Tuberization in potato at high temperatures: Responses to exogenous gibberellin,cytokinin and ethylene

Summary In potato (Solanum tuberosum L., cv. Sebago), benzyladenine (BA) promoted tuberization at high day/night temperatures (32°/18°C), while gibberrellic acid (GA) and chlorethylphosphonic acid (CEPA) reduced tuberization at low day/night temperatures (22°/18°C). These results are consistent with the hypothesis that temperature exerts its influence on tuber formation by altering the balance between endogenous gibberellins, cytokinins and inhibitors, but not ethylene.     

Net photosynthetic rate of potato at high temperatures

Summary Potato cultivars were grown in a glasshouse and plants periodically transferred to a growth chamber. When the ambient temperature in the growth chamber was raised from 15 to 40°C in steps of 5°C per hour, net photosynthetic rate decreased at temperatures above 20°C. At 40°C the rate was 37% of the rate at 20°C. A greater decrease in net photosynthetic rate occurred with plants of the cultivar Up-to-Date than with cultivars R100 and BP13. Low values of leaf diffusive resistance were recorded and changes in photosynthetic rate could not be explained by changes in this factor. When a constant ambient air temperature of 20°C was maintained while soil temperature was increased, net photosynthetic rate decreased.     

Tuber yield and tuber quality of several potato cultivars as affected by seasonal high temperatures and by water deficit in a semi-arid environment

Summary The effects of high temperatures and water deficit on potatoes were investigated under field conditions. Nine cultivars and one un-named seedling were grown in the spring and in the summer under high temperatures. In both seasons the cultivars were grown under 3 water regimes: adequate water supply, moderate water deficit, and severe water deficit that were achieved by a modification of the single line source sprinkler irrigation system. Severe drought reduced tuber yields in both seasons. Moderate tolerance to a moderate water deficit in the spring season was exhibited by Draga, Désirée, and Monalisa. Late and intermediate cultivars produced high tuber yields in the spring season, and early cultivars had relatively smaller yield losses in the summer. The extent of tuber disorders, sprouting, rotting and malformation, varied considerably. High temperatures enhanced sprouting, rotting and malformation and drought may enhance sprouting and malformation. This investigation was supported by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Yield response of potato genotypes to different soil water regimes in contrasting seasons of a subtropical climate

Summary Potato crops in subtropical climates are often subjected to water stress, resulting in low yields and poor tuber quality. The yield response of potato genotypes to water supply was investigated in six trials, three each in spring and autumn plantings. Trials were conducted under automated rain shelters, using an irrigation boom to impose five soil water regimes. The negative effect of water stress on tuber yield was more detrimental in spring than in autumn, because of higher atmospheric evaporative demand and higher temperatures in spring. An average yield reduction of 68% was recorded for the most severely stressed regime in spring plantings, while the mean reduction for the same treatment in autumn was only 42%. Genotypic differences in yield response to drought were clearly illustrated in spring, but not in autumn. This suggests that the choice of genotypes is only influenced by the availability of water in spring, when more drought tolerant genotypes should be used.     

The resistance of potato plants toErwinia carotovora subsp.atroseptica in relation to their calcium and magnesium content

Summary The effect of adding gypsum (CaSO₄) to growing media on the resistance toErwinia carotovora subsp.atroseptica (van Hall) Dye of potato (Solanum tuberosum L.) stems and mother and daughter tubers was examined in field and glasshouse experiments. The decayin situ of inoculated mother tubers from field plots treated before planting with gypsum was significantly delayed compared with tubers sampled from non-amended plots. Blackleg development was also significantly delayed in the gypsum-amended plots; however, for both mother tubers and stems the increased resistance associated with the application of gypsum later disappeared. Stem resistance tended to be related to tissue calcium and magnesium concentrations which were higher in plots treated with gypsum than in untreated plots. Daughter tubers produced in plots amended with gypsum generally contained a higher concentration of calcium in their cortex and were more resistant to decay byE. carotovora subsp.atroseptica but the effect was not consistent.     

Assessing progenies of potato for resistance to skin spot (Polyscytalum pustulans) in the glasshouse

Summary Crosses were made between six parents differing in susceptibility to skin spot and glasshouse-grown tubers from true seedlings of the nine resulting progenies assessed for resistance to the disease. The assessment was evaluated by a two-year comparison with the behaviour of field-grown tubers of the progenies and their parents. The correlations between progenies in the glasshouse and field were r=0.911 and 0.753 and those between the mid-parental values and the progeny means were high (r>0.864), indicating that parental differences were heritable. It is concluded that correlations were sufficient for glasshouse-grown tubers to be used for assessing large numbers of progenies in genetical studies and for eliminating highly susceptible progenies at an early stage in a breeding programme. R.L. Wastie died 16.01.96.     

Assessing potato cultivars in Tunisia for susceptibility to leak caused byPythium aphanidermatum

Summary The susceptibility of 21 potato cultivars to leak (watery wound rot) caused byPythium aphanidermatum was compared. Whole tubers were inoculated after wounding by dipping into a water suspension of 10³ oospores/ml and incubated for 3 days at 25°C. The mean penetration of tissue calculated from the recording of lesion width and depth and the qualitative assessment of rot extension were highly correlated. For 10 of 12 cultivars tested at least twice, consistent reactions were obtained: cvs Korrigane. Superstar, Safrane and Yesmina were moderately susceptible, whereas Atlas, Diamant, Mondial, Obélix, Spunta and Timate were susceptible to highly susceptible. Tubers originated from two locations and/or two cropping seasons: thus, the performance of these cultivars under different production conditions reveals a satisfactory level of agreement with the test. Moreover, ratings assigned are supported by field or store observations.     

External K requirement of young plants of potato, sugar beet and wheat in flowing solution culture resulting from different internal requirements and uptake efficiency

Summary Potato, wheat and sugar beet were grown in a growth chamber in tanks with flowing solutions containing K-concentrations of 1.5, 5, 15, 50 and 200 μM to find reasons for different K contents of solution needed to reach 90% maximum dry matter accumulation (external K requirement). All species showed variation in dry matter accumulation with varying K levels. To reach 90% maximum dry matter accumulation potato needed 40 μM K, whereas wheat and sugar beet needed 6.4 and 4.4 μM K respectively. These differences in external K requirement could not be explained by differences in their internal K requirement since the internal requirement of potato (7.7% K) was about one and a half times of that of sugar beet (5.4%) but its external requirement was nine times of that of sugar beet. At low K supply potato plants showed a lower influx and a reduced root growth as compared with wheat and sugar beet.     

A comparative study of phenylpropanoid metabolism in gamma irradiated and unirradiated potato tubers

Summary Phenylpropanoid metabolism in gamma irradiated potato tubers was studied by examining the pattern of incorporation of radioactivity from U-¹⁴C phenylalanine into caffeic acid. chlorogenic acid and the coniferyl and sinapyl moieties of lignin. During a post-irradiation period of 21 days a depletion in chlorogenic acid was observed. This is a result of its impaired synthesis as well as an accelerated conversion of chlorogenic acid to ferulic and sinapic acids and their deposition in lignin. The results offer an explanation for the lower level of chlorogenic acid invariably observed in irradiated potato tubers.     

Progeny tests to identify diploid potato clones homozygous at loci controlling resistance to PLRV

Summary Using potato parental lines homozygous at a locus or loci controlling resistance to potato leafroll virus (PLRV) can give advantages in the selection of resistant forms. In order to identify homozygous diploid clones their test-cross families were evaluated. All the clones that were test-crossed expressed resistance in primarily- and secondarily-infected plants and etiolated sprouts, and were derived from mating genotypes highly resistant to PLRV. Genotypes from test-cross families varied in resistance to PLRV, and one family was found which had only resistant genotypes, suggesting that the resistant parent of this progeny was homozygous at resistance loci. Evidence was gathered that resistance in some diploid clones may result from resistance to virus multiplication as well as restricted virus transport from leaves to tubers.     

Assessing progenies of potato for resistance to early blight

Summary Progenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.     

Verification of sap flow by heat balance method on three potato cultivars

Summary A heat balance method for measuring sap flow in actively growing plants was tested on three potato (Solanum tuberosum L.) cultivars Monona, Norchip and Atlantic. The method is based on applying a known heat source to the stem of an intact plant: by measuring the axial and radial heat dissipation the magnitude of sap flow can be quantified. The technique shows promise as 24 h accumulated sap flow measurements were highly correlated (r²=0.935, n=36) with gravimetric measurements of transpiration and produced an average root mean square error (RMSE) of 20 g d⁻¹. The accuracy of the method improved as daily accumulated flow increased. Under low daily flow rates overall RMSE increased, supporting the need for a heat storage term in the heat balance equation. Short term flow rates were less significantly correlated (r²=0.764, n=1572) and produced an average RMSE of 2.89 g h⁻¹. Identification of these short term flow rates during high flow periods may be difficult. The presence of water potential gradients and the likelihood of re-hydration during high flow events may have also affected the short term performance of the method. At low flow rates, many different errors may be introduced.     

Characterization of pectic substances from two potato cultivars with different sensitivities to prewarming

Summary Potato cultivars Chieftain and Kennebec were prewarmed at 70°C for 15 min. prior to heating at 100°C for 18 min. in a water bath. Chieftain exhibited a large increase in fracturability upon treatment while Kennebec showed a smaller increase. Pectic substances of the two cultivars were sequentially extracted in water, sodium hexametaphosphate (0.5%), hydrochloric acid (0.05M, 50°C), and sodium hydroxide (0.05M, 5°C). The largest fraction isolated from both cultivars consisted of hydroxide-soluble pectic substances, and was followed by the acid-soluble fraction. Chieftain contained significantly greater amounts of the hydroxide-soluble fraction than Kennebec. Ion exchange chromatography revealed that the extracted pectic substances from the two major fractions consisted of a charged pectin chain with attached neutral sugars. Gel filtration chromatography revealed wide molecular size distributions for the isolated pectic substances. Pectic neutral sugar content for the hydroxide-soluble fraction (50% of total pectic substances) was greater for Chieftain than for Kennebec.     

Leak syndrome of potato in Tunisia caused byPythium aphanidermatum andPythium ultimum

Summary TwoPythium spp. were isolated from diseased tubers exhibiting rots at harvest, in summer stores and also in refrigerated storage. Symptoms shared features described for both pink rot caused byPhytophthora erythroseptica and leak caused byPythium spp. The causal agents were identified asPythium aphanidermatum andP. ultimum by morphological and physiological observations and by fingerprinting using oomycete specific primers to amplify the internal transcribed spacer (ITS1) within ribosomal DNAs. The optimum temperatures for infection were 30°C forP. aphanidermatum and 25°C forP. ultimum, corresponding to the optimum temperatures for growth in vitro. The optimum concentration for infection of tubers inoculated by dipping in a suspension of oospores or hyphal swellings after wounding was found to be 10³ reproductive organs/ml, whereas the infection threshold was 10 reproductive organs/ml.     

Response of tubers of five potato cultivars to co-inoculation with US-1 and US-8 genotypes ofPhytophthora infestans

Summary The severity of late blight tuber rot in five potato cultivars (Green Mountain, Sebago, Dorita, AC Brador and Island Sunshine) resulting from inoculation with US-1/US-8 combinations of Canadian isolates ofPhytophthora infestans was evaluated. In addition, the potential for mixed (A1∶A2) inoculations to result in oospore formation was examined. In studies conducted in 1996 and 1997, cv. Dorita (and Island Sunshine in 1997) developed the least amount of surface or internal necrosis relative to the other cultivars following co-inoculation with US-1 and US-8 isolates ofP. infestans. Differences also were revealed among isolate combinations used for inoculation. The combination of a US-1 isolate from Prince Edward Island with a US-8 isolate from New Brunswick consistently produced the least amount of necrosis in tubers of the various cultivars. There was no evidence of oospore production in any of the tubers examined. AAFC Contribution No. 919     

Influence of irrigation regimes on growth and yield of potato cv. Spunta

Summary The effect of furrow and drip irrigation giving 0, 33, 66, 100 and 133% of the maximum evapotranspiration (ETM) was studied on leaf transpiration, stomatal resistance, tuber growth, yield and yield response of cv. Spunta. The research was carried out in Sicily in 1988 and 1989 on early potato crops grown during the winter/spring cycle. Increased water supply increased leaf transpiration, plant fresh weight, tuber growth rate, yield and earliness, and decreased stomatal resistance and tuber dry weight. A higher yield response was obtained at the lower water regimes (ETM of 33 and 66%). There were no significant differences between the two methods of irrigation.     

The use of hormonal and osmotic growth retardants in media used for the storage of potato germplasm in-vitro

Summary Cultures of 23 potato cultivars were examined for their responses to hormonal and osmotic growth inhibitors incorporated in media used for storage in-vitro. Cultivars differed in their tolerance of inhibitors and also in their growth on a Murashige and Skoog medium with 3% sucrose. Both osmotic and hormonal growth retardants restricted the development of shoot tips but there were significant cultivar x treatment interactions, indicating that the ranking of cultivars will vary with the media used. Such interactions may complicate the establishment of facilities for storage in-vitro. However, addition to the basal medium of 5 mg l⁻¹ abscisic acid reduced both the overall mean scores and, more importantly, the between cultivar variance; its use in conjunction with low temperature shows promise as a method for conserving potato germplasm in-vitro.     

Calibration of near infrared reflectance spectroscopy to estimate nitrogen concentration in potato tissues

Summary Calibrations are provided to relate near infrared reflectance (NIR) data to total N concentration in potato leaves, stems, and tubers, estimated by Dumas combustion. Separate calibrations are necessary for each tissue-type. the NIR models simulate Dumas [N] estimates accurately, quickly and cheaply and have been shown to be stable. The methods of deriving the calibrations, correcting them and then providing independent tests are described.     

The influence of leaf area,light interception and season on potato growth and yield

Summary Light interception in the photosynthetically active radiation (PAR) range (400 700 nm) was measured over two years in potato crop canopies. Light interception increased linearly with increasing leaf area index (L) up to values of 2.25, light interception increased at a decreasing rate until L=4.0 was attained when around 95% of the incoming radiation was intercepted. The equation I_l=I_oe^kl accounted for 92% of the variance in the relationship between light interception and L, where I_l is the irradiance on a horizontal plane below a leaf area index of L., and k (light extinction co-efficient)=0.335+0.151 (L) 0.0129 (L)². Crop growth rate was found to be linearly related to the PAR intercepted by the canopy in 1980, in the absence of any apparent water-stress. The photosynthetic conversion efficiency of the canopy (g dry weight MJⁱ PAR intercepted) was 3.42 and 2.49 for 1980 and 1979, respectively. Tuber yields were also found to be linearly related to PAR intercepted by the canopy over the whole season.

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Zusammenfassung In den Jahren 1979 und 1980 wurde die Lichtaufnahme der photosynthetisch aktiven Strahlung (PAR) im Bereich von 400–700 nm in Kartoffelbest?nden im Vereinigten K?nigreich gemessen. Die meteorologischen Daten zeigten, dass der Niederschlag in den Jahren sehr unterschiedlich war (Abb. 2); 1979 war überwiegend trocken, vor allem in der sp?teren Vegetationszeit, w?hrend 1980 allgemein ein nasses Jahr war. Die Lichtaufnahme stieg linear mit dem zunehmenden Blattfl?chenindex (L) bis zu L=2,25 an (wobei rund 73% der einfallenden Strahlung aufgenommen wurde) und über L=2,25 nahm die Lichtaufnahme mit einer abnehmenden Rate bis zu L=4,0 zu, wobei rund 95% der einfallenden Strahlung aufgenommen wurden (Abb. 3). Die Gleichung I_L=I_oe^kL gilt für 92% der Varianz in der Beziehung zwischen Lichtaufnahme und Blattfl?chenindex (L), wobei I_L=Strahlung auf einer horizontalen Fl?che unter einem Blattfl?chenindex von L und k (Lichtextinktionskoeffizient)=0,335+0,151(L)−0,0129(L)². Wenn die Konstante k (=0,72) verwendet wurde (Abb. 3) entsprach die Varianz für das ausgew?hlte Modell 88%. Zwischen dem Gesamttrockengewicht (TDW) und der PAR, die aufgenommen wurde, bestand in beiden Jahren ein signifikantes lineares Verh?ltnis. Abb. 4 zeigt die Daten für 1980. Durch den Nullpunkt geführt ergibt sich ein TDW=3,42 (PAR) und 2,49 (PAR) für 1980 bzw. 1979, das bedeutet, dass die Umwandlung von Lichtenergie in Trockensubstanz ohne ersichtlichen Wassermangel 1980 wirkungsvoller war. Abb. 5 zeigt die photosynthetische Wirksamkeit (g Trockengewicht MJ^l PAR) w?hrend der Vegetationszeiten zusammen mit den ?nderungen im Blattfl?chenindex L. Die Wachstumsrate des Bestandes stand 1980 in einem linearen Verh?ltnis zu der von den Bl?ttern aufgenommenen PAR, w?hrend sich für 1979, wo der Bestand stark unter Trockenheit litt, eine Abweichung ergab (Abb. 6). Obwohl w?hrend der beiden Jahre die photosynthetische Wirksamkeit (g Knollentrockengewicht MJ^l PAR, aufgenommen w?hrend der gesamten Vegetationszeit) für das Knollengewicht unterschiedlich war: Knollentrockengewicht=1,97 (PAR) und 2,37 (PAR) für 1979 bzw. 1980, zeigen die Daten, dass ein gesteigertes Wachstum entsprechend einer h?heren Lichtaufnahme zu h?heren Knollenertr?gen führt, unabh?ngig von einer Reihe ackerbaulicher Massnahmen.

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Résumé L'interception des radiations actives pour la photosynthèse (PAR), dans des longueurs d'onde de 400 à 700 nm, est mesurée durant très différente les deux années; 1979 fut particulièrement sec, surtout en fin de saison, alors que 1980 fut une année humide. La quantité de lumière interceptée, augmente linéairement avec l'index de surface foliaire (leaf area index) jusqu'à une valeur de L=4,25 (correspondant à 73% de radiations interceptées) et pour des valeurs supérieures, l'interception augmente à une vitesse décroissante jusqu'à L=4,0 correspondant à 95% de radiations captées (fig. 3). La relation I_L=I_oe^kL interpréte 92% de la variation dans la liaison entre la lumière interceptée et l'index de surface foliaire (L), où I_L est le rayonnement atteignant un plan horizontal situé sous un index foliaire L et K (coefficient d'extinction lumineuse)=0,335+0,151(L) −0,0129(L)². Si on fixe k à 0,72 (fig. 3), la part de variation expliquée par le modèle est de 88%. Une relation linéaire significative entre la matière sèche totale (TDW) cumulée et le PAR intercepté cumulé, a été établie pour les deux années et les données de 1980 sont portées dans la figure 4. Si on fait passer la régression par l'origine, on écrira pour 1979: TDW=2,49× deux années, 1979 et 1980, dans des cultures de pomme de terre du Royaume-Uni. Selon les données météorologiques, la pluviométrie fut et pour 1980: TDW=3,42×PAR. Ces relations indiquent que la conversion de lumière en matière sèche a été plus efficace en 1980 en l'absence de déficit hydrique. L'efficacité de la conversion photosynthétique (g de matière sèche/PAR intercepté) au cours de la saison, est indiquée avec les variations de L dans la figure 5. La vitesse de croissance de la culture est liée linéairement au PAR capté par la végétation en 1980, alors que cette liaison s'écarte de la linéarité en 1979, lorsque la culture est affectée par la sécheresse (fig. 6). Bien que l'efficacité de la conversion photosynthétique (g de poids sec de tubercule/PAR captée durant toute la saison) pour le poids de tubercules soit légèrement différente pour les deux années (en 1979 elle est égale à 2,37 (PAR), en 1980 elle est égale à 1,97 (PAR)). Les données indiquent que l'augmentation de la croissance de la récolte totale, expliquée par l'augmentation de la lumière captée, résultent également du rendement de plus en plus grand des tubercules (fig. 7), sur une série de traitements agronomiques.