly reduced the spread of PLRV in all years but its interaction with planting date was insignificant.     

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.     

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.     

Growing seed potatoes in the Sinai Desert

Summary Seed potatoes grown during winter in the Sinai Desert (Sharm el Sheik) yielded in autumn significantly more (17%) than commercial seed grown in spring. Seeds grown in winter in an agricultural area at Yotvata yielded similarly to the commercial controls. Almost no spread of PVY or PLRV was found at Sharm probably because of the very low alate population there, whereas at Yotvata the incidence of PLRV was over 40% probably as a consequence of a high aphid populations during the growing season. Alate populations were also observed in the Sinai Desert at A-tur, a completely arid area, and at Firan, an isolated oasis where agriculture is practised. At A-tur only a few alatae were trapped, but large numbers were found at Firan, especially starting in March, but not during winter the proposed season for growing seed potatoes. The possibility of growing high quality seed potatoes at Sharm is discussed. Contribution No 107, 1980 series, Volcani Center.     

Detection of potato viruses A,M, S,X, Yand leafroll and potato spindle tuber viroid from tissue culture plantlets using single leaf discs

Using enzyme-linked immunosorbent assay (ELISA) and dotimmunobinding assay (DIBA) for potato viruses A (PVA), M (PVM), S (PVS), X (PVX), Y^N (PVY^N), Y^O (PVY^O) and leafroll (PLRV) and nucleic acid spot hybridization (NASH) for potato spindle tuber viroid (PSTVd), virus and viroid were detected reliably from single leaf discs (6 mm) of tissue-culture plantlets. Leaf discs taken from leaf positions (1 to 8) (bottom to top) can be used for detection of all viruses except PLRV where the lower leaves had higher concentrations of virus than the leaves from the upper part of the plantlet. Virus cultures were maintained for 1 to 4 years in several potato cultivars. The levels of virus remained reproducible except for PVM concentration, which was found to be very low in cv. Green Mountain. Using densitometry software, the DIBA spots were quantified and results were comparable to A₄₀₅ values obtained by ELISA. PSTVd concentration as measured by densitometry from spots of NASH indicated no loss of viroid over 1–4 years in tissue culture in two potato cultivars.     

Resistance to potato leaf roll virus inSolanum brevidens

Summary Plants ofSolanum brevidens graft-inoculated with potato leaf roll virus (PLRV) grew vigorously and had a normal healthy appearance. Although presence of the virus was confirmed in all inoculated plants by graft tests to potato and/orDatura stramonium, recovery of PLRV fromS. brevidens PI 218228 usingPhysalis floridana and the aphidMyzus persicae was erratic and only few test seedlings became infected. Ease of recovery of the virus using aphids was not influenced by presence of a continuous graft union with infected potato. Testing ofS. brevidens PI 245763 withM. persicae was not possible due to poor aphid survival on plants of this accession.     

Epidemiology of potato leaf roll virus in the Fraser River delta of British Columbia

The spread of potato leaf roll virus (PLRV) and the resulting phloem necrosis in the tubers has been a limiting factor in the production of the Netted Gem (Russet Burbank) variety in southwestern British Columbia, Canada. Steckling sugar beets are an important overwintering host for nymphs and adults of the green peach aphid,Myzus persicae (Sulzer). By June, aphids are widely disseminated to the florets and new leaves of sugar beet and other hosts, including potato. Colonies with alates are produced on summer hosts which are not treated with insecticides. The peak of the flight of alates from the colonies on the summer hosts occurs during the first half of August. Those alates that were produced on PLRV-infected potato and which travel to other potatoes transmit the virus as soon as they feed. By the end of August, the sugar beet seed crops and the early and mid-season potato crops have been defoliated or harvested. Thus many colonies ofM. persicae are destroyed and the threat of PLRV spread diminishes. Crop and weed plants which serve as overwintering hosts become infested during late summer with alate aphids. Their offspring survive the winter in numbers which are determined by the weather and survival of host plants.     

Transmission of potato leafroll virus to or from tuber slices by aphids feeding through a membrane

Summary Eye-bearing slices, cut from healthy potato tubers and placed between Parafilm membranes, were inoculated with potato leafroll virus (PLRV) byMyzus persicae. PLRV was detected by ELISA and by transmission tests in tuber slices and in plants grown from the slices of the susceptible cv. Désirée, but not in those of the resistant cv. Arkula. These results suggest that PLRV replication and transport within tuber phloem is controlled by specific mechanisms of resistance.M. persicae was also able to acquire and transmit PLRV toPl floridana from slices cut from tubers of infected plants. The aphids effectively transmitted PLRV from slices cut from the sprouting rose end but they failed to transmit it from slices cut from the heel end of tubers.     

Relationships of defined PVX infection levels to verticillium wilt,yield, and quality of the Russet Burbank potato

Field studies were conducted over a three-year period to investigate effects of potato virus X (PVX) on the Russet Burbank potato cultivar. Seed (PVX-free and PVX-infected) used for this three-year study originated from the same PVX-free source and was grown and stored under similar conditions. PVX-free seed was found to increase yield over PVX-infected plots by 9 to 32%. With these yield benefits, effects of PVX on either the incidence of verticillium wilt or plant nutrition were not significant. There was a trend (P = 0.10) for a reduction of mean tuber weight when the PVX infection level exceeded 19%. Because of increases of undersized potatoes, the yields of U.S. #1 potatoes were reduced as levels of PVX infection were increased. With a PVX infection level of 36%, the yield of U.S. #1 tubers was reduced by 21% when compared with plots having 0% PVX. At an 88% infection level, the yield of U.S. #l’s was reduced still further (36% lower than plots with 0% PVX). Results demonstrate the importance of the level of PVX infection to potato production.     

Biological factors influencing the transmission of potato leafroll virus by different aphid species

Summary Macrosiphum euphorbiae, collected in the field from potato plants infected with potato leafroll virus (PLRV), transmitted the virus to fewer potato plants in a field trial than did laboratory-rearedMyzus persicae. In the laboratory,M. persicae was the only efficient vector of PLRV fromPhysalis floridana seedlings, potato sprouts or excised leaves toP. floridana. Two clones ofM. euphorbiae and one clone ofAulacorthum solani transmitted PLRV from infected potato plants toNicotiana clevelandii as effeciently asM. persicae but a clone ofAphis gossypii was an inefficient PLRV vector. An isolate of PLRV, whichM. persicae transmitted inefficiently from potato toN. clevelandii, was also transmitted inefficiently byM. euphorbiae andA. solani.     

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.