Effects of previous cropping and fungicide timing on the development of light leaf spot (Pyrenopeziza brassicae), seed yield and quality of winter oilseed rape (Brassica napus)

Light leaf spot, caused by Pyrenopeziza brassicae, was assessed regularly on double-low cultivars of winter oilseed rape during field experiments at Rothamsted in 1990-91 and 1991-92. Previous cropping and fungicide applications differed; seed yield and seed quality were measured at harvest. In each season, both the initial incidence of light leaf spot and the rate of disease increase were greater in oilseed rape crops sown after rape than those sown after cereals. The incidence of diseases caused by Phoma lingam or Alternaria spp. was also greater in second oilseed rape crops. In 1991-92 there was 42% less rainfall between September and March than in 1990-91, and much less light leaf spot developed. However, P. lingam and Alternaria spp. were more common. Only fungicide application schedules including an autumn spray decreased the incidence of light leaf spot on leaves, stems and pods, as indicated by decreased areas under the disease progress curves (AUDPC) and slower rates of disease increase. Summer sprays decreased incidence and severity of light leaf spot on pods only. In 1990-91, all fungicide treatments which included an autumn spray increased seed and oil yields of cv. Capricorn but only the treatment which included autumn, spring and summer sprays increased yields of cv. Falcon. No treatment increased the yields of cv. Capricorn or cv. Falcon in 1991-92. Fungicide applications decreased glucosinolate concentrations in the seed from a crop of cv. Cobra severely infected by P. brassicae in 1990-91, but did not increase yield.     

Biological Control of Groundnut Late Leaf Spot and Rust by Seed and Foliar Applications of a Powder Formulation of Pseudomonas fluorescens

Glasshouse and field trials were conducted to determine the efficacy of a talc-based powder formulation of Pseudomonas fluorescens strain Pf1 in controlling groundnut leaf spot ( Cercosporidium personatum ) and rust ( Puccinia arachidis ). Seed treatment with the talc-based powder formulation of the bacterium alone effectively reduced the severity of leaf spot and rust. When the treated seeds were sown in soil, the antagonist moved to the rhizosphere and multiplied well in it. Foliar application with the powder formulation effectively controlled the groundnut leaf spot and rust. P. fluorescens multiplied well in the phyllosphere after foliar application of powder formulation. Combined application of the P. fluorescens formulation to seed and foliage effectively controlled leaf spot and rust, and increased the pod yield in greenhouse and field tests.     

A comparative screening of hybrid,modern varieties and local rice cultivar for brown leaf spot disease susceptibility and yield performance

Five rice cultivars, one hybrid (WR96), three modern (BR16, BR26, and BRRI Dhan27) and one local (Pari) were screened for reaction to brown leaf spot disease caused by Cochliobolus miyabeanus and performance of yield-related characters. The severity of brown leaf spot varied with growth stages of rice plant as well as different cultivars tested under field condition. Low disease severity was observed at maximum tillering stage compared to moderate to high at dough stage, with hybrid cultivar WR96 showing highest disease, while local cultivar Pari had the lowest. Brown spot disease severity in different cultivars under induced epiphytic condition also followed the similar trend. The results also revealed that most of the yield-contributing characters examined showed wide variations among the cultivars. Modern cultivar BR16 produced the highest panicle length, number of grain per panicle and grain yield per hectare. At the same time as local cultivar Pari generated the lowest number of tiller per plant, panicle length, grain number per panicle and grain yield per hectare. Moreover, hybrid cultivar WR96 produced the highest percentage of spotted grain per panicle and seed yielding C. miyabeanus, and also the lower percentage of seed germination, while the reverse was observed in local cultivar Pari. These findings may allow producers and breeders to select rice cultivar, resistant or tolerant to brown leaf spot disease and to avoid significant reductions in grain yields.     

Assessment of resurgence of bacterial blight and its effect on cotton yield in northern Nigeria

Abstract

Cotton production in Nigeria causes fluctuating socio-economic and biotic factors. Bacterial blight induced by Xanthomonas campestris pv malvacearum causes the greatest yield loss annually. A study was therefore carried out to investigate the resurgence of the disease on 10 different cotton genotypes in Dowaya, Kem and Ngurore which are the major cotton areas of Adamawa state of Nigeria under field conditions. Other objectives were to determine the relationship between the different manifestations of bacterial blight and the yield of seed cotton and to identify resistance in the selected genotypes to the disease manifestations. Results revealed the presence of angular leaf spot, vein and boll rot manifestations of the disease in the study areas. The absence of vein blight symptoms in the Kem location did not result in higher yield because the severity of the leaf spot for this location was relatively higher than for the other two locations. Results also revealed that despite the high severity of angular leaf spot, high boll rot and vein blight incidences observed particularly on SAMCOT-11, SAMCOT-13 and ex-Benin in these locations with a high yield of seed cotton was recorded. The three multi-adversity resistant genotypes (MAR), TX-CDP37HH-1-83, TAMCOT SP-21S and TAMCOT CAMD-E recorded relatively lower severity and incidences in both cases. There was, however, a significantly negative correlation between angular leaf spot severity, boll rot incidence and yield at Kem location, significant negative correlation between angular leaf spot severity, boll rot incidence, vein blight and yield at Dowaya location, as well as significant negative correlation between angular leaf spot severity, vein blight and yield at Ngurore location. The tolerant and high yielding SAMCOT-11, SAMCOT-13 and ex-Benin should through breeding work be improved to be used for production in this area and its surroundings.     

Effects of light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus)

The relationship between development of light leaf spot and yield loss in winter oilseed rape was analysed, initially using data from three experiments at sites near Aberdeen in Scotland in the seasons 1991/92, 1992/93 and 1993/94, respectively. Over the three seasons, single-point models relating yield to light leaf spot incidence (% plants with leaves with light leaf spot) at GS 3.3 (flower buds visible) generally accounted for more of the variance than single-point models at earlier or later growth stages. Only in 1992/93, when a severe light leaf spot epidemic developed on leaves early in the season, did the single-point model for disease severity on leaves at GS 3.5/4.0 account for more of the variance than that for disease incidence at GS 3.3. In 1991/92 and 1992/3, when reasonably severe epidemics developed on stems, the single-point model for light leaf spot incidence (stems) at GS 6.3 accounted for as much of the variance. Two-point (disease severity at GS 3.3 and GS 4.0) and AUDPC models (disease incidence/severity) accounted for more of the variance than the single-point model based on disease incidence at GS 3.3 in 1992/93 but not in the other two seasons. Therefore, a simple model using the light leaf spot incidence at GS 3.3 (x) as the explanatory variable was selected as a predictive model to estimate % yield loss (y_r): y_r= 0.32x– 0.57. This model fitted all three data sets from Scotland, When data sets from Rothamsted, Rosemaund and Thurloxton in England were used to test it, this single-point predictive model generally fitted the data well, except when yield loss was clearly not related to occurrence of light leaf spot. However, the regression lines relating observed yield loss to light leaf spot incidence at GS 3.3 often had smaller slopes than the line produce, by the model based on Scottish data.     

Efficacy of some plant extracts in the management of cercospora leaf spot of groundnut in the Sudan savanna of Nigeria

Field trials were conducted to evaluate the efficacy of neem seed, garlic clove, onion bulb, ginger rhizome and pawpaw leaf extracts applied as foliar spray in controlling cercospora leaf spot of groundnut in the Sudan savanna of Nigeria during the 2002 and 2003 cropping seasons. Ridomil was used as a positive check while the control was left untreated. Three spray regimes (once, twice and thrice) were evaluated. A strip plot design with three replications was used in setting up the experiments. Ex-Dakar, a cercospora leaf spot susceptible Spanish Valencia groundnut variety, was used as planting material. All the plant extracts reduced the incidence and severity of cercospora leaf spot in both seasons compared to the untreated crops. However, neem seed and garlic clove extracts significantly reduced the incidence and severity of the disease compared to the other plant extracts. Ridomil was more effective in controlling the disease than the plant extracts. Three sprays with the plant extracts gave better control of the disease than one or two sprays in the season. The highest seed yield of 3115 kg/ha and 3311 kg/ha in 2002 and 2003, respectively, were obtained with neem seed extract treatment while the lowest seed yield of 2134 kg/ha and 2334 kg/ha in 2002 and 2003, respectively, were recorded from the untreated crops. Also the highest seed yield of 3124 kg/ha and 3418 kg/ha in 2002 and 2003, respectively were obtained following three sprays compared to 2523 kg/ha and 2641 kg/ha for one spray in 2002 and 2003, respectively and 2840 kg/ha and 3085 kg/ha for two sprays in 2002 and 2003, respectively. The highest haulm yield of 4121 kg/ha and 4089 kg/ha in 2002 and 2003, respectively were also obtained following treatment with neem seed extract. The lowest haulm yield of 2951 kg/ha and 3045 kg/ha in 2002 and 2003 respectively, were recorded from the control. Three sprays gave higher haulm yield (4265 kg/ha and 4279 kg/ha in 2002 and 2003, respectively) than one and two sprays in the season. Neem seed extract could therefore be used to control cercospora leaf spot and to improve groundnut production in the Sudan savanna of Nigeria.     

Fungal foliar diseases of Rauwolfia serpentina in wild,its seasonal occurrence,seed transmission and disease management

Rauwolfia serpentina is an important medicinal herb. Studies were conducted to determine causal organisms of foliar diseases in R. serpentina in Bhadra Wildlife Sanctuary during 2006–2009. The foliar disease incidence and its distribution and disease severity in nine state forest regions of the sanctuary were determined. The seedborne nature and transmission of the causal organism was also determined. The management of seedborne inoculum was done by seed dressing with fungicides. The effect of foliage infection on secondary metabolite content was also determined. Results of the present study indicated that Cercospora rauwolfiae is major leaf spot disease causing pathogen. The disease is homogeneously distributed through the study area. The foliar disease severity was high in Kagemanegiri forest during October–November. The minor leaf spot disease caused by Alternaria alternata occurred occasionally. Alternaria alternata is seedborne and seed transmitted and could be managed by seed treatment with Captra or Hyzeb. The secondary metabolites like alkaloids and steroids decreased with increase in foliar infection by C. rauwolfiae, while phenol and flavonoid contents increased. The study suggested that R. serpentina is affected in wild by C. rauwolfiae and A. alternata. The latter pathogen is seedborne and seed transmitted and controlled by seed treatment.     

Interrelationship between Leaf Gas-Exchange Characteristics,Area Leaf Mass,and Yield in Soybean (Glycine max L. Merr) Genotypes

Variability in leaf gas-exchange traits in thirteen soybean (Glycine max L. Merr) genotypes was assessed in a field experiment conducted at high altitude (1 950 m). Leaf net photosynthetic rate (P ^N) exhibited a high degree of variability at all the growth stages studied. P _N and other gas-exchange parameters exhibited a seasonal pattern that was similar for all the genotypes. P _N rate was highest at seed filling stage. P _N was positively and significantly associated with aboveground dry matter and seed yield. The area leaf mass (ALM) exhibited a strong positive association with leaf P _N, aboveground dry matter, and seed yield. The positive association between ALM, P _N, and seed yield suggests that this simple and easy to measure character can be used in breeding programmes as a surrogate for higher photosynthetic efficiency and eventually higher yield.     

Effects of Bradyrhizobium strain and host genotype,nodule dry weight and leaf area on groundnut (Arachis hypogaea L. ssp. fastigiata) yield

Effects of inoculating four Arachis hypogaea ssp. fastigiata cultivars with 17 Bradyrhizobium spp. strains were studied in a glasshouse experiment using a sandy soil devoid of an indigenous Bradyrhizobium population. Firstly, a wide range of parameters, indicative of symbiotic performance, were assessed for their influence on seed yield, by correlation and statistical analyses. It was found that nodule dry weight and leaf area were relevant parameters concerning seed yield. Secondly, the effects of host and strain genotype on those parameters were described.Variations in nodule dry weight did not have an effect on seed yield, except for cultivar Natal Common at lower nodule dry weight values. Therefore, it was concluded that the quantity of nitrogen fixing tissue met the demand for combined nitrogen and did not limit seed yield. This conclusion was further supported by the observation that at low nodule numbers per plant the nodule size increased to generate sufficient nitrogen fixing tissue.Leaf area, which comprises components for both photosynthetic capacity and plant development, was found to correlate well with seed yield. An increase in leaf area resulted in significant seed yield increases for all three spanish-type cultivars, but not for the valencia-type cultivar. Leaf area, thus, appeared as a factor limiting seed yield of spanish-type groundnuts.Cultivar performance concerning seed yield was significantly better for Natal Common compared to the other three cultivars, while Natal Common had a significantly lower plant (biomass excluding seed) dry weight value.Inoculation with different strains of Bradyrhizobium resulted in significantly different nodule dry weight values, but hardly led to significant differences in seed yield. This agreed with the finding that the amount of nitrogen fixing tissue appeared not to limit the availability of combined nitrogen.A large quantity of nitrogen was partitioned to the groundnut seeds: 62% to 76% of total accumulated nitrogen was located in the seeds.This study showed that testing for symbiotic effectiveness in the groundnut Bradyrhizobium symbiosis should include assessment of final (seed and biomass) yield, because parameters measured at stages prior to maturity, like nodulation parameters, may lead to flawed effectiveness ratings.     

Suppression of gray leaf spot (blast) of perennial ryegrass turf by Pseudomonas aeruginosa from spent mushroom substrate

Bacteria isolated from spent mushroom substrate (SMS) were evaluated for the suppression of Pyricularia grisea, the causal agent of gray leaf spot of perennial ryegrass (Lolium perenne) turf. Thirty-two of 849 bacterial isolates (3.8%) from SMS significantly inhibited the mycelial growth of P. grisea in vitro. Six bacterial isolates that afforded maximum inhibition of P. grisea were also refractory to Rhizoctonia solani, Rhizoctonia cerealis, Sclerotinia homoeocarpa, and Fusarium culmorum. Each of the six isolates was identified as Pseudomonas aeruginosa by fatty acid profile analysis. The biocontrol activity of the bacterial isolates was not compromised by a prolonged exposure to UV radiation in vitro. In controlled-environment chamber experiments, all 32 bacterial isolates were tested for suppression of gray leaf spot on Pennfine perennial ryegrass when applied as seed treatment or foliar sprays. Foliar applications of the bacteria (10⁸ cfu/ml 0.1% carboxymethylcellulose), but not the seed treatment, significantly reduced disease severity and incidence. The three most efficient isolates from foliar application treatments, which were among the six bacterial isolates identified as P. aeruginosa, were further evaluated for suppression of gray leaf spot as a function of timing of application. The three isolates of P. aeruginosa suppressed gray leaf spot in perennial ryegrass in Cone-tainers when applied at 1, 3, and 7 days prior to inoculation with P. grisea both in controlled-environment chamber experiments, and in potted ryegrass plants maintained in the field. All application intervals, regardless of the bacterial isolate, provided significant reduction of gray leaf spot severity. Suppression of gray leaf spot by isolates of P. aeruginosa under controlled-environment chamber conditions was not different from that observed in potted ryegrass plants maintained in the field. In field experiments, an isolate of P. aeruginosa provided significant suppression of gray leaf spot when applied at 1, 7, and 14 days prior to inoculation with P. grisea. The bacterium proved effective against gray leaf spot of perennial ryegrass maintained as fairway and rough heights. These results indicate that P. aeruginosa may be a potential biocontrol agent for gray leaf spot of perennial ryegrass turf.     

Celery leaf spot: sources of inoculum

The relative importance of infected celery seed, infected leaf debris in the soil, and infected wild celery, in the incidence of Septoria leaf spot in cultivated celery has been investigated. Infection can be caused when the sole source of inoculum is viable spores on the seed surface; such spores are considered to be the main cause of disease outbreaks. Of all the seed samples examined, 93% were infected by Septoria spp. In untreated seed samples, 40% carried viable spores which survived for up to 15 months on seed stored in the laboratory, and for longer periods on seed stored at -20d? C. However, ageing of seed is not recommended as a commercial control measure. The fungus was not found in seed embryos or endosperms but mycelium was present in pericarps and testas. Unconfirmed evidence suggests that in favourable circumstances new spores might be produced in old seed-borne pycnidia.     

Experiments with fungicide sprays in late summer and early autumn on sugar-beet root crops

Fentinhydroxide and benomyl sprayed on to sugar-beet root crops in July, August and September frequently increased yield of tops. Sugar yield was increased only if either powdery mildew or virus yellows was prevalent, when on average a single fentinhydroxide spray at 0·7 kg a.i./ha increased sugar yield by 8% and yield of tops by 13%. The mildew specific fungicide fluotrimazole also increased yield, but it could not be determined whether this was due to controlling powdery mildew or secondary parasitic fungi attacking yellows-infected plants. Repeated sprays of both fentinhydroxide and fluotrimazole, but not benomyl, appeared to be phytotoxic when applied in hot dry weather.     

Methods of assessment celery leaf spot (Septoria apiicola) in relation to fungicide evaluation

Six criteria for evaluating fungicides for control of celery leaf spot (Septoria apiicola) were compared. Two of these criteria consisted of yield measurements, of which marketable yield gave better statistical separation of the fungicides than gross yield. Of the other four criteria, assessment of leaf spot on a whole-plot basis was the most valuable. Overall disease rating on individual intact plants, rating of each petiole and numbers of diseased petioles per plant were less useful assessment criteria.     

Genotype Variability in Photosynthetic Characteristics in Finger Millet

High variability in leaf gas exchange and related traits were found in 30 genotypes of field grown finger millet. The variability in carbon exchange rate per unit leaf area (P _N) can be partly attributed to the differences in the stomatal conductance (g_s) and area leaf mass (ALM). The P _N was positively correlated with total dry matter (TDM). However, no relationship between P _N and seed yield was found. The leaf area showed a positive and significant correlation with total biomass. None of the other gas-exchange traits had significant relationship either with TDM or with seed yield. The ALM showed a strong positive association with P _N. However, it was not correlated with either total biomass or seed yield. As a result, the use of ALM as surrogate for P _N for identifying high biomass producing genotypes only had a limited value. Hence selection for high P _N would result in higher biomass producing types.     

Incidence and severity of frogeye leaf spot and associated yield losses in soybeans in agroecological zone II of Zambia

The incidence and severity of frogeye leaf spot of soybean (Glycine max (L.) Merr.) was studied in agroecological region II of Zambia during the 1997/98 crop growing season. A survey was conducted on farmers' fields on SCSI Kaleya, Magoye and Hernon-147 cultivars. Disease incidence and severity was assessed by monitoring disease increments at two weeks interval (beginning of January to April) from nine fields, three from each province. Soybean cultivars were evaluated for yield losses resulting from frogeye leaf spot. Field plots of each cultivar were either sprayed twice with benomyl (benlate) or not sprayed at all. The results showed that the incidence of frogeye leaf spot was highest in Southern province (5.1), followed by Lusaka province (4.9) while Central province had the lowest disease incidence (1.8). Values for area under disease progress curve (AUDPC) were significantly greater (P < 0.05) for Lusaka and Southern provinces than for Central province. Yields in benomyl protected plots ranged from 1444 kg ha⁻¹ to 2320 kg ha⁻¹ and were significantly different among the cultivars. Average yields of non protected plants were reduced by 30.5% for Kaleya, 35.6% for Hernon-147 and 37.2% for SCS1. Incidence and severity increased with time and varied depending on weather parameters and susceptibility of cultivars to the disease. Yield losses due to frogeye leaf spot occurred through a reduction in seed size. Differences in weather conditions and amount of inocula are believed to contribute to the observed variation in incidence and severity of the disease at different locations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of pea bacterial blight (Pseudomonas syringae pv. pisi) on the yield of spring sown combining peas (Pisum sativum)

Field trials to examine the effect of pea bacterial blight (Pseudomonas syringae pv. pisi) (Psp) on the yield of combining peas were carried out at five sites (HRI Wellesbourne, ADAS Rosemaund, ADAS Terrington, PGRO, SASA East Craigs) in the UK in 1990, 1991 and 1992. Healthy seed, cv. Solara, and seed naturally infected with Psp Race 2 was sown in large plots (c. 200 m²) in the open or under nets to prevent bird damage by pigeons. Despite relatively low disease severity levels (< 15% leaf area) and separation by at least 12 m of cv. Consort (resistant to Race 2) between plots there was considerable spread of disease into plots sown with healthy seed. Regression analysis demonstrated a significant relationship between yield and disease. Of the disease measurements examined, disease severity on the leaves (stipules) at growth stage 208 was found to be the best predictor of yield. A model containing environmental and bird damage terms, in addition to disease, suggested that a yield loss of 0.98 t/ha would be expected for a disease severity score of 1, equivalent to 5% leaf area affected, at growth stage 208.     

Quantitative trait analysis of seed yield and other complex traits in hybrid spring rapeseed (Brassica napus L.): 2. Identification of alleles from unadapted germplasm

Unadapted germplasm may contain alleles that could improve hybrid cultivars of spring oilseed Brassica napus. Quantitative trait loci (QTL) mapping was used to identify potentially useful alleles from two unadapted germplasm sources, a Chinese winter cultivar and a re-synthesized B. napus, that increase seed yield when introgressed into a B. napus spring hybrid combination. Two populations of 160 doubled haploid (DH) lines were created from crosses between the unadapted germplasm source and a genetically engineered male-fertility restorer line (P1804). A genetically engineered male-sterile tester line was used to create hybrids with each DH line (testcrosses). The two DH line populations were evaluated in two environments and the two testcross populations were evaluated in three or four environments for seed yield and other agronomic traits. Several genomic regions were found in the two testcross populations which contained QTL for seed yield. The map positions of QTL for days to flowering and resistance to a bacterial leaf blight disease coincided with QTL for seed yield and other agronomic traits, suggesting the occurrence of pleiotropic or linked effects. For two hybrid seed yield QTL, the favorable alleles increasing seed yield originated from the unadapted parents, and one of these QTL was detected in multiple environments and in both populations. In this QTL region, a chromosome rearrangement was identified in P1804, which may have affected seed yield.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Effect of carbendazim and mancozeb combinationon Alternaria leaf blight and seed yield in sunflower (Helianthus annus L.)

Abstract

Leaf blight caused by Alternaria helianthi (Hansf.) Tubaki & Nishihara, is the major disease of sunflower affecting the successful cultivation across India. Five individual fungicides and two combination fungicides were evaluated against this pathogen in laboratory and in field experiments. Among them, the combination of carbendazim + mancozeb completely (100%) inhibited the mycelial growth of A. helianthi, irrespective of the concentrations tested followed by carbendazim alone and metalaxyl + mancozeb under in vitro condition. In field conditions, the combination of carbendazim + mancozeb was found to be highly effective in reducing the leaf blight disease of sunflower in all the three experiments as compared to other fungicides and unsprayed control. The reduction of Alternaria leaf blight was also directly associated with an increase in seed yield. The economics of the fungicides spray has been worked out and the benefit cost ratio for the combination of carbendazim + mancozeb at 2.0 g/l was 7.1 as compared to unsprayed control. The overall analysis of the results revealed that the combination of carbendazim + mancozeb at 2.0 g/l can be used for the management of foliar diseases such as Alternaria leaf spot/blight in agricultural crops.     

The influence of foliar diseases and their control by selective fungicides on a range of groundnut (Arachis hypogaea L.) genotypes

Twenty groundnut genotypes were grown with various spray treatments which controlled either, only rust, or only leaf spot diseases, or all of these diseases or none of them. The genotypes varied in their resistance to these diseases, some having resistance to only one disease and some having resistance or susceptibility to all the diseases. Chemical control of the diseases resulted in variations in leaf area protection and in yield which were specific to each genotype. For some genotypes the diseases had little influence on yield and foliage, while for others yield and remaining green leaf were varied greatly by the control of diseases. For many of the genotypes the yield achieved was well related to variations in the green leaf remaining at maturity as a result of the spray treatments. Genotypes with good levels of genetic resistance did not have high yield potentials while those with the best yields when diseases were controlled were the most susceptible to these diseases.     

Incidence and control of black spot syndrome of tiger nut

Tiger nut (Cyperus esculentum) is a very profitable crop in Valencia, Spain, but in the last years, part of the harvested tubers presents black spots in the skin making them unmarketable. Surveys performed in two consecutive years showed that about 10% of the tubers were severely affected by the black spot syndrome whose aetiology is unknown. Disease control procedures based on selection of tubers used as seed (seed tubers) or treatment with hot‐water and/or chemicals were assayed in greenhouse. These assays showed that that this syndrome had a negative impact on the germination rate, tuber size and yield. Selection of asymptomatic seed tubers reduced drastically the incidence of the black spot syndrome with respect to using seed tubers with severe symptoms (selection of healthy seed tubers was not possible because the causal agent is undetermined). Thermal treatment of seed tubers with severe symptoms reduced the number of unmarketable harvested tubers by half but was detrimental for the germination. Chemical treatments of seed tubers with severe symptoms decreased the incidence of the black spot syndrome about 40% for sodium hypochlorite and about 10% for hydrochloric acid, trisodium phosphate and the fungicide trioxystrobin.