Foliage Blight Research Articles

Effects of Zoospore Concentration and Application Pressure on Foliage Blight of Catharanthus roseus Caused by Phytophthora nicotianae.

This study investigated the effects of inoculum concentration, application pressure, use of carbon dioxide (CO2), and agitation associated with passage through a spray nozzle on zoospore survival and on foliage blight caused by Phytophthora nicotianae. In a greenhouse experiment, plants of Catharanthus roseus were inoculated by spraying zoospore suspensions at pressures of 210, 420, and 630 kPa (30, 60, and 90 lbs/in2 [psi]). A low-pressure 35-kPa (5-psi) control inoculation was provided with a hand-operated aspirator-type mister. There was a consistent reduction in level of disease with increased application pressure, regardless of the zoospore concentration. To determine the source of this disease reduction, laboratory assays were conducted. Zoospore suspensions were pressurized to 210, 420, and 630 kPa with CO2 or air, then transferred from the pressure bottle into a flask by either spraying or pouring. From the flask, the suspensions were spread over plates of PARP-V8 agar and incubated for 72 h, at which time total colony numbers were recorded. CO2 significantly reduced zoospore survival. Pressure strength and method of spore transfer out of pressure bottles also impacted survival to lesser extents. There were significant interactions between pressure source and means of spore suspension transfer, and between pressure strength and means of spore transfer. These results may lead to development of alternative methods of water decontamination to prevent inoculum from entering crop systems through irrigation water.

Diseases of rattan in nurseries, plantations and natural stands in Kerala, India

A disease survey in rattan nurseries, plantations and natural stands in Kerala State, India, revealed that Calamus dransfieldii, C. gamblei, C. hookerianus, C. pseudotenuis, C. rotang, C. thwaitesii, C. travancoricus and C. vattayila are susceptible to various fungal pathogens in different growth phases. In nurseries, seedlings are affected with diseases caused by Bipolaris ellisii, Colletotrichum gloeosporioides, Corynespora cassiicola, Fusarium longipes, Guignardia calami, Sclerotium rolfsii and Rhizoctonia solani. Of these, seedling blight caused by Guignardia calami and seedling collar rot caused by Fusarium longipes are the most important diseases. In plantations and natural stands, rattans are affected by various foliage pathogens, such as Bipolaris ellisii, Colletotrichum crassipes, Colletotrichum gloeosporioides, Glomerella cingulata, Pestalotiopsis theae, Phomopsis palmicola, Phyllachora calamigena and Sphaerodothis. Among these, Colletotrichum infection on unopened spear (frond) and Sphaerodothis foliage blight caused severe damage to young as well as mature plants. Stem rot and staining, caused by Pellicularia filamentosa and Botryodiplodia theobromae, respectively, are the other important diseases. Nursery diseases can be effectively controlled by application of fungicides, viz., carboxin, mancozeb, carbendazim by seed dressing, soil drenching or by foliar spraying.

Incidence of potato tuber blight in Ecuador

Potato late blight, caused byPhytophthora infestans (Mont.) de Bary, is the most important biotic constraint to potato yield and productivity in Ecuador. Yields are severely reduced by foliage blight, but tuber blight has never been quantified in this country. To address this issue, three independent surveys were carried out in Ecuador to estimate the incidence of tuber infection byP. infestans. The first two (1998–1999) involved the collection and assessment of more than 8,000 tubers from the four provinces that produce the most potatoes: Carchi, Chimborazo, Pichincha, and Tungurahua. In the third survey (1999–2001), approximately 10,000 tubers were sampled from the two provinces producing the most potatoes, Carchi and Chimborazo, and from Canar and Bolivar, two provinces that produce relatively small amounts. In spite of confirmed foliage infection in most fields sampled, very few infected tubers were found. In 1999, an extremely low incidence of tuber blight (less than 0.1%) was detected in three samples (each of more than 1,000 tubers) from the province of Pichincha. In a separate survey in 1999, tuber blight was also found in three fields in the province of Carchi, but with very low incidence. Our data indicate that tuber blight does occur in Ecuador, but the incidence of the disease is extremely low. Factors that might suppress tuber blight in Ecuador are discussed.

Dissection of foliage and tuber late blight resistance in mapping populations of potato

The devastating late blight pathogen Phytophthora infestans infects foliage as well as tubers of potato. To date, resistance breeding has often focused on foliage blight resistance, but tuber blight resistance is becoming more and more important in cultivated potatoes. In this study, a reliable tuber assay for resistance assessment was developed and foliage and tuber blight resistance (R) was compared in four mapping populations. In the RH4X-103 population, tuber blight resistance inherited independently from foliage blight resistance. Three specific R genes against P. infestans were segregating. The Rpi-abpt and R3a genes function as foliage-specific R genes, whereas the R1 gene acts on both foliage and tuber. In the segregating populations SHRH and RH94-076, tuber and foliage blight resistance correlated significantly, which suggests that resistance in foliage and tuber is conferred by the same gene (could be R3b) and quantitative trait loci (QTL), respectively. In the CE population neither tuber nor foliage resistance was observed.

Interval Mapping of Quantitative Trait Loci for Resistance to Late Blight [Phytophthora infestans (Mont.) de Bary], Height and Maturity in a Tetraploid Population of Potato (Solanum tuberosum subsp. tuberosum)

Interval mapping of quantitative trait loci (QTL) for resistance to late blight, height, and maturity was performed on a tetraploid full-sib family of potato comprising 227 clones from a cross between a susceptible parent, 12601ab1, and a resistant cultivar, Stirling, which were of similar height and main crop maturity. Thirty-eight AFLP primer combinations provided 585 informative markers, and 23 SSRs proved useful for identifying linkage groups (LGs). A simplex QTL allele was found on LGV of Stirling close to marker STM3179, which was associated with early maturity, short plants, and susceptibility to blight and explained 54.7, 26.5, 26.3, and 17.5% of the variation for maturity, height, tuber blight, and foliage blight. When the residuals from the regressions of foliage and tuber blight on maturity were analyzed, there was no significant effect of a QTL on LGV, but a duplex QTL allele for resistance was found on LGIV of Stirling, which explained 30.7 and 13.6% of the variation for foliage and tuber blight on an additive model. Partial dominance for resistance explained even more of the variation, up to 37.2% for foliage blight. A major gene for blight resistance in Stirling was also mapped to LGXI.

Field validation of four decision support systems for the control of late blight of potatoes in Ireland

Field experiments using two cultivars (Rooster and King Edward) were carried out between 2001 and 2003 to compare the efficacy of the NegFry, Simphyt, ProPhy and Plant-Plus decision support systems (DSS) with routine 7-day fluazinam treatment for the control of potato late blight. Compared with the routine control, the NegFry and SimPhyt programmes resulted in a 58-44% reduction in application frequency. The ProPhy and Plant-Plus programmes resulted in more modest savings of between 10 and 25%. The date of disease onset was not significantly different between routine programmes and DSS programmes irrespective of the cultivar. None of the DSS’s resulted in inferior foliage blight control when compared with the routine application of fluazinam. DSS programmes generally out-yielded the routine treatment but differences were not significant. All DSS programmes give equivalent tuber blight control to the routine programme even with a very tuber blight susceptible cultivar.

Phytophthora nicotianae에 의한 일일초 역병

2003년 8월 청도시험장의 화분재배한 일일초에서 잎, 꽃, 꼬투리 및 줄기가 검게 시들고 말라죽는 증상으로부터 병원균을 분리<TEX>$.$</TEX>동정한 결과 Phytophthora nicotianae로 동정되었다 병원균의 형태적 특성은 뚜렷한 유두돌기를 가지고 비탈락성인 원형 혹은 난형의 유주자낭을 형성하였고, 크기는 31.0<TEX>${\times}$</TEX>38.0<TEX>$\mu\textrm{m}$</TEX>였고 다량의 후막포자를 형성하였으며 크기는 평균 직경이 30.5 <TEX>$\mu\textrm{m}$</TEX>였다 유성생식형은 자웅이주로 Al mating type이 관찰되었고 난포자의 크기는 직경 23.1 <TEX>$\mu\textrm{m}$</TEX>였다. 균사의 생육적온은 25∼3<TEX>$0^{\circ}C$</TEX>였다. 이상과 같이 국내 최초의 P. nicorianae에 의한 일일초 역병의 발생을 보고하는 바이다. A disease causing blights on leaves, stems, flowers, and pods of Vinca (Catharanthus roseus L.) was occurred in Aug. 2003 in Chengdo Peach Experiment Station. A species of Phytophthora was isolated from the diseased tissues. The causal fungus was identified as Phytophthora nicotianae on the basis of mycological characteristics and pathogenicity. Sporangia were ovoid to spherical, noncaducous, prominently papillate and averaged 38.0<TEX>${\times}$</TEX>31.0 <TEX>${\mu}{\textrm}{m}$</TEX> in dimension. Chlamydospores were abundantly produced on agar media and sized about 30.5 fm in diameter, The fungus was heterothallic and Al mating type. Oospores were measured 23.1 <TEX>${\mu}{\textrm}{m}$</TEX> in size. Optimum temperature for growth of the fungus was 25 to 3<TEX>$0^{\circ}C$</TEX>. This is the first report of occurrence of foliage blight of Vinca caused by P. nicotianae in Korea.

First Report of Web Blight on Yellow-Sage (Lantana camara) Caused by Rhizoctonia solani in Europe.

Lantana camara is increasingly grown in northern Italy as a potted plant and contributes to the diversification of offerings in the ornamental market. During the spring of 2001, selections of L. camara cuttings growing at a commercial farm located at Albenga (Riviera coast) exhibited tan leaf spots of irregular size and shape. Spots were at first isolated, 4 to 8 mm in diameter, and later coalesced and affected the entire plant. Heavily infected leaves, stems, and branches became blighted and were killed. Infected rooted cuttings also eventually died. Diseased cuttings showed a progressive reduction (to less than 20%) in rooting ability. Isolations from infected leaves and stems on potato dextrose agar (PDA), supplemented with 100 mg/liter of streptomycin sulphate, consistently yielded a fungus with mycelial and cultural characteristics resembling Rhizoctonia solani. The fungal isolates were further characterized as R. solani Kühn AG-4 based on hyphal anastomoses with several AG-4 tester isolates. Pathogenicity tests were performed by placing 5-day-old-fungal mycelial plugs, grown on PDA, at the base of five healthy yellow-sage stems and holding plants in a dew chamber at 18 to 22°C. After 2 days, foliage blight appeared on leaves of inoculated plants, and after 3 days, stems also became infected and entire plants wilted. Five noninoculated plants remained healthy. The fungal pathogen was reisolated from all inoculated plants. R. solani has been observed on L. camara in the United States (1) and the Philippines (2). To our knowledge, this is the first report of R. solani on L. camara in Europe.

Optimization of Sample Size and DNA Extraction Methods to Improve PCR Detection of Different Propagules of Phytophthora infestans.

The plant pathogen Phytophthora infestans causes a destructive blight of potato tubers and foliage. A rapid polymerase chain reaction (PCR) assay has been developed for detection of P. infestans in potato tubers. In this study, the effect of method of DNA extraction on different propagule types and the minimal number of propagules of P. infestans detectable by PCR were assessed using the PINF and internal transcribed spacer (ITS)5 primers. Sensitivity of the primers for PCR was high, and DNA was detectable at concentrations as low as 10 pg/ml. Zoospores and oospores responded differently to different extraction methods, whereas all extraction methods worked equally well for sporangia. Freeze-thaw DNA lysis, in which propagules were frozen at -80°C and thawed at 65°C three times for 15 min each, or direct PCR, in which propagules were placed directly in the reaction mix, were effective methods for PCR detection of sporangia or zoospores but were not effective methods for PCR detection of DNA in oospores of P. infestans. DNA from a single sporangium or oospore could be amplified by PCR after hexadecyltrimethyl-ammonium bromide (CTAB) or NaOH lysis extraction methods, whereas DNA from a single zoospore could be amplified by CTAB or direct PCR methods. "IsoCode" Stixs, used in forensic applications, were used to collect the pathogen from leaf and tuber lesions and provided another simple method to extract template DNA. PCR detection of the pathogen in infected tubers using PINF and ITS5 primers was compared to tissue isolation or visual observation. The probability of detection of P. infestans in infected tubers at 7 days post inoculation using the PCR assay, tissue isolation, or visual observation was 0.90, 0.80, and 0.75, respectively. The PINF and ITS5 primers provide a powerful tool for rapid and sensitive detection of zoospores, sporangia, and oospores of P. infestans when used with appropriate extraction methods, and could easily be deployed to reduce spread of the pathogen in potato tubers.

Comparison of the NegFry decision suport system with routine fungicide application for the control of potato late blight in Ireland

Field experiments between 1996 and 2000 compared the efficacy of fungicide programmes applied in accordance with the NegFry and Met Eireann (ME) decision support systems (DSS) for the control of late blight with 7- and 10-day routine fungicide programmes. The ME DSS reduced fungicide use by 68% and 54% respectively while NegFry reduced fungicide use by 49% and 27% compared with the 7- and 10-day programmes. The NegFry DSS was similar to the 10-day routine programme in terms of late blight control, quality and marketable yield. A similar result was found when the NegFry DSS was compared with a 7-day routine mancozeb programme (included for two seasons only). Within the NegFry DSS the use of fluazinam resulted in improved yield, foliage blight and tuber blight control compared with mancozeb, but this benefit was significant for tuber blight only. The ME DSS resulted in inferior disease control, yield and quality.

Reactions of some potato genotypes to late blight in Cameroon

Field experiments were conducted in Cameroon in 1995 and 1996 to evaluate reactions of different potato genotypes to late blight. There were significant differences among genotypes for tuber yield, late blight readings and earliness. The application of fungicides significantly increased potato yield but had a non significant effect on the damage due to foliage blight (Phytophthora infestans). The limited effect of fungicide treatment was because the late blight severity was so high that the eight fungicide applications could not provide sufficient level of disease control and/or the persistence rain throughout the growing season might have washed-off the applied fungicide, thus decreasing its effect. There was a significant year effect on the yield. The fifth late blight reading (LB5) was more related to yield than the later readings suggesting that the damage caused by the disease at an earlier stage of plant development contributed most to yield reductions. Several advanced genotypes had similar or superior performance to that of CIPIRA and TUBIRA released in Cameroon in 1992. Key Words: Cameroon, Phytophthora infestans, potato yield, Solanum tuberosum (African Crop Science Journal 2001 9(1): 209-214)

First Report of Web Blight on Verbena Caused by Rhizoctonia solani.

Web blight was observed on verbena (Verbena × hybrida) during July 1999 in a cultivar trial planting at Burden Research Plantation in Baton Rouge, LA. Foliage blight, stem lesions, and branch death were common symptoms on 12 of 24 cultivars in the trial. Plant death occurred in cvs. Babylon Florena (one of four plants), Purple Princess (two of four plants), and Taylortown Red (two of four plants). Isolations from infected leaves and stems on acidified water agar consistently yielded a fungus with the mycelial and cultural characteristics of Rhizoctonia solani. Pathogenicity tests were carried out by placing 5-day-old fungal mycelial plugs, grown on acidified potato dextrose agar, at the base of healthy verbena stems and holding plants in a dew chamber at 26°C. After 3 days, foliage blight and stem lesions appeared on inoculated plants, and plants were moved to a greenhouse where temperatures ranged from 23 to 32°C. Seven of nine inoculated plants died after 7 days; noninoculated plants remained healthy. The fungal pathogen was reisolated from all inoculated plants. The fungus was identified as R. solani anastomosis group (AG)-1 IB based on multinucleate condition, type of sclerotia produced, and ability to anastomose with R. solani tester isolates of AG-1 IB. This is the first report of web blight on verbena.

QTL for field resistance to late blight in potato are strongly correlated with maturity and vigour

Field resistance to Phytophthora infestans, the causal agent of foliage and tuber blight in cultivated potatoes, earliness (maturity) and vigour, were examined in a diploid segregating potato population grown in replicated trials over three consecutive growing seasons. A genetic linkage map of this population was constructed in parallel using PCR-based SSR, AFLP and CAPS markers. Analysis of the trait scores alongside the marker segregation data allowed the identification of regions of the genome which were significantly correlated with components of the respective characters. The most significant associations for all four traits were with marker alleles on potato linkage group V originating from the male (susceptible) parent. In the case of foliage resistance to late blight, the positions of the majority of the effects, which were located on eleven of the twelve potato linkage groups, have been detected in previous [16] and parallel studies [21]. The absence of Solanum demissum-derived R genes for hypersensitive response to late blight and the co-localisation of QTL for resistance, vigour and earliness suggest that developmental and/or physiological factors play a major role in determining the level of foliage resistance in this population. In contrast with previous findings, a negative correlation was found between foliage and tuber blight resistance.

Relationship between resistance to late blight in potato foliage and tubers of cultivars and breeding selections with different resistance levels

Due to changes in the pathogen population, late blight of potatoes caused byPhytophthora infestans has become a more difficult disease to manage and there is a need for new potato cultivars with greater and more stable disease resistance. Field studies are required to identify and characterize host resistance to late blight in both foliage and tubers but, as epidemics vary from year to year, combining multi-year results can be difficult. Residual maximum likelihood (REML) was successfully used to analyze data which demonstrated good correlations between foliar and tuber responses to late blight (US-1 genotype). In addition, studies on post-harvest inoculated tubers provided more reliable disease responses than field studies, and the disease resistance with this method correlated well with foliar disease responses. This tuber test would be a useful method of pre-screening selections for disease response prior to testing in the field.

Combination of resistance to potato late blight in foliage and tubers by intraspecific dihaploid protoplast fusion

Five dihaploid Solanum tuberosum genotypes, encompassing different levels of polygenically inherited resistance to potato late blight disease (Phytophthora infestans (Mont.) de Bary) in foliage and tubers, were used in four intraspecific protoplast fusion combinations. Vigorous growing putative hybrid calli were selected four weeks after electrofusion. Intact plants were regenerated from 6% of the selected calli. Verification of hybridity was accomplished by use of RAPD analysis which revealed that 53% of the regenerated plants were true somatic hybrids. The score of true somatic hybrids in the different fusion combinations ranged within 21% – 100%. The hybrid plants were analysed for resistance to foliage blight in a field trial and assessed for tuber blight resistance by use of a laboratory test. Resistance to late blight in foliage and tubers varied between the hybrids. Very high levels of resistance to both foliage and tuber blight were obtained in some hybrids. However, loss of resistance in some hybrids as compared to the parental plants were also observed. Possible reasons for the phenotypic disappearance of resistance to either foliage or tuber blight are suggested.

The effect of phenylamide fungicides on the control of potato late‐blight (Phytophthora infestans) in England and Wales from 1978 to 1992

During the period 1978–1992, phenylamide fungicides in co‐formulation with the dithiocarbamate fungicide mancozeb were tested for the control of potato late‐blight in 51 separate field experiments in England and Wales. Whilst there was a general trend over all the experiments which indicated that foliage blight was less severe where the phenylamide + dithiocarbamate mixture had been used, the benefit was more marked in some than in others. Despite the detection of phenylamide resistance, at some sites the mixture gave better control of foliage blight than the dithiocarbamate alone. At one site where continuous data were available, the additional benefit of the phenylamide compound for control of foliage infection was lost after 1986 coinciding with a rise in phenylamide resistance from 31.7% in 1986 to 81% in 1987. Where foliar blight epidemics occurred, yield responses to fungicide programmes compared with unsprayed controls ranged from 0 to +118.5% with a mean response of +30.2%. This is equivalent to 30.8 and 12.92 t/ha respectively. Standardized yield differences were calculated to allow inter‐trial and inter‐year comparisons and showed no benefit from the phenylamide fungicide applied at 14‐day intervals in 33 out of 38 experiments where foliar blight epidemics occurred. At one site, Cusum analysis of standardized yield differences following treatment with the phenylamide + dithiocarbamate mixture and the dithiocarbamate alone showed a mean benefit from the phenylamide mixture of 2.23 t/ha during the period 1978 to 1986. From 1987 to 1992, the yield benefit dropped to a mean level of 0.68 t/ha a decrease of 69.5%. In experiments where blight was not recorded, fungicide treatments had no deleterious effect on yields. Over all the trials, there was no effect of fungicide treatment on the incidence of tuber blight at harvest.

Use of seedling progeny tests for genetical studies as part of a potato (Solanum tuberosum subsp. tuberosum) breeding programme

A diallel set of crosses, including selfs and some reciprocal crosses, was made between 15 parents chosen for their male fertility from those included in a tetraploid potato (Solanum tuberosum subsp. tuberosum) breeding programme at the Scottish Crop Research Institute. Seedling progeny tests were used to evaluate the progenies for non-race-specific resistance to late blight (Phytophthora infestans) in both foliage and tubers, quantitative resistance to the white potato cystnematode (PCN) (Globodera pallida) and the commercial worth of their tubers as judged by breeders' visual preference. No reciprocal differences were found. Comparisons of the selfs and crosses revealed inbreeding depression for breeders' preference, which varied among the parents from negligible to severe, whilst there were also statistically significant differences for foliage and tuber blight, but not for PCN. When the selfs were omitted from the combining ability analyses, large differences in general combining ability (GCA) were found for all four traits, and smaller differences in specific combining ability for tuber blight and breeders' preference. The only statistically significant correlation between GCAs for different traits was a favourable one of r = 0.56 between foliage and tuber resistance to late blight. It was concluded that prospects were good for simultaneously improving all four traits by multitrait genotypic recurrent selection.

Correlation between resistance to late blight in foliage and tubers in potato clones from parents of contrasting resistance

The relationship between resistance to late blight in foliage and tuber was examined on 50 clones of each of five progenies from crosses where one parent was resistant in both foliage and tuber and the other susceptible. Foliage resistance was assessed in a field trial and tuber resistance in a laboratory test on glasshouse-grown tubers. The genetical and environmental components of variance and the phenotypic and genetical correlations between foliage and tuber blight scores were determined for each progeny. Foliage and tuber resistance were correlated, indicating either that both are determined by the same genes or by different linked genes.

Assessing general combining ability for late blight resistance and tuber characteristics by means of glasshouse seedling tests

Screening tests to detect resistance to late blight in both foliage and tubers were done on glasshouse-grown seedling progenies in parallel with visual assessments by three experienced potato breeders of the yield and quality of glasshouse-grown tubers of the same progenies. There were large differences between the parents of the progenies in their general combining ability (GCA) for both foliage and tuber blight, despite some variation due to specific combining ability for foliage blight. There were also differences between parents in their GCAs for visual preference scores, but these GCAs and those for blight resistance were not correlated. The blight-resistant cv. Stirling had the best combination of high GCAs for all three attributes. The use of these and other seedling progeny tests in a multitrait genotypic recurrent selection scheme is discussed.

Disease resistance inSolanum phureja and diploid and tetraploidS. tuberosum × S. phureja hybrids

DiploidSolanum phureja, diploid and tetraploidS. tuberosum × S. phureja hybrid, and tetraploidS. tuberosum backcross clones were assessed for resistance to commercially important diseases. There was a reduction in the expression ofS. phureja characteristics with increasing dosage ofS. tuberosum genetic material. The generally high resistance of theS. phureja group to common scab, potato leafroll virus and potato virus Y decreased, while resistance to gangrene, foliage and tuber blight tended to increase.