The area cultivated with wheat has been increasing in the savannahs of the state of Minas Gerais, Brazil. Aphids are usually one of the main pests of wheat in many regions of the world; however, little is known about the aphid population in this new environment. The southern region of Brazil, the main wheat production area, has had several problems as a result of aphids, but aphid populations and the resulting impact on wheat production have not been investigated in these new crop production areas. Understanding control strategies to manage this insect could be essential for the “Cerrado” wheat that is grown in this area. The application of silicon (Si) has the potential to reduce the population growth of wheat aphids; however no field studies have been reported. Hence, we evaluated the effect of Si fertilization via soil application on the aphid populations and species composition and on yield components of wheat in three locations in Minas Gerais; the experiment was repeated simultaneously in Uberlândia, at the experimental areas of UFU and IFTM, and in Montes Claros, at the experimental area of UFMG, using the cultivars BRS 264 and BRS 394. The aphids first appeared just before wheat earing; they were then sampled six times over the course of the study, seven days apart, starting from 45 days after sowing. The aphid species Sitobion avenae (Fabricius), Schizaphis graminum (Rondani), and Rhopalosiphum padi (Linnaeus) were observed in all three locations; S. avenae was the dominant species in all locations. The experimental area of UFU had the highest number of S. avenae aphids per tiller for both cultivars, while UFMG had the lowest populations. Aphid populations and wheat yield components were not affected by soil Si fertilization. There was no difference in yield as a result of location or cultivar, but the location UFU and the cultivar BRS 394 had the greatest average hectoliter weight.
Septoria leaf spot, caused by Septoria lactucae, is one of the major open-field diseases of lettuce (Lactuca sativa) in tropical and subtropical regions. However, there are few available studies dealing with the identification of useful sources of resistance to this disease. Here, a genetically diverse collection of 42 lettuce accessions was evaluated for Septoria leaf spot reaction under open-field conditions (natural inoculum) during the rainy season. The experimental design was randomized blocks with three replications (16 plants each). Although no immunity-like source was detected, 21 accessions displayed superior levels of rate-reducing resistance with significant lower Area Under Disease Progress Curve (AUDPC) values, encompassing seven accessions of the ‘Crispy green loose-leaf’, eight of the ‘Crispy purple loose-leaf’, two of the ‘Cos/Romaine’, two of the ‘Loose-leaf super crispy’, one accession of the ‘Butterhead’, and one accession of the ‘Iceberg’ morphotype. A subgroup of nine accessions with the highest levels of field resistance was also inoculated under greenhouse conditions with four S. lactucae isolates (collected in distinct geographic areas) in two assays at two distinct phenological stages. The cultivars ‘BRS Mediterrânea’ and ‘Vanda’ displayed lowest AUDPC values at the late vegetative/reproductive phenological phase. The remaining accessions displayed intermediate values of AUDPC, with the exception of the cultivar ‘Rubi’ (control), which exhibited moderate levels of susceptibility. The availability for lettuce breeding programs of genetic sources with higher and stable levels of resistance to S. lactucae will enable the development of more adapted commercial cultivars, increasing the sustainability of this crop across Neotropical regions.
A Deus por eu existir, por permitir que tudo isto acontecesse e por colocar em meu caminho pessoas maravilhosas que me ajudaram nas horas que mais precisei. Aos meus pais que sem dúvida nenhuma são a minha fortaleza e inspiração, aos meus maravilhosos irmãos por estarem sempre ao meu lado quando precisei. A toda minha família, meus tios, primos e primas, pelo apoio e incentivos nas horas de fraqueza e desânimo. Com toda certeza posso dizer que vocês são meus heróis. Ao meu Orientador, Prof. Dr. Marcus Vinicius Sampaio pelos inúmeros ensinamentos, pelas orientações no desenvolvimento e finalização deste projeto e pela paciência e mãos estendidas nos momentos de maiores dificuldades. Agradeço pela sua amizade. À Agroneli e à Ercal, pela doação do Agrosilício e Calcário, para a realização dos experimentos. Aos parceiros do LACOB-UFU, principalmente Anakely, Gabriel e Diego primeiramente pela amizade, paciência e brincadeiras. Também pelas inúmeras ajudas no desenvolvimento deste trabalho, com sol ou com chuva. Obrigado por estarem presentes quando mais precisei, vocês estão no meu coração.
Septoria leaf spot, caused by Septoria lactucae, is one of the major open-eld diseases of lettuce (Lactuca sativa) in tropical and subtropical regions. However, there are few available studies dealing with the identi cation of useful sources of resistance to this disease. Here, a genetically diverse collection of 42 lettuce accessions was evaluated for Septoria leaf spot reaction under open-eld conditions (natural inoculum) during the rainy season. The experimental design was randomized blocks with three replications (16 plants each). Although no immunity-like source was detected, 21 accessions displayed superior levels of rate-reducing resistance with signi cant lower Area Under Disease Progress Curve (AUDPC) values, encompassing seven accessions of the 'Crispy green loose-leaf', eight of the 'Crispy purple loose-leaf', two of the 'Cos/Romaine', two of the 'Loose-leaf super crispy', one accession of the 'Butterhead', and one accession of the 'Iceberg' morphotype. A subgroup of nine accessions with the highest levels of eld resistance was also inoculated under greenhouse conditions with four S. lactucae isolates (collected in distinct geographic areas) in two assays at two distinct phenological stages. The cultivars 'BRS Mediterrânea' and 'Vanda' displayed lowest AUDPC values at the late vegetative/reproductive phenological phase. The remaining accessions displayed intermediate values of AUDPC, with the exception of the cultivar 'Rubi' (control), which exhibited moderate levels of susceptibility. The availability for lettuce breeding programs of genetic sources with higher and stable levels of resistance to S. lactucae will enable the development of more adapted commercial cultivars, increasing the sustainability of this crop across Neotropical regions.
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