Screening of resistance to egyptian broomrape infection in tomato varieties

Parasitic weed species of the genus Orobanche are serious threat for the production of several crops in Europe, Africa and Asia. Research on resistant host plant varieties is one of the most effective management strategies for this parasitic weed. In this study, the susceptibility of twenty-nine tomato varieties to broomrape infection (Orobanche aegyptiaca) under greenhouse conditions was investigated. The employed experimental design was completely randomized with three replications. Differences in susceptibility to infection were monitored among tomato varieties based on their difference in the number of emerged shoots of broomrape and broomrape dry weight (shoots and tubercles). Date of Orobanche emergence varied over a period of 3 to 30 days between varieties. Very late infection was monitored for varieties of Cal-jN3, Viva, Caligen 86, Packmor, CSX 5013, Hyb. PS 6515 and Hyb Petopride5. Differences in the growth and fruit yield among tomato varieties were also found in response to broomrape infestation. Moderate levels of resistance were obtained in Viva, Caligen 86, Hyb. PS 6515, Hyb.Firenze (PS 8094) and Cal-jN3 among other tomato varieties. In contrast, varieties of Kimia-Falat, Hyb. Petopride II and Hyb.AP865 were the most susceptible hosts to Orobanche aegyptiaca.

Resistance of Raphanus raphanistrum to the herbicide metsulfuron-methyl

The ALS-inhibiting herbicides, especially metsulfuron-methyl, are widely used for weed control, mainly wheat and barley in southern Brazil. Raphanus raphanistrum is a major weed of winter crops. However, in recent years, R.raphanistrum, after being treated with metsulfuron, has shown no symptoms of toxicity, possibly due to herbicide resistance. Aiming to evaluate the existence of R.raphanistrum biotypes resistant to metsulfuron, an experiment was conducted in a greenhouse, in a completely randomized design with four replications. The plots consisted of pots with six plants. The treatments consisted of the interaction of resistant R. raphanistrum (biotype R) and susceptible R. raphanistrum (biotypes S) with ten doses of the herbicide (0.0; 0.6; 1.2; 2.4; 4.8; 9.6; 19.2; 38.4; 76.8 and 153.6 g i.a. ha-1). The application of the test herbicides occurred when the crop was at the stage of 3 to 4 true leaves. The variables analyzed were control and dry matter accumulation. Statistical analysis of dose-response curves was performed by non linear regression. Biotype S was susceptible to the herbicide even at doses below the recommended. Biotype R was insensitive to the herbicide obtaining values of resistance factor (F) higher than 85. The dose-response curve confirmed the existence of R. raphanistrum biotypes with high level of resistance to metsulfuron-methyl.

Does the resistance to glyphosate herbicide affect the competitive ability of ryegrass with soybean?

The objective this work was to investigate the competitive ability between resistant and susceptible ryegrass biotypes and of these with soybean crop. Four experiments were carried under greenhouse, in a completely randomized design with four replications, in 2011 and 2012. Treatments were arranged in additive series and replacement series assay. In each series, the proportions among ryegrass resistant and susceptible plants related to soybean were: 100:0, 75:25, 50:50, 25:75 e 0:100. Leaf area and shoot dry mass were evaluated. Competitiveness statistical analysis consisted in applying diagrams to the replacement series and alternative interpretations of the competitiveness indexes. The soybean crop had equivalent competitiveness to the susceptible ryegrass biotype and inferior to the resistant biotype, while the biotypes, both susceptible and resistant to glyphosate, present equivalent competitive ability. In general, the intraspecific competition is more harmful to ryegrass when in competition with soybean, while interspecific competition is predominant for culture.

Multiple resistance of Conyza sumatrensis to Chlorimuron­ethyl and to Glyphosate

Weed resistance to herbicides has been a major issue in Brazil, mainly due to the inefficiency of the herbicides used in no-till areas and to the high cost of these herbicide treatments. Failures in controlling the weed Conyza have been reported in Western and Northern grain crop areas in Paraná (Brazil). This work aimed to evaluate the potential occurrence of C. sumatrensis biotypes resistant to the herbicides chlorimuron-ethyl and glyphosate. Experiments were carried out under greenhouse conditions with four biotypes (Cascavel-2, Toledo-4, Tupãssi-6, and Assis Chateaubriand-7) possibly resistant to, as well as a population considered susceptible to chlorimuron-ethyl and glyphosate. To obtain dose-response curves, eight herbicide doses of chlorimuron-ethyl (0, 2.5, 5, 10, 20, 40, 80 and 160 g ha-1) and glyphosate (0, 90, 180, 360, 720, 1,440, 2,880 and 5,760 g e.a. ha-1) were applied and weed control and shoot biomass evaluations were made. Results provided evidence that two biotypes (Cascavel-2 and Tupãssi-6) were resistant to glyphosate and four biotypes (Cascavel-2, Toledo-4, Tupãssi-6 and Assis Chateaubriand-7) were resistant to chlorimuron­ethyl. Multiple resistance to glyphosate and chlorimuron was confirmed for biotypes Cascavel­2 and Tupãssi 6. This is the first report on multiple resistance in Conyza sumatrensis, worldwide.

Resistance of Amaranthus retroflexus to acetolactate synthase inhibitor herbicides in Brazil

When in competition with cotton, Amaranthus retroflexus can cause high yield losses. Due to the limited availability of selective herbicides registered for post emergence control of this weed, the same herbicides have been used repeated times over the last few years, which may have selected resistant biotypes. Biotypes of A. retroflexus collected from the main areas of cotton cultivation in Brazil were submitted to dose-response trials, by applying the herbicides trifloxysulfuron-sodium and pyrithiobac-sodium in doses equivalent to 0, ¼, ½, 1, 2 and 4 times the recommended rates. Resistance to ALS inhibitors was confirmed in biotypes of A. retroflexus. Biotype MS 2 from Mato Grosso do Sul, was cross-resistant to both trifloxysulfuron-sodium and pyrithiobac-sodium, while biotype MS 1 was resistant to trifloxysulfuron-sodium only. Likewise, singular and cross resistance was also confirmed in biotypes from Goiás (GO 3, GO 4 and GO 6), in relation to trifloxysulfuron­sodium and pyrithiobac-sodium. One biotype from Mato Grosso (MT 13) was not resistant to any of the ALS inhibitors evaluated in this work.

Reducing contact resistance in graphene devices

In this thesis, the contact resistance of graphene devices was investigated because high contact resistance is detrimental to the performance of graphene field-effect transistors (GFET). Method for increasing so-called edge-contact area was applied in device fabrication process, as few nanometers thick Ni layer was used as a catalytic etchant during the annealing process. Finally, Ni was also used as a metal for contact. GFETs were fabricated using electron beam lithography using graphene fabricated by chemical vapor deposition (CVD). Critical part of the fabrication process was to preserve the high quality of the graphene channel while etching the graphene at contact areas with Ni during the annealing. This was achieved by optimizing the combination of temperature and gas flows. The structural properties of graphene were studied using scanning electron microscopy, scanning confocal μ-Raman spectroscopy and optical microscopy. Evaluation of electric transport properties including contact resistance was carried out by transmission line method and four-probe method. The lowest contact resistance found was about at 350 Ωμm. In addition, different methods to transfer CVD graphene synthesized on copper were studied. Typical method using PMMA as a supporting layer leaves some residues after its removal, thus effecting on the performance of a graphene devices. In a metal assisted transfer method, metal is used as an interfacial layer between PMMA and graphene. This allows more effective removal of PMMA. However, Raman spectra of graphene transferred by metal assisted method showed somewhat lower quality than the PMMA assisted method

First report of Amaranthus viridis resistance to herbicides

Due to the limited number of herbicides registered for the control of dicot weeds in cotton crops, ALS inhibitors have been used on an intensive and recurrent basis. Given that, cases of poor weed control have been described after application of these herbicides in the main cotton producing areas in Brazil, the purpose of the present work was to evaluate the occurrence of resistance to ALS herbicides in Amaranthus viridis biotypes from those areas. Dose-response curves were prepared after pre-emergence applications of trifloxysulfuron-sodium (0; 1.8; 3.7; 7.5; 15 and 30 g ha-1) and pyrithiobac-sodium (0; 35; 70; 140; 280 and 560 g ha-1), equivalent to 0, ¼, ½, 1, 2 and 4 times the recommended commercial rates. The selection of trifloxysulfuron-sodium resistant biotypes of A. viridis was confirmed in samples from Bahia (BA 7, BA 8, BA 9 and BA 11). However, no resistance to pyrithiobac-sodium was found for biotypes either from Bahia or from Mato Grosso do Sul.

Effect of zone and crops rotation on Ischaemum rugosum and resistance to bispyribac-sodium in Ariari, Colombia

The objectives of this research were to evaluate (1) weed species presented in rice fields in relation to the geographical zone and crop rotation and (2) the resistance level of Ischaemum rugosum to the herbicide bispyribac-sodium. For the first objective, were sampled 79 commercial fields of rice to establish weed density, coverage, and rotation system in the evaluated fields with record of bispyribac-sodium application of at least five years. To reach the second objective, the seeds were collected from plants in commercial fields with different control levels of bispyribac-sodium herbicide. Seeds were germinated in trays under controlled conditions. When plants presented three leaves these were treated with bispyribac-sodium at different doses. Percentages of control and dry weight of plants were evaluated 12 days after treatments (dat). Dominant species in evaluated fields was I. rugosum, with a frequency of 100%, presenting escapes to different chemical commercial treatments. No significant differences were recorded between rotation systems, nevertheless, the most of I. rugosum population was found in the system rice-fallow-rice. The response of applications at different concentrations allows concluding that 65% of samples had resistance at different degrees reported as indexes from 2 to 42 which are related to rotation systems.

MULTIPLE RESISTANCE OF Sagittaria montevidensis BIOTYPES TO ACETOLACTATE SYNTHASE AND PHOTOSYSTEM II INHIBITING HERBICIDES

ABSTRACT The objective of this research was to evaluate the occurance of multiple resistance of Sagittaria montevidensis (SAGMO) biotypes to acetolactate synthase (ALS) and photosystem II (PSII) inhibiting herbicides through dose-response experiments. The experiment was conducted in a greenhouse from October 2012 to March 2013, in Pelotas, RS. The experimental design was completely randomized, with four replications. Treatments were arranged in a triple factorial design: two biotypes of S. montevidensis(SAGMO 35 - susceptible to herbicides and SAGMO 32 - suspected to be multiple resistance to ALS and PSII inhibiting herbicides), four herbicides (penoxsulam, (imazethapyr+imazapic), bentazon and saflufenacil) and 8 rates of these herbicides (1/32x, 1/16x, 1/8x, 1/4x, 1/2x, 0x, 1x, 2x, 4x, 8x, 16x, 32x and 64x). SAGMO 32 biotype presented high levels of resistance to penoxsulam, (imazethapyr+imazapic) and bentazon. For a 50% reduction in dry matter of the resistant biotype rate of 138 and 2.46 times higher than the label required for the susceptible biotype of the herbicides (imazethapyr+imazapic) and bentazon, respectively, are required. Saflufenacil may be used successfully to controlSagittaria montevidensis resistant in irrigated rice.

Molecular Basis for Resistance to Fluazifop-P-Butyl in Itchgrass (Rottboellia cochinchinensis) from Costa Rica

Rottboellia cochinchinensis is an annual grass weed species known as itchgrass, or "caminadora" in America´s Spanish speaking countries, and has become a major and troublesome weed in several crops. The application of fluazifop-P-butyl at recommended rates (125 g a.i. ha-1) was observed to be failing to control itchgrass in a field in San José, Upala county, Alajuela province, Costa Rica. Plants from the putative resistant R. cochinchinensis population survived fluazifop-P-butyl when treated with 250 g a.i. ha-1 (2X label rate) at the three- to four-leaf stage under greenhouse conditions. PCR amplification and sequencing of partial carboxyl transferase domain (CT) of the acetyl-CoA carboxylase (ACCase) gene were used to determine the molecular mechanism of resistance. A single non-synonymous point mutation from TGG (susceptible plants) to TGC (putative resistant plants) that leads to a Trp-2027-Cys substitution was found. This Trp-2027-Cys mutation is known to confer resistance to all aryloxyphenoxyproprionate (APP) herbicides to which fluazifop-P-butyl belongs. To the best of our knowledge, this is the first report of fluazifop-P-butyl resistance and a mutation at position 2027 for a Costa Rican R. cochinchinensis population.

Inheritance of blast resistance in rice to two Pyricularia grisea races, IB-1 and IB-9

Seven sources of resistance to the two predominant races IB-1 and IB-9 of the rice blast pathogen Pyricularia grisea were selected based on leaf blast reaction in tests conducted under controlled greenhouse conditions. Crosses involving resistant and susceptible parents were made to study the inheritance of the disease reaction for different sources of resistance. The F1 and F2 progenies of all crosses, including backcrosses to resistant and susceptible parents, were tested for reaction to leaf blast. The data showed that resistance is controlled by one to three genes that segregate independently in most of the donors. Non-allelic interaction among resistance genes, including dominant epistasis, was identified.

Genetic control of characters associated with bean golden mosaic geminivirus resistance in Phaseolus vulgaris L.

Bean golden mosaic is the most important viral disease of the bean crop (Phaseolus vulgaris L.) in Latin America. The genetics of resistance to a Brazilian strain of bean golden mosaic virus (BGMV), was studied in a 4 x 4 diallel cross without reciprocals, among the parental genotypes DOR 303, EMGOPA 201 Ouro, Carnaval, and Redlands Greenleaf C. Seedlings of the four parents, six F1 hybrids, 12 backcrosses, and F2 generations for each combination were inoculated on the eighth day after sowing by exposure to a viruliferous whitefly (Bemisia tabaci Genn.) population for 24 h, in a glasshouse, prior to transplantation to field conditions. The full set of two parents, F1, F2 and respective backcrosses for each combination was considered to be a family. Data were recorded and analyzed for foliar yellowing, plant dwarfing, and pod malformation, using a randomized block design, with two replications. Weighted generation mean analysis was performed for each of the six families. An additive gene action model was significant for the three characteristics evaluated. On the other hand, non-additive gene action had greater absolute value in most cases. Resistance to foliar yellowing conferred by genes from DRO 303 was highly heritable and was expressed equally well in the different genetic backgrounds evaluated. Such resistance may be oligogenic. Broad- and narrow-sense heritabilities were relatively high for all response traits. The three traits studied were all positively correlated, indicating that they can be simultaneously selected for enhancement. The highest correlation coefficient was obtained for dwarfing x pod malformation.

Inheritance of anthracnose resistance in common bean genotypes P.I. 207262 and AB 136

Bean (Phaseolus vulgaris) lines P.I. 207262 and AB 136, both resistant to delta and kappa races of Colletotrichum lindemuthianum, were crossed with Michelite, Dark Red Kidney, and Perry Marrow, susceptible to both races, and with Cornell 49-242, resistant to delta and susceptible to kappa. F1 and F2 reactions demonstrated that P.I. 207262 carries duplicate dominant genes for resistance to the delta race; AB 136 carries a dominant gene. These resistance genes are independent of the Are gene from Cornell 49-242. With respect to the kappa race, F1 and F2 data showed that the resistance controlled by P.I. 207262 and by AB 136 depends on a single dominant gene. Complementary factors were involved with AB 136 resistance to the delta race and with P.I. 207262 resistance to kappa.

Genetics of resistance to the fungus Helminthosporium sativum in wheat: use of culture filtrates in tissue culture

Six wheat genotypes and their F1 and F2 generations were exposed to the action of Helminthosporium sativum culture filtrates to examine the genetics of hexaploid wheat resistance. The objective was to improve the efficiency of breeding programs by identifying the action and number of genes involved in the resistance. The varied response of the tested genotypes to the culture filtrates allowed division of the genotypes into four groups: resistant, moderately resistant, moderately susceptible and susceptible. This variability was detected in the progeny, suggesting that the parents have distinct genetic constitutions. Additive gene action predominated and genetic gain was shown to be possible through selection. The genetic control of the resistance trait seems to be complex because of the presence of gene interaction and the difficulty of eliminating the environmental effects. The inheritance seems to be oligogenic

Effects of host resistance on the isozymatic patterns of Bipolaris sorokiniana (Dematiaceae, Moniliales)

Nine isolates of Bipolaris sorokiniana were inoculated on three cultivars of wheat plants (susceptible, moderately resistant, resistant). Eight days after the inoculation, the isolates were recovered (27 isolates) and the following isozymatic patterns were analyzed: esterase, alkaline phosphatase, acid phosphatase, malate dehydrogenase, and superoxide dismutase. The esterase system was the most polymorphic, and the isolates recovered from the susceptible cultivar showed the highest variability. This is evidence that this cultivar exerts low selection pressure on the pathogen