Goal. To study the resistance to the pathogen of powdery mildew of sunflower hybrid lines, to determine the nature of its inheritance in F1 hybrids, and the level of manifestation of valuable economic features in stable hybrid combinations. Methods. Field — to obtain F1 hybrids, determine the hit of lines and hybrids with powdery mildew, and study the economic characteristics of hybrids; laboratory — to determine the oil content in the seeds, and the mass of 1000 seeds; mathematic — to determine the degree of phenotypic dominance (hp) of resistance to powdery mildew, and assess the reliability of the research results. Results. Field studies were conducted in 2020–2025 based on the experimental field of the 4-field crop rotation of V.Ya. Yuriev Institute of Plant Production of NAAS. In the conditions of 4-field crop rotation, the distribution of powdery mildew of forms I and II, on average, in the studied lines-parental components was 20.5%. The stability of the lines varied within 3–9 points. According to the degree of dominance, the inheritance of resistance to the causative agent of the disease was carried out in 4 types: positive superdomination (20% of hybrid combinations), partial positive dominance (53%), intermediate inheritance (20%), and partial negative dominance (7%). At crossing lines with stability score 9 and lines with stability scores 3 and 5, partial positive dominance and positive superdomination of stability were established, which in such hybrid combinations was at the level of 92.1–100%. For example, the yield of seeds of the hybrid Vyrii resistant to powdery mildew in a demonstration test exceeded the average yield in the experiment by 28%. Conclusions. A high infectious background of fake powdery mildew of sunflower was created in the conditions of 4-field crop rotation, which contributed to the differentiation of the line-parental components and hybrids in terms of resistance to the causative agent of the disease. It was found that resistance to powdery mildew dominated in the hybrid generation F1. Lines X 06135 V, X 06134 V, and Cx 777 A, even when crossed with an unstable parent component, provided very high resistance of F1 hybrids to powdery mildew.

One of the most effective and at the same time environmentally friendly measures of integrated protection of wheat against diseases is the development of resistant varieties through breeding adapted to specific agroclimatic conditions. The purpose of the present study was the phytopathological evaluation of winter wheat collection samples on artificial infection backgrounds in the field and to determine the dominance of resistance of F₁ hybrids to Puccinia recondita and Tilletia caries. The study was conducted during 2023, 2024 in a selection crop rotation on natural and artificial infection backgrounds and in the laboratory of the winter wheat breeding laboratory of the V.M. Remeslo Myronivka Institute of Wheat of the National Academy of Agrarian Sciences of Ukraine according to generally accepted methods. 189 collection numbers of winter wheat were studied against artificial infectious backgrounds of brown rust and stinking smut. The study found that the varieties protected by resistance genes Arthur 71 (Lr9), McNair 2203 (Lr9), Agrus (Lr19), Century (Lr24+ Lr42), TAM-200 (Lr24+ Lr43), V1275 (Lr19), VR89Bo22 (Lr19) were immune to the pathogen Puccinia recondita; immunity to Tilletia caries was reflected by winter wheat varieties Rada (SVK), Famulus (DEU), SHARK/F4. 105W21 (USA), Reia (UKR), Ekspromt, Erythrospermum 24210, and Line 46 (UKR). When studying the composition of the population of Puccinia recondita, it was found that the average efficiency was shown by genes Lr10, Lr13, Lr25, and Lr34 (gene of age resistance) at the 5-10% degree of damage to the lines. The genes Lr9 and Lr19 stably maintained strong resistance and continued to be highly effective. In terms of resistance to Puccinia recondita, superdominance (heterosis) was found in five (14.72% of the total number of hybrid combinations) hybrid combinations Beres/Blueboy II, Beres/TAM-200, Matuo/TAM-200, Tobarzo/TAM-200, Matuo/Blueboy II. It was noted that the local population of the pathogen Tilletia caries is avirulent or slightly virulent to resistance genes: Bt6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21. The study of the genetics of resistance to this disease showed that among F1 hybrid combinations, 41.63% showed partial positive dominance (PPD). No overdominance to the pathogen of stinking smut was found

Drought is one of the main abiotic stressors affecting crops and causing significant yield losses. The creation of more resistant varieties and hybrids can reduce the negative effects of this factor. This study presents the results of diagnostics (2023, 2025) of drought resistance of F1 hybrids of grain and sugar sorghum obtained on the basis of isonuclear CMS-lines with different types of cytoplasm (A3, A4, 9E). Determination of drought resistance indicators (leaf tissue hydration, leaf water deficiency, cell membrane permeability) in the main critical phases of plant development ("heading", "flowering", "milk ripeness", "milk-wax ripeness") showed that the A4 type cytoplasm in hybrids with the L-50/14 lineage in the phase "flowering" had a significant effect on water deficiency (5.89%) compared with the cytoplasm A3 (10.59%). The isonuclear CMS-lines (A3, A4 and 9E Zheltozeornoe 10) of sorghum had medium drought resistance, and the pollinator lines (L-65/14, L-50/14) had high. Thus, the most sensitive phases for grain sorghum hybrids are "flowering" and "milk-wax ripeness", and for sugar – "flowering". It was found that water availability decreased with the development of plants and in the phase "flowering", "milk-wax ripeness" was 70.53-71.58%; indicators of water deficiency had higher values in the phase "milk-wax ripeness" (10.08-16.44%), and the degree of damage to cell membranes in sorghum leaves was noted in the phase "flowering" (23.74-36.75%). The results obtained are important in breeding programs for the creation of drought-resistant sorghum hybrids, and the indicators used can serve as diagnostic criteria for parental forms and hybrids with increased resistance to stress.

The pulse beetle, Callosobruchus spp., poses a threat to legumes by consuming the protein content of the grain, resulting in potential losses in storage ranging from 12 to 30%. Molecular marker technology helps to mitigate the breeding constraint in the development of bruchid resistance in green gram breeding programmes. In the present study, validation of locus-specific STSbr1 and STSbr2 markers linked with bruchid resistance was done using fifteen genotypes viz., VBN (Gg) 2 (susceptible) and Vigna radiata var. sublobata/2 (resistant), F1 hybrid, two susceptible and ten resistant RILs derived from the above parents. The marker STS br1 behaved as a dominant marker and produced an approximate allele size of 225 bp in the resistant parent, F1 hybrid and resistant RILs and absent in susceptible parent and susceptible RILs, which showed cent per cent co-segregation with bruchid resistance locus. Hence, it is concluded that STS br1 is linked with bruchid-resistant genes. The marker STS br2 behaved as a co-dominant marker and produced an approximate allele size of 470 bp in all the 15 genotypes evaluated (monomorphic) and did not differentiate the resistant and susceptible genotypes. The marker STS br1 could be used in marker-assisted selection to develop bruchid-resistant varieties and to screen the germplasm to identify bruchid-resistant donors in green gram.

Tomato is the major Solanaceous vegetable crop grown in Karimnagar District of Telangana. Alternaria tomatophila and Alternaria solani cause early blight disease and severe yield losses to the tomato growers in Karimnagar District. Early blight is the major problem in Karimnagar from June to September months causing severe crop losses to the tomato farmers. Usually farmers are spraying different fungicides based on Copper to control early blight disease for private hybrids. It controls 25-35% of the disease and increased cost of cultivation. Hence, early blight disease resistant hybrid Arka Abhed was tested against private hybrid in KVK, Karimnagar operational area. Data on disease incidence was collected at 15, 30, 60, 90,120 DAP in all the hybrids. The data revealed that Arka abhed recorded significantly very lower incidence of early blight disease than private hybrid during all crop growth stages. It recorded 1.5% early blight incidence whereas private hybrid recorded 32.4%. Reduced number of sprayings to control early blight disease were also significantly low i.e. two sprays were carried out whereas in private hybrid seven sprays were done during in rainy period. According to yield Arka Abhed recorded 68.3t/ha whereas it was 58.6t/ha in private hybrid. The peduncle in green in colour for long days and taste also same for all the days in storage period for 8-12 days in Arka Abhed. Average fruit weight is 86 gr to 112 grams were recorded.

Abstract Root and stalk rot (RSR) of maize (Zea mays L.) plants, caused by soil‐borne disease pathogens of the genus Pythium, can get worse in global warming. It has been known that the resistance of F1 hybrids often disaccords with those of their parental inbreds, which makes it difficult to develop resistant hybrids effectively. Best linear unbiased prediction (BLUP) is a standard mixed model equation, which is fitted for predicting hybrid performance by the parental inbreds of maize. The objective of this study was to evaluate simple parental‐progeny‐based BLUP in predicting single‐cross performance and to determine the importance of general combining ability of the resistance to Pythium RSR. The performance prediction of the parental inbreds from BLUP was consistent with empirical knowledge and was determined mostly useful, despite not using a coefficient of coancestry. Correlation coefficients between breeding values from BLUP and actual field data for hybrids, across different experiments from 2018 to 2019, were relatively high (R = 0.854 and 0.703, respectively). These results indicate the potential of the parental‐progeny‐based BLUP for maize single‐cross performance. This is the first report in predicting the resistance to this disease with BLUP, and the findings can be applied to routine breeding programs as well as to genome‐wide molecular polymorphism data to contribute to the future breeding programs.

We studied the effectiveness of anti-tuberculosis vaccination with BCG in mice of inbred strains and F1 hybrids (highly resistant to tuberculosis infection) that represent a wide range of genetically determined differences in susceptibility to infection with virulent Mycobacterium tuberculosis. The greatest relative effect was found in susceptible mice, with the exception of highly susceptible I/St mice that were practically not protected by vaccination. Despite significant effect of vaccination in inbred mice, their resistance to M. tuberculosis infection did not exceed that of non-vaccinated highly resistant F1 hybrids.

The recent association of a DNA betasatellite with Tomato yellow leaf curl virus in Israel – A new threat to tomato production

The study was carried out on 72 mango (Mangifera indica L.) cultivars and 107 mango F1 hybrids to group them based on degree of resistance to malformation during the period 2015-17. Intensity of malformation varied significantly among the mango cultivars and F1 hybrids under study. Out of 72 mango cultivars and 107 F1 hybrids studied, only three cultivars namely Bhadauran, Ilaichi and Arka Nilanchal were found to be completely free from the mango malformation disease (0%) and were categorised as resistant. Minimum disease incidence (<10%) was recorded in 11 mango cultivars, one mango species and in eight mango F1 hybrids, viz. H-2-6, H-2-14, H-3-6, H-4- 10, H-5-14, H-8-4, H-8-2. and H-8-11 and were categorized as tolerant. Twelve mango cultivars and 21 mango F1 hybrids were moderately susceptible (10-20%), while another 27 cultivars and 43 F1 hybrids were susceptible (20- 50%). The highest incidence of floral malformation intensity was recorded in 13 cultivars and 32 F1 hybrids which were categorized as highly susceptible (>50%) to mango malformation. The resistant and tolerant cultivars and F1 hybrids observed in the current study can be used as parents in future breeding programmes for developing a variety resistant to mango malformation.

Drought stress is one of the most important abiotic factors limiting crop productivity. A better understanding of the effects of drought on millet (Setaria italica L.) production, a model crop for studying drought tolerance, and the underlying molecular mechanisms responsible for drought stress responses is vital to improvement of agricultural production. In this study, we exposed the drought resistant F1 hybrid, M79, and its parental lines E1 and H1 to drought stress. Subsequent physiological analysis demonstrated that M79 showed higher photosynthetic energy conversion efficiency and drought tolerance than its parents. A transcriptomic study using leaves collected six days after drought treatment, when the soil water content was about ∼20%, identified 3066, 1895, and 2148 differentially expressed genes (DEGs) in M79, E1 and H1 compared to the respective untreated controls, respectively. Further analysis revealed 17 Gene Ontology (GO) enrichments and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in M79, including photosystem II (PSII) oxygen-evolving complex, peroxidase (POD) activity, plant hormone signal transduction, and chlorophyll biosynthesis. Co-regulation analysis suggested that these DEGs in M79 contributed to the formation of a regulatory network involving multiple biological processes and pathways including photosynthesis, signal transduction, transcriptional regulation, redox regulation, hormonal signaling, and osmotic regulation. RNA-seq analysis also showed that some photosynthesis-related DEGs were highly expressed in M79 compared to its parental lines under drought stress. These results indicate that various molecular pathways, including photosynthesis, respond to drought stress in M79, and provide abundant molecular information for further analysis of the underlying mechanism responding to this stress.

Tomato (Solanum lycopersicum L.) is an important vegetable crop cultivated in the tropical and sub-tropical regions of the world. Low productivity in India is due to occurrence of both biotic and abiotic stresses. Among the biotic stresses, tomato leaf curl disease, bacterial wilt, early blight and Groundnut Bud Necrosis Virus disease have become serious production constraints causing considerable yield loss in the major tomato growing areas of the country. Adoption of multiple disease resistant varieties or F1 hybrids would be the most appropriate way to address these diseases. At ICAR-IIHR, Bengaluru systematic breeding strategies were employed to pyramid genes for resistance to early blight, bacterial wilt and tomato leaf curl diseases and to develop advanced breeding lines& F1 hybrids with triple disease resistance. Stable source of resistance to early blight and bi-partite begomo-virus (Tomato Leaf Curl New Delhi Virus) has been identified in Solanum habrochaites LA-1777. Validation with molecular markers linked to tomato leaf curl virus resistance revealed that LA-1777 carryTy2 and other putative resistant genes. Several high yielding dual purpose hybrids were also developed for fresh market and processing with high level of resistance to multiple diseases. Cherry tomato lines have also been bred for high TSS, total carotenoids, total phenols, flavonoids, vitamin C, acidity and lycopene content. IIHR-249-1, IIHR-2101 (Solanum habrochaites LA-1777), IIHR- 2866 and IIHR-2864 recorded high values for quality parameters like total carotenoids, lycopene, vitamin C, total phenols, flavonoids and TSS. Drought tolerant root stock has been developed by an interspecific cross between S. habrochaites LA-1777 and S. lycopersicum (15 SB SB). Resistant sources have also been identified against Tuta absoluta, a serious insect pest reported from major tomato growing areas in the country in recent time. High temperature tolerant breeding lines are in pipe line.

Cucumber mosaic virus (CMV) and Chilli veinal mottle virus (ChiVMV) are aphid-borne major destructive viruses affecting chilli crops. Identification of resistant sources and understanding the genetic behaviour of resistance is essential for resistance breeding. In this study, fifty Capsicum genotypes were screened for CMV and ChiVMV resistance through mechanical inoculation. Symptoms varying from chlorotic local lesions to severe leaf distortion were observed and among the genotypes eighteen immune, eight highly resistant, five resistant and two moderately resistant genotypes were identified against CMV. For ChiVMV, dark green vein banding to severe shoe string symptoms were observed and among genotypes, seventeen were immune, one highly resistant, five resistant and two moderately resistant. Ten parents were selected and crossed in diallel fashion without reciprocals to produce 45 F1 hybrids and were screened for resistance against both the viruses separately. Only one hybrid IHR 2451 x IHR 500 showed resistance against CMV and all resistant x resistant F1 hybrids i.e. IHR 4503 x IHR 2451, IHR 4503 x IHR 500, IHR 2451 x IHR 500, IHR 3849 x IHR 2451 and IHR 3849 x IHR 500 were found resistant against ChiVMV. Further the inheritance studies using advanced populations showed that the CMV resistance is polygenic recessive and ChiVMV resistance is monogenic recessive in IHR 2451 and IHR 4503.

The genetic nature of bacterial wilt resistance was studied in bell pepper (Capsicum annuum L. var. grossum Sendt.) plants using the P1, P2, F1, F2 and backcross generations obtained from four crosses between four parental lines, viz, EC 464107, EC 464115, Kandaghat Selection and Sweet Happy I considered as standards for resistance and/or susceptibility. The evaluation trial was conducted in bacterial wilt sick plots along with two susceptible checks, namely Indira (Hybrid) and California Wonder (Open-pollinated variety) that were included after every 15th row to ensure uniform distribution of inoculum in the experimental fields. Simultaneously, in a separate block, the parents and their F1’s were also evaluated for twelve different horticultural traits. The findings revealed that bacterial wilt resistance was governed by a single dominant gene in the cross EC 464107 × Sweet Happy I, whereas two genes with dominant and recessive epistasis dictated resistance in the crosses EC 464107 × Kandaghat Selection and EC 464115 × Kandaghat Selection, respectively. Based upon the mean performance, the hybrid EC 464107 × Kandaghat Selection was the best in terms of total and marketable fruit yield, fruits per plant and fruit length, which underscores its importance to be exploited, especially during wet season. In addition, the resistant parents EC 464107 and EC 464115 can be used to develop bacterial wilt resistant F1 hybrids as they expressed complete or near complete dominance for resistance in combination with the moderately resistant and susceptible varieties Kandaghat Selection and Sweet Happy I. Backcrossing with commercial cultivars and recombinant breeding accompanied by selection would also help to evolve bacterial wilt disease resistant, high yielding and horticulturally desirable pure line varieties.

We report the first successful production of PRSV-P resistant backcross (BC) papaya plants following intergeneric hybridisation between C. papaya and a Vasconcellea species after 50 years of reports on unsuccessful attempts. This follows our previous reports of PRSV-P resistant F1 hybrids developed by intergeneric hybridisation between C. papaya and V. quercifolia. One PRSV-P resistant BC 1 (BC1) plant was produced after 114,839 seeds were dissected from 940 fruits. The seeds yielded 1,011 embryos and 733 germinated in vitro from which 700 developed into plantlets that were screened in a glasshouse and in the field under high disease pressure and exposure to inoculation by viruliferous aphids. From the PRSV-P resistant backcross 1 (BC1) male plant, 1465 plants [137 BC2, 546 SbC2 (BC2 sib-crosses), 147 BC3, 379 SbC3 and 256 BC4] were grown from seed and inoculated with PRSV-P and virus resistant BC3 and BC4 plants were selected from these generations. Presence or absence of virus was confirmed by ELISA serological tests. BC plants generally developed mild symptoms of PRSV-P after periods ranging from 5 to 18 months in the field but many showed the ability to produce new growth free of symptoms. All control plants developed severe symptoms after 3 months in the field. Some BC3 and BC4 plants were free from viral infection after 18 months in the field. Subsequently they developed very mild symptoms on their leaves and a few ringspots on their fruit. They continued to grow vigorously and produce fruit for 3 years under high disease pressure provided by the infected controls and other susceptible plants. Good quality marketable fruit were produced on these plants. Application of these results should lead to restoration of the papaya industry in virus-infested regions of the Philippines and worldwide.

The transfer of herbicide resistance genes from crops to related species is one of the greatest risks of growing herbicide-resistant crops. The recent introductions of imidazolinone-resistant wheat in the Great Plains and Pacific Northwest regions of the United States and research on transgenic glyphosate-resistant wheat have raised concerns about the transfer of herbicide resistance from wheat to jointed goatgrass via introgressive hybridization. Field experiments were conducted from 2000 to 2003 at three locations in Washington and Idaho to determine the frequency and distance that imidazolinone-resistant wheat can pollinate jointed goatgrass and produce resistant F1hybrids. Each experiment was designed as a Nelder wheel with 16 equally spaced rays extending away from a central pollen source of ‘Fidel-FS4’ imidazolinone-resistant wheat. Each ray was 46 m long and contained three rows of jointed goatgrass. Spikelets were collected at maturity at 1.8-m intervals along each ray and subjected to an imazamox screening test. The majority of all jointed goatgrass seeds tested were not resistant to imazamox; however, 5 and 15 resistant hybrids were found at the Pullman, WA, and Lewiston, ID, locations, respectively. The resistant plants were identified at a maximum distance of 40.2 m from the pollen source. The overall frequency of imazamox-resistant hybrids was similar to the predicted frequency of naturally occurring acetolactate synthase resistance in weeds; however, traits with a lower frequency of spontaneous mutations may have a relatively greater risk for gene escape via introgressive hybridization.

Natural killer (NK) cells are involved in graft rejection and may contribute to tumor recognition and elimination. Ogasawara et al. report that increased production of NKG2D ligands may be one mechanism by which certain tissues are prone to graft rejection and that antibodies against NKGD2 can prevent rejection in these cases. Oppenheim et al. report that localized high expression of NKG2D ligands inhibited NK cell function, contributing to evasion of the immune system by tumors. To study graft rejection, Ogasawara et al. evaluated NKG2D ligand expression (by antibody staining) of bone marrow cells from BALB/C or C57BL/6 mice that were transplanted into irradiated F 1 progeny from a BALB/C C57BL/6 cross, an example of F 1 hybrid resistance. The BALB/C cells expressed the ligand Rae-1 and were rejected by the F1 progeny mice. The C57BL/6 mouse cells were also rejected, but they did not express any NKG2D ligands; thus, there are at least two mechanisms for NK cell-mediated rejection. Depletion of the NK cells from the recipient mice allowed the transplanted cells from both parental strains to survive; however, only in the case of the BALB/C transplanted cells did neutralizing antibodies to NKG2D increase the incorporation of the transplanted cells in the spleens of the recipient mice. The Rae-1 ligand was also the focus of the studies by Oppenheim et al. In this case, two kinds of transgenic mice were generated: those expressing Rae-1ε in squamous epithelium only (lines 110 and 121) and those expressing Rae-1ε ubiquitously (line 187). Both types of transgenic mice showed decreased abundance of NKG2D-positive NK cells; however, the abundance of other proteins (such as CD94) typically expressed by this population of NK cells was normal. Thus, the NKG2D receptor itself appeared to be down-regulated rather than the cell population depleted. Coculturing of NKG2D-positive splenocytes with the splenocytes from the 187 line (high Rae-11ε) resulted in loss of NKG2D from the nontransgenic cells. Injection of a mixture of splenocytes from the 187 line and control splenocytes into control mice or transgenic mice showed that clearance of the Rae-1-positive cells was impaired in the transgenic mice. Activation of the NK cells with poly (I:C) restored killing of the Rae-1-positive cells in the epithelial transgenic mice only, suggesting that a residual population of NKG2D-positive cells could be rescued in the 110 and 121 lines. Finally, the transgenic mice showed increased susceptibility to tumorigenesis (chemical induced and injection of tumor cells). Thus, the NKG2D receptor is a critical player in tumor surveillance and graft rejection. K. Ogasawara, J. Benjamin, R. Takaki, J. H. Phillips, L. L. Lanier, Function of NKG2D in natural killer cell-mediated rejection of mouse bone marrow grafts. Nat. Immunol. 6 , 938-945 (2005). [Online Journal] D. E. Oppenheim, S. J. Roberts, S. L. Clarke, R. Filler, J. M. Lewis, R. E. Tigelaar, M. Girardi, A. C. Hayday, Sustained localized expression of ligand for the activating NKG2D receptor impairs natural cytotoxicity in vivo and reduces tumor surveillance. Nat. Immunol. 6 , 928-937 (2005). [Online Journal]

The MBP-reactive repertoire is shaped by recognition of minor histocompatibility antigens

Unacceptable levels of contamination by aflatoxin, a carcinogenic toxin, produced by Aspergillus flavus Link:Fr can halt the sale and shipment of maize (Zea mays L.) grain. Our objectives were to: (i) determine the relative resistance to A. flavus and aflatoxin accumulation in F1 hybrids produced by crossing promising resistant maize inbreds, regardless of heterotic pattern; (ii) investigate the genetic basis of resistance for this subset of inbreds through diallel analysis; and (iii) determine which inbreds are the most promising sources of resistance for molecular marker mapping and breeding programs. Two historically important inbreds and six inbreds tentatively associated with reduced ear rot and inhibition of aflatoxin production were crossed in all combinations. The resulting F1 hybrids were evaluated for two years. Ears were inoculated 20 to 24 d after midsilk by a pinboard method and a mixture of conidia of Aspergillus flavus Link:Fr. isolates. Individual ears from each plot were rated by scoring the percent visible rot in the inoculated area. Aflatoxin B1 levels in harvested ears were determined by an indirect competitive ELISA. The highest level of resistance for ear rot and aflatoxin accumulation was detected for resistant inbred × resistant inbred F1 hybrids, but they were not significantly different from many resistant inbred × historically important inbred F1 hybrids. Diallel analysis indicated general combining ability (GCA) effects for ear rot and aflatoxin levels were highly significant among hybrids overall, and for the inbreds Tex6 and Oh516. The results indicate that Tex6 and Oh516 are promising resistance sources for molecular marker mapping and breeding programs in diverse genetic backgrounds.

We tested how the status of the parent taxa, host or non-host, influences the resistance of F1 hybrids to herbivores. To do this we used two different hybrid lines. Hand pollination was used to produce pure individuals and F1 hybrids between Salix caprea and S. repens, and S. caprea and S. aurita. Leaves from these individuals were presented to adults of two chrysomelid species, Lochmaea caprea and Crepidodera fulvicornis, in multiple-choice preference tests. Lochmaea caprea showed an additive response: its level of grazing of the F1 hybrids of S. caprea (host) and S. repens (non-host) was mid-way between that of the parent species. This was consistent with the inheritance pattern of condensed tannins in hybrids. This suggests an additive inheritance of resistant traits and a linear (dose dependent) response by the herbivore. When both parent taxa (S. caprea and S. aurita) were hosts, L. caprea utilization did not differ between any of the plant categories (F1 hybrids and parents). Crepidodera fulvicornis exhibited a dominant response towards the susceptible parent for the S. caprea ¥ S. repens crosses and a dominant response towards the resistant parent for S. caprea ¥ S. aurita crosses. This indicates that C. fulvicornis might respond to changes in resistant trait at specific thresholds. Our results suggest that different herbivores, even those with a similar host plants range, differ in their response to hybrids. One way to gain knowledge of the proximate and ultimate explanations for these differences could be to compare the response of different herbivores to different distinct hybrid lines.

Inheritance studies have indicated that resistance to the root-knot nematode (Meloidogyne javanica) in carrot inbred line ’Brasilia-1252’ is controlled by the action of one or two (duplicated) dominant gene(s) located at a single genomic region (designated the Mj-1 locus). A systematic search for randomly amplified polymorphic DNA (RAPD) markers linked to Mj-1 was carried out using bulked segregant analysis (BSA). Altogether 1000 ten-mer primers were screened with 69.1% displaying scorable amplicons. A total of approximately 2400 RAPD bands were examined. Four reproducible markers (OP-C21700, OP-Q6500, OP-U12700, and OP-AL15500) were identified, in coupling-phase linkage, flanking the Mj-1 region. The genetic distances between RAPD markers and the Mj-1 locus, estimated using an F2 progeny of 412 individuals from ’Brasilia 1252’×’B6274’, ranged from 0.8 to 5.7 cM . The two closest flanking markers (OP-Q6500 and OP-AL15500) encompassed a region of 2.7 cM . The frequency of these RAPD loci was evaluated in 121 accessions of a broad-based carrot germplasm collection. Only five entries (all resistant to M. javanica and genetically related to ’Brasilia 1252’) exhibited the simultaneous presence of all four markers. An advanced line derived from the same cross, susceptible to M. javanica but relatively resistant to another root-knot nematode species (M. incognita), did not share three of the closest markers. These results suggest that at least some genes controlling resistance to M. incognita and M. javanica in ’Brasilia 1252’ reside at distinct loci. The low number of markers suggests a reduced amount of genetic divergence between the parental lines at the region surrounding the target locus. Nevertheless, the low rate of recombination indicated these markers could be useful landmarks for positional cloning of the resistance gene(s). These RAPD markers could also be used to increase the Mj-1 frequency during recurrent selection cycles and in backcrossing programs to minimize ’linkage drag’ in elite lines employed for the development of resistant F1 hybrids.