Crop connectivity under climate change: future environmental and geographic risks of potato late blight in Scotland

The impact of climate change on dispersal processes is largely ignored in risk assessments for crop diseases, as inoculum is generally assumed to be ubiquitous and nonlimiting. We suggest that consideration of the impact of climate change on the connectivity of crops for inoculum transmission may provide additional explanatory and predictive power in disease risk assessments, leading to improved recommendations for agricultural adaptation to climate change. In this study, a crop‐growth model was combined with aerobiological models and a newly developed infection risk model to provide a framework for quantifying the impact of future climates on the risk of disease occurrence and spread. The integrated model uses standard meteorological variables and can be easily adapted to various crop pathosystems characterized by airborne inoculum. In a case study, the framework was used with data defining the spatial distribution of potato crops in Scotland and spatially coherent, probabilistic climate change data to project the future connectivity of crop distributions for Phytophthora infestans (causal agent of potato late blight) inoculum and the subsequent risk of infection. Projections and control recommendations are provided for multiple combinations of potato cultivar and CO₂ emissions scenario, and temporal and spatial averaging schemes. Overall, we found that relative to current climatic conditions, the risk of late blight will increase in Scotland during the first half of the potato growing season and decrease during the second half. To guide adaptation strategies, we also investigated the potential impact of climate change‐driven shifts in the cropping season. Advancing the start of the potato growing season by 1 month proved to be an effective strategy from both an agronomic and late blight management perspective.     

Infection Potential of Hairy Nightshade (Solanum sarrachoides) by Phytophthora infestans and Late Blight Implications of the Alternate Host

Infection of hairy nightshade ( Solanum sarrachoides Sendt.) by Phytophthora infestans has been reported. However, the epidemiological significance of hairy nightshade to potato late blight is not well known. Disease development and infection rates of P. infestans were quantified on hairy nightshade relative to tomato (cv. Brandywine) and potato (cv. Shepody) hosts to evaluate infection potential at 14, 18, 22 and 26°C and 72, 82, 87, and 92% relative humidity (RH). The susceptibility of hairy nightshade to inoculum levels, weed ontogeny, and sporangia production potential were also investigated. Late blight development varied among hairy nightshade, tomato and potato hosts. Pathogen infection rates ranged from 0.0325 to 0.4674 gompits/day (unit for quantifying infection rates), and were significantly (P < 0.05) greater on potato and tomato than on hairy nightshade. Late blight severity was variably affected by RH. Disease levels on hairy nightshade varied with inoculum load; and ranged from 9 to 26% and 26 to 37% at low (5 × 10³) and high (25 × 10³) sporangia concentrations, respectively. Late blight was recorded irrespective of hairy nightshade ontogeny, and was significantly greater on 8–10 than 4–6-week-old plants. These results indicate that pathogen, environmental and host factors affect late blight development on hairy nightshade.     

Epidemiology of grey mildew and Alternaria blight of cotton

Grey (Areolate) mildew (Ramularia areola) and Alternaria blight (Alternaria macrospora) are two important fungal foliar diseases affecting cotton in India. Both the diseases are polycyclic in nature. The primary inoculum for grey mildew is through conidia or ascospores from infected debris and/or perennial cottons and the secondary spread is through primarily infected leaves. Whereas for Alternaria blight the spread is initially from seed-borne inoculum (in Gossypium herbaceum and Gossypium arboreum cottons) and/or crop debris and the secondary spread is from sporulating lesions on older leaves. Both R. areola and A. macrospora require a temperature regime of 20–30?°C with prolonged high humidity (>80%) and frequent rains for infection and disease development. However, it has been observed that cool weather coupled with prolonged dewy periods in the absence of rains has also been found conducive for the development of both the diseases. So, suitable epidemiological tools and models are required to predict the disease development, spread and to design suitable management practices.     

THE EPIDEMIOLOGY OF PHYTOPHTHORA INFESTANS

Temperature and relative humidity of air within and above potato crops were recorded throughout the growing seasons of 1951-8, with wet- and dry-bulb mercury-in-steel thermographs. Diurnal periodicity curves of successive weeks showed that conditions within the crop changed, relative to those above, as the crop grew. When much bare ground was exposed, the air within the crop was warmer and less humid at midday than at 4 ft. above ground, particularly in dry and sunny weather. The growth of the foliage and the amount of sunshine and rain determined how quickly this pattern was replaced by one with smaller temperature differences and crop humidity slightly in excess of that above it, at all times of day. Rain on crops with dense foliage almost completely eliminated temperature differences and gave relative humidities over 90% that persisted in the crop for a larger proportion of each day than in the screen. Finally, as the disease defoliated the crop and again exposed the soil, the relationship partly reverted to that early in the season.
Above the crops, curves of the number of hours per day with relative humidity not less than 90%, rose and fell with the passing of wet spells. At first this was also true within crops, but when foliage was dense the rise in relative humidity after rain often persisted through intervals of dry weather. Such conditions usually preceded the appearance of potato blight in epidemic proportions by 1–3 weeks. It is difficult to account for the regularity of blight outbreaks by seasonal climatic changes, and although many factors are probably involved, changes in ecoclimate seem important. When knowledge about the response of Phytophthora infestans is related to the meteorological observations and to the dates of blight outbreak, the growth of potato crops seems often to be self-destructive, because it progressively modifies the immediate environment to favour the spread of the crop's most destructive pathogen.     

Effectiveness of SIMBLIGHT1 and SIMPHYT1 models for predicting Phytophthora infestans in north-eastern United States

Accurate prediction of Phytophthora infestans outbreak in a cropping season is crucial for the effective management of late blight on potato. The SIMBLIGHT1, SIMPHYT1 and modified SIMPHYT1 models were assessed for predicting late blight outbreaks relative to NOBLIGHT model by using climatic and crop data from field experiments at Presque Isle, ME, from 2004 to 2009. The dynamics of late blight infection pressures were computed by SIMPHYT3 model to assess the conduciveness of environmental conditions for late blight infection and potential for disease development. Infection pressure indicated conditions were moderately conducive for late blight development but varied across years. The SIMPHYT1 model recommended fungicide applications to commence on 11 July, 21 July, 8 July, 10 July, 7 July and 7 July for 2004, 2005, 2006, 2007, 2008 and 2009, respectively. The modified SIMPHYT1 model (US-version) recommended similar fungicide application dates for the same years with the exception of 2007. Model simulations of disease outbreak differed from actual recorded observations in untreated plots by 24–65 days. Simulation of SIMBLIGHT1 based on high and low soil moisture conditions in the field resulted in vast differences in dates of first fungicide application. Validation of the models (differences in the number of days between recommendation of fungicide treatment and late blight outbreak) indicated a better goodness of fit for the models (intervals of 6–20 days from the start of fungicide application to first disease outbreak). The NOBLIGHT model was accurate in forecasting the timing of first fungicide applications for late blight control. Significant improvements in late blight predictions could result if these models were modified to account for external sources of inoculum, by combining weather-based forecasts with spore traps, disease detection methods or complimentary systems.     

Efficacy of essential oils and biopesticides on Phytophthora infestans suppression in laboratory and growth chamber studies

Control of late blight by alternative products is important for reduction of fungicide inputs and potato production costs. The efficacy of essential oils and biopesticides for inhibition of growth of Phytophthora infestans on media and suppression of late blight on potato plants in growth chambers was examined. Growth of pathogen isolates of diverse genotypes was evaluated on Rye B media amended with essential oils (lavender, thyme, thyme borneal, and oregano) and the biopesticide Serenade (Bacillus subtilis strain QST 713). Over 90% inhibition of pathogen growth was achieved with oregano and Serenade amendments. The protective foliar application of Serenade, an aerated compost tea (ACT), Effective Microorganism mix (EM), and oregano, resulted in disease suppression of 5-40% relative to the untreated control. ACT had no significant suppressive effects (0-15% reduction), EM resulted in mild suppression (15-30% reduction), and oregano and Serenade consistently resulted in moderate disease reduction (20-40%). No oil or biological treatment produced disease control comparable to the chemical control chlorothalonil, which resulted in disease reductions of 80-98%. Both oregano and Serenade resulted in some phytotoxicity at high doses. These results suggest that the natural products and biological amendments tested are not sufficient for effective late blight control by themselves; however, when used in combination with other established disease control practices, these approaches may contribute to improved, integrated, and more sustainable management options for late blight.     

Effects of Plant Contact, Inoculation Pattern, Leaf Wetness Regime, and Nitrogen Supply on Inoculum Efficiency in Rice Sheath Blight

An experimental design was developed which allowed the measurement of inoculum efficiency (IE) represented by lesions of a leaf-borne disease such as rice sheath blight. In this design. IE is measured as the ratio of newly established lesions on trap plants relative to the inoculum present in a canopy, i.e. lesions artificially established on source plants, IE of the rice sheath blight pathogen, Rhizoctonia solani , was studied under semi-controlled conditions in which the effects of the following factors were measured; contact frequency among host tissues, amount and location of inoculum in the canopy, leaf wetness regime, and nitrogen content of the host plant. The conduciveness of these factors to sheath blight infection was measured in terms of IE which was expressed as the ratio of the density of daughter lesions on trap rice hills to the density of mother lesions on the inoculated quadrat hills. IE generally declined with the three successive batches of trap hills used in the experiments. It was significantly higher at closer plant spacings and under interrupted leaf wetness regimes. IE was not affected by the amount, nor by the location, of inoculum (mother lesions) in the canopy, but was significantly lower in hills with high total nitrogen content.     

致病疫霉拮抗菌株B25-I-3的鉴定及其次级代谢产物

【背景】粘细菌是一类具有社会性行为的高等原核生物,能产生丰富、多样、新颖的具有生物活性的次级代谢产物,具有很大的研究开发价值。【目的】从土壤样品中筛选出对致病疫霉(Phytophthora infestans)具有拮抗作用的粘细菌,并对其次级代谢产物进行研究。【方法】对分离到的一株拮抗P. infestans菌株,结合形态观察和16S rRNA基因序列分析确定其分类地位,并通过单因素分析与正交优化相结合的方法对菌株的发酵参数进行研究。采用滤纸片法对其浓缩发酵液中活性物质的稳定性及抗菌活性进行检测,并通过薄层色谱法(thin layer chromatography,TLC)与高效液相色谱法(high performance liquid chromatography,HPLC)等初步分离后,将具有抗P. infestans活性的组分利用液相色谱-质谱联用技术(HPLC-MS)进行检测,最后通过离体叶片法测定活性物质对马铃薯晚疫病的防病作用。【结果】从土壤样品中分离得到的菌株B25-I-3对P. infestans表现出较强的拮抗活性,经鉴定为橙色粘球菌(Myxococcus fulvus)。其拮抗P. infestans的活性物质主要存在于胞外,产活性物质的最优发酵条件为：摇床转速180 r/min,接种量10%,培养温度30 °C,发酵周期7 d。该菌株产生的活性物质耐受蛋白酶K以及紫外线与自然光照射,对温度耐受性极强,而且易于在低温下保存,对枯草芽孢杆菌(Bacillus subtilis)、金黄色葡萄球菌(Staphylococcus aureus)、大肠杆菌(Escherichia coli)、酿酒酵母(Saccharomyces cerevisiae)、立枯丝核菌(Rhizoctonia solani)、尖孢镰刀菌(Fusarium oxysporum)、向日葵核盘菌(Sclerotinia sclerotiorum)均有不同程度的抑制作用。其对P. infestans的拮抗组分中含有N-(3-氨基-2-羟丙基)-N-甲基硫酸二酰胺[N-(3-amino-2-hydroxypropyl)-N-methylsulfuric diamide]与甲基(2R)-2-叠氮基-3-羟基-2-甲基丙酸酯[methyl(2R)-2-azido-3-hydroxyl-2-methylpropanoate],该活性物质能明显抑制P. infestans侵染马铃薯叶片且对不同品种的叶片均无损伤作用。【结论】研究为M. fulvus B25-I-3活性物质的分离鉴定及抗马铃薯晚疫病生物农药的研发提供了基础数据。     

Evaluation of fungicides to control potato late blight (Phytophthora infestans) in the plains of Nepal

Fungicide application is an effective management option to control late blight of potato (caused by Phytophthora infestans). Field experiments were conducted to evaluate the efficacy of recently introduced and previously used fungicides on late blight management and potato yields in the western plains of Nepal in 2015 and 2016 crop seasons. Fungicides and a non-treated control (NTC) were replicated three times in a randomized block design planted with late blight susceptible cultivar Cardinal. Chlorothalonil, copper oxychloride, dimethomorph, fenamidone + mancozeb, mancozeb and metalaxyl were sprayed in 2015. In 2016, carbendazim was used instead of chlorothalonil. The area under disease progress curve (AUDPC) was consistently reduced in years by dimethomorph (90% and 65% in 2015 and 2016, respectively), fenamidone + mancozeb (68% and 62%) and mancozeb (40% and 47%) compared with the NTC. Similarly, tuber yield was increased with the application of dimethomorph (266% and 146% in 2015 and 2016, respectively), fenamidone + mancozeb (211% and 155%) and mancozeb (136% and 116%) compared with the NTC. Chlorothalonil reduced AUDPC by 43% and increased tuber yield by 170% in 2015. Other fungicides either had inconsistent results or did not reduce late blight severity and consequent effects on potato yield. The overall benefit–cost ratio was highest for dimethomorph in both years. These results show efficacy of dimethomorph, fenamidone + mancozeb and mancozeb in reducing late blight severity and increasing potato tuber yield in the plains of Nepal.     

The significance of tuber damage and inoculum concentration of Phoma exigua var. foveata in the development of gangrene in stored potato tubers

The susceptibility to gangrene infection of wounds of various shapes and depths on potato tubers was studied by inflicting wounds using differently-shaped brass teeth and rods of different diameters. Inoculating wounds with spore suspensions or damaging tubers which had been previously contaminated with Phoma exigua var. foveata or which had been recently lifted from plots of field experiments showed that wounds in which tissue was crushed were most susceptible to infection. Over a wide range of inoculum concentrations and in experiments using several different cultivars the incidence of infection of any wound type was compared to that of the standard severe cut and crush wound. Using a probit transformation a linear relationship was established, the slope of the line indicating the relative susceptibility of the wound. In 1977 and 1978, crops of cv. Pentland Dell were surveyed for damage incidence, inoculum and inoculum potential on arrival at a commercial bulk store. Nets of tubers buried among the tuber bulk were recovered after storage and gangrene incidence compared with damage and inoculum assessments. Inoculum potential and incidence of severe damage both influenced disease development but damage incidence was of greater importance, showing that priority should be given to decreasing damage and to curing to promote rapid wound healing in endeavours to control the disease.     

Effects of meteorological factors on the levels of <Emphasis Type="Italic">Alternaria</Emphasis> spores on a potato crop

Alternaria solani Soraeur produces early blight in Solanum tuberosum L., leading to significant agricultural losses. The current study was carried out on the extensive potato crop situated in north-western of Spain during 2007, 2008 and 2009. In this area potato crops are the most important source of income. In this work we used a Hirst-type volumetric spore-trap for the aerobiological monitoring of Alternaria spores. The highest spore concentrations were recorded during the 2009 cycle (10,555 spores), and the lowest concentrations were recorded during the 2008 cycle (5,471 spores). Over the 3 years of study, the highest concentrations were registered during the last stage of the crop. The aim of the study was to observe the influence of meteorological factors on the concentration of Alternaria spores, which can lead to serious infection and early blight. Prediction of the stages during which a crop is particularly vulnerable to infection allows for adjustment of the application of fungicide and is of environmental and agricultural importance. For this reason, we tested three models (P-Days, DD and IWP) to predict the first treatment and decrease the negative effect that these spores have on potato crops. The parameter that showed the most significant correlation with spore concentrations was minimum temperature. We used ARIMA (autoregressive integrated model of running mean) time-series models to determine the forecast. We considered weather data as predictor variables and the concentration of spores on the previous day as the fixed variable.     

Reaction of Certain Solanaceous and Asteraceous Plant Species to Inoculation with Phytophthora infestans in Cameroon

Experiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (S. lycopersicon) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agroecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry and potato infected the same host plants as well as gboma eggplant (S. macrocarpon) and two asteraceous weeds; Billy goatweed (Ageratum conyzoides) and Dichrocephala (Dichrocephala integrifolia). Inoculum from potato caused late blight symptoms on haemorrhage plant (Aspilia africana); while inoculum from tomato resulted in late blight on worowo (Solanecio biafrae). This is the first report of late blight infection on S. macrocarpon, A. conyzoides, Sol. biafrae and Asp. africana in Cameroon. The research results indicate that some asteraceous and solanaceous weeds may be alternative hosts of P. infestans in the potato agroecosystem.     

Epidemiological analysis of risk factors for the spread of potato viruses in Switzerland

Virus diseases represent important economic threats to the production of seed potatoes worldwide, yet little quantitative information is available on the relative merits of different measures of virus control applied singly or in combination. In this study, we compiled data from the national seed certification programme on the incidence of Potato Virus Y (PVY) and Potato Leaf‐roll Virus (PLRV) in potato tubers in Switzerland for the years 1990–2009 and used generalised linear models to investigate the influence of key epidemiological factors on infection risk. Results showed that post‐harvest virus incidence increased with initial inoculum levels, with the largest change in infection risk occurring between fields with no inoculum and those with low levels of inoculum. Virus incidence decreased with increasing altitude of fields. Surprisingly, infection risk was considerably lower for imported seed lots even though the model controlled for the effect of inoculum level, potato variety and other confounders. Overall, variety was the most important factor influencing virus risk. The results of the present analysis are useful to fine‐tune decision‐support systems that predict disease risk under different epidemiological scenarios.     

Efficacy of fungicide combinations,phosphoric acid and plant extract from stinging nettle on potato late blight management and tuber yield

Late blight caused by Phytophthora infestans is a major constraint to potato production. Inadequate control of the disease has often resulted in potato yield losses. We assessed the efficacy of fungicides, phosphoric acid and stinging nettle extract combinations for late blight control at two locations in Kenya. Disease severity, relative area under disease progress curves (RAUDPC), pathogen lesions and tuber yield were quantified during the 2008 and 2009 cropping cycles. The application of metalaxyl alternated with phosphate resulted in the greatest suppressive effects on late blight. The average late blight severity ranged from 3.5 to 34% in 2008 and 4.7 to 50% in 2009 at Tigoni location. RAUDPC for the same location ranged from 5 to 40% and 5 to 50% in 2008 and 2009, respectively. Similar levels of late blight severity were recorded at Marimba location in both years. Lesion growth and pathogen lesion numbers on potato plants differed significantly (p < 0.05) among treatments. Fungicides, phosphoric acid and stinging nettle extract varied in late blight control. Potato tuber yield varied among treatments. Phosphoric acid treatment had significantly (p < 0.05) greater tuber yield compared to metalaxyl at both locations. Field plots treated with plant extracts from stinging nettle resulted in the lowest tuber yield compared to other treatments with the exception of the untreated control. Fungicides, phosphoric acid, stinging nettle extract and their combinations can be readily effective in the suppression of late blight severity and pathogen lesions with moderate increases in tuber yield.     

Some epidemiological aspects of post-bloom fruit drop disease (Colletotrichum gloeosporioides) in citrus

Fluctuations in the incidence and amount of post-bloom fruit drop disease of citrus caused by Colletotrichum gloeosporioides in Belize prevent economic disease control. During the cooler drier months of the year when blossom infection is common there are variations in the incidence of rainfall and associated climatic parameters, and in the pattern of flowering. Large amounts of disease develop when periods of rain followed by prolonged wetness occur during peak blossoming periods. Blossoms are most susceptible during the open flower stage and infection of terminal flowers invariably results in infection of all other flowers on the spike. Disease incidence is greater in the lower parts of the trees, but flowering is greater in the upper regions. Large numbers of Colletotrichum spores are produced during wet conditions from apparently healthy leaves and from diseased flowers, but these rapidly lose viability when dried. Few spores are produced from old persistent calices (buttons). Although spores from leaves were a less potent inoculum source than those from flowers, they could provide the initial inoculum to commence flower infection when blossoming starts.     

Seasonal Migration of Meloidogyne chitwoodi and its Role in Potato Production

Seasonal vertical migration of Meloidogyne chitwoodi through soil and its impact on potato production in Washington and Oregon was studied. Nematode eggs and second-stage juveniles (J2) were placed at various depths (0-180 cm) in tubes filled with soil and buried vertically or in holes dug in potato fields. Tubes were removed at intervals over a 12-month period and soil was bioassayed on tomato roots. Upward migration began in the spring after water had percolated through the tubes. Nematodes were detected in the top 5 cm of tubes within 1-2 months of burial, depending on depth of placement. Potatoes were grown in field plots for 4 or 5 months before the tubers were evaluated for infection. One hundred eggs and J2 per gram soil placed at 60 and 90 cm caused significant tuber damage at the Washington and Oregon sites, respectively. At the Washington site, inoculum placed at 90, 120, and 150 cm caused potato root infection without serious impact on tuber quality, but inoculum diluted 2-8 times and placed at 90 cm did not cause root or tuber infection. Nematode migration was dependent on soil texture; 9 days after placement at the bottoms of tubes, J2 had moved up 55 cm in sandy loam soil (Oregon) but only 15 cm in silt loam (Washington). Thus, the importance of M. chitwoodi which occur deep in a soil profile may depend on soil texture, population density, and length of the growing season.     

A pathogen-responsive cDNA from potato encodes a protein with homology to a phosphate starvation-induced phosphatase

Infiltration of potato leaves with the phytopathogenic bacteria Pseudomonas syringae pv. maculicola induces local and systemic defense gene expression as well as increased resistance against subsequent pathogen attacks. By cDNA-AFLP a gene was identified that is activated locally in potato leaves in response to bacterial infiltration and after infection with Phytophthora infestans, the causal agent of late blight disease. The encoded protein has high homology to a phosphate starvation-induced acid phosphatase from tomato. Possibly, decreased phosphate availability after pathogen infection acts as a signal for the activation of the potato phosphatase gene.     

Tuber Blight Development in Potato Cultivars in Response to Different Genotypes of Phytophthora infestans

Migrations or introduction of new genotypes of Phytophthora infestans to a specific region imposes a different perspective for potato production. During 2009–2010, a late blight epidemic affected the Northeastern United States, which quickly spread through several states. The epidemic was characterized by the appearance of a new genotype of P. infestans designated US‐22, which was isolated from tomato and potato. Potato tubers are an essential component of late blight epidemics where the pathogen cannot overwinter on Solanaceous plants. Six potato cultivars were inoculated with 12 isolates of P. infestans (five different genotypes), including isolates of the genotype US‐22. Tuber blight development was characterized in terms of tissue darkening expressed as area under the disease progress curve values and lenticel infection. The responses indicated that US‐8 was more aggressive than US‐22, but US‐22 isolates obtained from potato were more aggressive on potato than those acquired from tomato. Tuber periderm responses to infection were limited, yet US‐8 isolates infected the periderm more often than US‐22 isolates. There were significant differences among the cultivars tested but cv. Jacqueline Lee was the most resistant overall. Although isolates of P. infestans genotype US‐22 were less aggressive in comparison with US‐8 isolates, US‐22 isolates still infected potato tubers and were as aggressive us US‐8 isolates on some cultivars. Management of late blight caused by isolates of US‐22 through host resistance may be feasible but imposes a different set of criteria for consideration from those that US‐8 imposed.     

Transgenic Potatoes Expressing a Novel Cationic Peptide are Resistant to Late Blight and Pink Rot

Potato is the world's largest non-cereal crop. Potato late blight is a pandemic, foliar wasting potato disease caused by Phytophthora infestans, which has become highly virulent, fungicide resistant, and widely disseminated. Similarly, fungicide resistant isolates of Phytophthora erythroseptica, which causes pink rot, have also become an economic scourge of potato tubers. Thus, an alternate, cost effective strategy for disease control has become an international imperative. Here we describe a strategy for engineering potato plants exhibiting strong protection against these exceptionally virulent pathogens without deleterious effects on plant yield or vigor. The small, naturally occurring antimicrobial cationic peptide, temporin A, was N-terminally modified (MsrA3) and expressed in potato plants. MsrA3 conveyed strong resistance to late blight and pink rot phytopathogens in addition to the bacterial pathogen Erwinia carotovora. Transgenic tubers remained disease-free during storage for more than 2 years. These results provide a timely, sustainable, effective, and environmentally friendly means of control of potato diseases while simultaneously preventing storage losses.     

THE REACTION OF VIRUS-INFECTED POTATO PLANTS TO PHYTOPHTHORA INFESTANS

The growth of Phytophthora infestans was retarded on leaves of potato plants that had been artificially inoculated with virus X or with virus Y.
Using different virus strains and potato varieties, the effect of virus infection on blight development was found to be greater, the more severe the systemic virus symptoms exhibited on the infected leaves before P. infestans inoculation.
The development of the fungus was never increased by virus infection.
The reduced blight development on virus-infected leaves is partially caused by an increase of resistance to infection. It is also suggested that virus infection alters the nutritional status of leaves to one less favourable for the development of P. infestans.