Preliminary selection of antagonists ofErwinia carotovora subsp.atroseptica (Van Hall) Dye for application during green crop lifting of seed potato tubers

Summary Green crop lifting (GCL) for haulm killing was developed in The Netherlands and offers ideal conditions for controlling the blackleg pathogenErwinia carotovora subsp.atroseptica (Eca) by antagonists. Based on the use of mini-tubers or young tubers from field crops, two bioassays for wound protection were developed. GCL was simulated by artificially skinning or wounding tubers, inoculating the damaged skin with Eca, treating with antagonists and incubating in either potting compost or outside in field soil. Mainly fluorescent pseudomonads, pre-screened for in vitro antagonistic activity on agar and high soft rot reducing ability on tuber slices, were tested in the mini-tuber bioassay. Strains giving the highest degree of wound protection were further tested individually and in combination under field conditions in the young tuber bioassay. One individual strain and two combinations, resulting in reduction of contamination levels on skinned surfaces of 85% and between 60% and 70%, respectively, show good potential for biological control of blackleg.     

Comparative performance of potato crops raised from microtubers induced in the dark versus microtubers induced in light

Summary The performance of potato crops raised from two types of microtuber, green (induced in light-dark photoperiod) and white (induced in continuous darkness), of 18 genotypes was studied for 22 morphological and agronomic characters. Mean squares due to microtuber type, genotype and their interaction were mostly significant for various characters. Green microtubers were better than white microtubers for subsequent crop performance for most of the characters including tuber yield and general impression. This was mainly due to more eyes and shorter dormancy in green microtubers than in white microtubers. The in vitro system of microtuberization by serial culture of axillary buds in separated nodes, as used in the present study, was found to be genetically stable for the propagating material.     

Relative salinity tolerance of potato cultivars assessed byin vitro screening

One hundred and thirty European and North American potato cultivars were assayedin vitro for salinity (NaCl) tolerance. A modified single-node cutting bioassay was used in which cultivars were exposed to a range of NaCl levels (0, 40, 80, and 120 mM), in a Murashige and Skoog-based medium, for 1 month. Evaluations were performed twice for each cultivar at each salt level, using five single-node cuttings. Six vegetative growth parameters (shoot and root lengths, fresh and dry weights) were measured at the time of harvest and corrected for differences in cultivar vigor. These relative values were subjected to multivariate cluster analysis. The sum of the relative rankings at 40, 80, and 120 mM NaCl partitioned the cultivars into 8 units. The cultivars Amisk, BelRus, Bintje, Onaway, Sierra, and Tobique were in the most salinity tolerant unit and in the top cluster group for vigor with the exception of Tobique. These cultivars can be recommended for further study.     

Assessing the tolerance toGlobodera pallida of resistant potato genotypes by means of field and pot tests

Summary The tolerance toGlobodera pallida of 15 potato genotypes with a high level of resistance toG. pallida was assessed by measuring their tuber yield in heavily infested fields and in nematicide treated strips in the same fields. Tolerance was also assessed in pots in the glasshouse by measuring the total biomass after 35 and 70 days growth in heavilyG. pallida infested soil and in uninfested soil. Large differences in tolerance between the genotypes were observed. High correlations were observed between tolerance assessments made in the field experiments and between field and pot experiments. No relationship was found between tolerance and maturity. Shoot and root dry weight were about equally affected by the nematode.     

Transgenic potatoes expressing anErwinia pectate lyase gene — results of a 4-year field experiment

Summary Four potato lines of cv. Désirée that express the pectate lyase (PL) isoenzyme 3 ofErwinia carotovora subsp.atroseptica were examined in a 4-year field experiment with respect to plant development, tuber yield and resistance of tuber tissue toErwinia soft rot. The PL3 degrades plant cell wall pectin into unsaturated oligogalacturonates eliciting plant defence responses. In one line, enzyme expression was controlled by the CaMV 35S promoter (C) and in three lines it was driven by the potato patatin B33 promoter (D). Plant development of the D-lines in field plots was not distinguishable from that of the non-transgenic counterpart. Also tuber yield was not too different. By contrast, plants of the C-line were smaller than those of the nontransformed counterpart and also showed reduced tuber yield. There were no significant differences in dry mass, starch and protein content of tuber tissue between PL transgenic and non-transgenic potatoes. But compared with the latter, field-grown tubers expressing the PL displayed an enhanced resistance toErwinia soft rot. Thus, average rotting caused byEc-bacteria was diminished in tubers of PL-transgenic lines by 34.1%. The resistance of tubers toEc soft rot was significantly correlated with the PPO activity in tuber tissue.     

Physiology of the Potato: New Insights into Root System and Repercussions for Crop Management

Potato roots are concentrated mostly in the plow layer up to 30 cm in soil depth. Some roots extend up to 100 cm depth and the total root length throughout the soil profile reaches about 10–20 km m^?2 area. There are large differences in root mass (dry weight and length) in the plow layer between cultivars, breeding lines and wild relatives. The differences are generally stable across different environmental conditions, such as locations with different soil types, fertilizer rates and planting densities. Under favourable environmental conditions without severe shortage of water and nutrients, root mass differences between genotypes are related to maturity class: late genotypes continue root growth longer, and attain larger root mass and deeper rooting than early genotypes. Differences in root mass become clear at the start of flowering, much earlier than differences in shoot mass. Root mass is negatively correlated with early tuber bulking. However, root mass generally shows positive correlations with shoot mass and final tuber yield. Differences in root mass also exist amongst genotypes of the same maturity class. Using root mass in the plow layer and tuber yield as selection criteria, Konyu cultivars were bred in Japan. They showed significantly less reduction of leaf conductance and photosynthesis, leaf area and tuber yield than commercial cultivars under dry soil conditions. To assist breeding for root characters, new methods have been developed to assess the ability of roots to penetrate into hard soil layers using pots with paraffin-vaseline discs and the ability to absorb under low water potential in vitro. Physiological research on root characteristics contributed in the past, and will continue to do so in the future, to the development of new cultivars with high drought tolerance and to the improvement of irrigation practice.     

Inheritance of resistance to late blight in foliage and tubers of progenies from parents differing in resistance

Summary TenSolanum tuberosum genotypes differing in resistance to late blight (Phytophthora infestans (Mont.) de Bary) in foliage and tubers were intercrossed to determine the inheritance of disease resistance in their progenies. Plots of 10–15 clones per progeny were established in each of 2 years and resistance assessed by field or laboratory tests. The parental genotypes were similarly tested each year. The parents differed in general combining ability (GCA) for both foliage blight (FB) and tuber blight (TB). The parental and GCA scores were significantly correlated for both aspects of the disease, but the correlations between foliage and tuber scores for parents and for GCAs were not significant. Three parental genotypes were highly resistant in both foliage and tubers, and the genotype with the highest GCA for resistance to both FB and TB (cv. stirling) is recommended as the best parent. There was no evidence of strong genetic correlation between both aspects of resistance, and it is suggested that both be selected for in a breeding programme.     

Relationship between potato cyst nematodes and their principal host. IV. Tolerance of potato cultivars and the effect of potato cyst nematode on initial plant growth

Summary Greenhouse experiments on the effects of white potato cyst nematode infestations (Globodera pallida Stone) on initial growth and development of a series of potato cultivars are compared with the results of field experiments on sandy and sandy-peat soils on the effect of nematode density on tuber yield. A simple greenhouse test, assessing root growth response to potato cyst nematode infection, provided a good insight into a cultivar's tolerance performance in the field early in the growing season. As a very limited number of plants is needed for the greenhouse test, screening for tolerance can be conducted in the early stages of a breeding programme.     

Field and laboratory studies on the control of nematode and aphid virus vectors in potatoes by pesticides applied as side-bands

Field trials were undertaken with a prototype machine to determine whether virus vector nematodes and aphids were controlled by the carbamoyl oxime pesticides aldicarb (Temik 10G) and oxamyl (Vydate 10G) incorporated into the ridge of a growing potato crop. The treatments were applied at tuber initiation (7 or 8 weeks after planting) and were compared with similar amounts of the same pesticides applied in-furrow at planting. All aldicarb treatments significantly decreased the incidence of tobacco rattle virus spraing transmitted by trichodorid nematodes. However, the side-banded treatments were less effective than the in-furrow treatments applied at similar rates. Numbers of aphids infesting the crop were significantly and similarly decreased by both methods of application. Pesticide treatments did not significantly increase yield, and total tuber yields from the standard infurrow and the side-banded treatments were similar. To provide further information on the efficacy and movement of carbamoyl oxime pesticides between different isolated root systems on single parent tubers, replicated pot experiments were made. Parent tubers were maintained with a physical barrier between a root system treated with pesticide and another left untreated. In a nematode bioassay Meloidogyne incognita was added to both the treated and untreated root systems to test for the presence of nematicidal activity. The number of root-galls which developed in 8 weeks were counted. Both aldicarb and oxamyl decreased the number of galls on the treated root system. However, little evidence of translocation through the parent tuber was found, the number of galls on the untreated roots being largely unaffected. The roots of plants grown from tubers treated in a similar manner were tested for the presence of aldicarb and oxamyl residues by gas-liquid chromatography. No translocated pesticide was detected. In aphid bioassays, using excised leaves, 3–5 weeks after applying aldicarb at 20 and 40 mg a.i./pot or 4–9 weeks after applying aldicarb at 80 mg a.i./pot, aphid survival was always significantly less on treated stems than on non-treated stems growing at the opposite end of the tuber or on control stems growing from untreated tubers. However, there was some evidence for translocation through the parent tuber as fewer aphids survived on leaves from non-treated stems than from untreated control stems.     

Resistance of Potato Tubers to a Highly Aggressive Isolate of Phytophthora infestans in Relation to Tuber Age

The goal of these studies was to evaluate the influence of tuber age on the expression of resistance to Phytophthora infestans in five selected potato genotypes (three cultivars and two clones) varying in tuber resistance and maturity type, and also to select the best time for testing potato tubers for resistance to blight. Resistance was evaluated by inoculating whole tubers at 13 different times as they progressively aged during growth and storage. Tuber age was expressed as weeks after planting. Tubers were rated from week 13 (late July) until week 43 (late February) for tubers planted on 27–28 April, over three consecutive seasons (2001–2003). Analysis of variance performed on tuber resistance data showed significant effects of genotype, year and tuber age. Significant contributions of genotype × year, genotype × tuber age, year × tuber age and year × genotype × tuber age interactions were also detected. A slight increase in tuber resistance with tuber age was observed for cvs Bzura, Sokół and Irga, while the opposite trend was observed for the clones 97-A-63 and DG 92-227. Changes in tuber resistance with age of tested genotypes were not related to their maturity type. The period of most stable expression of tuber resistance was observed when tubers were tested between the 16th and 28th week after planting.     

A Greenhouse Assay for Powdery Scab (<Emphasis Type="Italic">Spongospora subterranea</Emphasis> f. sp. <Emphasis Type="Italic">subterranea</Emphasis>) Resistance in Potato

The plasmodiophorid pathogen Spongospora subterranea f. sp. subterranea causes powdery scab disease of potatoes (Solanum tuberosum L.), which severely affects tuber quality. Adequate chemical control of the disease is lacking, so breeding resistant potato cultivars is important. Little is known about the mechanisms or genetics of host resistance, as the epidemiology of the pathogen makes research on the disease difficult. An environmentally controlled disease screen that allows the accurate and repeatable assessment of diseased tubers (rather than a ranking system) is required to study host resistance in more detail. A high-throughput greenhouse disease assay is described that has been used to assess varying levels of tuber disease resistance of potato genotypes for three consecutive Southern Hemisphere growing seasons (2001–2002, 2002–2003, 2003–2004). This assay allows the evaluation of symptoms on tubers to verify resistance, rather than inferring the tuber infection on the basis of root galling or zoosporangial root infection. The assay was used to determine the level of resistance of genotypes of both known and unknown resistance status. The assay clearly distinguished the susceptible and resistant standards, and the results were highly correlated over the three seasons. The most efficient ways of assessing tuber disease susceptibility of genotypes are discussed. The consistency of the results and the ability to screen many genotypes confirms the value of the assay as a tool for early-generation selection in a plant breeding programme.     

Root System Development Including Root Branching in Cuttings of Cassava with Reference to Shoot Growth and Tuber Bulking

Summary

In spite of the important role it plays for water and nutrient acquisition, information on the root system development in cassava (Manihot esculenta Grantz) is limited. To examine the root length and branching pattern with reference to shoot growth and tuber bulking, we grew cassava plants in containers under natural climatic conditions in the southern end of Sumatra Island, Indonesia. One 20-cm length cutting of cassava (cv. Ardira IV) was planted in either a plastic bucket or a wooden box. The containers, which were filled with heavy clay soil, had different sizes depending on the growing period. At 30, 60, 100, 140, 180, and 270 days after planting (DAP), both the shoot and roots were sampled for quantitative analysis. The dry weight of both shoot and roots increased rapidly with the leaf area. The axile root number, however, decreased from 60 to 140 DAP as a result of the abscission of roots emerging from the basal part of the cutting during tuber bulking. The total root length reached its maximum at 60 DAP and significantly decreased thereafter because of decay and decomposition during tuber bulking. On the other hand, the root branching either increased the branching order or retained it, as determined from a topological point of view. The root branching during the later growing period compensated for the decrease in total root length and contributed to maintain a sufficient root surface area. The surviving roots with a well-developed branching pattern could absorb water and nutrients essential for tuber bulking.     

Assessment of the field resistance of potato genotypes with major gene resistance to late blight (Phytophthora infestans (Mont.) de Bary) using inoculum comprised of two complementary races of the fungus

Summary Two races ofPhytophthora infestans, differing in virulence against four major (R) genes for resistance, were used to assess the field resistance of differential (R) genotypes, both singly and mixed together in equal proportions. The mixed inoculum led to an over-estimation of the foliage resistance of genotypes with which only one of the races was compatible, by up to two scoring categories of a 1–9 scale in field trials and, to a lesser extent, in glasshouse tests depending on the differential and the test. Assessment of tuber resistance was not significantly affected. The R₁₀ and R₂ differentials showed a higher level of field resistance in the foliage and tubers, respectively, than the other genotypes. It is concluded that assessments of genotypes which may possess R genes, using mixed inoculum, should be interpreted with caution, and apparent high levels of field resistance confirmed through genetic studies of the inheritance of the resistance.     

Physiological effects of calonyctin on development and yield of potato

Summary Foliar sprays of calonyctin, a natural plant growth regulator extracted from the leaves ofCalonyction aculeatum (L.) House, at a concentration 0.05 activity units, increased the tuber yield of six potato (Solanum tuberosum L.) cultivars by 7–19% (mean 15%) during 1993 and 1994. Physiological differences between calonyctin-treated and untreated potato plants were usually detected 30–40 days after spraying them with calonyctin. The chlorophyll content of treated potato leaves increased, and the chlorophyll a:b ratio decreased. By 40 days after treatment the root oxidizability and soluble protein contents of different parts of the plants also increased. Their subsequent decline as the plants aged was inhibited by calonyctin. It is concluded that calonyctin delayed the senescence of potato plants and increased tuber growth at later stages of development.     

Impact of Agronomic Strategies (Seed Tuber Pre-sprouting,Cultivar Choice) to Control Late Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) on Tuber Growth and Yield in Organic Potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Crops

In order to optimize potato crop management in organic farming systems, knowledge of crop growth processes in relation to limitations and reductions by nitrogen (N) and disease is necessary. This paper examines the effect of different prevention measures (seed tuber pre-sprouting, choice of cultivars: resistance to Phytophthora infestans; earliness of tuber initiation) against disease-related constraints on yields, depending on the N-mediated growing conditions of organic potato crops. Under conditions of a relatively high N supply, accelerating the early development and tuber initiation of potato crops by seed tuber pre-sprouting (yield increase of c. 18–23%) or the selective choice of cultivars with an earlier tuber initiation (yield increase of c. 0–21%) are the most effective strategies in combating late blight. They bring forward the crop development c. 7–10 days, escaping the negative impact of the fungus on tuber growth. Under conditions of a relatively low N supply, these strategies do not affect final tuber yield. The reason for the differences of the effect depending on N supply of the crops is, that the lower the N supply, the shorter the period of time over which tuber growth takes place, independent of whether P. infestans becomes severe or not. Tuber growth of organic crops low in N has mostly ceased by the time late blight becomes potentially important for limiting yield, with the consequence that preventative measures against P. infestans are meaningless. Surprisingly, the level of cultivar haulm resistance to late blight did not affect tuber yields in years with an early and strong late blight development. Probably, the positive effect of a longer resistance to the fungus (c. 1 week) was counterbalanced by a later tuber initiation (also c. 1 week). In years with a moderate late blight incidence, less susceptible cultivars were able to produce higher tuber yields on fields with a lower N availability (c. 17–20%), probably due to higher N use efficiency and a better match of N mineralization and N uptake. Under conditions of a relatively high N supply, the tested cultivars with a higher haulm resistance to late blight were not able to improve tuber yields.     

The effectiveness of using a minituber crop for selection of agronomic characters in potato breeding programmes

Summary Performance of 20 potato genotypes was studied for seven agronomic characters in crops raised from minitubers and normal seed tubers. Correlation coefficients were computed between minituber crop and normal seed crop in order to study the selection efficiency at minituber crop level. The performance of normal seed crop was significantly better than the minituber crop for various characters including tuber yield and its components. Correlation coefficients between minituber and normal seed crop were significant for various characters except number of stems and number of tubers. Highest correlation coefficient (r=0.86) was for tuber yield followed by average tuber weight (r=0.67) and number of nodes (r=0.63). The results suggest that selection for tuber yield can be practised at the minituber crop level in potato breeding programmes     

Bacillus thuringiensis cry1Ab gene confers resistance to potato againstHelicoverpa armigera (Hubner)

Summary Helicoverpa armigera is one of the important insect pests adversely affecting the yield of potatoes in India. A synthetic gene encoding the insecticidal crystal protein (Cry1Ab) ofBacillus thuringiensis (Bt) has been introduced into five genotypes of potato usingAgrobacterium tumefaciens. Southern analysis of DNA from transgenic plants confirmed the integration and copy number of the transgene. Double-antibody quantitative sandwich ELISA analysis demonstrated high levels of Cry1Ab protein expression in transgenic plants. Insect bioassays on the leaves of transgenic plants showed considerable protection against the larvae ofH. armigera in terms of leaf area consumed and larval weight reduction.     

Transmission and yield effects of a gibberellin mutant allele in potato

Summary A selected clone ofSolanum tuberosum Group Andigena PI 347773 (clone Adg 11.1) and the cultivar Superior had previously been shown to be heterozygous at a gibberellin related dwarfing locus, ga₁. Experiments were conducted to test for gametophytic selection for alleles at the ga₁ locus in reciprocal crosses and for the effect of genotype on tuber yield. The genotypes of individuals from superior-Adg 11.1 reciprocal F₁ families were determined by test crossing. Genotypic classes could be distinguished by the percentages of dwarf seedlings in their test cross progeny. No differences were found in the genotypic distributions of the reciprocal families, which indicates gametophytic selection at this locus is not the cause of reciprocal yield differences. Superior-Adg 11.1 individuals classified by ga₁ locus genotype were evaluated for tuber yield. Tuber yields were highly correlated with genotype in both reciprocal families. Yields followed the pattern of simplex>duplex>triplex, indicating that the recessive mutant ga₁ allele exhibited a dose effect stimulating yield.     

Monoxenischer Resistenztest für Kartoffelgenotypen gegenüber dem ZystennematodenGlobodera pallida. 1. Kultivierung der Genotypen

Zusammenfassung Zur routinem?ssigen Resistenzbestimmung von Kartoffelgenotypen gegenüberGlobodera pallida (Stone) Behrens (Pa3) wurde ein monoxenischesin vitro-Verfahren entwickelt, dessen Grundlage die keimfreie Kultivierung der Testgenotypen in einem N?hragarmedium unter definierten Bedingungen war. Dadurch konnte die vollst?ndige Entwicklung der Nematoden sowie die Dimension ihres N?hrzellensystems in den transparenten Kartoffelwurzeln kontinuierlich beobachtet werden. Der Test erm?glichte die Selektion resistenter Genotypen anhand geringer quantitativer Unterschiede in der vermutlich polygen-vererbten Resistenzreaktion. Für die Anzucht keimfreier Pflanzen aus Kartoffelsamen und- knollen wurden spezielle Verfahren entwickelt und an mehreren Genotypen geprüft. Die dabei festgestellte Variabilit?t, insbesondere bei der Wurzelbildung, erforderte für den geeigneten Zeipunkt der Nematodenzugabe die Ausarbeitung eines Wurzelboniturschemas. Die Genotypen konnten nach dem Test in T?pfen weiterkultiviert werden.

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Summary A monoxenic resistance test for routine use was developed to determine the resistance of potato genotypes to the cyst nematodeGlobodera pallida (Stone) Behrens. The basis of the procedure is the aseptic cultivation of the genotypes under test in a nutrient medium in defined conditions. It was possible with it to observe invasion, the development of the nematodes, as well as the dimensions of their feeding cells in the transparent potato roots. Small, quantitative differences, due presumably to the polygenically determined resistance reactions of the genotypes, could be distinguished, and selection for resistance was feasible. For routine trials special procedures were developed using surface sterilisation of potato seed and etiolated sprouts which gave high levels of sterility. The genotypes from seeds could be tested directly, but those from etiolated sprouts had to be prepared by stem cutting. A root system was obtained which correlated with known ratings. Each genotype established from seed and etiolated shoots, developed at different rates, as did their root systems, and no definite timespan could be set before nematode introduction. Growing the cultivars under light before the test resulted in faster root development (Table 2), and a higher nematode infestation than in darkness (Figure 4). The time for nematode inoculation was determined by a rating system based on the location of the perimeter of the root system (Figure 5). In this way physiological factors and the individual growth rate of each genotype were allowed for, with the aim of assessing possibly high levels of nematode infection. At the end of the test the seedling genotypes can be removed from sterile culture and grown on in pots. Where genotypes form minitubers (Table 1) it is possible to proceed early to the next stage in cultivation or to store them trouble-free.

     

Validation of a simple potato growth model in the North Central United States

A simple potato growth model was validated in 1985 and 1986 at two dryland sites, Grand Forks, ND and Rosemount, MN, and one irrigated site, Hancock, WI. At each site, Russet Burbank potatoes were grown to maximize yield. Leaf area index and leaf, stem, root, and tuber biomass data were collected from replicated experiments every two weeks. Soil matric potentials, minimum and maximum temperatures, and solar radiation also were measured. Among sites, crop development rates and solar radiation receipts were similar, but final tuber yields differed by as much as 35 Mg/ha. Model predictions of leaf, stem, and tuber dry weights were similar to observed data both in terms of maximum values attained and seasonal development except for the experiment in Grand Forks in 1986 where the model over-estimated final tuber yield by 23 Mg/ha (115%). Soil aeration or salinity, factors not currently modeled, may account for this discrepancy. Modeled yield responses to defoliation were compared with field data from one of the experimental locations. At levels of defoliation below fifty percent, proportional yield reductions were similar between observed and modeled crops.