Reaction of potato varieties toPotato mop-top virus infection in the andes

The unexpected detection ofPotato mop-top virus (PMTV) in potatoes growing at several locations in the U.S.A. and Canada in 2002 has led to the realization that this soil-borne virus may be widespread throughout the potato-producing regions of both countries. A lack of information concerning the response of U.S. cultivars to PMTV infection caused us to examine the effects of PMTV on field-grown plants at three locations in the Peruvian Andes where the virus and its fungal vector,Spongospora subterranea, are endemic. All 21 U.S. cultivars tested proved susceptible to PMTV infection, especially at La Victoria where the overall incidence of both PMTV and powdery scab was high. Symptom expression in the foliage proved to be an unreliable indicator of virus infection, and thus, more reliable serological (NCM-ELISA) and nucleic acid-based techniques (NASH and RT-PCR) were used to monitor tuber tissue for the presence of PMTV. As much as 25% of field-grown tubers of cvs Kennebec, Monona, and Norland were infected with PMTV, but no correlation between virus infection and either the incidence or severity of powdery scab for any variety was apparent. Although PMTV infection did not result in the appearance of spraing or other internal necrotic reactions resembling those reported from many North American and European locations, a disproportionate proportion of infected tubers did exhibit a reticulate surface cracking. In hydroponic culture, the proportion of cracked tubers increased dramatically when the nutrient solution was seeded with virus-infestedS. subterranea. Comparatively few tubers of cvs Monona and Russet Burbank exhibited this surface cracking, suggesting that these two varieties may be somewhat tolerant to PMTV infection.     

Evaluation of dihaploid populations from potato varieties and breeding lines

Summary Dihaploid populations from 20 varieties and 11 breeding lines ofSolanum tuberosum differed greatly in the occurrence and frequency of mutant phenotypes, in tuberization, flowering, pollen stainability, 2n-pollen production and resistance toGlobodera rostochiensis pathotype Ro-1. One population contained up to 61.7% lethal mutants: 39.1% of the total of 5377 dihaploids obtained did not tuberize, and 32.4% of 825 vigorous dihaploids did not flower. Of 825 vigorous dihaploids, 26.9 and 3.9% respectively had a pollen stainability higher than 20 and 60%. Among 222 dihaploids with a pollen stainability higher than 20%. 23.0% produced some 2n-pollen and none of these had a stainability higher than 60%. Among the dihaploid populations investigated the proportion of resistant to susceptible dihaploids ranged from 8:26 to 62:8.     

Comparison of cDNA hybridisation and other tests for the detection of potato mop-top virus

Summary Potato mop-top virus (PMTV) was most easily detected in potato leaf material by ELISA which proved more reliable than ISEM or inoculation of indicator plants with sap or extracted nucleic acid. Nucleic acid hybridisation tests using complementary DNA (cDNA) to PMTV were more reliable than ELISA, ISEM or inoculation of indicator plants for detecting PMTV in tissue from spraing-affected tubers. Unreliable results were obtained when cDNA was used to detect virus in tubers with deep cracks, indicative of secondary symptoms. Tuber tissue examined by ISEM taken from either side of a necrotic arc show that relative virus concentration varies considerably over very short distances. ELISA on sprouts and stems from spraing-affected tubers also show that virus distribution is highly variable.

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Zusammenfassung Potato-Mop-Top-Virus wurde in Blattmaterial von Kartoffeln durch den ELISA nachgewiesen, welcher sich als verl?sslicher erwies als ISEM oder Inokulation von Indikator-pflanzen mit Saftextrakten oder extrahierter Nukleins?ure. Tabelle 1 zeigt, dass Saftextrakte oder extrahierte Nukleins?ure von 7 von 13 Symptom-aufweisenden Kartoffel-pflanzen auch Symptome aufNicotiana debneyi und/oderChenopodium amaranticolor hervorriefen. Mittels ELISA konnte von Symptom-aufweisendem Blattmaterial PMTV in 10 von 12 verd?chtigen Pflanzen ermittelt werden, im Vergleich dazu mittels ISEM nur bei 7 von 12 Pflanzen (Tabelle 2). Knollen mit fleckenartigen Symptomen (‘spraing’) wurden angekeimt und 4 Tage lang bei Licht oder Dunkelheit aufbewahrt. Andere Knollen wuchsen bis zur Reife unter Gew?chshausbedingungen. Mittels ELISA konnte bei Keimen und Trieben PMTV ?fter in Keimen von im Dunkeln gehaltenen Knollen nachgewiesen werden (Tabelle 3). ISEM, in 5 mm-Abst?nden an der Oberfl?che von Knollen, von 2 cm innerhalb eines nekrotischen Krieses bis 2 cm ausserhalb des nekrotischen Kreises genommen, zeigte, dass der Virusgehalt im Bereich sich entwickelnder Nekrosen am gr?ssten war (Tabelle 4). Nukleins?ure-Hybridisationstests bei Verwendung komplement?rer DNA gegen PMTV war verl?sslicher als ELISA, ISEM oder Inokulation von Indikatorpflanzen zum Nachweis von PMTV im Gewebe von Knollen mit Flecken. Unzuverl?ssige Ergebnisse ergaben sich, wenn cDNA zum Nachweis des Virus in Knollen mit sekund?ren Symptomen verwendet wurde (Tabelle 5).

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Résumé Le virus du mop-top de la pomme de terre a été détecté dans du matériel foliaire de pomme de terre par ELISA qui s'est révélé plus fiable que l'ISEM ou que l'inoculation de plantes indicatrices avec des extraits de sève ou d'acide nucléique. Le tableau 1 montre que les extraits de sève ou d'acide nucléique de 7 plantes sur 13 de pommes de terre présentant des sympt?mes ont induit des sympt?mes surNicotiana debneyi et/ouChenopodium amaranticolor. ELISA appliqué sur du matériel foliaire présentant des sympt?mes, a détecté le PMTV dans 10 plantes suspectes sur 12 comparé à 7 sur 12 avec l'ISEM (Tableau 2). Les tubercules présentant des sympt?mes d'arcs nécrotiques ont été mis à germer et placés ou bien à la lumière ou bien à l'obscurité pendant 4 jours. D'autres tubercules ont été cultivés jusqu'à maturité en conditions de serre. Les tests ELISA sur germes et tiges ont détecté le PMTV plus souvent dans les germes de tubercules conservés à la lumière (Tableau 3). L'ISEM sur des tissus de tubercules prélevés tous les 5 mm à la surface d'un tubercule, à partir de 2 cm à l'intérieur d'un arc nécrotique jusqu'à 2 cm à l'extérieur de l'arc, a montré que la teneur en virus était plus forte dans une zone où se développe la nécrose (Tableau 4). Les tests d'hybridation de l'acide nucléique utilisant de l'ADN complémentaire de l'ARN du PMTV ont été plus fiables qu'ELISA, l'ISEM ou l'inoculation de plantes indicatrices pour détecter le PMTV dans le tissu de tubercules montrant des arcs nécrotiques. Des résultats peu fiables ont été obtenus quand le cDNA a été utilisé pour détecter le virus dans les tubercules présentant des sympt?mes secondaires (Tableau 5).

     

Some studies on the distribution and incidence of potato mop-top virus in Peru

Symptoms of PMTV are distributed widely in potatoes in the highlands (Andes) of Peru, but have not been found in coastal plantings; they were observed in 9 out of 22 Peruvian Departments. Incidences of over 10% of affected plants in one or more crops were found in 14 different localities. Thirteen cultivars with symptoms were observed, 9 wereSolanum tuberosum subsp.andigena Juz. & Buk., 3 were hybrids ofS. tuberosum subsp.andigena xS. tuberosum subsp.tuberosum L orS. Curtilobum Juz. & Buk. and 1 wasS. juzepczukii Buk. Symptoms were also seen in 29 clones of the potato germplasm collection of the International Potato Center. Distribution and prevalence of PMTV in Peru appear to be related to those rainfall and temperature conditions that favour its fungus vectorSpongospora subterranea (Wallr.) Lagerh.     

Evaluation in pot and field trials of resistance of potato cultivars and breeding lines to common scab caused byStreptomyces scabies

Summary The resistance to common scab of nine cultivars and eight advanced breeding lines of potatoes, fiveSolanum andigenum Juz. et Buk. clones, and three potato breeding lines selected for resistance to common scab, was investigated in a field and a pot trial. In the pot trial potaroes were planted in inoculated coarse river sand in plastic pots (150 mm in diameter) placed on irrigated subsoil in a glassfibre house. In a field trial potatoes were planted in an artificially infested field. The harvested tubers were scored individually for scab incidence according to two scales, viz. a 1–5 point scale for percentage surface covered with scab and a 1–3 point scale for lesion type. A scab index value was calculated for each tuber. A significant correlation coefficient of 0.82 was obtained for the results of the two tests.     

Breeding progress for potato chip quality in North American cultivars

Forty-four potato cultivars, released in the period between 1876 and the present were grown concurrently in field trials, stored simultaneously in three different environments, then evaluated for chip quality. They represented cultivars historically used and/or bred for potato chip production. Quality factors measured were tuber solids, chip color, reducing sugar levels, sucrose levels, and percent of defect-free chips. Tuber solids tended to increase in the late period cultivars, but trends were erratic. The release of Lenape marked the beginning of an increase in tuber solids that has continued to the present. There was a significant trend for lower reducing sugars and better chip color that corresponded to increasingly later cultivar release dates. Since about 1960, progress toward lower reducing sugars and better chip color has been constant, regardless of whether tubers were stored at 4.4 C, stored at 4.4 C and reconditioned, or stored at 10 C. Late period cultivars tended to have a greater percentage of defect-free chips in comparison to those released earlier, with most of the improvement coming during the last few years. This study provided evidence that potato breeders have made significant progress in developing cultivars with good chip quality. Evidence was also found that Lenape was a landmark cultivar and has been an important contributor to the observed breeding progress     

Alternative hosts for potato mop-top virus, genus Pomovirus and its vectorSpongospora subterranea f.sp. subterranea

Summary Seventeen weed species common in the potato fields in Denmark were grown in a hydroponic system infested with viruliferous zoospores ofSpongospora subterranea f.sp.subterranea carrying potato mop-top virus (PMTV). The plants were examined for infection with PMTV andS.s.s. using DAS-ELISA and based on visible symptoms. Only two weed species were found to be infected with PMTV,Chenopodium album andSolanum nigrum, whereas 13 became infected withS.s.s. C. album was infected with PMTV by mechanical inoculation were the infection became systemically and the leaves showed necrotic spots.S. nigrum became local infected with PMTV by mechanical inoculation. By inoculation with viruliferousS.s.s. the roots ofS. nigrum became infected but in three weeks PMTV had not spread into the top of the plants.Nicotiana benthamiana was used as a control susceptible toS.s.s. and PMTV.     

Development and evaluation of potato breeding lines with introgressed resistance to Columbia root-knot nematode (Meloidogyne chitwoodi)

Columbia root-knot nematode (Meloidogyne chitwoodi) (CRN) is a serious pest of potato in the Pacific Northwest of the USA. Because this nematode can reproduce rapidly within a single growing season, small initial populations are capable of causing crop loss in the Columbia Basin of Washington or Oregon. Presently, soil fumigation is the main treatment for controlling CRN on potato. Developing potato varieties with resistance to CRN is highly desirable to reduce the cost of control and to alleviate concerns about the effects of fumigants on the environment. Resistance to CRN race 1 was found in two wildSolanum species. Resistance fromS. bulbocastanum was introduced via protoplast fusion and fromS. hougasii via sexual hybridization. Subsequent breeding consisted of repeated backcrossing and selection. The dominant monogenic inheritance was expressed in undiminished fashion across several backcross generations. When tested in replicated trials in three locations, selected resistant clones from the BC₄ and BC₅ of theS. bulbocastanum introgression populations had total marketable yields and yields of >113-g (4 oz) tubers as good or better than standard potato varieties tested in replicated yield trials in three locations. Percentage of tubers weighing more than 113 g in the highest yielding clones was not significantly different from commercial standards. The resistance phenotype, typified by failure of the nematode to reproduce on the root systems, was sufficiently effective to prevent economic damage in a field exposure. All CRN-resistant clones are pollen sterile. Germplasm listed is available upon request.     

Inheritance of extreme resistance to potato virus Y in potato

Summary Segregation for extreme resistance to PVY was evaluated in progenies derived from crossing two extremely resistant potato clones with parents differing in resistance. Resistance was evaluated after mechanical inoculation with PVY^O and PVY^N, and after graft inoculation with PVY^O. Biological and serological tests (ELISA) were used for virus detection. The extreme resistance is governed by a single dominant gene, but observed segregations deviated from the expected ratios. Considerable modifying effects were detectable, depending on the potato genotype and virus isolate, for a significant excess of susceptible genotypes was observed in some progenies. Moreover, genotypes with non-parental types of resistance to PVY were observed.     

Selection of first-year potato seedlings for resistance to potato leaf roll virus

Summary In families obtained from crossing pairs of parents with high resistance to potato leaf roll virus (PLRV), individual clones differ greatly in their level of resistance. Inoculation of first-year seedlings was effective in selecting more resistant families, but it was not so effective in selecting more resistant individual clones.     

Evaluation of a new approach in potato breeding in Mexico

A new approach in the breeding of potatoes in Mexico is described, in which the progenies of different crosses are evaluated in consecutive plantings under different ecological conditions in three zones with different growing seasons. Yields and manipulation of the genetic material were adequate in all the three zones. The new system saves as much as 40% in time as compared with the conventional breeding programs. Some of the selected clones outyielded the control by 50% to 150%. Other implications and advantages of the system are discussed.     

Early detection of Verticillium wilt resistance in a potato breeding program

Nine potato clones/cultivars selected for varying degrees of Verticillium wilt (VW) resistance based on degree of vascular colonization, were intercrossed and outcrossed to 13 uncharacterized clones. Based on growth characteristics of 3,535 seedling transplants and an assay quantifyingV. dahliae in potato vascular tissue, 404 clones were selected for further tests. The average number ofVerticillium dahliae colony forming units (CFU) expressed as Log₁₀(CFU + l)/0.1 ml of plant sap for the 404 clones was 2.3, and 1.3 and 3.7 for resistant Reddale and susceptible Kennebec checks, respectively. Thirty-five clones (8.66%) had CFU values equal to or less than Reddale suggesting that VW resistance is a readily transmitted trait.