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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]

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]