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Candidatus Liberibacter solanacearum haplotype B (CLsoB) is an economically important pathogen of tomato (Solanum lycopersicum L.) crops in New Zealand and Central and North America. Currently, resistant cultivars of tomato are not available as a management tactic because breeding programmes lack sources of resistance. Therefore, the objective of this study was to identify sources of resistance in tomato to CLsoB. Forty‐six landraces of tomato were collected from several states in Mexico and were inoculated with CLsoB using 20 infested adults of Bactericera cockerelli per plant. Two assays were done over two years under greenhouse conditions. In the first trial, landraces FC22 and FC44 showed a significantly higher proportion of resistant plants, less symptom severity and longer incubation time compared with the other forty‐four landraces and two susceptible cultivars. In the second assay, resistance to CLsoB of the landraces FC22 and FC44 was confirmed because they had again significantly greater numbers of resistant plants, less symptom severity, relative lower CLsoB titers and longer incubation time relative to the other genotypes. All plants considered resistant from both assays had DNA of CLsoB. Results indicate that all resistant plants from these landraces are promising sources for the development of tomato cultivars with resistance to CLsoB. [ABSTRACT FROM AUTHOR]

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Mediterranean (Q biotype) is a major pest of tomato (Solanum lycopersicum L.; Solanaceae) globally. To our knowledge, no whitefly resistant cultivar has been released commercially, and breeding programs are hampered by the lack of resistance sources to this insect which are related closely to the cultivated tomato. Two non-free-choice experiments on B. tabaci with 22 landrace (S. lycopersicum) and wild tomato (S. lycopersicum var. 'cerasiforme') populations from Mexico were performed to find sources of antibiosis resistance to this insect. Plants were infested with 20 insects per 1 leaflet of each plant using plastic micro-cages. In both assays, the number of adults and eggs were counted at 4 d post infestation, the number of nymphs (12 d post infestation), new adults, and non-glandular trichomes at 28 d post infestation. The highest B. tabaci resistance was detected in the UTC-SV13 population followed by UTC-SV12, UTC-SV1, and UTC-SV3 with a range of 15.0 to 20.0 dead adults, 0.0 to 16.5 eggs, 0.0 to 12.6 nymphs, 0.0 to 9.7 new adults per leaflet, and with a reproduction index of 0.0 to 21.7. Ten populations showed an intermediate level of resistance significantly lower in the number of dead adults, eggs, nymphs, new adults, and reproduction index compared to the commercial cultivar ('Bonny Best') used as the standard. The remaining 8 genotypes and the commercial cultivar were fully susceptible to B. tabaci. The number of non-glandular trichomes correlated significantly with the number of eggs, nymphs, and new adults emerging from the infested plants, suggesting that the density of non-glandular trichomes is favorable for whitefly reproduction. Those genotypes with moderate to high levels of resistance to B. tabaci are potential candidates for developing commercial tomato cultivars with some resistance levels to this insect. [ABSTRACT FROM AUTHOR]

Se estudió bajo condiciones controladas en invernadero el índice de atracción de adultos y preferencia de oviposición de Bemisia tabaci Mediterranean en ocho poblaciones criollas (Solanum lycopersicum) y catorce poblaciones silvestres (S. lycopersicum var. cerasiforme) de tomate, así como la relación de estos parámetros de resistencia tipo antixenosis con la densidad de tricomas no-glandulares que son características que pueden prevenir la infestación de este insecto. Cinco poblaciones silvestres y tres criollas mostraron una resistencia alta, y tres poblaciones criollas y una silvestre tuvieron una resistencia intermedia. El resto de las poblaciones y un cultivar comercial fueron altamente susceptibles porque fueron significativamente más atraídos por los adultos y preferidos para la oviposición de este insecto, indicando que existen diferentes niveles de resistencia tipo antixenosis. El número de tricomas no-glandulares no se correlacionó con ninguno de los parámetros de resistencia, indicando que no existe relación entre estos parámetros y que la resistencia observada en estos genotipos puede ser debida a otros factores como compuestos volátiles que repelen a este insecto. Estas poblaciones de tomates con diferentes niveles de resistencia tipo antixenosis pueden utilizarse para producir cultivares de tomate menos atractivas para la infestación de este insecto y como barreras físicas que rodeen los cultivos de tomate para repeler las infestaciones de B. tabaci Mediterranean. The index of attraction of adults and oviposition preference index of Bemisia tabaci Mediterranean in eight landraces populations (Solanum lycopersicum) and 14 wild populations (S. lycopersicum var. cerasiforme) of tomato was studied under greenhouse conditions, as well as the relationship of these parameters of antixenosis resistance with the density of non-glandular trichomes that are a trait that can prevent infestations of this insect. Five wild and three landraces tomato populations showed high resistance, and three landraces and one wild populations had intermediate resistance. Other populations and a commercial cultivar were very susceptible because they were significantly more attractive for adults and preferred them for oviposition. The results indicate that there are different levels of antixenosis resistance in these tomato populations. The number of non-glandular trichomes did not correlate with any of the resistance parameters, indicating there is no relationship between these parameters and that the resistance observed in these genotypes may be due to other factors such as volatile compounds that repel this insect. These tomato populations with different levels of antixenosis-type resistance can be used to generate less attractive tomato cultivars for this insect and as physical barriers that surround tomato crops to repel B. tabaci Mediterranean infestations. [ABSTRACT FROM AUTHOR]

A new disease on greenhouse pepper (Capsicum annuum L.) plants in Culiacan, Mexico with symptoms of chlorosis, wilting and vascular necrosis was observed in 2014. Sixty diseased pepper plants were collected from three different areas of the Culiacan Valley to determine the causal agent of the disease and analyse the potential risk presented by this disease in this region. Fusarium oxysporum was recovered consistently (88% of samples collected) and identified based on cultural, morphological and pathogenicity tests, as well as by PCR amplification and DNA sequencing of the TEF-1α gene. Two pathogenicity tests with 10 monoconidial isolates of F. oxysporum, which were selected randomly from diseased tissues, produced disease symptoms similar to those observed on pepper plants in the greenhouses. Symptoms were different from the typical root rot, wilting and necrosis caused by F. solani and F. oxysporum f. sp. radicis-capsici and instead matched those reported for F. oxysporum f. sp. capsici causing pepper wilt. The results suggest that the causal agent of pepper wilt in the samples analysed was F. oxysporum. This is the first report of pepper wilt caused by this fungus in Mexico, and this disease is a potential threat for pepper production in this region. [ABSTRACT FROM AUTHOR]

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major pest of the tomato (Solanum lycopersicum L.) crop worldwide, mostly because of resistance to insecticide that has been associated with endosymbionts. Although knowledge of biotypes in the B. tabaci complex and its endosymbionts is critical for developing pest management strategies, limited information is available on the pest in the Culiacan Province of Mexico. In total, 249 samples of whiteflies were collected from tomato plants of four growers in the Culiacan Valley to analyze the genetic identity of the B. tabaci complex and its endosymbionts. PCR and phylogenetic analyses on the mitochondrial cytochrome oxidase I gene (mtCO1) revealed MEAM1, MED, and indigenous genetic groups in 53, 19, and 28%, respectively, of B. tabaci on tomatoes. Individual whiteflies were examined for endosymbionts through specific primers and phylogenetic analyses on the 16S rRNA and the 23S rRNA genes. Incidence of Portiera, Hamiltonella, Rickettsia, Wolbachia, and Cardinium was 81, 46, 28, 9, and 13%, respectively, in the B. tabaci samples analyzed. A new bacterium-endosymbiont in the genus Orientia was found and described in 63% of the samples of B. tabaci. A mixture of the endosymbionts Rickettsia+UAS_511+Cardinium was observed in 10% of samples of B. tabaci MED, while in the MEAM1 biotype, a combination of Hamiltonella+UAS_511 was in 32% of the samples analyzed. The study highlights the diversity and distribution of B. tabaci and its endosymbionts throughout the Culiacan Province and provides evidence for control of the insect pest. [ABSTRACT FROM AUTHOR]

Pepper huasteco yellow vein virus (PHYVV) is a major disease in pepper (Capsicum annuum) that causes quantitative and qualitative losses to the crop in Central America and part of North America. To date, no resistant cultivars are available, and breeding is hampered by the lack of knowledge of the inheritance of this trait. Sources of resistance to PHYVV have been identified in the wild peppers of Mexico. The objectives of this study were to determine the grade of dominance, to analyze the maternal influence, and to estimate the number of genes involved in this resistant trait to PHYVV in the resistant wild pepper accession UAS12. Three susceptible parent lines-'Anaheim' (Ana), 'Ancho Gigante' (AG), and 'Yolo Wonder' (YW)-were crossed with resistant UAS12 accession to develop F1 (reciprocal), F2, and BC1 progenies in three families. Plants from this study were inoculated with PHYVV through Bemisia tabaci, evaluated phenotypically, and the segregation of disease scores was studied. A single recessive gene was found to control resistance to PHYVV in the resistant UAS12 accession, although segregation patterns suggested that other minor genes could participate in the expression of this resistant trait. No proof was found for maternal inheritance of PHYVV resistance. The gene symbol phv is proposed for PHYVV resistance in UAS12 accession in pepper. These results provide useful information for the design of pepper breeding programs in the introgression of this trait into commercial pepper backgrounds. [ABSTRACT FROM AUTHOR]

Mexico, the center of origin of maize (Zea mays L.), has taken actions to preserve the identity and diversity of maize landraces and wild relatives. Historically, spatial isolation has been used in seed production to maintain seed purity. Spatial isolation can also be a key component for a strategy to minimize pollen-mediated gene flow in Mexico between transgenic maize and sexually compatible plants of maize conventional hybrids, landraces, and wild relatives. The objective of this research was to generate field maize-to-maize outcrossing data to help guide coexistence discussions in Mexico. In this study, outcrossing rates were determined and modeled from eight locations in six northern states, which represent the most economically important areas for the cultivation of hybrid maize in Mexico. At each site, pollen source plots were planted with a yellow-kernel maize hybrid and surrounded by plots with a white-kernel conventional maize hybrid (pollen recipient) of the same maturity. Outcrossing rates were then quantified by assessing the number of yellow kernels harvested from white-kernel hybrid plots. The highest outcrossing values were observed near the pollen source (12.9% at 1 m distance). The outcrossing levels declined sharply to 4.6, 2.7, 1.4, 1.0, 0.9, 0.5, and 0.5% as the distance from the pollen source increased to 2, 4, 8, 12, 16, 20, and 25 m, respectively. At distances beyond 20 m outcrossing values at all locations were below 1%. These trends are consistent with studies conducted in other world regions. The results suggest that coexistence measures that have been implemented in other geographies, such as spatial isolation, would be successful in Mexico to minimize transgenic maize pollen flow to conventional maize hybrids, landraces and wild relatives. [ABSTRACT FROM AUTHOR]