Mechanisms of resistance to potato leafhopper,Empoasca fabae (Harris), in potato

Potato genotypes were evaluated for resistance to natural infestations of the potato leafhopper,Empoasca fabae (Harris), in the field. Characterization of Type A and B glandular trichomes, phenolic properties of Type A trichomes, glycoalkaloid content and composition,E. fabae adult and nymph infestation, leaf damage (hopperburn), yield, and yield reduction were determined on genotypes PI 473331 and PI 473334 (accessions ofSolatium berthaultii (Hawkes)), NY123 and Q174-2 (advanced hybrids), and Elba and Allegany (commercial cultivars). Regarding the Type A trichome, PI 473334 was most pubescent, followed by PI 473331, both had high levels of enzymatic browning; on PI 473334 no glycoalkaloids were detected, while on PI 473331 solamargine and solasonine were present. Those genotypes were the least infested by adults; moreover, nymphs were never found on their leaves. PI 473331 and Q174-2 possess Type B trichomes, the latter had levels of Type A trichome comparable to the first and to NY123, while displaying high levels of phenolic oxidation of Type A and very low levels of glycoalkaloids. Although Q174-2 had intermediate infestation ofE. fabae, it suffered a yield reduction comparable to the control cultivar Allegany. The density of Type A trichomes of NY123 was relatively low, even though the browning assay results were significantly elevated. Foliage of this genotype was found to contain the four types of glycoalkaloids studied at high levels.Empoasca fabae infestation on NY123 was intermediate, and it yielded well on infested plots, but suffered an intermediate yield reduction. Elba presented densities of Type A similar to NY123. It suffered the lowest yield reduction despite its high levels of leafhopper infestation and hopperburn. Its tolerance might be associated with its phenology, since it is a late-maturing cultivar. High scores of the modified enzymatic browning assay were correlated with high infestation and high leaf damage. Results indicated a significant correlation between leafhopper infestation and hopperburn.     

Inheritance of potato glycoalkaloids

Significant differences in tuber glycoalkaloid (TGA) content were found among parents and among family means in a two year study of 10 tetraploid crosses. TGA contents of the parents ranged from 3.6–36 mg/100 g, with an average content of 10 mg/100 g. Offspring variations within families were generally continuous, indicating polygenic inheritance. Heritability (1-year—1-replicate base) ranged from 86–89% in the broad sense and from 66–84% in the narrow sense. It was concluded that TGA content is highly heritable. The use of parents with high TGA contents in a breeding program is discussed.     

Inheritance study of tuber glycoalkaloids in a wild potato,Solanum chacoense bitter

Studies were made of segregating families from crosses between accessions of Solanumchacoense Bitter differing in steroid glycoalkaloids. The major glycoalkaloids were isolated from tubers and identified by thin-layer chromatography. Simple segregation ratios of 3:1 in an F₂ and 1:1 in backcrosses were obtained for the presence:absence of solanine, chaconine, and commersonine. To explain the simultaneous segregation of the three glycoalkaloids, we tentatively hypothesize that: (1) solanine and commersonine are determined by alternative codominant alleles at a single gene locus; (2) a major gene for chaconine segregates independently of the solanine/commersonine locus; and (3) a recessive gene linked with the commersonine allele is epistatic to the chaconine gene, causing the production of β-chaconine instead of the usual α-chaconine. The F₂ distribution could be fit to the ratio 3:6:3:1:2:1, seen as combining the 1:2:1 segregation of solanine: solanine + commersonine: commersonine and the 3:1 segregation of presence: absence of chaconine.     

Genetic and environmental control of potato glycoalkaloids

Genetic and environmental factors that can cause potato tubers and processed products to have excessive glycoalkaloid levels (> 20 mg/100 g fresh wt) are reviewed and discussed. Measures that breeders, growers, processors, and distributors might take to maintain glycoalkaloid levels at their present low levels are suggested.     

Extreme resistance to infection by potato virus X in genotypes of wild tuber-bearingSolanum species

Summary Clones derived from thirty-one different accessions (nineteen of Argentine origin) belonging to eightSolanum species were screened for resistance to infection by potato virus X strain cp (PVX cp) by mechanical inoculation of plantlets that had been micropropagated in vitro. Estimates of PVX multiplication obtained by enzyme linked immunosorbent assay and slot blot nucleic acid hybridization allowed the identification of resistant clones derived from five accessions belonging toS. commersonii S. oplocense, S. sparsipilum andS. tuberosum andigena. Resistant genotypes supported PVX concentrations 5 to 15 times smaller than did the susceptible control cultivar Spunta. Graft inoculation test confirmed the presence of extreme resistance similar to that conferred by the ‘immunity’ gene X¹ (also called RX_act).     

The significance of wild species for potato breeding

Summary The writer discusses the selection work performed at the Max-Planck-Institute at Cologne-Vogelsang. Attention was particularly concentrated on finding crosses with wild species resistant to diseases and plagues. The writer discusses in turn the results obtained with resistance toPhytophthora infestans, Alternaria solani, Rhizoctonia solani, Streptomyces scabies, Spongospora subterranea, Synchytrium endobioticum, virus diseases,Heterodera rostochiensis and Colorado beetle. He also refers to various difficulties that occur in crosses with wild species.

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Zusammenfassung Der Verfasser bespricht die Selektionsarbeit, die im Max-Planck-Institut in K?ln-Vogelsang verrichtet worden ist. Die Aufmerksamkeit war vor allem darauf konzentriert, Kreuzungen mit Wildarten zu suchen, die resistent sind gegen Krankheiten und Sch?dlingsplagen. Nacheinander bespricht der Verfasser die Ergebnisse, die erreicht worden sind mit der Resistenz gegenPhytophthora infestans, Alternaria solani, Rhizoctonia solani, Streptomyces scabies, Spongospora subterranea, Synchytrium endobioticum, Viruskrankheiten,Heterodera rostochiensis und Kartoffelk?fer. Ferner nennt er einige Schwierigkeiten, die bei Kreuzungen mit Wildarten entstehen.

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Résumé L'auteur donne un exposé sur l'oeuvre sélectionnaire, entreprise à l'Institut-Max-Planck à Cologne-Vogelsang. Une attention particulière a été apportée notamment à la recherche de croisements avec des éspèces sauvages résistant aux maladies et aux pestes. L'auteur traite ensuite des résultats que donne la résistance àPhytophthora infestans, Alternaria solani, Rhizoctonia solani, Streptomyces scabies, Spongospora subterranea, Synchytrium endobioticum, maladies virologiques,Heterodera rostochiensis et au doryphore. Pour conclure, il traite de quelques difficultés que soulèvent les croisements avec des variétés sauvages.

     

Influence of phosphorus and potassium fertilization on damage to alfalfa,Medicago sativa L., by the alfalfa weevil,Hypera postica (Gyllenhall) and potato leafhopper,Empoasca fabae (Harris)

In a field study, the effects of phosphorus and potassium fertilization on damage caused by the potato leafhopper, Empoasca fabae (Harris), and alfalfa weevil, Hypera postica (Gyllenhall), to alfalfa, Medicago sativa L., were studied. Potato leafhopper and alfalfa weevil populations were either controlled with insecticides or allowed to develop as untreated controls. Insect management treatments were applied to alfalfa managed under high and low soil fertility regimes. Alfalfa grown under high soil fertility appeared more favourable for alfalfa weevil populations but was able to tolerate more defoliation. Populations of alfalfa weevil larvae were 34% higher on fertilized stands. On the other hand, potato leafhopper populations were as much as 43% higher on low-fertility stands. Alfalfa weevil damage caused a carry-over effect which reduced both plant height and yield of the second cutting. Fertilization negated this effect on height but not on yield. Stands damaged by potato leafhopper recovered more slowly after harvest, but fertilization reduced this effect. Yields from first-cutting alfalfa (which is not infested by the potato leafhopper) the following year were 10% greater on fertilized stands where leafhopper control had been applied the previous season. Plots infested by potato leafhopper suffered greater yield losses under low-fertility management. Leafhopper control and fertilization, alone and in combination with one another, negated these effects.     

Steroid glycoalkaloids and related compounds as potato quality factors

The steroid glycoalkaloids are triterpenoid derivatives which are found in all tissues of the potato plant including the tubers. The compounds are largely localized in the peel of tubers, but tissue beneath the peel rapidly accumulates the steroid glycoalkaloids to levels equal to or greater than those in the peel as a result of injury or environmental stress. The accumulation is restricted to the outer 1–2 mm of injured or stressed tuber. Potatoes containing over 0.02% steroid glycoalkaloids are considered toxic to man, and at this concentration they would impart a distinctly bitter flavor. The accumulation of steroid glycoalkaloids is suppressed and the accumulation of sesquiterpenoids is elicited in tubers infected by various pathogens and nonpathogens including the late blight pathogen,Phytophthora infestans. Arachidonic acid and eicosapentaenoic acids, two polyunsaturated fatty acids isolated fromP. infestans, are potent inhibitors of steroid glycoalkaloid accumulation. Both acids elicit the localized accumulation of sesquiterpenoids including rishitin, lubimin, phytuberin, phytuberol and solavetivone. Rishitin and lubimin generally comprise 85–90% of the total sesquiterpenoids which accumulate. The steroid glycoalkaloids and sesquiterpenoids appear to have a role in disease resistance to some fungal pathogens. Both groups of compounds are synthesized via the acetate-mevalonate pathway. Arachidonic and eicosapentaenoic acids appear to inhibit steroid glycoalkaloid accumulation at the level of the conversion of farnesyl pyrophosphate to squalene and they activate the biosynthesis of sesquiterpenoids. The reduction of steroid glycoalkaloids in potato foliage and tubers for health and flavor considerations should be considered relative to the ability of tubers and foliage to accumulate sesquiterpenoids in response to infection and its influence on disease and insect resistance.     

Response of six wild potato species to chloride and sulfate salinity

Eleven accessions belonging to six species ofSolanum (S. bulbocastanum,S. chacoense, S. gourlayi, S. microdontum, S. papita, and S.sparsipilum) were tested for resistance to salt. Resistance was measured by survival and growth (dry weight of tops) of plants treated with solutions of NaCl and Na₂SO₄. The six species could be grouped into four classes based on good to poor resistance to salt solutions (1.S. chacoense, 2.S. gourlayi, 3.S. microdontum, S. sparsipilum, S. bulbocastanum and 4.S. papita). There was a close relationship (r=0.94**) between the survival of plants and growth of surviving plants treated with salt solutions. There was no relationship between known heat or drought resistance of various accessions and salt resistance. Results indicate there is a large genetic base available to improve the salt resistance of the cultivated potato.     

Solanum serratoris: a new wild ecuadorian potato species

A new wild Ecuadorian tuber-bearing species ofSolanum,S. serratoris (SeriesTuberosa, Sect.Petota is described and illustrated. This species from the eastern-Andean region of provincia Morona-Pastaza has been named in honor of Dr. Richard L. Sawyer, founder of the International Potato Center, Lima, Peru.     

Origin and inheritance of solarmarine glycoalkaloids in commercial potato cultivars

Tuber tissues of 123 commercial cultivars were tested for their ability to synthesize solamarine glycoalkaloids. Eleven cultivars including ‘Kennebec’ and ‘White Rose’ synthesized major concentrations of solamarines, ranging between 42 and 85% of total glycoalkaloid, when tuber slices were exposed to light during wound-healing. Tuber tissues of the other 112 cultivars did not synthesize solamarines, or they synthesized only trace concentrations of these unusual glycoalkaloids. Nine of the 11 solamarine-synthesizing cultivars have a common ancestor, USDA 96-56. This parental clone synthesizes major solamarine concentrations and it also carries the R₁ gene for late blight resistance that it inherited fromSolatium demissum. Results of solamarine analyses of foliage from 47 USDA 96-56 selfed progeny suggest that this parental clone is the source of a major gene(s) for solamarines present in 9 of the commercial cultivars. However, there appeared to be an alternative source of a gene(s) for solamarines because ‘White Rose’, with onlyS. tuberosum ancestors, also synthesized major solamarine concentrations. There was no association between the R₁ gene for late blight resistance and the ability to synthesize solamarines in 31 USDA 96-56 selfed progeny that were analyzed for both characters.     

Tuber and starch quality of wild and cultivated potato species and cultivars

Summary Between 1993 and 1998 205 different potato cultivars and 1220 accessions/genotypes of wild and cultivated potato species from the IPK Genebank Gatersleben were evaluated. Parameters interesting for starch isolation and especially for the use of starch were determined. Altogether, there was a higher variability in wild potato species than in cultivated potatoes for all characteristics investigated: dry matter content, starch content, protein content, amylose content and mean particle diameter of starch granules.     

Stolon characteristics and tuber initiation in a wild potato species (Solanum demissum Lindl.)

Summary Solanum demissum Lindl. is a short-day dependent, tuber-bearing species. In vitro propagated genetically identical plants were grown under long-day (16 h) conditions at 20°C day and 15°C night temperatures. Subsequently, from day 0 onwards, plants were exposed to shortday (10 h) conditions and grown in a multi-compartment system that allowed stolon initiation, stolon branching, stolon growth and tuber initiation to be monitored twice weekly. These frequent measurements resulted in detailed life-histories of all 841 stolon tips formed until day 46. Tuber initiation was irregular under these well-defined conditions; at day 46 only 106 stolon tips showed subapical swelling. This irregularity of tuber initiation was also observed within stolons. It is therefore suggested that tuber initiation depends on characteristics of the stolon or stolon branch, and several such characteristics were analyzed to obtain information on their potentially determining role in tuber initiation. No positive correlations were found between subapical swelling and branching order, stolon and stolon-branch age, longitudinal growth rates of stolons and stolon branches, and attachment of the stolon to the main stem.     

Identification of late blight, Colorado potato beetle, and blackleg resistance in three Mexican and two South American wild 2x (1EBN)Solanum species

Wild potatoes are important sources of genes for resistance to disease and insect pests. A collection of wild Mexican and South AmericanSolarium species from the US potato Genebank was evaluated under laboratory and/or field conditions for their reaction to late blight (Phytophthora infestans), Colorado potato beetle (CPB,Leptinotarsa decemlineata Say), and blackleg (Erwinia carotovora subsp.atroseptica (van Hall) Dye) in order to identify individual genotypes with multiple resistance genes. Late blight inoculations using aggressive isolates (US-8/A2 and US-11/A1 mating types) of P.infestans revealed a wide range of variation for resistance between and within the accessions of the wild species tested. For late blight, susceptible as well as moderately to highly resistant genotypes were observed in all the species tested. However, at least one accession from the three Mexican and one South American wild diploid species tested showed a relatively uniform high level of resistance toP. infestans. These includedS. bulbocastanum, S. pinnatisectum, S. cardiophyllum, andS. circaeifolium. Two accessions from South American speciesS. commersonii were highly susceptible to late blight. For the Colorado potato beetle test, only one species,S. pinnatisectum appeared uniformly resistant to CPB under field conditions. Results of screening for blackleg resistance showed that there were major differences between genotypes in the wild species. Accessions ofS. circaeifolium PI 498119 andS. bulbocastanum PI 243504 were identified as having significantly higher blackleg resistance than cultivated potato and the other wild species tested. However, genotypes from these two accessions were more susceptible to late blight and CPB. Characterization of theP. infestans isolate P1801C.16 used for late blight evaluation and multi-locus isolate tests using US-8/A2 and US-11/A1 races revealed that the resistance inS. pinnatisectum genotypes tested corresponded to a race-non-specific genetic system, which was different from any existing R genes.Solanum pin-natisectum genotypes with both high levels of late blight and CPB resistance as well as blackleg resistance genotypes identified in the present study represent a diverse gene pool that may be useful for development of new potato cultivars with multiple disease and insect resistance. The potential utilization of these valuable sources for improvement of cultivated potato is discussed.     

Mature-plant resistance of potato plants against potato virus YO (PVYO)

Summary Mature-plant resistance of potato plants against potato virus Y^O (PVY^O) was studied in field experiments in 1976–1979 in southern Sweden. At intervals of 7 days, from mid June until mid August, PVY^O was mechanically inoculated to one well-developed upper leaf per stem of each plant. Each week, a new group of plants were inoculated. In 1976–1977, the natural spread of PVY^O by aphids was studied in relation to three different stages of potato plant development. The results of mechanical inoculation demonstrated that mature-plant resistance increases during July in southern Sweden but there were great differences between developmental stages. Early planting with sprouted seed resulted in plants with a considerable mature-plant resistance in mid July when late developed potato plants still were very susceptible.

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Zusammenfassung In Südschweden wurden zwischen 1976 und 1979 Untersuchungen durchgeführt, um zu prüfen, wann und in welchem Mass die Sorte Bintje im Sommer eine Altersresistenz gegen das Kartoffelvirus Y^O (PVY^O) ausbildet. 1977 wurden drei Gruppen von Kartoffelpflanzen unterschiedlicher Entwicklungsstadien mit PVY^O mechanisch inokuliert und von Mitte Juni bis fast Mitte August wurden jede Woche neue Gruppen von Pflanzen inokuliert. Nach der Ernte Anfang September wurden die Knollen auf PVY^O geprüft. Ebenso wurde die natürliche übertragung von PVY^O durch L?use von PVY^O-Infektorpflanzen auf benachbarte gesunde Pflanzen in drei verschiedenen Entwicklungsstadien untersucht. Die Ergebnisse der mechanischen Inokulation von Kartoffelpflanzen-früh und normal entwickelt-zeigen, dass die Altersresistenz der Sorte Bintje im Juli anstieg und Anfang August fast vollst?ndig ausgebildet war. Wurden die Kartoffeln sp?t gepflanzt, waren die Pflanzen Ende Juli noch sehr anf?llig für eine mechanische Inokulation und ein grosser Teil der Knollen war PVY^O-infiziert (Abb. 1, Tab. 2). Die natürliche übertragung von PVY^O bei verschiedenen Entwicklungsstadien der Pflanzen zeigte, dass die Zahl PVY^O-infizierter Knollen anstieg, wenn die Kartoffeln sp?t im Vergleich zur normalen Pflanzzeit gelegt wurden, mit und ohne Vorkeimung (Tab. 3). Die st?rkere Ausbreitung von PVY^O im Jahr 1976 gegenüber 1977 (Tab. 3) k?nnte mit dem st?rkeren Auftreten und der früheren Ausbreitung der L?use, vor allem vonRhopalosiphum padi (Tab. 4), im Jahr 1976 in Beziehung stehen.

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Résumé Des expérimentations sont menées dans le sud de la Suède entre 1976–1979; elles ont pour but de déterminer à quel moment et jusqu'à quelle limite des plantes de la variété Bintje présentent la résistance à maturité vis-à-vis du virus Y^O (PVY^O) au cours de l'été. En 1977, trois groupes de plantes à différents stades de développement sont inoculés mécaniquement avec PVY^O et chaque semaine, de la mi-juin à la mi-ao?t, de nouveaux groupes sont inoculés. Après la récolte, début septembre, des tubercules sont indexés pour déterminer PVY^O. La dissémination naturelle de PVY^O par les aphides, est également étudiée à partir de plantes-sources de PVY^O vers des plantes voisines saines, présentant trois différents stades de développement. Les résultats de l'inoculation mécanique de plantes à deux stades de développment précoce et normal, montrent que la résistance à maturité augmente pendant le mois de juillet pour la variété Bintje et est pratiquement totale vers le début du mois d'ao?t. Lorsque la plantation est tardive, les plantes sont encore très sensibles à l'inoculation mécanique et une forte proportion de tubercules est contaminée par PVY^O (figure 1, tableau 2). La dissémination naturelle de PVY^O pour des plantes à différents stades, montre que la proportion de tubercules atteints de PVY^O augmente lorsque les tubercules sont plantés tardivement par rapport à la date normale, avec ou sans prégermination (tableau 3). La dissémination plus importante de PVY^O en 1976 par rapport à 1977 (tableau 3) pourrait être correlée à celle des aphides également plus importante et plus précoce en 1976, notamment celle deRhopalosiphum padi (tableau 4).

     

The effects of colchicine doubling of potato dihaploid X wild species hybrids on eelworm resistance and pollen ‘stainability’

Summary Diploid potato clones (dihaploid x wild species hybrids) and their colchicine doubled, tetraploid counterparts were compared for resistance to eelworm (Globodera rostochiensis andG. pallida) and for pollen ‘stainability’ as an indicator of viability. The responses due to doubling were not uniform. For eelworm resistance, three of the five clone pairs showed no differences; in one pair the tetraploid was significantly more susceptible to one pathotype but not to two others and in the remaining pair, the tetraploid was significantly more susceptible to both pathotypes used. In eleven of fourteen pairs tested for pollen ‘stainability’, the tetraploid had significantly less ‘good’ pollen. In one case, the tetraploid had significantly more ‘good’ pollen. Generally there was sufficient ‘good’ pollen to allow further crossing at the tetraploid level.

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Zusammenfassung Fünf diploide Kartoffelklone, Kreuzungen zwischen anf?lligen Dihaploiden und nematodenresistenten Vermehrungen vonSolanum spegazzinii, S. vernei und einer nicht-beschriebenen, mitS. sparsipilum verwandten peruanischen Art, wurden hinsichtlich ihrer Resistenz mit ihren Colchicin-verdoppelten Gegenstükken verglichen. Tabelle 1 zeigt die verwendeten Nematoden-Populationen (Globodera rostochiensis undG. pallida) zusammen mit der Anzahl gebildeter Zysten. Die Reaktionen gegenüber Verdopplung waren nicht einheitlich; drei der fünf Klonpaare zeigten keine Unterschiede, bei einem der Paare war der tetraploide Teil signifikant anf?lliger gegen einen der Pathotypen, aber nicht gegen zwei andere, und beim letzten Paar war der tetraploide Teil gegen beide verwendeten Pathotypen signifikant anf?lliger. Obwohl die tetraploiden Pflanzen generell ein etwas gr?sseres Wurzelsystem entwickelten als die diploiden und eine gr?ssere Oberfl?che für die Einwirkung der Nematodenlarven boten, liess sich der Schluss ziehen, dass dies nur geringe Auswirkung auf die Feststellbarkeit von Unterschieden zwischen Vertretern der Ploidiepaare hatte. Die Zahl der Eier pro Zyste wurde durch die Resistenz der Pflanzen im Testmaterial nicht beeinflusst. Die Ergebnisse deuten auf gleiche oder niedrigere Grade der Nematodenresistenz durch die Colchicin-Verdopplung. Allerdings deutet die Uneinheitlichkeit der Reaktion darauf hin, dass die Produktion einiger ‘verdoppelter’ Klone mit erh?hter Resistenz doch nicht ganz auszuschliessen ist. Colchicinverdoppelte Klone mit Resistenz im Duplex-Stadium dürften hohen potentiellen Wert als Eltern für weitere Züchtungen auf tetraploidem Niveau haben, vorausgesetzt sie behalten ausreichende Fertilit?t bei. Pollen-‘F?rbbarkeit’ als Indikator der m?nnlichen Fertilit?t wurde in einem gr?sseren Umfang bei Ploidiepaaren, von denen die meistenS. acaule und/oderS. stoloniferum in der Elternschaft hatten, untersucht. Die Ergebnisse zeigt Tabelle 2. In 11 von 14 Paaren hatten die Tetraploiden signifikant weniger ‘gute’ Pollen, in einem Falle signifikant mehr. Generell waren ausreichend ‘gute’ Pollen vorhanden, um weitere Kreuzungen auf tetraploider Ebene zu gestatten. Die Rückkehr auf die tetraploide Ebene via Colchicin-Verdopplung l?sst deshalb einen hohen Anteil verwertbarer Elternlinien für die Erzeugung nematodenresistenter St?mme erwarten.

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Résumé Cinq cl?nes diplo?des obtenus par croisement entre dihaplo?des sensibles aux nématodes et résistants, issus deS. spegazzinii, S. vernei et d'une espèce péruvienne non décrite associée àS. sparsipilum, ont été comparés, pour leur résistance, avec leurs homologues tétraplo?des. Les populations de nématodes (Globodera rostochiensis etG. pallida) qui ont été utilisés sont présentées dans le tableau 1 avec le nombre de kystes nouvellement formés. La réponse donnée par le doublement des chromosomes n'a pas été uniforme; trois des cinq cl?nes n'ont pas montré de différences avec leurs homologues diplo?des; dans un cas le tétraplo?de a été significativement plus sensible à un pathotype mais pas aux deux autres et dans le dernier cas, le tétraplo?de a été significativement plus sensible aux deux pathotypes utilisés. Bien que les plantes tétraplo?des développent généralement un système radiculaire légèrement plus important et présentent une plus grande surface à l'infection par les larves de nématodes que les diplo?des, on conclut que cela a eu peu d'effet au niveau des différences observées entre les deux types de plo?die. Le nombre d'oeufs par kyste n'a pas été affecté sur les plantes résistantes, dans le matériel testé. Ces résultats suggèrent que des degrés similaires ou moindre de résistance aux nématodes peuvent résulter du doublement chromosomique d? à l'effet de la colchicine. Cependant, la non uniformité des réponses fait en sorte que la création de quelques cl?nes tétraplo?des résistants aux nématodes pourrait se faire. De tels cl?nes, ayant des gènes de résistance au niveau duplex, auraient une grande valeur potentielle comme parents pour les hybridations futures au stade tétraplo?de s'ils gardent une fertilité suffisante. La coloration du pollen comme indicateur de fertilité male a été étudiée sur une large gamme de plo?die doublée ayantS. acaule et/ouS. stoloniferum dans la parenté. Les résultats de ces tests sont donnés dans le tableau 2. Dans onze des quatorze paires comparées le tétraplo?de a eu un pollen significativement moins bon que le diplo?de. Dans un cas le tétraplo?de a présenté un pollen significativement meilleur. Cela parait suffisant pour prendre en considération le croisement au niveau tétraplo?de. Par le retour au state tétraplo?de sous l'effet de la colchicine ont peut s'attendre à obtenir de fortes proportions de géniteur valables pour la création de variétés résistantes aux nématodes.

     

Solanum burtonii,a new wild potato species from Ecuador

Before 1960 knowledge of the wild potato species from Ecuador was very limited. We knew only three tuber bearing species:Solanum paucijugum Bitt.,S. pichinchense Bitt. et Sodiro andS. solisii Hawkes. However, during the last two decades information has increased greatly with the researches of Donovan S. Correll and the writer. So, to the aforementioned species we must addS. albornozii, S. cyanophyllum, S. regularifolium, S. suffrutescens andS. minutifoliolum found by Correll;S. calacalinum, S. correlli andS. tundalomense discovered by me. With this opportunity, I present another new wild potato species from Ecuador,Solarium burtonii, named in honor of Prof. Dr. W. Glynn Burton as a recognition to his outstanding contributions in the field of potato physiology.     

The geographical distribution,inheritance and pest-resisting properties of sticky-tipped foliar hairs on potato species

Summary Near Cochabamba in Bolivia, plants ofSolanum berthaultii with sticky-tipped foliar hairs only have been collected but further south near Sucre, both sticky-tipped and pointed-tipped forms of this species and ofS. tarijense occur. Further south still, in Tarija, and in the border region of Argentina, only pointed-tippedS. tarijense has been collected but at Salta sticky-tippedS. tarijense has been found. InS. tarijense andS. herthaultii, the presence of sticky-tipped hairs (for which an aqueous fluoroscein solution is a selective stain) on adult foliage is controlled by a single dominant gene: plants with this character were more resistant to the aphidMyzus persicae and to the miteTetranychus urticae, and trapped more of the thripsThrips tabaci. In addition to the dominant gene, at least one set of recessive genes was needed for the full expression of this character in crosses withS. phureja and withS. tuberosum ev. Pentland Crown.T. urticae were trapped on second-generationS. tuberosum × berthaultii with this type of hair. Part of this work was done at the International Potato Center (CIP), Apartado 5969, Lima, Peru.