Phoma Macdonaldii Research Articles

Occurrence of Phoma macdonaldii, the Causal Agent of Sunflower Black Stem Disease, in Sunflower Fields in China.

Phoma macdonaldii Boerma is the pathogen of sunflower black stem disease, causing dark black, oval to long lesions on stems of sunflower plants. Infection during early growth stages can reduce yield by 10 to 30% (3). This fungal disease is distributed mainly in North and South America and Europe. In China, the first case was reported in Xinjiang in 2008 (1), and was believed to be introduced as a result of hybrid sunflower seeds being imported from abroad. The Chinese government included this fungus into its quarantine pests list in 2010 (2). Since China imports a great number of sunflower seeds to grow in its Northern provinces from epidemic areas such as the United States, Argentina, and France, monitoring the disease occurrence in planting areas became crucial. During 2010 and 2011 growing seasons, surveys were conducted in 37 commercial farms or individual households in 12 counties of five areas (Xinjiang, Inner Mongolia, Ningxia, Hebei, and Beijing). A total of 185 suspicious samples of sunflower black stem disease were collected and all were found from imported hybrid seed fields. The presence of P. macdonaldii was confirmed as following: 4 mm2 tissue pieces cut from lesion margins were disinfected with 1% NaOCl, plated on APDA (acid potato dextrose agar, 4.5 to 5.0 pH adjusted with lactic acid), and incubated at 25°C with 12L:12D photoperiod. After 3 days of incubation, colonies were opalescent or ivory in color, and fluffy or flocculent in appearance. After 4 to 6 days, a large number of spherical or oblate black-brown pycnidia were formed separately or in clusters with thin wall and papillate ostiole in diameter of 135 to 324 μm (average 178 μm). A light pink or opalescent gelatinous substance (pycnidiospores) exuded from the ostiole. Pycnidiospores were single celled, oval or kidney-shaped and hyaline both with and without oil balls, and 1.5 to 3.0 μm × 3.0 to 6.5 μm (average 2.0 × 4.7 μm). Sequences of ITS1-5.8S- ITS2 rDNA fragment of all isolates (GenBank Accession No. JQ979487, JQ979488) were identical and had 100% homology with P. macdonaldii isolates from Xinjiang (HM003206) and Australia (DQ351823, DQ351825) and 99% homology with isolates from the former Yugoslavia (DQ351821, DQ351822) in GenBank. Pathogenicity studies of the isolate were performed by injecting 10 × 106/ml spore suspension into the hypocotyl of four true leaves of sunflower seedlings with a syringe. Sterile water was injected as control. After being inoculated in a plastic bag in the shade at room temperature for 48 h, the plastic bag was removed and the seedlings were grown under natural light. Symptoms of black stem disease were observed in all P. macdonaldii inoculated seedlings and the fungus was reisolated from the lesions for confirmation. The current survey found that 105 of 185 suspicious samples were P. macdonaldii positive and were all from four counties in Xinjiang, suggesting that the disease has not spread to other areas since its introduction. The monitoring of sunflower black stem disease is continuing, as is the research for measuring P. macdonaldii adaptability in China and the development of rapid molecular detection technology.

Low plant density can reduce sunflower premature ripening caused by Phoma macdonaldii

In France, premature ripening (PR) is a widespread damage of a fungal disease of sunflower caused by Phoma macdonaldii. Previous results indicated that girdling canker at the stem base, caused by P. macdonaldii, was its primary cause. Previous studies have reported the influence of nitrogen and water supply on the incidence and severity of PR but an additional study was required to analyze the effect of plant density on the level of attack for a more comprehensive cultural control of PR.In a 2-year field study (2008 and 2009) in Toulouse (France), a susceptible cultivar (cv. Heliasol) artificially inoculated at star bud stage with P. macdonaldii was grown at three plant densities (4, 6.5 and 9plantsm−2) factorially combined with three N fertilization rates (0, 50/75 and 150kgNha−1) and two water regimes (irrigated and rainfed). P. macdonaldii symptoms were scored weekly to calculate the area under disease progress curve (AUDPC) and percentage of PR plants. Microclimatic conditions were monitored using thermo-hygrometers within the crop. The fraction of photosynthetically active radiation intercepted by the canopy (fPARi) and leaf area index (LAI) were measured at anthesis. Plant water status during the disease progression was characterized by crop simulation (SUNFLO) and N status at anthesis was assessed from shoot N content (Nm) analysis and N Nutrition Index (NNI) calculation.Increasing plant density resulted in a greater proportion of PR plants, and this proportion increased further when N was applied at 150kgha−1, the highest rate, and the crop was not irrigated. Despite differing canopy development, differences in microclimatic conditions between density levels were too small to explain the PR differences. However plant N concentration and diameter at stem base were closely related to PR incidence. Thin plants (grown at high density) with non-limiting N supply were the most susceptible to premature ripening.This study opens new avenues for the control of PR through crop management and emphasizes the key role of plant morphology in the development of the disease. Stem base diameter is a morphological trait that could be manipulated through crop management (plant density, N fertilization) and probably breeding in the future when developing integrated disease management systems in sunflower.

Identification of Phoma macdonaldii Boerema causing black stem of sunflower in China

A severe disease was observed on sunflower (Helianthus annuus L.) in Ili, Xinjiang China, in 2005. The causal agent was isolated from infected tissues, and its pathogenicity confirmed. Pathogenicity tests showed that the fungus could infect sunflower, which developed the same symptoms under artificial inoculation conditions to those observed in the field. The fungus was identified based on morphological and cultural characteristics as Phoma macdonaldii Boerema. Identifications were confirmed by comparison of the 18S rDNA partial sequence, 28S rDNA partial sequence, and the internal transcribed spacer (ITS) regions 1 and 2, including 5.8S rDNA (ITS1‐5.8S-ITS2). This is the first report of black stem of sunflower caused by P. macdonaldii in China.

Sunflower Diseases Remain Rare in California Seed Production Fields Compared to North Dakota

The majority of United States sunflower production is in seven Midwestern states, but hybrid planting seed is almost exclusively produced in California. Due to the lack of summer rains and furrow irrigation, California-produced seed is relatively disease free and thus it regularly meets phytosanitary restrictions imposed by many countries. For the 15-year period from 1997 to 2011, 7231 seed fields in northern California were inspected and samples processed at the state diagnostic laboratory (California Department of Food and Agriculture). Rust (Puccinia helianthi) was the most prevalent quarantine disease, found in 4.3% of fields. Stalk rot (Sclerotinia sclerotiorum) and downy mildew (Plasmopara halstedii) were the only other quarantine pathogens observed, found in 2.6% and 0.5% of the 7231 fields, respectively. Many sunflower pathogens have never been recorded in California, including Phoma macdonaldii, Phomopsis helianthi, or any virus. North Dakota, the state with the highest US sunflower production, had quarantine pathogens in 88% of 1263 fields surveyed from 1995 to 2011. Phoma macdonaldii, Sclerotinia sclerotiorum, Puccinia helianthi, Phomopsis helianthi, Plasmopara halstedii, and Verticillium dahliae were recorded in 62, 54, 37, 33, 14, and 12%, respectively, of North Dakota fields. Accepted for publication 5 November 2012. Published 14 December 2012.

Detection and identification of Phoma macdonaldii in sunflower seeds imported from Argentina

China has been importing sunflower hybrid seeds for commercial planting from other countries in recent years. Tianjin Entry-Exit Inspection and Quarantine Bureau isolated nine fungal strains similar to Phoma macdonaldii, which causes black stem, from Argentine sunflower seeds. Isolations were made from the debris in with seed not from the seed were slow-growing on PDA, velutinous or flocculent form, irregular on the edge, milk white to ivory color. These isolates were observed for appearance of pycnidia containing guttulate conidia on PDA and on sterile filter paper. DNA extractions from mycelia of the isolates were amplified by ITS1/ ITS4 and ActF1/R1 primers. Compared with the sequences in the NCBI database, these sequences had a similarity of 98–100% with Phoma macdonaldii. All isolates were tested on four true-leaf sunflower seedlings using hypocotyls inoculation. Typical black oval lesions were found on the stem after 7 d and black pycnidia were found on the lesions. Based on the morphological characteristics, sequences analysis and pathogenicity test, these nine isolates were identified as Phoma macdonaldii. This is the first intercept record of Phoma macdonaldii from imported sunflower seeds in China.

Influence of soil tillage and Phoma macdonaldii on sunflower (Helianthus annuus L.) yield and oil quality

Influence of soil tillage and Phoma macdonaldii on sunflower (Helianthus annuus L.) yield and oil quality

Evaluation of Inoculation Methods to Reproduce Sunflower Premature Ripening Caused by Phoma macdonaldii.

Three inoculation methods were evaluated for effectiveness to cause sunflower premature ripening (PR). Evaluations were conducted on a sunflower (Helianthus annuus) cultivar susceptible to PR in replicated, multilocation experiments under greenhouse conditions. Plants were inoculated with Phoma macdonaldii, either with mycelium, conidia, or infected residues at the stem base or with buried residues. Disease severity (DS) was measured by percent girdling necrosis at the stem base and percent final PR; the infection spread was assessed using the area under the disease progress curve (AUDPC). Inoculation with mycelia or 1 × 106 spores/ml caused significantly more DS and PR than lower spore concentrations or infected residues (P < 0.05). Amending soil with residues induced root necrosis but no PR. P. macdonaldii was mainly isolated at the stem base and above but rarely on root systems. Microscopic evaluations showed that hyphae colonized mainly the cortex and vascular stem tissues. The overall results demonstrated a clear role of aerial infection in PR compared with soilborne inoculum, and that inoculation at the stem base with a spore suspension could be used for screening genotypes for resistance to PR.

The resistance response of sunflower genotypes to black stem disease under controlled conditions

Phoma black stem, caused by Phoma macdonaldii , is one of the most important diseases of sunflower in the world. The sources of resistance to Phoma black stem were investigated. A total of 184 genotypes, including some recombinant inbred lines (RILs), several M6 mutant lines obtained by gamma irradiation of seed of the genotype AS 613, and other genotypes from different countries, were evaluated against an aggressive French isolate (MP6) in controlled conditions. The study was carried out in a randomized complete block design with three replicates. Each replicate consisted of 10–12 seedlings. Twenty μL of spore suspension (106 pycnidiospores mL-1) were deposited on the intersection of the cotyledon petiole and the hypocotyl of sunflower plantlets at the two-leaf stage. The percentage of the area exhibiting disease symptoms was scored on the two cotyledon petioles of each of the plantlets three, five and seven days after inoculation. The disease progress rate (rd), as the slope of the regression line for disease severity against time, was also calculated. Analysis of variance detected significant differences among sunflower genotypes for disease severity 7 days after inoculation, as well as for the disease progress rate. A strong correlation (r=0.96, P <0.01) was found between disease severity 7 days after inoculation and the disease progress rate. The inbred lines F1250/03 (origin: Hungary), M5-54-1, M6-862-1 (mutant lines), SDR 18 (origin: USA) and two wild Helianthus accessions, 1012 Nebraska and 211 Illinois, (wild type) were highly resistant to Phoma black stem. These findings will assist breeders in choosing parent plants for breeding durable resistance to Phoma black stem.

Assessment of sunflower genotype tolerance to Phoma macdonaldii

Sunflower genotypes with differing susceptibility to <i>Phoma macdonaldii<i/>, the causal agent of sunflower black stem disease, were inoculated artificially with an aggressive fungal strain according to various modalities. A first series of experiments carried out in a greenhouse on plants at various phenological stages (2-leaf pairs, 5-6 leaf pairs, budding and early flowering) showed that the behaviour of sunflower cultivars, distributed into different susceptibility groups, remained unchanged irrespective of the phenological stage reached at the time of the inoculation. The development of the symptoms varied with genotype susceptibility to the disease: it was fast with coalescing necrotic spots on the stems for the most susceptible cultivars. The intensity and the development rate of the symptoms were also increased when the inoculation had been carried out at later stages. Two additional series of experiments were carried out in the field. In each series, a first block accounted for natural contaminations and a second block was inoculated artificially. The development of the symptoms and the susceptibility groups within the two blocks were identical to those observed in the greenhouse. These results led to the validation of an early inoculation test, at the cotyledon stage, which accounts satisfactorily for the behaviour of sunflower cultivars under natural conditions and is thus likely to be used in breeding programs.

Phoma du tournesol et dessèchement précoce : point sur les avancées de la recherche

Phoma macdonaldii is the causal agent of black stem disease of sunflower (Helianthus annuus L). In France, the incidence and severity of the disease increased dramatically in the early 90s and the entire sunflower cropping area is now affected. Premature ripening appeared in 1994: it is at the present time one of the most widespread and detrimental diseases of sunflower. Recent investigations confirmed that stem base girdling canker due to P. macdonaldii is the primary cause of this syndrome. Crop management and varietal susceptibility can influence significantly the incidence and severity of P. macdonaldii attacks and premature ripening. Partial resistance and presence of tissue-specific resistance genes have also been demonstrated.

Nitrogen and water management can limit premature ripening of sunflower induced by Phoma macdonaldii

Premature ripening (PR) is one of the most important diseases of sunflower in France since the 90s. Previous results indicated that girdling canker of the stem base, caused by Phoma macdonaldii was its primary cause but elucidation of critical environmental factors involved is crucial for better control of the disease. A field study was conducted in three contrasting cropping seasons (2006–2008) and investigated the effect of N fertilization (0, 75 and 150 kg N ha −1) and water regime (rainfed, irrigated) on two cultivars with artificial inoculation (AI) and natural infection (NI). Disease assessment was recorded weekly to calculate the area under disease progress curve (AUDPC) and the final percentage of PR plants. Data showed that high levels of N fertilization led to significantly ( P < 0.05) more PR than non-fertilization. Water deficit conditions were significantly ( P < 0.05) involved in disease severity, and AUDPC and PR were increased when dry conditions were associated with high N supply. This was true for two cultivars which differed in their susceptibility to the disease but cv. Heliasol RM was significantly ( P < 0.05) more affected than cv. Melody, partially resistant to PR. Despite contrasting weather patterns, these results demonstrated a clear role of crop management and environmental conditions on the incidence and severity of stem base attacks responsible for the PR syndrome. These findings suggest that sunflower crop husbandry should be adapted to minimize premature ripening induced by P. macdonaldii.

Characterisation of sunflower root colonisation by Phoma macdonaldii

Phoma macdonaldii, the causal agent of black stem disease of sunflower (Helianthus annuus), also attacks roots and collars of the plants, resulting in early death. Totally resistant lines do not exist for infection of the aerial parts, but tolerant lines have been characterised. This paper presents a study on colonisation of a partially resistant and a susceptible sunflower line by P. macdonaldii. The fungus was transformed with a constitutively expressed reporter gene encoding the jellyfish green fluorescent protein via Agrobacterium tumefaciens, and colonisation of sunflower roots by this transformed strain was studied by various microscopy techniques including confocal and scanning electron microscopy. The results show that penetration of the fungus into the root occurred through natural fissures or through the epidermis and was similar in both lines. In contrast, the colonisation rate of the stele was reduced in the partially resistant line, and the morphology of the fungal hyphae was also affected. The effect on hyphal morphology was strongest in the stele, indicating a localised production of defence compounds in this line.

Genetic variation and identification of molecular markers associated with partial resistance to Phoma macdonaldii in gamma-irradiation-induced mutants of sunflower

A study was undertaken to evaluate the genetic variability among gamma-irradiation-induced sunflower mutants for partial resistance to phoma black stem, caused by Phoma macdonaldii, and to identify putative molecular markers associated with partial resistance. A population of 60 mutant lines and the original line AS613 were evaluated with an aggressive French isolate of P. macdonaldii (MP6) under controlled conditions. Mutants with partial resistance to phoma black stem were identified. Variance in partial resistance and molecular markers, generated with 17 amplified fragment length polymorphism (AFLP) primer combinations, were estimated. Genetic analysis revealed that partial resistance in the mutant line M6-54-1 was controlled by recessive gene(s). The F1 hybrid (developed by crossing M6-54-1 with a susceptible inbred ENSAT-B4) was, however, significantly less susceptible than the susceptible parent, indicating that the difference between the F1 hybrid and its parents in reaction to phoma black stem cannot be fully explained by the recessive gene model. Dominance between alleles (epistasis) caused reduced susceptibility in the F1 progeny, which were also clearly reflected in distributions of phenotypic reactions of F2 and backcross seedlings. Generation mean analysis confirmed that epistatic effects contributed significantly to genetic variation in phoma black stem resistance in M6-54-1. Using multiple regression analysis, eight AFLP markers associated with partial resistance to phoma black stem were identified. Predicted reactions of all mutants to the disease based on their marker profiles were not significantly different from the observed values. The same AFLP primer combinations were used to map quantitative trait loci in the F2 population and F3 families, and one AFLP marker (E33M61-11) was found to be tightly linked to phoma black stem susceptibility.

Chemical composition and antifungal activity of Salvia sclarea (Lamiaceae) essential oil

Clary sage (Salvia sclarea L.) is native to Southern Europe and is cultivated worldwide. The essential oil of clary sage was analyzed as a potential antifungal agent. The main compounds in the oil were linalyl acetate (52.83%) and linalool (18.18%). Food poisoning agents, spoilage fungi, and plant and animal pathogens were among the tested fungal species. The microdilution method was used to establish minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC). The commercial antimycotic bifonazole was used as a control. A concentration of 25 ?l/ml showed fungicidal activity against Aspergillus, Penicillium, and Fusarium species and Trichoderma viride. For the species Mucor mucedo and Aspergillus viride, the MFC was 15?l/ml; for Candida albicans, it was 10 ?l/ml, as in the case of bifonazole. Fungistatic and fungicidal activities of the oil against Cladosporium cladosporioides and Trichophyton menthagrophytes were recorded at concentrations of 2.5 ?l/ml and 5 ?l/ml. The most sensitive micromycetes were Cladosporium fulvum, Alternaria alternata, Phomopsis helianthi, and Phoma macdonaldii, where a concentration of 2.5 ?l/ml was lethal.

Differential expression of defence-related genes between compatible and partially compatible sunflower– Phoma macdonaldii interactions

A population of 120 sunflower mutant lines (M6), developed by seed irradiation with γ-rays, and their original line (‘AS-613’) was evaluated with an aggressive French isolate of Phoma macdonaldii (‘MP6’). Four mutant lines as well as the original line were chosen and their reactions evaluated against seven P. macdonaldii isolates. Contrast interactions in the response of the original line ‘AS613’ and its mutant line ‘M6-54-1’ versus two Phoma black stem isolates ‘MA6’and ‘MP8’ were observed. The mutant line also showed partial resistance to the ‘MP10’ isolate. These six line/isolate combinations were used to assess the profile of 12 genes potentially associated with the partial resistance of sunflower to P. macdonaldii using quantitative real-time RT-PCR. Five genes out of 12 showing changes in gene expression less than 2.0-fold were excluded from statistical analysis. The expression of three out of seven genes was found to be up-regulated by infection. Genes encoding for phenylalanine ammonia-lyase 2 (PAL2) and a thaumatin-like protein, showed significant differences in expression between partially compatible and compatible interactions of the original line and its mutant challenged by ‘MP8’ and ‘MA6’ isolates, so that the degree of induction was higher in the partially compatible interaction than in the compatible ones. No significant difference in gene expression level of the above-mentioned genes was observed between the original line and its mutant contaminated by the ‘MP10’ isolate. The expression of four out of seven genes was down-regulated in both lines across three isolates. A straightforward correlation between expression levels of genes encoding for the HD-Zip transcription factor and protein phosphatase and disease symptoms was observed in the original line and its mutant challenged by the ‘MA6’ isolate so that the degree of repression was higher in the partially compatible interaction than in the compatible ones. This suggests an active inhibition of host genes upon pathogen infection.

Genotype‐isolate interaction for resistance to black stem in sunflower (Helianthus annuus)

Two experiments were undertaken to determine the partial resistance of sunflower genotypes to seven isolates of Phoma macdonaldii. In the first experiment, 28 genotypes, including recombinant inbred lines and their parents, M6 mutant lines developed by gamma irradiation, and some genotypes from different geographical origins, were used. The experiment consisted of a split‐plot design with three replications, each with 12 seedlings per genotype per isolate, in controlled conditions. Seven days after inoculation, plantlets were scored on a 1–9 scale for percentage necrotic area. Highly significant differences were observed among genotypes, isolates and their interactions. The presence of a differential interaction between genotypes and P. macdonaldii isolates was confirmed in a second experiment using 12 genotypes representing large variability for partial resistance to P. macdonaldii isolates, as identified in the first experiment. Inbred lines B454/03, ENSAT‐B5 and LC1064C were the most susceptible sunflower genotypes, whereas two American lines SDR19 and SDR18 presented high partial resistance to all P. macdonaldii isolates studied. The least and most aggressive isolates were MA6 and MP3, respectively. Isolates interacted differentially with sunflower genotypes. This study identified two genotypes (AS613 and PAC2) presenting specific resistance to isolate MP8. The results also showed a wide range of isolate‐nonspecific partial resistances among the lines tested. The information presented here could assist sunflower breeders to choose parents of crosses for breeding of durable resistance to phoma black stem disease.

Quantitative trait loci associated with isolate specific and isolate nonspecific partial resistance to Phoma macdonaldii in sunflower

Black stem, caused by Phoma macdonaldii , is one of the most important diseases of sunflower in the world. Quantitative trait loci (QTLs) implicated in partial resistance to two single pycnidiospore isolates of P. macdonaldii (MP8 and MP10) were investigated using 99 recombinant inbred lines (RILs) from the cross between sunflower parental lines PAC2 and RHA266. The experimental design was a randomized complete block with three replications. High genetic variability and transgressive segregation were observed among RILs for partial resistance to P. macdonaldii isolates. QTL-mapping was performed using a recently developed high-density SSR/AFLP sunflower linkage map. A total of 10 QTLs were detected for black stem resistance. The phenotypic variance explained by each QTL (R 2 ) was moderate, ranging from 6 to 20%. Four QTLs were common between two isolates on linkage group 5 and 15 whereas the others were specific for each isolate. Regarding isolate-specific and isolate-nonspecific QTLs detected for partial resistance, it is evident that both genetic effects control partial resistance to the disease isolates. This confirms the need to consider different isolates in the black stem resistance breeding programmes. The four SSR markers HA3700, SSU25, ORS1097 and ORS523_1 encompassing the QTLs for partial resistance to black stem isolates could be good candidates for marker assisted selection.

Genetic analysis of partial resistance to black stem (Phoma macdonaldii) in sunflower as measured by a seedling test

AbstractPhoma black stem caused by Phoma macdonaldii is one of the most important diseases of sunflower in France. To determine the inheritance of partial resistance to the disease, five sunflower genotypes with a wide range of genetic variability for partial resistance were crossed in diallel fashion. Resistance was measured as reaction of seedlings to infection by P. macdonaldii. Two separate experiments were undertaken in a controlled growth chamber. In each experiment the parental genotypes and their F1 hybrids were inoculated by one of the two selected isolates (MP8 and MP10). Analysis of variance for each of two isolates showed significant variability among parents and F1 hybrids for disease severity score. Combined analysis of variance detected significant interactions between sunflower genotypes and Phoma isolates, suggesting that partial resistance to Phoma black stem should be isolate‐specific. General and specific combining ability effects for resistance to Phoma black stem were highly significant for each of the two isolates, indicating that both kinds of gene effect were important in controlling the inheritance of partial resistance to Phoma black stem. On the basis of the results from this seedling test, the cross between M6‐54‐1 and ENSAT‐R5 genotypes, which are the best general combiners for MP8 and MP10, respectively, could be of value in improving black stem partial resistance to these P. macdonaldii isolates.

Genetic control of partial resistance to ‘collar’ and ‘root’ isolates of Phoma macdonaldii in sunflower

Phoma macdonaldii is one of the most important pathogens of sunflower (Heliantus annuus) in France. In order to determine the inheritance of resistance to the disease, five sunflower genotypes with wide genetic variability for resistance to two ‘collar’ and two ‘root’ Phoma isolates were crossed in a diallel programme. Four separate experiments were undertaken under controlled conditions. In each one, the response of parental genotypes and their F1 hybrids were evaluated with one of the four Phoma isolates. Analysis of variance was performed to determine the effects of genotype on disease severity score when inoculated with ‘collar’ or ‘root’ Phoma isolates and showed significant variability among parents and F1 hybrids for disease severity score. Diallel analysis showed that general combining ability (GCA) and specific combining ability (SCA) effects for resistance to ‘collar’ and ‘root’ Phoma isolates were highly significant for each of the four isolates indicating that both kinds of gene effects were important in controlling the resistance. The GCA/SCA ratios were more than one for three out of four isolates showing that additive genetic effects were more important than non-additive effects for resistance to three of the studied Phoma isolates. Hence, conventional breeding methods could be recommended to achieve genetic improvement to such ‘collar’ and ‘root’ Phoma isolates.

QTL mapping of partial resistance to Phoma basal stem and root necrosis in sunflower ( Helianthus annuus L.)

Phoma macdonaldii infects different tissues of sunflower and causes reduction in yield and oil content. The aim of present research was to identify genomic regions involved in partial resistance of sunflower to four Phoma macdonaldii basal stem and root necrosis isolates using our improved map constructed with 191 SSR and 304 AFLP markers. The experiment was conducted using F9 recombinant inbred lines (RILs) from a cross between ‘PAC2’ and ‘RHA266’. Results showed that ‘PAC2’ was more resistant than ‘RHA266’ to basal stem necrosis isolate ‘TA6’ and root necrosis isolate ‘TA4’. By contrast ‘RHA266’ was more resistant than ‘PAC2’ to basal stem necrosis isolate ‘TA9’ and root necrosis isolate ‘TA2’. Transgressive segregation was observed for partial resistance to all four isolates. Some recombinant lines presented partial resistance or susceptibility to all isolates. Twenty-seven QTL with phenotypic variance ranging from 7 to 29% were detected. Among them 13 were ‘isolate-specific’ and others were common for partial resistance to different isolates (isolate-non-specific). Most of the QTLs in common have major effects for resistance to each isolate. The ‘isolate-non-specific’ QTLs were located on linkage groups (LG) 5, 6, 8, 12, 13 and 15. The markers ‘HA3555’ on LG12 and ‘E33M48_26’ on LG6 as well as ‘E33M48_20’ on LG13, which are each linked to QTLs of different basal stem and root necrosis isolates, could be used in marker-assisted selection to introduce tolerance to four Phoma macdonaldii isolates into elite sunflower breeding lines.