Late blight on potato in Flanders, Belgium: field trials and characteristics of the Phytophthora infestans population

Commercial fungicides were tested in the field for efficacy on foliar late blight caused by Phytophthora infestans. The fungicide treatments for late blight control were conducted at either 7- or 10-day intervals. The effect of the fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in July and at the beginning of August due to high temperatures and lasting drought. Foliar disease severity significantly affected potato tuber yields. Lowest tuber yield was noted in plots with high late blight infection levels (nontreated control and an experimental mixture of organic acids (Vi-Care, 1 l/ha)) while highest yields were recorded in plots with low late blight infection. Late blight infection on leaf level was not significantly correlated with % tubers that showed late blight symptoms. No fungicide scheme completely arrested epidemic development under the environmental conditions of the trial. The effect of propamocarb hydrochloride + chlorothalonil (Tattoo C, 2.5 kg/ha) was less suppressive for P. infestans than the other fungicides tested for both interval systems. However, fenamidone + mancozeb (Sereno, 1.5 kg/ha), zoxamide + mancozeb (Unikat Pro, 1.8 kg/ha), dimethomorph + mancozeb (Acrobat, 2 kg/ha), cyazofamide + heptamethyltrisiloxane (Ranman 200 ml A/ha + 150 ml B/ha) and cymoxanil + famoxadone (Tanos, 0.6 kg/ha) controlled P. infestans most effectively for both interval systems. Also the other fungicides controlled foliar late blight sufficiently. Only small differences were observed between the different treatments. A total of 51 isolates of P. infestans were collected from disease outbreaks in commercial potato crops and private gardens in 2003. Isolates were recovered successfully from single lesions of diseased potato foliage. Not from all isolates pure cultures were obtained due to contaminations with Fusarium species and bacteria. The structure of the population was analysed phenotypically. Characteristics of the isolates included in vitro growth rate, mating type, in vitro sensitivity to the phenylamide fungicide metalaxyl-M and allozyme genotype at glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) loci

Study on the STOP effect of fungicide combinations to control late blight in potato

The effectiveness of different fungicide combinations to control late blight and the STOP effect of these fungicide combinations for the control of foliar and tuber blight under high infection pressure was investigated. Last summer late blight development was arrested in July due to high temperatures and lasting drought. In August the weather was cloudy, rather cold and a lot of rain. These weather conditions were very favourable for late blight. Due to the heat waves of June and July the foliage started to die allready in August and P. infestans developped very fast in the second part of August. Because of that no incidence of foliage blight was scored. No significant differences in yield were observed for the different treatments applied. The combination cyazofamid + heptamethyltrisiloxaan (Ranman) + propamocarb + chlorothalonil (Tattoo C) had the highest yield. The percent diseased tubers fluctuated between 14,9 and 45,1 % for the different treatments tested. The amount of blighted tubers was lowest for fluazinam (Shirlan) + cymoxanil +chlorothalonil (Mixanil) and fluazinam (Shirlan) + benthiavalicarb + mancozeb (Valicarb)

Study on the curative and eradicant action of fungicide combinations to control late blight in potato

Commercial fungicide combinations were tested in the field for efficacy on foliar late blight caused by Phytophthora infestans in substitution of tin. When the first disease symptoms appeared, the tested fungicide treatments for late blight control were applied 3 times at 3-day intervals. The effect of the fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in June due to high temperatures and lasting drought. August was characterized by rather low temperatures and high rainfall. These weather conditions were very favourable for the development of late blight. The foliar protection against P. infestans was comparable for all the tested fungicide combinations. The effect of combinations with dimethomorph + mancozeb (AcrobatC, 2.5 kg/ha) was less suppressive for P. infestans than the other fungicides tested. Lowest foliar disease severity was recorded in plots treated with fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha). Furthermore, highest tuber yield was noted in plots treated with fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha). The percentage blighted tubers fluctuated between 5 and 11 %. No fungicide combinations completely arrested epidemic development under the environmental conditions of the trial. However, fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha) controlled P. infestans most effectively

Effect of adjuvants on the efficiency of dimethomorph plus mancozeb (Acrobat 2 kg:ha) on the control of late blight

Industrial adjuvants were tested in combination with dimethomorph plus mancozeb (Acrobat 2 kg/ha) in the field to investigate their efficacy on foliar late blight caused by Phytophthora infestans. The tested adjuvant fungicide treatments for late blight control were applied 5 times at 7-day intervals. The effect of the adjuvant fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in July due to high temperatures and lasting drought. August was characterized by rather low temperatures and high rainfall. These weather conditions were very favourable for the development of late blight. Due to the heat waves of June and July the foliage started to die allready in Agust. Because of that no incidence of foliage blight was scored. No significant differences in yield were observed for the different treatments applied. The addition of an adjuvant had a clearly positive effect on the tuber yield. In the control 12,7 % infected tubers were observed. The mean tuber infection of plots sprayed with the Acrobat-adjuvant combinations was 7,4 %

Effect of adjuvants on the efficiency of benthiavalicarb plus mancozeb (Valbon 1.6 kg/ha) on the control of late blight in potato

Industrial adjuvants were tested in combination with benthiavalicarb plus mancozeb (Valbon 1.6 kg/ha) in the field to investigate their efficacy on foliar late blight caused by Phytophthora infestans. The tested adjuvant-fungicide treatments for late blight control were applied 6 times at 7-day intervals. The effect of the adjuvant-fungicide treatments on epidemic development, tuber blight and tuber yields were determined. Because of the favourable weather conditions a high disease pressure could be observed. The incidence of foliage blight was scored and at the end of the growing season the disease level was lower in plots sprayed with the Valbon-adjuvant combinations than in plots treated with only Valbon. The addition of an adjuvant had a clearly positive effect on the tuber yield although the differences were not significant. In the plots treated with Valbon 6.9 % infected tubers were observed. The mean tuber infection of plots sprayed with the Valbon-adjuvant combinations fluctuated between 2.3 and 15.6 %

Genetische veränderte Azalee: Kompakt ohne Wuchsemmer

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Threonine accumulation in a mutant of Arabidopsis thaliana (L.) Heynh. with an altered aspartate kinase

After mutagenesis, M(2) seedlings of Arabidopsis thaliana were grown on a selective medium containing toxic concentrations of lysine and threonine. One of the LT-resistant mutants (RLT 40) was studied at the biochemical and genetical levels. A six-fold increase in free threonine content was found in 8-day-old mutant plantlets compared with the wild type. The total amino acid content of the mutant was also remarkably increased, essentially due to increased levels of aspartate, threonine, methionine, isoleucine and lysine. As one of the possible reasons for the LT-resistance resides in a change of the regulatory properties of the first enzyme of the aspartate pathway, aspartate kinase (EC 2.7.2.4), the feedback-inhibition pattern of aspartate kinase was examined in the mutant and the wild type. In Arabidopsis after ion-exchange chromatography of whole plant extracts, three peaks of activity were detected corresponding respectively to a threonine-sensitive isoform, to a lysine-sensitive form and a form insensitive to both inhibitors. The threonine accumulation in RLT 40 could be related to a partial insensitivity of the lysine-sensitive form of aspartate kinase. Genetical analysis showed that the resistance gene behaved as a dominant, monogenic nuclear trait. Linkage analysis, performed with a multiple marker line, indicated that the mutation is located on chromosome 2, 36.0 cM from the er locus and 19.8 cM from the py locus on chromosome 2. This partially lysine-insensitive mutant of aspartate kinase offers ways to a map-based approach for cloning the gene coding for the corresponding isoform in plants

The rlt11 and raec1 mutants of Arabidopsis thaliana lack the activity of a basic-amino-acid transporter

The concentration dependence of the influx of L-lysine in excised roots of Arabidopsis thaliana seedlings was analyzed for the wild-type (WT) and two mutants, rlt11 and raec1, which had been selected as resistant to lysine plus threonine, and to S-2-aminoethyl-L-cysteine, respectively. In the WT three components were resolved: (i) a high-affinity, low-capacity component [K-m=2.2 mu M; V-max=23 nmol .(g FW)(-1). h(-1)]; (ii) a low-affinity, high-capacity component [K-m=159 mu M; V-max=742 nmol .(g FW)(-1). h(-1)]; (iii) a component which is proportional to the external concentration, with a constant of proportionality k=104 nmol .(g FW)(-1). h(-1). mM(-1). The influx of L-lysine in the mutants was lower than in the WT, notably in the concentration range 0.1-0.4 mM, where it was only 7% of that in the WT. In both mutants the reduced influx could be fully attributed to the absence of the low-affinity (high-K-m) component. This component most likely represents the activity of a specific basic-amino-acid transporter, since it was inhibited by several other basic amino acids (arginine, ornithine, hydroxylysine, aminoethylcysteine) but not by L-valine. The high-affinity uptake of L-lysine may be due to the activity of at least two general amino acid transporters, as it was inhibitable by L-valine, and could be further dissected into two components with a high affinity (K-i=1-5 mu M) and a low affinity (K-i=0.5-1 mM) for L-valine, respectively. The rlt11 and raec1 mutant have the same phenotype and the corresponding loci were mapped on chromosome 1, but it is not yet clear whether they are allelic

Characterization of Phytophthora infestans isolates collected from potato in Flanders, Belgium

A collection of 49 isolates of Phytophthora infestans, collected from blighted potato foliage in 1998 in Flanders, were analysed for mating type, response to metalaxyl (48 isolates), allozymes of glucose-6-phosphate isomerase (Gpi), peptidase ( Pep) and restriction fragment length polymorphism ( RFLP) with probe RG57 (39 isolates). Forty-one A1 and eight A2 isolates were detected. Resistance to metalaxyl was frequently observed: 30 resistant, four intermediate and 14 sensitive isolates were found. Gpi genotypes 100/100 and 90/100 occurred in 30 and nine isolates, respectively. The dominating banding pattern for Pep was 100/100 (32 isolates), but genotypes 96/96, 96/100 and 83/96, never previously reported in continental western Europe, were also identified. Thirteen RG57 fingerprint were observed. On the basis of combined traits, 15 multilocus genotypes were revealed among 39 isolates. Genotypic diversity measured by the normalized Shannon diversity index was 0.56. The results indicate that, besides asexual variation and/or migration, sexual events may have played a role in the establishment of the isolates studied