Late Blight Resistant Varieties Research Articles

Impact of Introduced Tomato Cultivars and Chemical Fungicides on the Occurrence and Intensity of Late Blight in Western Cameroon

Late blight, caused by Phytophthora infestans, is the main constraint to tomato production and exportation in Cameroon. The objective of this study was to evaluate the impact of chemical and tomato varieties in the control of tomato Late blight in the field for the improvement of tomato production in the west region of Cameroon. Seedlings of 7 tomato varieties produced in the nursery were transplanted into pits each containing 100 g of fowl droppings and 30 g of the nematicide Carbofuran 5%. From the 21st day after transplanting, the different fungicides were applied every four days. Data were collected on the incidence, severity of the disease at different stages of plant growth and development and on yields. The results showed that the AVTO1219 and AVTO1311 varieties were less sensitive to Late blight. The control plants of AVTO1219 variety showed incidences of 7.7, 11.7 and 16.7% and severities of 1.7, 14.9 and 17.2% in the vegetative, flowering and fruiting phases respectively. Control plants of CLN1462A, CLN1464A, CLN1464B, RIOGRANDE 2 and RIOGRANDE + varieties showed incidence of 100% from the flowering phase. Control plants of varieties AVTO1213 (17.29 t ha-1) and AVTO1311 (11.33 t ha-1) produced the highest yields. Bonsoin was the more effective fungicide and AVTO1311 was the more effective variety to manage disease. However, the combination of Bonsoin with the AVTO1219 and AVTO1311 varieties was most effective in controlling late blight of tomatoes in the field. These results suggest that to improve tomato production, Late blight resistant varieties should be used and effective fungicides applied as treatments.

Transcriptome analysis of scions grafted to potato rootstock for improving late blight resistance

BackgroundLate blight seriously threatens potato cultivation worldwide. The severe and widespread damage caused by the fungal pathogen can lead to drastic decreases in potato yield. Although grafting technology has been widely used to improve crop resistance, the effects of grafting on potato late blight resistance as well as the associated molecular mechanisms remain unclear. Therefore, we performed RNA transcriptome sequencing analysis and the late blight resistance testing of the scion when the potato late blight-resistant variety Qingshu 9 and the susceptible variety Favorita were used as the rootstock and scion, respectively, and vice versa. The objective of this study was to evaluate the influence of the rootstock on scion disease resistance and to clarify the related molecular mechanisms.ResultsA Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that the expression levels of genes related to plant–pathogen interactions, plant mitogen-activated protein kinase (MAPK) signaling pathways, and plant hormone signal transduction pathways were significantly up-regulated in the scion when Qingshu 9 was used as the rootstock. Some of these genes encoded calcium-dependent protein kinases (CDPKs), chitin elicitor receptor kinases (CERKs), LRR receptor serine/threonine protein kinases (LRR-LRKs), NPR family proteins in the salicylic acid synthesis pathway, and MAPKs which were potato late blight response proteins. When Favorita was used as the rootstock, only a few genes of late blight response genes were upregulated in the scion of Qingshu 9. Grafted plants using resistant variety as rootstocks inoculated with P. infestans spores showed significant reductions in lesion size while no significant difference in lesion size was observed when susceptible variety was used as the rootstock. We also showed that this induction of disease resistance in scions, especially scions derived from susceptible potato varieties was mediated by the up-regulation of expression of genes involved in plant disease resistance in scions.ConclusionsOur results showed that potato grafting using late blight resistant varieties as rootstocks could render or enhance resistance to late blight in scions derived from susceptible varieties via up-regulating the expression of disease resistant genes in scions. The results provide the basis for exploring the molecular mechanism underlying the effects of rootstocks on scion disease resistance.

Genome-wide association analysis for late blight resistance of potato resources

<p indent=0mm>The mining of broad-spectrum resistance genes is the basis of the breeding of potato varieties with high late blight resistance. In this study, 288 samples of late disease resistance selected by the International Potato Center (CIP) for years were planted and were investigated for two consecutive years, which could provide some theoretical and material basis for breeding of late blight resistant varieties and help to study on disease resistance mechanism. The late blight resistance of each sample was evaluated using AUDPC and sAUDPC values. The population simplified genome sequencing was performed by SLAF-seq and carried out by genome-wide association analysis in order to discover the genetic loci and candidate genes related to late blight resistance. There were wide genetic differences in resistance to late blight among 288 samples. Through genome-wide association analysis, based on five analytical models, a total of 82 loci significantly correlated with late blight resistance were identified. Combined with genomic annotation, there were 54 candidate genes known or likely to be associated with late blight resistance in the association interval. Among them, 23 genes were resistant genes, including late blight resistance gene <italic>R1</italic> homolog, <italic>Sw-5</italic> homolog (<italic>R8</italic>) and <italic>Rpi-vnt1</italic>, as well as gene encoding pleiotropic resistance protein. Five genes encoded MAPK protein and WRKY transcription factor; one gene was involved in the JA pathway; three genes were associated with salicylic acid pathway; six genes were related to the course of the disease; three genes were involved in the synthesis of phenylpropionic acid. Other genes related to resistance to late blight included HMGR gene (2) and cytochrome P450 (21).

Simulating crop-disease interactions in agricultural landscapes to analyse the effectiveness of host resistance in disease control: The case of potato late blight

Disease-resistant potato varieties can play a key role in sustainable control of potato late blight. However, when these varieties are more widely used, resistance breakdown can occur as a result of pathogen adaptation. Here we focussed on potato cultivation in the Netherlands, where new (single gene) resistant varieties have been introduced over the last ten years. This new generation of late blight resistant varieties has moderate yield levels and does not meet all market requirements. As a result, adoption rates for resistant varieties have been low so far. We developed a spatially explicit agent-based model to simulate potato production, disease spread and pathogen evolution at the landscape level. We analysed how late blight severity, resistance durability and potato yield are affected by the spatial deployment of a resistant variety, with a lower potential yield than susceptible varieties. The model was applied to an agricultural region in the Netherlands (596 km2) and was run for a period of 36 years using daily weather data as input for crop growth and disease dynamics. The short- and long-term effects of the deployment of a resistant variety were analysed with the model. With respect to short-term dynamics, years were analysed independently to study between year variation. The model demonstrated that in most years, susceptible fields without fungicide application suffered severe yield losses and resistant fields performed better despite their lower potential yield. Resistance breakdown was observed in a small fraction of fields with the resistant variety, but this did not affect mean potato yield or disease incidence in the short term since it occurred at the end of the growing season. Increasing the fraction of potato fields with the resistant variety strongly reduced late blight infection within a landscape. With respect to the long-term effects, the model showed the emergence and spread of a virulent strain over time. The virulent strain gradually took over the pathogen population, decreasing mean potato yields from fields with the resistant variety. This occurred in all landscape compositions where the resistant variety was deployed to different extents. It was found that low as well as high proportions of fields with the resistant variety could increase durability of resistance. With these findings, the model provided more insight into the opportunities and risks related to the use of plant resistance in disease control, an important and sustainable disease management strategy.

Evaluation of potato (Solanum tuberosum L.) genotypes for resistance to late blight at Sinana Southeastern Ethiopia

Late blight caused by Phytophthora infestans (Mont.) de Bary, is one of the most significant constraints to potato production in Bale high lands and other regions of Ethiopia. Hence, this requires to develop high yielding and late blight resistant varieties. Therefore, this study was conducted to determine host resistance of potato against Phytophthora infestans in order to develop late blight resistant/tolerant genotypes. The experiment was laid out in randomized complete block design with three replications at Sinana Agricultural Research Center during 2014 main cropping season. The genotypes showed highly significant (P&lt;0.01) differences for all the characters studied. Genotypes exhibited wide ranges of mean values for all characters. The highest total tuber yield (46.1 t ha-1) was obtained from the advanced clone, CIP-392640.524 followed by Belete (41 t ha-1). Late blight appeared early on farmer's cultivar Kellacho (48 days after planting) and late on advanced clones CIP- 399062.102(74 days after planting). Percent severity index (PSI) and area under disease progress curve (AUDPC) ranged from 33.91 to 91.67% and 105 to 2370, respectively. Eleven newly introduced clones and the released variety "Belete" recorded PSI 33 to 39.7% and AUDPC 105 to 264.1. Hence, these genotypes can be categorized as moderately resistant. The study revealed the presence of considerable variability in tested genotypes for economically important traits and the higher chance of selecting genotypes with high yield and moderately resistant to late blight. However, it appears that further evaluation of genotypes across seasons and locations to identify genotypes that could be released as varieties seem to be quite pertinent.Int. J. Agril. Res. Innov. &amp; Tech. 6 (1): 21-25, June, 2016

The Solanum demissum R8 late blight resistance gene is an Sw-5 homologue that has been deployed worldwide in late blight resistant varieties.

Key messageThe potato late blight resistance geneR8has been cloned.R8is found in five late blight resistant varieties deployed in three different continents. R8 recognises Avr8 and is homologous to the NB-LRR protein Sw-5 from tomato.The broad spectrum late blight resistance gene R8 from Solanum demissum was cloned based on a previously published coarse map position on the lower arm of chromosome IX. Fine mapping in a recombinant population and bacterial artificial chromosome (BAC) library screening resulted in a BAC contig spanning 170 kb of the R8 haplotype. Sequencing revealed a cluster of at least ten R gene analogues (RGAs). The seven RGAs in the genetic window were subcloned for complementation analysis. Only one RGA provided late blight resistance and caused recognition of Avr8. From these results, it was concluded that the newly cloned resistance gene was indeed R8. R8 encodes a typical intracellular immune receptor with an N-terminal coiled coil, a central nucleotide binding site and 13 C-terminal leucine rich repeats. Phylogenetic analysis of a set of representative Solanaceae R proteins shows that R8 resides in a clearly distinct clade together with the Sw-5 tospovirus R protein from tomato. It was found that the R8 gene is present in late blight resistant potato varieties from Europe (Sarpo Mira), USA (Jacqueline Lee, Missaukee) and China (PB-06, S-60). Indeed, when tested under field conditions, R8 transgenic potato plants showed broad spectrum resistance to the current late blight population in the Netherlands, similar to Sarpo Mira.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-016-2740-0) contains supplementary material, which is available to authorized users.

Rpi-blb2 gene from Solanum bulbocastanum confers extreme resistance to late blight disease in potato

The Rpi-blb2 gene (R gene) from the Mexican wild potato species, Solanum bulbocastanum, was introduced into the potato variety Desiree by agro-infection in order to confer resistance to late blight which is still the most important disease of the potato worldwide. A total of 148 putative transgenic events was obtained by selection based on hygromycin resistance of which 127 appeared to contain the Rpi-blb2 gene. To rapidly identify the highly resistant transgenic events, we used an in vitro assay with one isolate of Phytophthora infestans and a whole-plant assay with two isolates. Nine transgenic events were highly resistant to both isolates and four of these contained single copy T-DNA and did not contain backbone vector sequences. The transcript abundance of Rpi-blb2 was low in infected and uninfected leaves and did not correlate with the resistance level determined in whole plants. We proceeded with high dose inoculation of whole plants of three highly and moderately resistant transgenic events, which resulted in lesions with low levels of sporulation in a few cases. Reinfection was not successful in any of the cases. Hence our results show that a high level of resistance to LB, including extreme resistance, can be obtained through the Rpi-blb2 gene and that heavy inoculation did not readily increase virulence in our test conditions. These transgenic events will be used for either multi-line deployment or R gene stacking by conventional breeding in order to release late blight resistant varieties which will need limited fungicide use, if any.

Transformation of the potato variety Desiree with single or multiple resistance genes increases resistance to late blight under field conditions

Late blight, caused by Phytophthora infestans, remains the most devastating disease in potato resulting in economic costs that sum up 5.2 billion euros, globally. The use of resistant varieties is a powerful, viable and environmentally friendly alternative or supplement for the current, commonly deployed chemical control strategies. In this study, we set out to improve the susceptible potato variety Desiree by transformation with single or multiple late blight (R) resistance genes. Rpi-sto1, Rpi-vnt1.1 and a stack of Rpi-sto1:Rpi-vnt1.1:Rpi-blb3, were transformed and eight, eight, and ten independent transformants (events) respectively, were selected because of absence of vector backbone, low T-DNA copy number, responsiveness to the cognate Avr effectors, P. infestans resistance in detached leaf assays (DLAs) and preliminary field experiments. The performance of the selected events was studied under field conditions in The Netherlands and Belgium, after P. infestans inoculation and/or to natural late blight infection during two consecutive growing seasons. All selected events were more resistant than the non-transformed susceptible reference clone. The different individual R genes, however, contributed to different levels of resistance. The selected events were also compared to conventionally bred late blight resistant varieties with (partially) known R gene content. Generally, it was found that plants with single R genes showed a lower level of resistance than plants with R gene stacks. Only the events harbouring three late blight R genes remained unaffected until the end of the growing season, in both locations and in both growing seasons.

Potato breeding in the Netherlands: a successful participatory model with collaboration between farmers and commercial breeders

Participatory Plant Breeding (PPB) is mostly considered relevant to smallholder agriculture in developing countries. PPB involves getting farmers to participate in plant breeding to overcome shortcomings in the formal plant breeding system. The potato breeding system in the Netherlands has a long standing tradition of farmer participation in breeding. This PPB differs from the ‘standard’ PPB model as there is substantial private sector involvement and the system is situated in a modern, western context. Since its inception, farmer-breeders have contributed substantially to developing this potato breeding system, which supplies a large diversity of crop varieties that are grown in very varied environmental conditions around the world and for different consumer markets. This paper describes the current organizational structure and practices, provides some historical background and analyses the functions, relations and interactions of the major actors in the system. It argues that a historically international and commercially orientated potato sector was able to prosper because of a supportive political and legal context, which provided public institutional support to private sector potato breeding activities. Farmers’ knowledge and skills are particularly well expressed and vital in breeding in potato—a very heterogeneous and vegetatively-propagated crop. A new PPB initiative called BioImpuls recently emerged and engages organic potato farmers in a search to develop late blight-resistant varieties for the organic sector. This supports the argument that farmers’ knowledge can substantially contribute to modern and diversified breeding. While Dutch potato breeding is a special case in various respects, our analysis identifies several key attributes which could inform the design of successful PPB programmes in developing countries.

Broad spectrum late blight resistance in potato differential set plants MaR8 and MaR9 is conferred by multiple stacked R genes

Phytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this “de-stacking” approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varieties.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-011-1757-7) contains supplementary material, which is available to authorized users.

Evaluation of a short-day adapted tetraploid potato population with horizontal resistance toPhytophthora infestans under long-day conditions in northern Maine

Phytophthora infestans (Mont.) de Bary, the cause of late blight, has rapidly overcome major (R) gene resistance in potatoes. A population of short-day adapted tetraploid potatoes with horizontal resistance to late blight was developed at the International Potato Center in Lima, Peru. True seed from this population was obtained from the NRSP-6 Project at Sturgeon Bay, WI for the purpose of evaluating its potential to contribute to the breeding effort for late blight resistance in the United States. In 1996, 552 single hills were planted on Chapman Farm, Presque Isle, ME; only 448 tuberized. In 1997, these clones were planted on Chapman Farm for increase; 129 were saved, 53 failed to tuberize, and 266 were discarded because they were sprouted at harvest. In 1998 and 1999, 69 clones were tested for their reaction to late blight in replicated plots on Aroostook Farm, Presque Isle, ME. Percent infected foliage was estimated three times toward the end of the season and used to compute area under the disease progress curve. Broad-sense heritability for horizontal resistance to late blight was estimated as 0.78 with a 95% confidence interval of 0.64 to 0.86. Using detached leaflet assays, these clones were inoculated with US-8 strains ofP. infestans, and the diameter of the lesion was measured 7, 8, 9, 10 and 11 days after inoculation. The correlation between field resistance and the detached leaflet assay was very low (0.18<r<0.24). Some clones from this population are highly resistant to the US-8 strain of P.infestans and represent another source of breeding material for developing late blight resistant varieties in the future. However, very late maturity, short dormancy, poor tuberization and low fertility levels may limit the usefulness of this germplasm in northern USA latitudes.

Inheritance Analysis and Identification of SSR Markers Linked to Late Blight Resistant Gene in Tomato

Late blight caused by Phytophthora infestans is the most serious disease of tomato production in China. Studies on the genetics of resistance and identification of molecular markers are very useful for breeding late blight resistant varieties. The objective of this paper was to study the inheritance of late blight resistance and identify simple sequence repeat (SSR) markers associated with resistance allele in tomato ( Lycopersicon esculentum Mill). The results came from an F 2 progeny of 241 plants derived from a cross between 5 # inbred line that is susceptible to late blight and a resistant accession CLN2037E. The late blight responses of F 2 plants were tested by artificially inoculation of detached-leaflets in plate and natural infection assayed under greenhouse conditions. Both methods showed that the resistance is dominant and inherited as monogenic trait. Genetic mapping and linkage analysis showed that the late blight resistance gene Ph-ROL was located on chromosome 9 with a genetic distance of 5.7 cM to the SSR marker TOM236.

Late blight resistant varieties for Cameroon

In October 1992 the first three late blight resistant varieties developed under local conditions were officially released in Cameroon. This resulted from the first four years of research collaboration between the Institute of Agricultural Research (IRA) of Cameroon and the International Potato Center (CIP). The three varieties were selected from a group of 95 advanced clones sent by CIP in early 1988. The new varieties are well adapted to the highlands of the country, where late blight is the main pathological constraint on potato production. CIPIRA (CIP 381381.13) is a variety with white skin, as compared to TUBIRA (CIP 381406.6) and BAMIRA (CIP 720055) which have a red skin. These varieties have shown a consistent late blight reaction between 1–3 (scale of l=immune to 9=highly susceptible) during the four years of field trial evaluations, a growing cycle of 90–125 days at elevations between 1,000-2,000 m, and an average potential yield of 30–40 ton/ha under low fertilizer inputs (60/60/40 kg NPK/ha). Seed will be available for distribution to farmers in late 1994, utilizing a basic seed production scheme based on mass production of rooted stem cuttings developed by the IRA/CIP Project in Cameroon.