Foliar Resistance Research Articles

Mapping Solanum berthaultii-based Late Blight (Phytophthora infestans) Resistance in a Diploid Population

Late blight, caused by the oomycete Phytophthora infestans (Mont) de Bary, is the most important disease of cultivated potato (Solanum tuberosum L.). An efficient long-term strategy for controlling late blight infection involves integration of host plant resistance to disease management programs. In this study, a diploid potato population segregating for late blight resistance was generated from an interspecific cross (MSX902) between S. tuberosum x S. chacoense hybrid (84SD22) and a late blight resistant Solanum berthaultii hybrid (Ber83). A total of 129 progeny and two parents were tested for foliar resistance against the US-23 P. infestans genotype using detached-leaf bioassays and inoculated field trials (2014 and 2015). Distribution of foliar late blight resistance and susceptibility was bimodal in both types of phenotype evaluation, suggesting a major R-gene may be associated with the resistance. A major QTL for late blight resistance on chromosome 10 was detected using both detached leaf bioassay and field trial data. The SNP marker solcap_snp_c1_15219 (26.5 cM) was at the peak of the QTL. Additionally, a minor QTL on chromosomes 5 was linked to SNPs solcap_snp_c1_3793. These SNP markers closely linked to the late blight resistance QTL can be used for marker-assisted breeding.

Screening of Groundnut (Arachis hypogaea L.) Genotypes for Identification of Sources of Resistance against Leaf Spot Disease

Background: Groundnut (Arachis hypogaea L.) is the fourth most important oil seed crop in the world. The early and late spots are a foliage disease more common and more destructive of groundnut which cause severe yield losses up to 70% and reduces the quality of the pod and fodder. Recent efforts have targeted on developing resistant source against leaf spot disease which are helpful for discarding the hazardous toxic chemical compounds used for controlling the disease. The current study aimed to identify the sources of resistance to leaf spot from the newly identified genotypes as well as from wild species and to study the way in which these were responding to the to the disease development. Methods: Seventy three groundnut genotypes were screened against late leaf spot disease under artificial epiphytotic conditions in field at AICRP on Groundnut, MPKV, Rahuri during kharif 2015-16. The observations of disease intensity and rate of infection were recorded. Result: Among the Seventy three groundnut genotypes, 10 genotypes showed resistant and 33 genotypes showed the moderately resistant reaction to leaf spot disease. The 25 entries showed the susceptible and 05 genotypes showed the highly susceptible reaction to the leaf spot disease. All the susceptible cultivars belong to A. hypogaea sub. sp. fastigiata var. fastigiata to as Spanish bunch. These 10 resistant genotypes of groundnut including two wild species viz., RHRG 6083, KDG 128, GPBD 4, ICGV 94118, ICGV 4983, ICG 12672, ICGV 13160 (A. batizocoi), ICGV 13165 (A. cardenasi), ICG 11426 and ICGV8193 were selected for intensive artificial screening under glasshouse conditions and also confirmed resistance. The resistant lines will be useful to develop introgression lines using marker-assisted backcrossing approach to improve foliar fungal disease resistance in popular groundnut varieties.

Identification of Interspecific Potato Hybrids with Combined Resistance to Late Blight (Phytophthora Infestans) and Nematode (Globodera Rostochiensis)

Abstract Late blight (agent Phytophthora infestans) and potato cyst nematode (PCN) caused by Globodera rostochiensis are economically important pathogens, which may significantly reduce potato yields. In this study interspecific potato hybrids were used as a source of resistance for combined resistance to economically important potato pathogens: late blight and cyst nematode. The aim of our study was to identify hybrid progenies with combined resistance to both pathogens and to verify the applicability of several molecular markers associated with resistance to G. rostochiensis pathotype Ro1 to identify resistant plants. Ninety-two clones of eleven original interspecific potato hybrids obtained in crosses with the cultivated S. tuberosum group tuberosum, S. tuberosum group Andigena, S. tuberosum group Phureja and wild S. guerreroense, S. microdontum, S. kurtzianum, S. neoantipoviczii and S. tarijense potato species were screened in bioassays and by molecular markers. PCN resistant or moderately resistant clones were found among the progenies of nine hybrids. Results were highly correlated with resistance status detected by molecular markers linked to the H1 (marker 57R) and Gro1-4 (marker Gro1) genes. Marker CP113 (linked to the H1 gene) was not polymorphic and failed to detect resistance status. Combination of foliar late blight resistance and resistance to PCN was identified in hybrids obtained in crosses with plants of species S. microdontum, S. tarijense and S. phureja and in the hybrid between S. guerreroense and Black’s P. infestans race differential carrying gene R-5.

Cell Wall Acetylation in Hybrid Aspen Affects Field Performance, Foliar Phenolic Composition and Resistance to Biological Stress Factors in a Construct-Dependent Fashion.

The production of biofuels and “green” chemicals from the lignocellulose of fast-growing hardwood species is hampered by extensive acetylation of xylan. Different strategies have been implemented to reduce xylan acetylation, resulting in transgenic plants that show good growth in the greenhouse, improved saccharification and fermentation, but the field performance of such plants has not yet been reported. The aim of this study was to evaluate the impact of reduced acetylation on field productivity and identify the best strategies for decreasing acetylation. Growth and biological stress data were evaluated for 18 hybrid aspen lines with 10–20% reductions in the cell wall acetyl content from a five year field experiment in Southern Sweden. The reduction in acetyl content was achieved either by suppressing the process of acetylation in the Golgi by reducing expression of REDUCED WALL ACETYLATION (RWA) genes, or by post-synthetic acetyl removal by fungal acetyl xylan esterases (AXEs) from two different families, CE1 and CE5, targeting them to cell walls. Transgene expression was regulated by either a constitutive promoter (35S) or a wood-specific promoter (WP). For the majority of transgenic lines, growth was either similar to that in WT and transgenic control (WP:GUS) plants, or slightly reduced. The slight reduction was observed in the AXE-expressing lines regulated by the 35S promoter, not those with the WP promoter which limits expression to cells developing secondary walls. Expressing AXEs regulated by the 35S promoter resulted in increased foliar arthropod chewing, and altered condensed tannins and salicinoid phenolic glucosides (SPGs) profiles. Greater growth inhibition was observed in the case of CE5 than with CE1 AXE, and it was associated with increased foliar necrosis and distinct SPG profiles, suggesting that CE5 AXE could be recognized by the pathogen-associated molecular pattern system. For each of three different constructs, there was a line with dwarfism and growth abnormalities, suggesting random genetic/epigenetic changes. This high frequency of dwarfism (17%) is suggestive of a link between acetyl metabolism and chromatin function. These data represent the first evaluation of acetyl-reduced plants from the field, indicating some possible pitfalls, and identifying the best strategies, when developing highly productive acetyl-reduced feedstocks.

The effect of agronomic factors on crop health and performance of winter wheat varieties bred for the conventional and the low input farming sector

It has been frequently suggested that varieties bred/selected under conventional farming conditions lack important traits required for optimum performance under low agrochemical input conditions. However, there is limited scientific information about interactions between cultivars bred/selected for the low input vs conventional farming sector and innovative crop agronomic strategies on crop health, yield and quality parameters to support this hypothesis. The main objective of this pilot study was therefore to compare the effect of contrasting fertilisation and crop protection regimes used in organic and conventional farming on crop health and performance parameter in two wheat varieties developed for organic/low input and conventional farming systems respectively.Results indicate that both leaf phenolic and flavonoid compounds, were positively associated with use of the ‘long straw’ variety Aszita and to a lesser extent composted FYM fertiliser inputs, while they were negatively associated with mineral N-fertiliser inputs, plant N uptake and use of the ‘short straw’ variety Solstice. On the other hand foliar and ear disease severity were positively associated with plant N uptake, use of the variety Solstice and the use of mineral fertilisers, while they were negatively associated with composted FYM fertiliser inputs, leaf phenolic/flavonoid concentrations and the use of the variety Aszita.Overall findings suggest that low input farming-focused breeding programmes might deliver varieties such as Aszita that have lower yield potential, but have higher grain protein, leaf phenolic concentrations, and foliar disease resistance under low-input conditions. Future studies should investigate whether the higher foliar phenolic levels found in low input varieties are linked to disease resistance and if they are also expressed in the grain.

Linkage Mapping for Foliar Necrosis of Soybean Sudden Death Syndrome.

Sudden death syndrome (SDS) foliar symptoms consist of foliar chlorosis, foliar necrosis, leaf marginal curling, and premature defoliation, but resistance screening has been evaluated mostly based on the overall SDS foliar severity rather than on a specific foliar symptom. This study generated an F2 population derived from crossing the susceptible variety Sloan and the resistant germplasm line PI 243518, which exhibits resistance to both foliar chlorosis and necrosis. A total of 400 F2 lines were evaluated for foliar chlorosis, foliar necrosis, and overall SDS foliar symptoms, separately. Genotyping-by-sequencing was applied to obtain single nucleotide polymorphisms (SNPs) in the F2 population, and linkage mapping using 135 F2 lines with 969 high-quality SNPs identified a locus on chromosome 13 for foliar necrosis and SDS foliar symptoms. The locus partially overlaps with loci previously reported for SDS on chromosome 13, which is the third time the region from 15.98 to 21.00 Mbp has been reproduced independently and therefore qualifies this locus for a new nomenclature proposed as Rfv13-02. In summary, this study generated a new biparental population that enables not only the discovery of a locus for foliar necrosis and SDS foliar symptoms on chromosome 13 but also the potential for advanced exploration of SDS foliar resistance derived from the germplasm line PI 243518.

LATE BLIGHT RESISTANCE OF WILD POTATO SPECIES UNDER FIELD CONDITIONS IN THE NORTHWEST OF RUSSIA

Background. Despite the great efforts made by breeders, late blight remains a paramount cause of significant potato harvest losses. Introgression of various resistance genes from wild Solanum L. species is the main method to increase the resistance in potato cultivars. Field resistance is considered to be more durable than those induced by the action of single R genes. To this end, resistance sources should be selected from а wide range of species under severe natural infection.Material and methods. As the material for evaluation, 1141 accessions of 99 wild potato species belonging to 15 taxonomic series according to the system of J. Hawkes were used. Each accession was assessed for 3–5 years. A 1–9 point scale was employed to score the damage of plants every week starting from the first symptoms of the disease, where 9 meant the absence of any symptoms, and 1 the entirely damaged plant. The plants scoring 6 to 9 points were considered resistant.Results and conclusions. As a result of the long-term field observations, wild potato species, represented in the current evaluation by numerous accessions, were characterized for foliar resistance to late blight; individual introductions resistant to late blight were also identified. Some of those studied in the 1980s showed high resistance in the end of the 1990s through the 2000s. The highest percentage of resistant accessions/species was identified among the species with areas of distribution in Mexico. A group of Central American species and large part of species with areas of distribution in South America expressed high level of interspecific polymorphism in foliar resistance to late blight.

Assessing Rate-Reducing Foliar Resistance to Anthracnose Crown Rot and Fruit Rot in Strawberry.

Anthracnose fruit rot and anthracnose crown rot (ACR) caused by two species complexes of the fungus referred to as Colletotrichum acutatum and Colletotrichum gloeosporioides, respectively, are major pathogens of strawberry in North Carolina. Anthracnose epidemics are common when susceptible cultivars and asymptomatic planting stocks carrying quiescent Colletotrichum infection or hemibiotrophic infection (HBI) are planted. The main objective of this study was to assess resistance to HBI and ACR in strawberry. Strawberry cultivars and breeding lines were spray inoculated with isolates of C. acutatum or C. gloeosporioides. Four epidemiological parameters providing estimates of rate-reducing resistance to HBI and ACR in strawberry cultivars and lines were evaluated in repeated experiments in controlled environments in a greenhouse. HBI severity, measured as the percentage of total leaf area covered by acervuli, was estimated visually and by image analysis. ACR severity was rated weekly for wilt symptoms, and relative area under disease progress curve scores were calculated for comparing strawberry cultivars and lines. Significant differences (P ≤ 0.005) in HBI severity were found among strawberry genotypes; however, the correlations were not remarkable between Colletotrichum species (r = 0.4251). Although significant variation in resistance was observed for ACR, this was also weakly correlated (r = 0.2430) with resistance to C. gloeosporioides HBI. Overall, rate-reducing resistance to HBI and ACR in strawberry identified in this study could be utilized in breeding programs to develop durable resistance to anthracnose in North Carolina.

Genotype × Environment Studies on Resistance to Late Leaf Spot and Rust in Genomic Selection Training Population of Peanut (Arachis hypogaea L.).

Foliar fungal diseases especially late leaf spot (LLS) and rust are the important production constraints across the peanut growing regions of the world. A set of 340 diverse peanut genotypes that includes accessions from gene bank of International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), elite breeding lines from the breeding program, and popular cultivars were screened for LLS and rust resistance and yield traits across three locations in India under natural and artificial disease epiphytotic conditions. The study revealed significant variation among the genotypes for LLS and rust resistance at different environments. Combined analysis of variance revealed significant environment (E) and genotype × environment (G×E) interactions for both the diseases indicating differential response of genotypes in different environments. The present study reported 31 genotypes as resistant to LLS and 66 to rust across the locations at 90 DAS with maturity duration 103 to 128 days. Twenty-eight genotypes showed resistance to both the diseases across the locations, of which 19 derived from A. cardenasii, five from A. hypogaea, and four from A. villosa. Site regression and Genotype by Genotype x Environment (GGE) biplot analysis identified eight genotypes as stable for LLS, 24 for rust and 14 for pod yield under disease pressure across the environments. Best performing environment specific genotypes were also identified. Nine genotypes resistant to LLS and rust showed 77% to 120% increase in pod yield over control under disease pressure with acceptable pod and kernel features that can be used as potential parents in LLS and rust resistance breeding. Pod yield increase as a consequence of resistance offered to foliar fungal diseases suggests the possibility of considering ‘foliar fungal disease resistance’ as a must-have trait in all the peanut cultivars that will be released for cultivation in rainfed ecologies in Asia and Africa. The phenotypic data of the present study will be used for designing genomic selection prediction models in peanut.

Improvement of three popular Indian groundnut varieties for foliar disease resistance and high oleic acid using SSR markers and SNP array in marker-assisted backcrossing

Foliar fungal diseases (rust and late leaf spot) incur large yield losses, in addition to the deterioration of fodder quality in groundnut worldwide. High oleic acid has emerged as a key market trait in groundnut, as it increases the shelf life of the produce/products in addition to providing health benefits to consumers. Marker-assisted backcrossing (MABC) is the most successful approach to introgressing or pyramiding one or more traits using trait-linked markers. We used MABC to improve three popular Indian cultivars (GJG 9, GG 20, and GJGHPS 1) for foliar disease resistance (FDR) and high oleic acid content. A total of 22 BC3F4 and 30 BC2F4 introgression lines (ILs) for FDR and 46 BC3F4 and 41 BC2F4 ILs for high oleic acid were developed. Recurrent parent genome analysis using the 58 K Axiom_Arachis array identified several lines showing upto 94% of genome recovery among second and third backcross progenies. Phenotyping of these ILs revealed FDR scores comparable to the resistant parent, GPBD 4, and ILs with high (~80%) oleic acid in addition to high genome recovery. These ILs provide further opportunities for pyramiding FDR and high oleic acid in all three genetic backgrounds as well as for conducting multi-location yield trials for further evaluation and release for cultivation in target regions of India.

Foliar disease resistant and productive mutants from the introgression lines of peanut (Arachis hypogaea)

AbstractWith an objective of developing the induced mutants for superior productivity and resistance to foliar diseases in peanut, two introgression lines (IL‐3 and IL‐4) derived from ABK genomes of peanut were subjected to gamma and sodium azide mutagenesis. Evaluation of M1, M2 and M3 generations could identify foliar disease resistant and productive mutants. Large‐scale evaluation of M4 mutants during the rainy season of 2017 confirmed the superiority of 12 mutants over the respective parents and the best check (GPBD 4). The selected mutants were resistant to leaf spots (early and late) and rust diseases, and significantly more productive than the parents and GPBD 4. ddRAD‐Sequencing of these mutants identified the single nucleotide polymorphisms (SNPs) when compared to their parents. The genes harbouring these structural mutations were also identified. However, no copy number variations (CNVs) were observed between the mutants and the parents. The selected mutants carried resistant‐type alleles at the marker loci linked to foliar disease resistance. These promising mutants (M8) are currently under initial trials of variety development for commercial release.

The genome of cultivated peanut provides insight into legume karyotypes, polyploid evolution and crop domestication

High oil and protein content make tetraploid peanut a leading oil and food legume. Here we report a high-quality peanut genome sequence, comprising 2.54 Gb with 20 pseudomolecules and 83,709 protein-coding gene models. We characterize gene functional groups implicated in seed size evolution, seed oil content, disease resistance and symbiotic nitrogen fixation. The peanut B subgenome has more genes and general expression dominance, temporally associated with long-terminal-repeat expansion in the A subgenome that also raises questions about the A-genome progenitor. The polyploid genome provided insights into the evolution of Arachis hypogaea and other legume chromosomes. Resequencing of 52 accessions suggests that independent domestications formed peanut ecotypes. Whereas 0.42–0.47 million years ago (Ma) polyploidy constrained genetic variation, the peanut genome sequence aids mapping and candidate-gene discovery for traits such as seed size and color, foliar disease resistance and others, also providing a cornerstone for functional genomics and peanut improvement.

Genome wide association study identifies novel single nucleotide polymorphic loci and candidate genes involved in soybean sudden death syndrome resistance.

Fusarium virguliforme is a soil borne root pathogen that causes sudden death syndrome (SDS) in soybean [Glycine max (L.) Merrill]. Once the fungus invades the root xylem tissues, the pathogen secretes toxins that cause chlorosis and necrosis in foliar tissues leading to defoliation, flower and pod drop and eventually death of plants. Resistance to F. virguliforme in soybean is partial and governed by over 80 quantitative trait loci (QTL). We have conducted genome-wide association study (GWAS) for a group of 254 plant introductions lines using a panel of approximately 30,000 SNPs and identified 19 single nucleotide polymorphic loci (SNPL) that are associated with 14 genomic regions encoding foliar SDS and eight SNPL associated with seven genomic regions for root rot resistance. Of the identified 27 SNPL, six SNPL for foliar SDS resistance and two SNPL for root rot resistance co-mapped to previously identified QTL for SDS resistance. This study identified 13 SNPL associated with eight novel genomic regions containing foliar SDS resistance genes and six SNPL with five novel regions for root-rot resistance. This study identified five genes carrying nonsynonymous mutations: (i) three of which mapped to previously identified QTL for foliar SDS resistance and (ii) two mapped to two novel regions containing root rot resistance genes. Of the three genes mapped to QTL for foliar SDS resistance genes, two encode LRR-receptors and third one encodes a novel protein with unknown function. Of the two genes governing root rot resistance, Glyma.01g222900.1 encodes a soybean-specific LEA protein and Glyma.10g058700.1 encodes a heparan-alpha-glucosaminide N-acetyltransferase. In the LEA protein, a conserved serine residue was substituted with asparagine; and in the heparan-alpha-glucosaminide N-acetyltransferase, a conserved histidine residue was substituted with an arginine residue. Such changes are expected to alter functions of these two proteins regulated through phosphorylation. The five genes with nonsynonymous mutations could be considered candidate SDS resistance genes and should be suitable molecular markers for breeding SDS resistance in soybean. The study also reports desirable plant introduction lines and novel genomic regions for enhancing SDS resistance in soybean.

Characterization of Early Blight Resistance in Potato Cultivars.

Early blight, caused by the fungus Alternaria solani, is one of the most economically important foliar diseases of potatoes worldwide. In this study, 217 tetraploid old and modern potato cultivars were evaluated for foliar resistance to early blight in field experiments in Pennsylvania in 2016 and 2017. Relative area under the disease progress curve (RAUDPC) was calculated based on visual assessment of foliar disease during the growing season each year. RAUDPC ranged from 0.0090 to 0.7372 in 2016 and from 0.0215 to 0.7889 in 2017, respectively. Significant differences in resistance to A. solani among cultivars were found (P < 0.0001). A significant interaction was found between cultivar and environment (P < 0.0001). Cluster analysis classified the cultivars into five groups: resistant, moderately resistant, intermediate, moderately susceptible, and susceptible. Broad-sense heritability for early blight resistance was estimated as 0.89 with a 95% confidence interval of 0.86 to 0.92. All cultivars were also evaluated for foliage maturity in separate field trials in 2016 and 2017, and a strong negative correlation between early blight resistance and maturity was found. Maturity-adjusted RAUDPC was calculated by regressing maturity on RAUDPC; predicted values more than two standard deviations greater or less than observed values were used to identify cultivars with greater genetic susceptibility or resistance to early blight, respectively, independent of maturity. Although most resistant and moderately resistant cultivars showed late maturity and most susceptible cultivars showed early maturity, a few exceptions were found.

QTL mapping of resistance to bacterial fruit blotch in Citrullus amarus.

Six QTLs were associated with affected leaf area in response to inoculation with Acidovorax citrulli in a recombinant inbred line population of Citrullus amarus. Acidovorax citrulli, the causal agent of bacterial fruit blotch (BFB) of cucurbits, has the potential to devastate production of watermelon and other cucurbits. Despite decades of research on host-plant resistance to A. citrulli, no germplasm has been found with immunity and only a few sources with various levels of BFB resistance have been identified, but the genetic basis of resistance in these watermelon sources are not known. Most sources of resistance are plant introductions of Citrullus amarus (citron melon), a closely related species that crosses readily with cultivated watermelon (Citrullus lanatus L.). In this study, we evaluated a recombinant inbred line population (N = 200), derived from a cross between BFB-resistant (USVL246-FR2) and BFB-susceptible (USVL114) C. amarus lines, for foliar resistance to A. citrulli in three replicated greenhouse trials. We found the genetics of BFB resistance to be complicated by strong environmental influence, low heritability and significant genotype-by-environment interactions. QTL mapping of affected leaf area identified six QTL that each explained between 5 and 15% of the variation in BFB resistance in the population. This study represents the first identification of QTL associated with resistance to A. citrulli in any cucurbit.

Evaluation of late blight foliar resistance of potato cultivars in northern Baltic conditions.

The main aim of this study was to evaluate foliar late blight resistance and yield of selected foreign and Estonian potato cultivars to determine the most promising cultivars for the northern Baltic region. We hypothesized that local cultivars have higher late blight (Phytophthora infestans) resistance and yield due to higher blight resistance. Potato late blight observation field trials were carried out in 2012 and 2013 in Einola Farm, Tartu County, Estonia. In both growing seasons, 12 potato cultivars were compared, nine from the Dutch Breeding Company Agrico and three from the Estonian Crop Research Institute. They comprised four early cultivars: Ranomi, Esmee, Romie and Maret, four early-medium cultivars: Toluca, Mariska, Madeleine and Teele and four medium-late/late cultivars: Excellency, Bellefleur, Manitou and Anti. Of these, only two, Anti and Toluca, qualified as highly foliar late blight resistant. This research clearly indicates that, despite unfavourable conditions for the pathogen, late blight is able to destroy potato foliage in most of these cultivars before the end of the growing season in northern Baltic conditions. This reflects local genetic heterogeneity of populations of P. infestans, probably associated with the presence of strains adapted to a wide range of humidity conditions. In 2012 that had late blight favourable weather, the cultivar Toluca showed high foliar blight resistance, as it reached the maximum yield compared to most other cultivars which were susceptible or very susceptible to late blight and had drastically reduced yield. However, although the late blight infection was not recorded in the growing season 2013, the cultivar Toluca did not tolerate the dry weather well and its tuber yield remained significantly lower than that in all other cultivars. Additionally, in 2013, a potato early blight (Alternaria solani) outbreak was recorded with the two most susceptible cultivars being the local cultivar Teele and the Dutch cultivar Excellency.

Genetic imprints of domestication for disease resistance, oil quality, and yield component traits in groundnut (Arachis hypogaea L.).

Ploidy difference between wild Arachis species and cultivated genotypes hinder transfer of useful alleles for agronomically important traits. To overcome this genetic barrier, two synthetic tetraploids, viz., ISATGR 1212 (A. duranensis ICG 8123 × A. ipaensis ICG 8206) and ISATGR 265-5A (A. kempff-mercadoi ICG 8164 × A. hoehnei ICG 8190), were used to generate two advanced backcross (AB) populations. The AB-populations, namely, AB-pop1 (ICGV 91114 × ISATGR 1212) and AB-pop2, (ICGV 87846 × ISATGR 265-5A) were genotyped with DArT and SSR markers. Genetic maps were constructed for AB-pop1 and AB-pop2 populations with 258 loci (1415.7cM map length and map density of 5.5 cM/loci) and 1043 loci (1500.8cM map length with map density of 1.4cM/loci), respectively. Genetic analysis identified large number of wild segments in the population and provided a good source of diversity in these populations. Phenotyping of these two populations identified several introgression lines with good agronomic, oil quality, and disease resistance traits. Quantitative trait locus (QTL) analysis showed that the wild genomic segments contributed favourable alleles for foliar disease resistance while cultivated genomic segments mostly contributed favourable alleles for oil quality and yield component traits. These populations, after achieving higher stability, will be useful resource for genetic mapping and QTL discovery for wild species segments in addition to using population progenies in breeding program for diversifying the gene pool of cultivated groundnut.

Different loci associated with root and foliar resistance to sudden death syndrome (Fusarium virguliforme) in soybean.

Different loci associated with root resistance to F. virguliforme colonization and foliar resistance to phytotoxin damage in soybean. Use of resistant cultivars is the most efficacious approach to manage soybean sudden death syndrome (SDS), caused by Fusarium virguliforme. The objectives of this study were to (1) map the loci associated with root and foliar resistance to F. virguliforme infection and (2) decipher the relationships between root infection, foliar damage, and plot yield. A mapping population consisting of 153 F4-derived recombinant inbred lines from the cross U01-390489 × E07080 was genotyped by SoySNP6K BeadChip assay. Both foliar damage and F. virguliforme colonization in roots were investigated in the field, and a weak positive correlation was identified between them. Foliar damage had a stronger negative correlation with plot yield than F. virguliforme colonization. Twelve loci associated with foliar damage were identified, and four of them were associated with multiple traits across environments. In contrast, only one locus associated with root resistance to F. virguliforme colonization was identified and mapped on Chromosome 18. It colocalized with the locus associated with foliar damage in the same environment. The locus on Chromosome 6, qSDS6-2, and the locus on Chromosome 18, qSDS18-1, were associated with resistance to SDS phytotoxins and resistance to F. virguliforme colonization of roots, respectively. Both loci affected plot yield. Foliar damage-related traits, especially disease index, are valuable indicators for SDS resistance breeding because of consistency of the identified loci and their stronger correlation with plot yield. The information provided by this study will facilitate marker-assisted selection to improve SDS resistance in soybean.

Phosphites attenuate Sclerotinia sclerotiorum-induced physiological impairments in common bean

Phosphites, marketed as foliar fertilizers and resistance activators, have been shown to be useful for the control of diseases in many profitable crops. Despite the importance of white mold, caused by Sclerotinia sclerotiorum, to reduce common bean yield, knowledge of the phosphites´ effect on disease control at the physiological level is still missing. In this study, the leaf gas exchange and chlorophyll a fluorescence parameters variable-to-maximum chlorophyll a fluorescence ratio (Fv/Fm), photochemical yield [Y(II)], yield for dissipation by down-regulation [Y(NPQ)], yield for non-regulated dissipation [Y(NO)], and electron transport rate (ETR) as well as the concentrations of photosynthetic pigments in common bean plants that were sprayed with zinc (Zn) or copper (Cu) phosphites and challenged or not with S. sclerotiorum were determined. Based on the in vitro assays, Zn and Cu phosphites inhibited fungal mycelial growth in a dose-dependent manner, but the Cu phosphite showed to be more fungitoxic. Lesion area and white mold severity were reduced by Zn and Cu phosphites, but the Zn phosphite was more effective. Fungal infection dramatically decreased the values of net carbon assimilation rate, stomatal conductance to water vapor and transpiration rate on non-sprayed plants. Increases in internal CO2 concentration indicated that fungal-induced photosynthetic impairments were chiefly governed by biochemical limitations, but these impairments were greatly abrogated in the Zn and Cu phosphite-sprayed plants. Similarly, the photochemical dysfunctions stemmed from S. sclerotiorum infection were limited in the Zn and Cu phosphite-sprayed plants. Concentrations of chlorophyll a + b and carotenoids decreased on inoculated plants, but lower reductions were recorded on Zn and Cu phosphites-sprayed plants. In conclusion, the potential of Zn and Cu phosphites in attenuate the S. sclerotiorum-induced physiological impairments in common bean leaflets was demonstrated and may be an effective mean for managing this disease under field conditions.

Temporal Dynamics of Fusarium virguliforme Colonization of Soybean Roots.

Soybean sudden death syndrome (SDS) caused by Fusarium virguliforme is one of the most yield limiting soybean diseases in the United States. SDS disease symptoms include root rot and foliar symptoms induced by fungal toxins. Soybean cultivar resistance is one of the most effective SDS disease management options, but no cultivar displays complete resistance. Soybean SDS foliar symptoms are the primary phenotype used to screen and breed for SDS resistance. Root rot or root colonization measures are seldom utilized, partly due to the lack of convenient and accurate methods for quantification of F. virguliforme. In this study, greenhouse and field experiments were conducted to determine the temporal dynamics of F. virguliforme colonization of soybean roots using quantitative real-time PCR (qPCR). The infection coefficient (IC), or ratio of F. virguliforme DNA to soybean DNA, was determined in soybean cultivars with different SDS foliar resistance ratings. In greenhouse experiments, F. virguliforme was detected in all cultivars 7 days after planting (DAP), with a peak in IC at 14 DAP. All soybean cultivars developed SDS foliar symptoms, but F. virguliforme soybean root colonization levels did not significantly correlate with SDS foliar symptom severity. In field experiments, SDS foliar symptoms developed among soybean cultivars in alignment with provided foliar resistance ratings; however, the F. virguliforme IC were not significantly different between SDS foliar symptomatic and asymptomatic cultivars. F. virguliforme was detected in all cultivars at the first sample collection point 25 DAP (V3 vegetative growth stage), and the IC increased throughout the season, peaking at the last sample collection point 153 DAP (postharvest). Collectively, appearance and disease severity ratings of SDS foliar symptoms were not associated with F. virguliforme quantity in roots, suggesting a need to include F. virguliforme root colonization in breeding efforts to screen soybean germplasm for F. virguliforme root infection resistance. The findings also demonstrates root colonization of the pathogen on nonsymptomatic soybean cultivars leading to persistence of the pathogen in the field, and possible hidden yield loss.