Evaluation of Differential Lines and a Collection of Sunflower Parental Lines for Resistance to Broomrape (Orobanche cernua) in Spain

Broomrape (Orobanche cernua Loelf.) is a sunflower parasite which has become a potential threat to this crop in Spam with an increasing incidence in recent last years. In order to investigate the racial situation of the parasite in Spam and to evaluate the resistance of differentials and inbred lines currently used in breeding programmes, two experiments were carried out. In the first, two sets of European sunflower differentials were inoculated with three broomrape populations from different geographical origin. The second experiment studied the reaction to the parasite of 38 inbred lines in comparison with resistant and susceptible checks. Reactions of differential lines resistant to known European broomrape races ranged from complete immunity of lines P-1380-2A and ‘Jdanovski 8281’ to complete susceptibility of ‘Record’ and the universal suscepts. These results confirmed the existence of several physiological races of broomrape in Spain and a different racial composition from that of Eastern Europe. Results from the second experiment showed good resistance of half the restorer lines tested and 36 % of the maintainers and cms lines. This material together with the resistant differential lines constitutes good starting material to be used in developing cultivars resistant to broomrape populations in Spain.     

Inheritance of resistance to race F of broomrape in sunflower lines of different origins

A new race F of broomrape overcomes all known resistance genes in cultivated sunflower, but recently, sources of resistance against race F have been developed. The objective of the present research was to study the inheritance of resistance to race F in crosses between 12 resistant sunflower breeding lines, derived from three different sources of resistance, and the susceptible male‐sterile line P‐21. Parental lines and F₁, F₂, F₃ and BC₁ generations were evaluated for broomrape resistance. Segregations in the F₂ and BC₁ to resistant parent approached resistant to susceptible ratios of 1: 15 and 1: 3, respectively, in most of the crosses, suggesting a double dominant epistasis. However, segregations of 3: 13 and 1: 1 for F₂ and BC₁, respectively, indicating a dominant‐recessive epistasis, were also found. The F₃ data confirmed these results. Owing to the recessive nature of this resistance, it must be incorporated into both parental lines for developing resistant hybrid cultivars.     

Inheritance of resistance to broomrape (Orobanche cumana Wallr.) race F in a sunflower line derived from wild sunflower species

Genetic resistance to broomrape (Orobanche cumana Wallr.) race F in sunflower line J1, derived from the wild perennial species Helianthusgrosseserratus Martens and Helianthus divaricatus L., has been reported to be controlled by dominant alleles at a single locus, Or6. However, deviations from this monogenic inheritance have been observed. The objective of the present study was to gain insight into the inheritance of resistance to broomrape race F in the sunflower line J1. F₁, F₂, F₃ and BC generations from crosses between J1 and three susceptible lines, P21, NR5 and HA821 were evaluated. F₁ hybrids showed both resistant (R) and moderately resistant (MR) plants, the latter having a maximum of five broomrape stalks per plant compared with >10 in the susceptible parents. This indicated incomplete dominance of the Or6 alleles. F₂ plants were classified as R, MR or susceptible (more than five broomrape stalks per plant). Three different segregation ratios were observed: 3 : 1, 13 : 3 and 15 : 1 (R + MR : S), suggesting the presence of a second gene, Or7, whose expression was influenced by the environment. A digenic model was confirmed, based on the evaluation of F_2:3 families.     

R-41, a sunflower restorer inbred line, carrying two genes for resistance against a highly virulent Spanish population of Orobanche cernua

The inheritance of resistance to a highly virulent population of sunflower broomrape (Orobanche cernua) has been studied in R-41, a Spanish sunflower restorer inbred line. Using the cytoplasmic male-sterile inbred line HA-89 (cms; very susceptible to this population of broomrape) as a female parent, progenies of the cross with R-41, i.e. Fl, F2 and BC1 to both parents, as well as the parental lines, were analysed for their reaction to the broomrape population EC-94. The goodness of fit of the observed vs expected segregation ratios indicated that the inheritance of resistance to broomrape in line R-41 is conferred by two independent dominant genes.     

Reproductive behaviour and broomrape resistance in interspecific hybrids of sunflower

Interspecific hybrids and backcross generations between the wild perennial species Helianthus resinosus, Helianthus paucifiorus, Helianthus laevigatus, Helianthus nuttallii ssp. nuttallii T. & G. and Helianthus giganteus, resistant to broomrape (Orobanche cernua) and susceptible inbred lines were obtained to study crossability to cultivated sunflower and the transmission and expression of resistance to this parasitic weed. Conventional crosses with all the species tested were successful except for the crosses with diploid H. giganteus, for which embryo rescue techniques were needed to overcome hybrid incompatibility. Pollen viability and seed set were highest for F₁ hybrids with hexaploid species and lowest for those with the diploid H. giganteus. We evaluated F₁, BC₁F₁, some BC₂F₁ plants and the wild and cultivated parents. The wild species and interspecific hybrids were resistant to broomrape infection except for H. nuttallii, which showed segregation, indicating that the resistance is dominant. The crossability and resistance of F₁, and back-cross generations of species with different ploidy levels indicate that the transfer of broomrape resistance to cultivated sunflower is feasible.     

Resistance in two Lycopersicon species to an Arkansas isolate of tomato spotted wilt virus

Summary Tomato spotted wilt virus (TSWV) was obtained from infected tomatoes in commercial fields in Arkansas in 1985. A greenhouse screening procedure for identifying tomatoes resistant to TSWV was established using an enzyme-linked immunosorbent assay (ELISA) to detect infected plants. Symptom expression was variable and symptom expression was not reliable for identifying infected plants. Germplasm evaluated for resistance to one typical Arkansas isolate (85–9) of TSWV included: twenty cultivars and breeding lines of Lycopersicon esculentum Mill, 52 accessions of L. pimpinellifolium (Jusl.) Mill and 8 accessions of L. peruvianum (L.) Mill. All cultivated accessions and breeding lines evaluated were susceptible. Some individual plants in several accessions of L. pimpinellifolium were resistant and nearly all plants of the L. peruvianum accessions that were evaluated were resistant to isolate 85–9.Dept. of Plant Pathology     

Sources of resistance to broomrape (Orobanche crenata Forsk.) in narbon vetch

Little is known about the levels of resistance to Orobanche crenata available in narbon vetch. A germplasm collection of 200 accessions of narbon vetch (Vicia narbonensis L.) originating from different countries was screened for resistance to crenate broomrape under field conditions. Thirteen accessions were selected for more detailed screening under controlled conditions and for additional field testing. Resistance to O. crenata was manifested by lower germination of broomrape seeds, reduced emergence of Orobanche shoots and fewer root attachments per narbon vetch plant. Differences in pod yield among narbon vetch accessions were also found in response to Orobanche infestation. Finally, eight accessions were selected and identified as new sources of narbon vetch resistant to broomrape.     

Inheritance of resistance to race 330 of Plasmopara halstedii in three sunflower lines

Sunflower lines RHA‐274, HA‐61 and RHA‐325 were studied for their resistance to race 330 of downy mildew (Plasmopara halstedii). The same inbred line, with normal (HA‐89) or sterile cytoplasm (cmsHA‐89) was used in all the crosses as susceptible parent, and, in each cross, only one genotype of the resistant parent was studied. The resistant‐to‐susceptible ratios obtained in the BC₁ and F₂ progenies from the crosses of the lines RHA‐274 and HA‐61 to cmsHA‐89 and HA‐89, respectively, suggested that, in each resistant line, two dominant genes are responsible for resistance to this downy mildew race. One of the genes (A) is epistatic to the other (B), and the recessive allele b in homozygosity is also epistatic to aa, with plants carrying aabb genotypes being resistant. Resistance to race 330 seemed to be controlled by two complementary genes in the sunflower inbred line RHA‐325, the dominant allele of one of them being present in cmsHA‐89. In the genotypes HA‐89 or cmsHA‐89, the existence of genes that modify the expected segregations following the crosses with resistant parents is proposed. It is concluded that, although major genes have been described as responsible for monogenic resistance to downy mildew, other types of regulation of this character, such as complementarity and epistatic relationships, do occur.     

Inheritance of resistance to Pyrenochaeta lycopersici in tomato

Summary Tomato accessions (Lycopersicon sp.), along with commercial cultivars and breeding lines were grown in a field infested with the brown root rot (BRR) organism, Pyrenochaeta lycopersici and evaluated for resistance. Three L. esculentum Mill. accessions, P.I. 260397, P.I. 262906 and P.I. 203231, were resistant and were used as male parents in crosses designed to transfer resistance to tomatoes of fresh market type. Through analysis of parental generations and F₁ and F₂ progenies from three crosses the heritability of resistance in the broad sense was estimated to range from 25 to 43 percent. The minimum number of genes influencing resistance was estimated to be from 4 to 8.Florida Agricultural Experiment Stations Journal Series Paper no. 317.     

Resistance to Sclerotinia sclerotiorum of 'high oleic' sunflower inbred lines

Cultivation of sunflower (Helianthus annuus L.) is strongly affected by Sclerotinia sclerotiorum. To identify new sources of genetic diversity for sunflower breeding 25 sunflower inbred lines were analysed using eight Amplified Fragment Length Polymorphism (AFLP) primer combinations and their genetic similarities (GS) were estimated. Data were used to develop a Unweighted Pair Group Method using Arithmetic Averages (UPGMA) dendrogram. GS values of 0.58‐0.98 were observed but with no separate groupings dependant on oil quality. The inbred lines were screened for their reaction to inoculation with Sclerotinia sclerotiorum (Lib.) de Bary. Sunflower heads were artificially inoculated with S. sclerotiorum in three environments. Head infection was monitored after 1 week (lesion length) and 2 weeks (head rot). The F5 generation of a cross between a resistant (SWS‐B‐04) and a susceptible inbred line (SWS‐B‐01) was also tested for sclerotinia reaction across three environments. Significant differences in sclerotinia resistance, moderate heritabilities and a high correlation between the two assessments were observed. Inbred lines with a high level of resistance could be identified. These lines can be used for further breeding to improve sunflower sclerotinia resistance and to develop superior new hybrids.     

Genetic control of resistance to the aphid Brevicoryne brassicae in the wild species Brassica fruticulosa

Initial studies have shown variable resistance in Brassica fruticulosa to the aphid Brevicoryne brassicae The aim of this work was to fix high levels of resistance to B. brassicae in true breeding lines of B. fruticulosa and obtain data on the genetic control of resistance. Plants from initially variable B. fruticulosa accessions were selfed to produce inbred resistant and susceptible lines that were studied in three separate experiments to determine the extent to which resistance to B. brassicae had been fixed. Results from three experiments using successive generations of resistant and susceptible inbred lines showed that continued selection resulted in resistant inbred lines that supported an average of three aphids per plant compared with an average of 96 aphids per plant for susceptible inbred lines. Data collected from an experiment determining the resistant phenotype of lines including the selfed progenies and the F₁ and F₂ progeny of a cross between resistant and susceptible individual plants indicated that the resistance was not controlled by a single gene.     

Resistance to Spodoptera litura (Fabr.) in Helianthus species and backcross derived inbred lines from crosses involving diploid species

Spodoptera litura (Fabr.), the tobacco caterpillar, is a major defoliator on sunflower in the tropics. Genetic variability for resistance to S. litura is limited in the cultivar germplasm of sunflower. In the present investigation, 43 accessions of 17 wild Helianthus species of the annual and perennial habit groups were evaluated along with cultivated sunflower under field and no-choice conditions in the laboratory for resistance to this pest. Under field conditions, H. occidentalis and H. argophyllus were found to be immune with no leaf damage and few accessions of the species belonging to section Divaricati were found to be resistant. Laboratory bioassays against neonate, two and 4-day-old larvae confirmed resistance both in terms of high larval mortality and low larval weight gain in eight species viz., H. occidentalis, H. argophyllus, H. tuberosus, H. maximiliani, H. mollis, H. simulans, H. divaricatus and H. hirsutus. Intra-accessional variability was observed and accessions of few species showed varied reaction (resistant, partially resistant to susceptible) to the target pest. Field evaluation of 224 backcross derived inbred lines from five cross combinations involving diploid species under high natural pest incidence revealed low damage in plants derived from crosses involving H. argophyllus and H. petiolaris.     

Colocation of downy mildew (Plasmopara halstedii) resistance genes in sunflower (Helianthus annuus L.)

Summary The Pl6 locus in the inbred sunflower (Helianthus annuus L.) line HA335 giving resistance to French races of downy mildew (Plasmopara halstedii (Farl.) Berl. & de Toni. was localized by molecular techniques. A bulked segregant analysis was made on the F2 progeny from a cross between this line and H52, a downy mildew susceptible line. The resistance gene in HA335 was found to have the same linked RFLP marker loci as those determined for Pl1 (resistance to race 1 in the line RHA266) on linkage group 1 of the consensus RFLP map of the cultivated sunflower. Pl1 and Pl6 thus appear either to be allelic or closely linked. The implications for sunflower breeding are discussed.     

Identification of PCR markers linked to different Or genes in sunflower

Broomrape is a parasitic plant that significantly decreases yield of sunflower. Breeding for resistance has proved to be the most efficient method for suppressing broomrape infestation in the field; however, new races of parasite constantly emerge, and new resistance genes need to be discovered and introduced into cultivated sunflower lines. The aim of this work was to test SSR markers from linkage group 3 (LG3) to investigate whether they could be used for identification of a particular Or gene. Twenty sunflower inbred lines were used, and polymorphism between the lines with various resistance genes and genetic background was investigated. The used markers revealed DNA polymorphism between the investigated lines. Strong association of markers from LG3 with Or₆, as well as Or₄ and Or₂ genes, was found. Identified markers could be used for introduction of these resistance genes into commercial sunflower lines and for establishment and identification of differential lines.     

Evaluation of French Brassica oleracea landraces for resistance to Plasmodiophora brassicae

A total of 240 kale, 38 cabbage and 126 winter cauliflower French landraces from the B. oleracea genepool of INRA were assessed for resistance to clubroot caused by Plasmodiophora brassicaeWoron. Two French isolates of the pathogen (K and SJ) were used in the experiments under controlled conditions. The reaction of the 126 cauliflower accessions to naturally occurring clubroot was also evaluated in field trials. Kales exhibited considerable variation for expression of disease resistance and high levels of resistance were found in several accessions. In this group, single resistant plants were observed in most of the morphological types and from quite different geographical origins. Cabbage accessions were moderately to highly susceptible to both isolates. All cauliflower populations proved to be highly susceptible to K isolate and moderately susceptible to SJ isolate. In field trials, cauliflowers were also severely infected. Two lines selected from a resistant kale population were highly resistant against a large range of pathotypes of the pathogen. These lines presented a sufficient level of resistance to be directly useful in the breeding program in order to develop cauliflower and broccoli hybrids resistant to clubroot. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of Brassica oleracea germplasm with improved resistance to Verticillium wilt

Two hundred and ninety‐nine accessions representing 11 cultivar groups of Brassica oleracea and eight additional accessions of the wild species B. cretica, B. incana, B. insularis and B. villosa were screened for resistance to Verticillium wilt. A disease index (DI) was calculated for each accession, and a correction of the DI was carried out to compensate for a fluctuating infection level between 11 independent trials. A total of 235 , or 77% of the accessions tested, had a DI_corr less or equal to the oilseed rape cv. ‘Express’ (DI_corr= 2.81), the reference cultivar. Only one accession of the wild species, B. incana, showed an enhanced level of resistance (DI_corr= 2.01). Twenty‐four accessions, distributed over eight cultivar groups of B. oleracea were selected for subsequent crosses involving B. rapa. Hybrid plants with 14 accessions were resultant and seed was obtained from crosses where the cultivar groups acephala, alboglabra, botrytis, capitata, gemmifera, italica and sabellica were used as female parents. When progeny of the produced resynthesized rapeseed lines were evaluated for Verticillium wilt resistance, three lines showed a significantly lower disease index (P ≥ 0.01) compared with the cv. ‘Express’. This source of resistance is now being crossed to advanced breeding material of oilseed rape.     

Screening and selection of eggplant and wild related species for resistance to <Emphasis Type="Italic">Leveillula taurica</Emphasis>

Screening for resistance to powdery mildew of Solanum melongena and wild related species was made in the field under natural infection conditions. A total of 172 accessions originating from several geographical parts of the world were tested. Single plant selection for resistance was carried out and open-pollination was used. Most S. melongena accessions were susceptible or highly susceptible to the disease. By S₀ to S₃ selection, an increase in the overall powdery mildew resistance level of S. melongena population was obtained and four S. melongena lines possessing a high level of resistance were obtained. Among the wild Solanum species, S. laciniatum and S. nigrum showed to be non-host plants of L. taurica. S. quinquangolare showed no symptoms of powdery mildew, S. linnaeanum, S. aculeatissimum, S. aviculare, S. pseudocapsicum were highly resistant, S. spinosissimum was resistant, S. gilo, S. capsicoides were susceptible or highly susceptible, and plants of S. sisymbriifolium showed a widely variable disease reaction. Four S. melongena resistant lines were obtained: PAVEG 10187 S₃, PAVEG 10196 S₃, P.I. 230279 S₃ and P.I. 419198 S₃. These S. melongena lines together with the resistant wild species could be used for genetic studies, classical breeding programs and biotechnological applications.     

Development of drought‐tolerant breeding lines derived from Helianthus annuus × H. argophyllus interspecific crosses

Helianthus argophyllus is a wild species known as “silver sunflower”, which possesses several traits, including morphological traits that increase drought tolerance. Therefore, introgressions between chosen cultivated lines and two H. argophyllus accessions were made, and segregating generations were established. Important agronomic traits including single heading, high pollen fertility, silver canopy (indicating more cuticular wax), and content of cuticular waxes and oil were selected over six segregating generations. The resulting F₆ lines showed introgression of water saving traits, as they had lower excise leaf water loss, with comparable yield to standard checks. However, these F₆ lines were late maturing and showed poor flowering synchronization between the cultivated and introgressed lines. Introgressed line “D‐22” was particularly promising as a breeding line, with superior agronomic and drought resistance traits. This line had the potential to be used as an inbred parental line for introgression of drought resistance traits into elite sunflower germplasm. Combining ability analysis of the introgressed lines further showed their potential for heterosis breeding or to be used as parental lines in breeding programme.     

Resistance of sunflower inbred lines to various forms of attack by Sclerotinia sclerotiorum and relations with some morphological characters

Summary Twenty sunflower inbred lines were studied for their reactions to 7 Sclerotinia sclerotiorum tests on different plant parts. A principal component analysis (P.C.A.) and t-tests on the means of resistant and susceptible groups indicated that reactions of inbred lines to infection of capitula by ascospores are independent from those to ascospore infections of terminal buds. They are even more contrasted with the results of any test measuring mycelial extension. However, for the last, there is a close association between the reactions of roots, leaves and capitula. Of the inbred lines, some showed good levels of resistance to most forms of attack, others were generally susceptible and there were some with good resistance to one particular form of attack. A P.C.A. of 18 morphological and field characters showed no general association between these characters and Sclerotinia sclerotiorum test results, although it was found that lines resistant to mycelial extension on capitula were generally earlier than those that were more susceptible. It is proposed that breeding programmes for general resistance to Sclerotinia sclerotiorum should include a combination of two or three tests.     

Inheritance and allelic relationships of fertility restoration genes for seven new sources of male-sterile cytoplasm in sunflower

The inheritance of fertility restoration of six mitomycin C and streptomycin‐induced cytoplasmic male‐sterile (cms) mutants and one cms line derived from Native American cultivar PI 432513 in sunflower was evaluated. These seven new cms sources were also compared with the commercially used cms PET1 (Helianthus petiolaris Nutt.) cytoplasm, using USDA inbred lines with restoration genes (Rf₁) specific for cms PET1 and new restoration lines identified for cms PI 432513. Restoration genes for cms PI 432513 were found in ‘Armavir’, VNIIMK, P21 and male‐fertile (MF) plants of PI 432513. F₂ and F₃ segregation ratios of crosses between cms PI 432513 and these restoration sources indicated a single dominant gene controlled fertility restoration. Progenies of cms PI 432513 testcrossed with F₁’s of half‐diallel crosses among the respective four homozygous restoration lines and RHA 274 suggested that the restoration genes of RHA 274, VNIIMK, P21 and PI 432513 were at the same locus. Restoration genes from VNIIMK, P21 and PI 432513 satisfactorily restored pollen stainability in the heterozygous condition. A very weak expression of the Rf gene in ‘Armavir’ was observed in the heterozygous condition. Fertility restoration capability of these genes for the six mutant cms HA 89 and cms HA 89 (in PET1 cytoplasm) was observed. The mutant cms HA 89 lines were also restored completely by RHA 266, RHA 274, RHA 280 and RHA 296, and F₂’s segregation ratios indicated single dominant gene control, implying a common cytoplasmic male sterility in all lines. F₁’s of half‐diallel crosses among RHA 266, RHA 273, RHA 274, RHA 280 and RHA 296 were testcrossed onto the cms lines, and their all MF progenies among lines, except RHA 280, confirmed that fertility restoration was controlled by a single Rf₁ gene locus. The restoration gene in confection line RHA 280, namely Rf₃, was at a different locus than Rf₁ and was equally capable of restoring all the cms lines. Cms HA 89 mutants and cms PI 432513 are in H. annuus cytoplasm, and are agronomically equal in hybrid performance to the cms PET1 used in commercial sunflower hybrids. These new cms lines will provide immediate alternative cms sources for reducing the genetic vulnerability resulting from the exclusive use of the single cms source PET1 in sunflower hybrid production.