Influence of oxygen concentration and storage factors on susceptibility of potato tubers to bacterial soft rot (Erwinia carotovora)

Summary Potato tubers were injected with 10 μl of each of six inoculum levels (from 1 · 10⁶ to 5 · 10⁹ cells ml) ofErwinia carotovora var.atroseptica (van Hall) Dye. Analysis of the Weibull plot indicated that the bacteria acted independently and that all tubers were equally susceptible to decay. The amount of decay was significantly higher at 2% than at 6 and 10% oxygen. Under aerobic conditions at 22°C the bacteria multiplied quickly for no longer than 24 h but in a nitrogen atmosphere populations increased rapidly for 72 h at which time decay symptoms appeared. Changes in relative humidity had no effect on the diameter of decay induced by injecting six levels of inoculum into tubers but at 16°C decay developed significantly faster than at 10°C. Tubers treated with rindite to break dormancy initially decayed more than untreated tubers but 10 weeks after treatment, they decayed to a lesser extent. Susceptibility of tubers, treated with Furarex to break dormancy, was relatively constant throughout the storage period: untreated tubers. however, decreased in susceptibility after four weeks' storage.

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Zusammenfassung Kartoffelknollen (Sorte Russet Burbank) wurden mit 10 μl von 6 verschiedenen Suspensionen zwischen 1 · 10⁶ und 5 · 10⁹ Zellen/ml vonErwinia carotovora var.atroseptica (van Hall) Dye. inokuliert. Der Prozentsatz von inokulierten Stellen (injected loci), die bei 2% Sauerstoff in F?ulnis übergingen, aufgetragen auf einer Weibull-Skala als Funktion des Gehaltes an Inokulum, ergab eine Gerade mit einheitlichem Anstieg (Fig. 1) und zeigte Homogenit?t in der Anf?lligkeit der Knollen und unabh?ngige Wirkung der Bakterien. Ein Anstieg der ED₅₀ war mit einer Zunahme der Sauerstoffkonzentration positiv korreliert (Fig. 2). In Luft und in Stickstoffatmosph?re wurden ?nderungen der Population vonE. carotovora var.atroseptica, die den Kartoffelknollen injiziert wurden, in vivo untersucht (Fig. 3A). Unter aeroben Bedingungen nahm die Zahl der Zellen in den ersten 24 Stunden schnell und dann nur langsam zu; F?ulesymptome entwickelten sich nicht. Im Gegensatz dazu nahm die Zahl der Zellen unter anaeroben Bedingungen bis zu 72 Stunden zu und zu dieser Zeit war die F?ule bereits sichtbar. Der Hemmung des Bakterienwachstums unter aeroben Bedingungen folgte ein schnelles Wachstum, wenn die Knollen in anaerobe Bedingungen gebracht wurden (Fig. 3B). Mit frisch geernteten Knollen (Sorte Red La Soda), die in Florida gewachsen waren, wurde der Einfluss der Sauerstoffkonzentration, der Temperatur, der relativen Luftfeuchtigkeit und der Keimruhe auf die Knollenanf?lligkeit untersucht. Einige Knollen wurden mit Fusarex (Tetrachlornitrobenzol) behandelt, um die Keimruhe aufrecht zuerhalten und einige mit Rindite (?thylenchlorhydrin, ?thylendichlorid, Tetrachlorkohlenstoff, 7∶3∶1), um die Keimruhe zu brechen. Unterschiede in der Anf?lligkeit wurden durch ausmessen der F?uledurchmesser erfasst, die sich an jeder Injektionsstelle mit einer der 6 Konzentrationen entwickelten. Die F?ule war bei 16°C st?rker als bei 10°C (Tabelle 1) und die Unterschiede im Ausmass der F?ule zwischen den beiden Temperaturen waren bei der st?rksten Konzentration in allen Versuchen am gr?ssten (Fig. 4). Die F?ule entwickelte sich bei 2%. Sauerstoff schneller als bei 6 und 10% (Tabelle 2). Eine Woche nach der Ernte faulten die mit Rindite behandelten Knollen in einem gr?sseren Ausmass als die mit Fusarex behandelten oder die unbehandelten Knollen (Tabelle 3). In den folgenden Wochen nahm die Anf?lligkeit ab und 10 Wochen nach der Ernte waren die F?ulen in den mit Rindite behandelten Knollen signifikant geringer als in den mit Fusarex behandelten oder den unbehandelten Knollen. Die mit Fusarex behandelten Knollen waren 4 Wochen nach der Ernte weniger anf?llig als nach 1 Woche, aber nach 7 Wochen war die Anf?lligkeit wieder auf dem ursprünglichen Niveau. Bei unbehandelten Knollen nahm die Anf?lligkeit in diesem und in vorangegangenen Versuchen nach 4 Wochen Lagerung signifikant ab. Verschiedene relative Luftfeuchtigkeiten hatten keinen Einfluss auf die Zahl oder das Ausmass der F?ulen. Die Injektionstechnik zeigte, dass relativ kleine Unterschiede in einem Umweltfaktor wie z.B. Sauerstoff einen signifikanten Einfluss auf die Anf?lligkeit für Nassf?ule haben. Dieses Verfahren ist wichtig für die Auslese auf Resistenz gegen Nassf?ule in den Züchtungsprogrammen und für die Bestimmung eines m?glichen Effektes anderer Faktoren und chemischer Behandlungen auf die Anf?lligkeit für Nassf?ule.

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Résumé Des tubercules de la variété Russet Burbank ont été inoculés par injection de 10 μl d'un mélange de 6 inoculumd'Erwinia carotovora var.atroseptica (van Hall) Dye, à des taux variant entre 1 · 10⁶ et 5 · 10⁹ cellules ml. Le pourcentage des points d'injection évoluant par la suite en pourriture ayant été reporté sur graphique, les auteurs constatent qu'il est fonction du taux d'inoculum. Comme on peut l'observer aprés ajustement sur l'échelle de Weibull, on a une droite avec une pente unitaire (Fig. 1), cela a montré une homogénéité dans la sensibilité des tubercules et une action indépendante pour les bactéries. Une augmentation de ED₅₀ est corrélée de maniére positive avec une augmentation de la concentration en Oxygéne (Fig. 2). In vivo, des modifications de la populationd'E. carotovora varatroseptica aprés injection dans les tubercules ont été observées en condition normale d'aération et en atmosphéres azotées. (Fig. 3 A). En conditions aérobies, le nombre de cellules a augmenté rapidement pendant 24 h, ensuite il n'a évolué que lentement et les sympt?mes de pourritures ne sont pas apparus. Au contraire, en conditions anaérobies, le nombre de cellules augmenté pendant 72 h. à ce moment la pourriture devient visible. L'arrêt de la croissance bactérienne en conditions aérobies a été suivi d'une augmentation rapide de la population bactérienne, quand on place ensuite ces tubercules en conditions anaérobies (Fig. 3B). Les effets de la concentration en oxygéne, de la température, de l'humidité relative et de la dormance du tubercule, sur la sensibilité, ont été étudies avec des tubercules provenant de Floride (var. Red la Soda) et venant d'être récoltés. Une partie des tubercules a été traitée avec Fusarex (tétrachloronitrobenzène) afin de maintenir la dormance et l'autre partie avec de la rindite (éthylène chlorohydrine, éthylène dichloré, carbone tétrachloré · 7∶3∶1) pour lever la dormance. Des différences de sensibilité ont été mises en évidence par analyse des diamètres des surfaces malades apparaissant au niveau de chaque point d'injection avec l'un des six taux d'inoculum. L'importance des pourritures est plus élevée à 16°C qu'à 10°C (tableau 1) et les différences au niveau de la quantité de pourritures entre les 2 températures étaient plus importantes pour les taux d'inoculum les plus forts dans toutes les expérimentations (Fig. 4). Les pourritures se sont développées plus rapidement avec 2% d'oxygène qu'avec 6 et 10% (tableau 2). Une semaine après la récolte, les tubercules ayant été traités à la rindite ont pourri dans une plus grande mesure que ceux traités au Fusarex ou que les témoins (tableau 3). La sensibilité décroit les semaines suivantes, ainsi, 10 semaines après la récolte, les mesures enregistrées ont été significativement plus faibles pour les tubercules traités à la rindite que pour ceux traités au Fusarex ou pour les témoins. Les tubercules ayant été traités au Fusarex ont été moins sensibles, quand on les a testés 4 semaines après la récolte, que ceux testés après 1 semaine, mais après 7 semaines, leur sensibilité est revenue au niveau intial. Des tubercules non traités, à la fois dans cette expérimentation et dans d'autres études préliminaires ont une sensibilité à la maladie qui décroit de manière significative après 4 semaines de conservation. Le taux d'évolution de la maladie n'a pas été affecté par différentes humidités relatives. La technique d'injection s'est révélée intéressante car elle a montré des différences relativement faibles: même avec le facteur environnement (oxygéne) dont le r?le est important pour les changements de sensibilité à la pourriture molle. Ce procédé pourrait être utilisé dans un programme de sélection orienté vers la recherche de gènes de résistance à l'égard des pourritures bactériennes, dans la détermination des effets possibles d'autres facteurs, et de l'influence des traitements chimiques sur la sensibilité aux pourritures humides.

     

Influence of post-harvest storage temperature and gamma irradiation on potato carotenoids

Summary A comparative study of nine Indian potato varieties showed a good correlation between their total carotenoid content and the tuber flesh colour. Regardless of varietal differences, carotenoid level showed an increase during storage at ambient temperature (25–30°C) and to a lesser extent at 2–4°C and 15°C. Tubers exposed to an irradiation dose of 10 krad for sprout inhibition showed decreased levels of carotenoids during storage, particularly at 15°C where 50% loss was observed after 6 months of storage. Irradiated tubers stored for seven months at 15°C, on reconditioning at 34–35°C for 6 to 12 days showed a 2- to 6-fold increase in their carotenoid content.     

Effects of soybean genotype and growing location on oil and fatty acids in tofu

Soyfood products like tofu are becoming popular among American consumers due to health benefits. In order to increase production to meet consumer demands, it is imperative that factors that effect quantity and quality of tofu be characterized. The present study was conducted to determine the effects of soybean genotypes and growing locations on contents of oil and fatty acids in tofu which was prepared from twelve soybean genotypes (BARC-8, BARC-9, Enrei, Hutcheson, MD86-5788, Nakasennari, S90-1056, Suzuyutaka, V71-370, V81-1603, Ware, and York) grown at three southern U.S. locations (Huntsville, Alabama; Princess Anne, Maryland; and Petersburg, Virginia) during 1995. The results showed that tofu quality was determined by the soybean genotype. The tofu made from seeds of high seed-protein and low seed-oil genotypes (BARC-8 and BARC-9) resulted in tofu with low contents of oil (15.8 and 11.3 g/100g, respectively) and total saturated fatty acids (2.59 and 160 g/100g, respectively). Tofu made from seeds of conventional grain type genotypes, such as Hutcheson, resulted in higher oil (24.0 g/100g) and total saturated fatty acids (3.80 g/100g) contents in tofu. Effects of growing environment on contents of oil were not significant but tofu made from seeds grown in Alabama had significantly higher content of total saturated fatty acids (3.50 g/100g) as compared to that made from seeds grown in Maryland (2.88 g/100g) or Virginia (2.96 g/100g). Tofu made from seeds of large and medium-seeded genotypes had higher contents of total monounsaturated fatty acids in tofu as compared to that made from small-seeded genotypes. Highly positive correlation existed between contents of oil, 18:1, 18:2, total saturated, and total unsaturated fatty acids in the seeds and their contents in the tofu (+0.80, +0.75, +0.79, +0.62, +0.68, respectively). These results indicated that tofu quality is governed by soybean genotype, seed size and growing location.     

Composition and variation in vitamin C,carotenoids, protein,nitrate and oxalate contents inCelosia leaves

Twenty two lines/accessions belonging to 5 species ofCelosia were analysed for their nutritional and antinutritional composition. The nutrient contents, vitamin C varied from 18.8 to 53.6 mg/100 g, carotenoids 9.1 to 15.1 mg/100g, protein 2.1 to 5.9%, while the antinutritional factors, nitrate 0.18 to 0.46% and oxalate 0.98 to 3.93%. Moisture ranged 81 to 89%. Variation of these parameters with leaf position and the amino acids profile of some promising lines was also evaluated.     

Comparison of the effect of storage environment on tuber contamination withErwinia carotovora

Summary One tonne boxes of seed potatoes cv. Désirée contaminated withErwinia carotovora were held in four different types of farm stores. In general, contamination fell rapidly immediately after harvest and rose later in the storage season. The extent of these changes varied considerably with store type. The greatest reduction was from a log count of 5.5 to 2.1 after one month storage, followed by a rise to 5.1 prior to planting. No relationship was found between store temperature, relative humidity and change in contamination. There was some evidence that reduction in contamination was related to duration of ventilation, and rise in contamination to onset of sprouting. A sample held at a constant 4°C showed little reduction in contamination, and no rise occurred later in the storage season.     

Effect of wet incubation time and temperature on infection, and of storage time and temperature on soft rot lesion expansion in potatoes inoculated withErwinia carotovora ssp.Carotovora

Summary Infection and lesion expansion studies were carrried out on potato tubers. In the infection study, the tubers were inoculated withErwinia carotovora ssp.carotovora (Ecc) and exposed to incubation temperatures of 10–25 °C for 3–48 h of wetness. In the lesion expansion study, the tubers were exposed to 12 h of wetness at 20 °C to establish infection, and then·stored at temperatures of 4–16 °C for 15–90 d, at 95% RH. The volume of diseased tissue was determined and the data were transformed to proportion of maximum volume diseased (PVD). Infection was close to zero for 3 and 6 h wet incubation time, regardless of incubation temperature, and reached the maximum in 12 h of wetness at 20 °C. Significant lesion expansion occurred at a storage temperature of 16 °C after about 60 d of storage time. Cubic models of infection and lesion expansion potentials explained 95 and 96% of the variations in infection and lesion expansion, respectively.     

Influence of ambient forced-air ventilation rate on potato storage wastage

Summary Potatoes were stored in three insulated bins having ventilation rates of 0.0190, 0.0306 and 0.0417 m³/s·t. The results showed that in the climate of northern Italy potatoes can be stored successfully at ventilation rates of not less than 0.0306 m³/s·t resulting in product weight loss of less than 2.0% after 100 days' storage. The incidence of diseases and of sprouting was very low at rates of 0.0306 and 0.0417 m³/s·t, but greater at 0.019 m³/s·t because of the higher tuber temperature. Laboratory tests simulating ambient conditions confirmed the validity of a thermodynamic model simulating air-potato heat exchange.     

Lipids of high-yielding varieties of cashew (Anacardium occidentale L.)

Cashew kernel lipids from high-yielding varieties have been characterised. Neutral lipid accounted for 96% while glycolipid and phospholipid accounted for the remaining 4%. Triglycerides were very rich in unsaturated fatty acids (oleic and linoleic) while glycolipids were rich in saturated fatty acids (lauric and myristic). Varietal difference was noticed with respect to the composition of neutral and glycolipids. Composition of phospholipid did not differ among high-yielding varieties.     

Loss of vitamin C (L-ascorbic acid) during long-term cold storage of Dutch table potatoes

Summary Loss of vitamin C (L-ascorbic acid) from Dutch table potatoes during storage at 5–6°C over 8 months from November to July, was studied in two seasons. L-Ascorbic and dehydroascorbic acid were analysed by HPLC. The amount of dehydroascorbic acid was negligible. Total loss of L-ascorbic acid varied between 21 and 60%. Some potato lots lost L-ascorbic acid rapidly in the first four months, others more gradually over the whole storage period. The L-ascorbic acid levels detected were 75–150% higher in the period March–June, but 35% lower in the period December–February than those indicated by the step-wise decreases in the Dutch Food Composition Table.     

Influence of variety,date of harvest and storage time on factors connected with the crystallisation on canned scorzonera (Scorzonera hispanica)

In the period 1983–1986, research was carried out into the inulin content of scorzonera during ripening and storage. Since the inulin content is determining for the occurrence of crystallisation with canned scorzonera, the effects of the varieties, the time of harvest and storage of the scorzonera were investigated.The changing of the inulin content on the conversion into reducing sugars was checked; the effect of the dry matter and nitrate content were also defined.The aim was to define whether the determination of the inulin content was a useful parameter for the ripening of the scorzonera. On the whole, the different varieties showed remarkable difference where fructosanes+inulin, as well as pure inulin, were concerned.A significant decrease of the inulin content was obtained from the middle of November, by so far that it was below the limit above which crystallisation takes place.A two-month storage period of scorzonera harvested in early October also led to a very low inulin content, so that no problems could occur while canning. Storage conditions of the scorzonera seemed of importance too.The nitrate content of the different scorzonera varieties was low, although some variations were noted. The crops harvested in early December showed considerably lower contents when compared to those harvested in early October or mid-November.The inulin content as well as the content of reducing sugars are a useful parameter to determine the maturity of the scorzonera.This research was subsidized by the Instituut tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw (I.W.O.N.L.).     

Effect of haulm treatment and harvest time on incidence of tuber rots of potato (Solanum tuberosum L.) after standard wounding and on frequency of stem lesions caused byPhoma foveata Foister

Summary Various haulm treatments and harvest times differentially influenced the incidence of storage rots in potato tubers (Solanum tuberosum L.) in field experiments in Sweden performed over 4 years. The incidence of gangrene caused byPhoma foveata Foister (Phoma exigua var.foveata (Foister) Boerema) increased in cv. Bellona after spraying haulms with diquat as did the amount of infection caused byFusarium avenaceum (Corda ex. Fr.) Sacc. in all three cultivars (Bintje, Bellona, and Magnum Bonum). The lowestP. foveata infection levels occurred after pulling haulms. Late harvesting increased the frequency ofP. foveata in cvs Bintje and Bellona both at 2 and 4 wks interval between haulm treatment and harvest. Tuber and visible stem infection caused byP. foveata were correlated for cvs Bintje and Bellona, but not for cv. Magnum Bonum. The possible relation between tuber and stem infection is discussed.     

Oil content and fatty acid composition of promising IndianBrassica campestris L. (Toria) genotypes

Seeds of sixty four genotypes ofBrassica campestris L. (Toria) were analyzed for oil content and fatty acid composition. Oil content varied from 38.9% to 44.6%. Major fatty acids viz. oleic, linoleic, linolenic, eicosenoic and erucic acids exhibited ranges from 10.1% to 17.3%, 5.9% to 14.5%, 5.2% to 15.0%, 7.7% to 13.7% and 39.6% to 59.9%, respectively. Compared to the standard cultivar ITSA, four genotypes contained 5 to 8% lower content of erucic acid; and six genotypes contained significantly higher content of linoleic acid. Oil was positively correlated with erucic acid. The observed inverse relationship between linoleic and erucic acid contents might be utilized in breeding nutritionally better Toria cultivars with both high linoleic and low erucic acid contents.     

The oil content and fatty acid composition of various genotypes of cauliflower,turnip and radish

Seeds of thirteen genotypes of cauliflower, four of turnip and seven of radish were analysed for oil content and fatty acid composition. Turnip and radish had higher oil content as compared to cauliflower. Oleic, linoleic + eicosenoic and erucic acids were the major fatty acids in the oils of these seeds. Levels of erucic acid were in the order of radish < turnip < cauliflower. Compared to cauliflower and turnip seeds, radish seeds contained higher amounts of palmitic, oleic, and linolenic + eicosenoic acids and lower amounts of linoleic and erucic acids.     

Effect of fertilization treatments on yield parameters and mucilage and fat contents in roots of moghat (Glossostemon bruguiri Desf.)

Moghat plants,Glossostemon bruguieri, Desf., received three levels of both N and K fertilizers, either alone or in combination, with a basic dose of P for all the treatments. The results with one and two year old plants revealed the importance of potassium for higher yield of roots, reflected in greater length and diameter. The lower level K₁ was enough to attain that goal and the N₁K₁ treatment was the best in this regard. On the other hand, N fertilization rather favoured the vegetative growth and seed yield. Both N and K fertilization decreased the mucilage content of the roots, but increased their fat content. The root yield after two years increased by 72% compared with one year old plants. That increment was rather dependent on the root diameter than its elongation. The mucilage content was doubled, while the fat content decreased.     

Potato tuber sugar content during development and storage (10°C): possible predictors of storage potential and the role of sucrose in storage hexose accumulation

Summary Reducing sugar and sucrose contents of potato tubers (Solanum tuberosum L.) from six cultivars were monitored both during the growing season and after a four months storage period at 10°C. Significant correlations were found between tuber sugar contents (sucrose, reducing and total) measured at harvest and the reducing sugar content after storage. Similarly, in five of the six cultivars, the sucrose loss and the corresponding reducing sugar gain during storage were significantly correlated.     

Physico-chemical composition and characterisation of the seed and seed oil ofSclerocarya birrea

The physicochemical composition ofSclerocarya birrea was assessed by standard methods and was found to contain 11.0% Crude oil, 17.2% Carbohydrate, 36.70% Crude protein 3.4% fibre and 0.9% crude saponins. The fatty acid distribution in the seed oil was obtained by fractionating the volatised fatty acid by GC-MS. The oil is made up of nine fatty acids of which palmitic, stearic and arachidonic acids are the most dominant.     

顶孢霉菌代谢产物对玉米圆斑病菌生长和发育的影响

利用菌丝生长速率法和孢子萌发法研究顶孢霉代谢产物对玉米圆斑病菌生长的抑制能力。结果表明,顶孢霉发酵液对玉米圆斑病菌分生孢子萌发和菌丝生长均有抑制作用。菌丝生长速率测定表明,含有顶孢霉菌代谢产物的培养基（D+P）圆斑病菌菌丝的生长速率低于含有玉米圆斑病菌代谢产物的培养基（Y+P）和空白对照PDA的生长速率,菌丝生长速率分别为65.0、86.5、87.5 mm/d;以Y+P和PDA为对照,D+P对玉米圆斑病菌在第1天和第2天时抑制率最高,均达58%以上;在1 mL PDA体系中,顶孢霉发酵液添加量为0.5 mL时,抑制率可达100%,不同浓度处理间及其与对照处理间顶孢霉发酵液抑制率差异显著（P=0.05）;同一处理不同培养天数顶孢霉发酵液抑制率也有显著差异（P=0.05）。孢子萌发实验表明,经顶孢霉发酵液处理后的玉米圆斑孢子萌发率降低,在发酵液浓度为0.9 mL/mL时,萌发率仅为24%,抑制率可达66.67%, EC50约为68 mL/100 mL,且孢子经发酵液处理后产生畸形,不能正常发育。     

Effect of processing method on the quality of cowpea (Vigna unguiculata) flour for akara preparation

An indigenous food mixture containing rice flour, milk coprecipitate, sprouted green gram paste and tomato pulp (2: 1: 1: 1 w/w) was developed and called a RCGT food mixture. It was autoclaved (1.5 kg/cm², 15min, 121 °C), cooled and fermented with 2% liquid culture (containing 10⁶ cells/ml broth). Two types of fermentations were carried out i.e. one step single culture fermentation [L. casei or L. plantarum (37 °C, 24 hr.)] and sequential culture fermentation [S. boulardii (25 °C, 24 hr.) +L. casei (37 °C, 24 hr.)]; [S. boulardii (25 °C, 24 hr.) + L. plantarum (37 °C, 24 hr.)]. All fermentations drastically reduced the contents of phytic acid, polyphenols and trypsin inhibitor activity while significantly improving the in vitro digestibilities of starch and protein. Sequential culture fermentations brought about further changes compared to one step single culture fermentation.     

小麦β-酮脂酰CoA合成酶基因KCS的克隆与酵母表达

超长链脂肪酸是生物体内众多重要物质的合成底物。KCS基因编码β-酮脂酰CoA合成酶,该酶具有底物特异性,参与超长链脂肪酸延伸的缩合反应,是超长链脂肪酸合成的限速步骤。为了探究小麦KCS基因在超长链脂肪酸合成中的功能,采用同源克隆的方法从小麦(Triticum aestivum L.)中克隆出KCS基因后,利用生物信息学对其编码序列进行分析,并在酿酒酵母(Saccharomyces cerevisiae)中对其进行真核表达。结果表明,小麦TaKCS6基因的开放阅读框为1 287bp,编码428个氨基酸残基。结构域预测结果显示,TaKCS6蛋白含有III型聚酮合酶脂肪酸延伸酶和C末端3-酰基ACP合酶III结构域,属于KCSs蛋白家族。序列比对分析结果显示,TaKCS6氨基酸序列与拟南芥及其他植物的KCS6氨基酸序列在两个功能结构域上和活性位点保守。酵母表达结果显示,TaKCS6基因编码的蛋白参与C24以上超长链脂肪酸的延伸。     

Effect of haulm treatments on the formation of microsclerotia ofVerticillium dahliae Kleb. on potato

Summary In four pot experiments, potato plants of cv. Element were artificially infected withV. dahliae. At an early and a late harvest haulms were killed chemically, by burning or by various other treatments, including cutting them into pieces of different lengths and keeping the debris on the soil surface or covering with soil. After 4 weeks the plant material was air-dried and the number of microsclerotia per mg was determined. At the early harvest, in two experiments, the chemical treatment yielded more microsclerotia than the cutting treatments. Covering colonised haulm tissue with non-sterilised soil was effective in inhibiting microsclerotia formation. Shorter haulm pieces led to fewer microsclerotia at the later harvest if the material was kept on the soil surface. The variation in microsclerotial yield and in treatment effects among the different experiments was large.