Effects of cropping history and origin of seed potatoes on population structure of Phytophthora infestans

The effects of origin of seed potatoes and the cropping history on the phenotypic structure of Phytophthora infestans populations was studied in northern Hessia, central Germany, from 2000 to 2002. Populations originating from fields with a history of potato cropping with only short or no rotation (old fields) were compared with populations from new fields, i.e., where no potatoes had been grown for at least 30 years and seed potatoes were either imported from breeders or produced on-farm (certified). The main goal was to determine the importance of seed potato infection in the establishment of new P. infestans populations. Isolates were characterized for mating type, virulences and rep- (repetitive extragenic palindromic) PCR fingerprints. Among a total of 639 isolates sampled from 31 sites, mating types A1 and A2 co-existed in all three years in 60–92% of the sites. Over all three years, 53 pathotypes were detected in a subsample of 272 isolates. Isolates originating from the new fields had significantly higher frequencies of the virulences v1, v2, v3, v6 and v7, indicating general effects of seed introduction into a new region. Thirty-six fingerprints were detected in a subsample of 281 isolates of which 22 were unique while four occurred in all three years and in many sites. Pathogen populations from potato fields that were grown from seed tubers of geographically different origin differed significantly based on χ ² tests. While the Nei genetic distances were less than .1 among the local populations, distances to the US lineages US-1, US-6, US-7 and US-8 ranged from .22 to .47; however, the bootstrap values were not significant. Populations from old fields were more diverse and 14 of the 22 rep-PCR types occurred there among 132 isolates tested in comparison to six in the new fields (n = 140 isolates) and two among six isolates from volunteers. The results also suggest that both sexual and asexual reproduction play a role.     

Concepts of plant health – reviewing and challenging the foundations of plant protection

Plant health is a frequently used but ill‐defined term. However, there is an extensive literature on general health definitions and health criteria in human medicine. Taking up ideas from these philosophical debates, concepts of plant health are reviewed and a framework developed to locate these concepts according to their position in several philosophical controversies. In particular, (i) the role of values in defining plant health in a naturalist versus a normativist approach; (ii) negative and positive definitions of plant health; (iii) reductionist versus holistic perspectives; (iv) the focus on functionality versus resilience, i.e. the ability of the plant to perform under stress with or without human interference; (v) materialist versus vitalist approaches; and (vi) biocentric versus anthropocentric views, are surveyed. The ways in which these perspectives relate to mainstream and alternative approaches to plant protection are explored and we suggest how the contradicting views might be reconciled. It is argued that none of these perspectives is without inherent contradictions, but that by combining contrasting approaches it is possible to provide a comprehensive though fuzzy concept. Rather than giving a new definition of plant health, a conceptual framework is developed that suggests what questions may be answered in debates on plant health issues and how such debates could be organized.     

Efficacy of copper alternatives applied as stop-sprays against Plasmopara viticola in grapevine

Journal of Plant Diseases and Protection - The six products, Armicarb, Vitisan, lime sulphur, Caso, Calce Fiocco and Ulmasud, were tested for their ability to control downy mildew (Plasmopara...     

Susceptibility of wild carrot (Daucus carota ssp. carota) to Sclerotinia sclerotiorum

Sclerotinia soft rot, caused by Sclerotinia sclerotiorum, is a severe disease of cultivated carrots (Daucus carota ssp. sativus) in storage. It is not known whether Sclerotinia soft rot also affects wild carrots (D. carota ssp. carota), which hybridise and exchange genes, among them resistance genes, with the cultivated carrot. We investigated the susceptibility of wild carrots to S. sclerotiorum isolates from cultivated carrot under controlled and outdoor conditions. Inoculated roots from both wild and cultivated plants produced sclerotia and soft rot in a growth chamber test. Two isolates differed significantly in the ability to produce lesions and sclerotia on roots of both wild carrots and cv. Bolero. Flowering stems of wild carrots produced dry, pale lesions after inoculation with the pathogen, and above-ground plant weight was significantly reduced 4 weeks after inoculation in a greenhouse test. Wild and cultivar rosette plants died earlier and fewer plants survived when inoculated with the pathogen under outdoor test conditions. Cultivar plants died earlier than wild plants, but survived as frequently. Plants inoculated in the crown died earlier and at a lower frequency than plants inoculated on leaves. Wild carrots may thus serve as a host of S. sclerotiorum and thus eventually benefit from any uptake of resistance genes, among them transgenes, via introgression from cultivated carrots.     

Plant disease management in organic farming systems

Organic farming (OF) has significantly increased in importance in recent decades. Disease management in OF is largely based on the maintenance of biological diversity and soil health by balanced crop rotations, including nitrogen‐fixing and cover crops, intercrops, additions of manure and compost and reductions in soil tillage. Most soil‐borne diseases are naturally suppressed, while foliar diseases can sometimes be problematic. Only when a severe disease outbreak is expected are pesticides used that are approved for OF. A detailed overview is given of cultural and biological control measures. Attention is also given to regulated pesticides. We conclude that a systems approach to disease management is required, and that interdisciplinary research is needed to solve lingering disease problems, especially for OF in the tropics. Some of the organic regulations are in need of revision in close collaboration with various stakeholders. © 2015 Society of Chemical Industry     

Effects of host and pathogen genotypes on inducibility of resistance in tomato (Solanum lycopersicum) to Phytophthora infestans

Thirteen tomato (Solanum lycopersicum) accessions were tested for inducibility of resistance against two isolates of Phytophthora infestans using BABA (dl ‐3‐amino butyric acid) as the inducing agent. In a more detailed trial, six of the accessions were assessed for inducibility of resistance to six P. infestans isolates on three leaves of different age per plant. Plants were inoculated 1 week after treatment with BABA. Area under the disease progress curve (AUDPC), sporulation capacity (SC) and infection efficiency (IE) were all affected by treatment with BABA. On leaves of all ages AUDPC was most affected by induction (43–100% reduction on the youngest leaves) followed by SC (14–100%) and IE (0–100% reduction). Tomato genotypes varied significantly in inducibility of resistance against P. infestans and the degree of induction generally decreased with increasing leaf age, whilst the absolute susceptibility with respect to AUDPC and SC rarely changed. The level of induction was not always related to the resistance level of the tomato accession and it was significantly influenced by the pathogen isolate used for challenge inoculation. The results show that inducibility of resistance is a selectable trait that is, however, isolate‐specific.     

Challenges to Organic Potato Farming: Disease and Nutrient Management

For organic potato producers the two main challenges are disease and nutrient management. Both factors are limited by regulations that on the one hand prohibit the use of chemical fertilisers, especially nitrogen and, on the other hand, most synthetic pesticides. Late blight, caused by Phytophthora infestans is commonly thought to be the factor most limiting yield. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper the state of the art of organic potato management with respect to disease and nutrient management is summarised. In a second part, the interactive effects of N-availability in the soil, climatic conditions and late blight were studied in the presence and absence of copper fungicides from 2002–2004 for the mid-early main-crop potato cv. Nicola. From the experimental work it became clear that copper fungicides in most cases do slow down epidemics adding an average of 3 days to the growth duration. However, only 30% of the variation in yield could be attributed to disease reduction. A model including disease reduction, growth duration and temperature sum from planting until 60% disease severity was reached, and soil mineral N contents at 10 days after emergence could explain 75% of the observed variation in yield. However, the model failed when N-supply was extremely high. The implications of the results on the management of organic potatoes with respect to cultivar choice, nutrient and disease management are discussed. In conclusion, several points emerge from the results: In organic farming, yields are foremost limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deducted from results in conventional farming because of the strong interaction with nutrient status. Resistance clearly remains the most important strategy against late blight in organic potato production. However, as important or even more important than resistance is the early development and bulking behaviour and the ability of a cultivar to make use of organic nutrients efficiently. In the absence of efficient organic pesticides it is possible to reduce blight pressure to a certain extent by arranging the crop in small narrow fields perpendicular to the main wind direction neighboured either by non-hosts or completely resistant potatoes.     

What is the SMARTest way to breed plants and increase agrobiodiversity?

The evaluation and use of the vast diversity contained in plant genetic resources (PGR) is a main challenge for today’s plant breeding. The use of molecular markers has hugely increased the knowledge about genetic diversity and great hopes are raised about the potential of marker assisted selection [MAS; sometimes also termed SMART breeding (Selection with Markers and Advanced Reproductive Technologies)] to help increasing the use of PGR and maintaining crop genetic diversity. Another approach growing attention has been paid to over the past two decades and which also aims to increase variation in crops is evolutionary and participatory breeding (EPB). In this paper we discuss both the potential of marker-assisted breeding strategies and the potential of EPB breeding to contribute to the maintenance, increase and development of agrobiodiversity. The potentials of molecular markers in the evaluation and use of PGR and their documented contribution to agrobiodiversity are reviewed and results from guided interviews with scientists and breeders are given. Despite tremendous research efforts involving molecular markers, it is still difficult to obtain a clear picture how molecular markers contribute to the use of PGR in plant breeding. Minor and major crops do not benefit to the same degree from recent developments in marker technology. It therefore depends at least in part on economic considerations whether SMART breeding or EPB strategies or both are implemented in the breeding process of a crop. A general decision in favor or against MAS or EPB when breeding for diversity would not yield optimum results.