A suite of plants from the maize genus Zea L. (Poaceae) and the specialist herbivore Dalbulus maidis (DeLong and Wolcott, 1923) (Hemiptera: Cicadellidae) were used to test the hypotheses that anti-herbivore defenses are affected by plant life-history evolution and human intervention through domestication and breeding for high yield. The suite of plants included a commercial hybrid maize (Zea mays ssp. mays L.), a landrace maize, two populations of annual Balsas teosinte (Z. mays ssp. parviglumis Iltis & Doebley), and perennial teosinte (Z. diploperennis Iltis, Doebley & Guzman). Leaf toughness and pubescence, oviposition preference, and feeding and oviposition acceptance parameters were compared among the suite of host plants looking for effects of transitions in life history (perennial to annual teosinte), domestication (annual teosinte to landrace maize), and breeding (landrace maize to hybrid maize) on defenses against D. maidis. Observations on leaf toughness suggested that the life history and domestication transitions weakened the plant’s resistance to penetration by the herbivore’s mouthparts and ovipositor, as expected, while observations on pubescence suggested that the breeding transition led to stronger defense in hybrid maize compared to landrace maize, contrary to expectation. Observations on oviposition preference of D. maidis coincided with the expectations that life history and domestication transitions would lead to preference for Balsas teosinte over perennial teosinte, and of landrace maize over Balsas teosinte. A negative correlation suggested that oviposition preference is significantly influenced by leaf toughness. Observations on host plant feeding and iii oviposition acceptance under no-choice conditions suggested that D. maidis equally accepts all host plants considered in this study, thus these observations did not support the hypotheses associated with the life history, domestication, and breeding transitions evident in the herbivore’s host genus. Overall, the results of this study suggested that plant defenses against specialist herbivores are variably affected by plant life history evolution, domestication, and breeding. Additionally, the study’s results suggested that chemical defenses may play a role in Zea antiherbivore defense because the two physical defenses that were evaluated (i.e. leaf toughness and pubescence) only partially explained host preference of D. maidis

In one study, a suite of plants from the maize genus Zea L. (Poaceae) and the specialist herbivore Dalbulus maidis (DeLong and Wolcott, 1923) (Hemiptera: Cicadellidae) were used to test the hypotheses that anti-herbivore defenses are affected by plant life-history evolution and human intervention through domestication and breeding for high yield. The suite of Zea host plants included one Mexican commercial hybrid maize Zea mays ssp. mays L., a landrace variety of maize, two populations of Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley), and perennial teosinte (Z. diploperennis Iltis, Doebley & Guzman). This suite of host plants includes three Transitions evident within the genus Zea: life history form perennial to annual life cycle evident between perennial teosinte and Balsas teosinte, domestication transition from wild annual to domesticated annual evident between Balsas teosinte and landrace maize, and; breeding transition from landrace cultivar to a hybrid cultivar. The transitions were correlated with differences in plant defenses, as indicated by corn leafhopper performance. Results showed a performance gradient, suggesting a pattern in which plant defense is stronger in perennial than annual plants, Balsas teosinte than landrace maize, and in landraces than in hybrid maize. Furthermore, results suggested that domesticated maize would be the least defended, most suitable host for corn leafhopper. In a second study, haplotype diversity was assessed to address structuring and interconnectedness among samples of corn leafhopper collected in the southwestern region of Mexico to address microevolution. The geographic focus of the study was maintained within an area encompassing the presumed centers of radiation of Dalbulus and its host genus Zea, and of maize domestication. Samples were complemented with samples of corn leafhopper sequences available at GenBank. Results revealed seven haplotypes from three host plants within Zea: perennial teosinte, Balsas teosinte, and maize. Furthermore, genetic differentiation was present and haplotype diversity appears to correlate with differences in genetic structure between perennial teosinte and maize. One haplotype was found to be present throughout all sites, which appears to parallel the spread of maize cultivation. As maize cultivation spread beyond its area of domestication, corn leafhoppers colonized perennial teosinte, further suggesting that subsequent decreases in maize cultivation in perennial teosinte habitat created a refuge where perennial teosinte- adapted haplotypes could persist. Altogether, my research suggests that the combination of historical expansion of maize cultivation expansion and the weaker anti-herbivore defenses associated within maize domestication appears to have favored genotypes particularly adapted for exploiting maize.

O enfezamento vermelho, causado por um fitoplasma, foi registrado no Brasil no início da década de setenta, sendo relatado como de pequena importância para a cultura do milho. A partir de meados dos anos oitenta, com a introdução dos plantios de safrinha e dos cultivos irrigados, a doença passou a ser considerada de relevância econômica. Atualmente, o enfezamento se constitui em uma das mais importantes doenças do milho, sendo, inclusive, fator limitante para produção em função da região, do híbrido escolhido e da época de plantio.Um ponto crítico no manejo da doença se refere ao escasso conhecimento sobre a sobrevivência do patógeno e do inseto vetor (Dalbulus maidis) durante a ausência da cultura do milho no campo. Este tipo de informação pode ser útil principalmente na redução do inóculo inicial do patógeno, visando um controle mais eficiente da doença. Assim sendo, o presente trabalho teve por objetivo avaliar algumas gramíneas, usadas na formação de pastagens, e espécies daninhas, que ocorrem na cultura do milho, como potenciais hospedeiros alternativos do fitoplasma e do seu vetor . Treze espécies de capins e ervas daninhas foram experimentalmente inoculadas com o fitoplasma do enfezamento vermelho do milho, através de cigarrinhas infectivas. Avaliações foram feitas com base na observação de sintomas, na detecção molecular do fitoplasma nos tecidos das plantas inoculadas e na contagem de insetos sobreviventes nestas plantas inoculadas. A detecção foi feita por duplo PCR e a identificação do fitoplasma foi realizada pela análise de RFLP, com as enzimas de restrição AluI, RsaI, KpnI e MboI. Das treze espécies testadas, o fitoplasma foi encontrado nos capins colonião (Panicum maximum), marmelada (Brachiaria plantaginea) e braquiária (Brachiaria decumbens), através da amplificação do 16S rDNA, visualizado em gel de agarose na forma de bandas. Os insetos sobreviveram nos três capins até o final do período de experimentação, revelando que os capins foram capazes de abrigar a cigarrinha. Estes resultados demonstraram a possibilidade destas espécies atuarem como potenciais hospedeiros alternativos para o patógeno e o seu vetor, em condições naturais. Estas informações poderão contribuir para novas investigações, na busca de melhor conhecimento sobre a epidemiologia da doença, principalmente quanto à sobrevivência do fitoplasma e da cigarrinha vetora. / Maize bushy stunt, caused by a phytoplasma, was reported in Brazil in the beginning of the seventies, and it was considered as not important for corn. Since the middle of the eighties decade, when the later planting practice and irrigation were adopted, the disease became relevant. Currently, maize bushy stunt represents one of the most important diseases and has caused significant losses. In some conditions the disease can limit the production, especially in relation to the region, used hybrids and crop season. A critical point to disease control is the lack of about survival of pathogen and vector, during the absence of corn crop on the field. This kind of information can be useful to promote the reduction of the initial inoculum, aiming a more efficient disease control. Thus, the objective of the present study was to evaluate some grasses and weeds species as potential alternative hosts of the maize bushy stunt phytoplasma and its vector Dalbulus maidis. Thirteen botanical species were experimentally inoculated with the phytoplasma by using infective leafhoppers. Evaluations were based upon symptom observation, molecular detection of the phytoplasma in tissue of inoculated plants and the of number of insects present in the plants. Detection was conducted by nested PCR and phytoplasma identification by RFLP analyses, using AluI, RsaI, KpnI and MboI as restriction enzymes. Phytoplasma was detected in three species, Panicum maximum, Brachiaria plantaginea and Brachiaria decumbens based on amplification of 16S rDNA, visualized as specific band in agarose gel. Insects remain on alive on the plants belonging to those three species up to the end of the assays. Thus, the present study showed the possibility of those species as potential alternative hosts to the pathogen and its vector, under natural conditions. The results can contribute for new investigations, in order to understanding the epidemiology of the disease, especially in relation to phytoplasma and vector survival.

O enfezamento vermelho, causado por um fitoplasma, foi registrado no Brasil no início da década de setenta, sendo relatado como de pequena importância para a cultura do milho. A partir de meados dos anos oitenta, com a introdução dos plantios de safrinha e dos cultivos irrigados, a doença passou a ser considerada de relevância econômica. Atualmente, o enfezamento se constitui em uma das mais importantes doenças do milho, sendo, inclusive, fator limitante para produção em função da região, do híbrido escolhido e da época de plantio.Um ponto crítico no manejo da doença se refere ao escasso conhecimento sobre a sobrevivência do patógeno e do inseto vetor (Dalbulus maidis) durante a ausência da cultura do milho no campo. Este tipo de informação pode ser útil principalmente na redução do inóculo inicial do patógeno, visando um controle mais eficiente da doença. Assim sendo, o presente trabalho teve por objetivo avaliar algumas gramíneas, usadas na formação de pastagens, e espécies daninhas, que ocorrem na cultura do milho, como potenciais hospedeiros alternativos do fitoplasma e do seu vetor . Treze espécies de capins e ervas daninhas foram experimentalmente inoculadas com o fitoplasma do enfezamento vermelho do milho, através de cigarrinhas infectivas. Avaliações foram feitas com base na observação de sintomas, na detecção molecular do fitoplasma nos tecidos das plantas inoculadas e na contagem de insetos sobreviventes nestas plantas inoculadas. A detecção foi feita por duplo PCR e a identificação do fitoplasma foi realizada pela análise de RFLP, com as enzimas de restrição AluI, RsaI, KpnI e MboI. Das treze espécies testadas, o fitoplasma foi encontrado nos capins colonião (Panicum maximum), marmelada (Brachiaria plantaginea) e braquiária (Brachiaria decumbens), através da amplificação do 16S rDNA, visualizado em gel de agarose na forma de bandas. Os insetos sobreviveram nos três capins até o final do período de experimentação, revelando que os capins foram capazes de abrigar a cigarrinha. Estes resultados demonstraram a possibilidade destas espécies atuarem como potenciais hospedeiros alternativos para o patógeno e o seu vetor, em condições naturais. Estas informações poderão contribuir para novas investigações, na busca de melhor conhecimento sobre a epidemiologia da doença, principalmente quanto à sobrevivência do fitoplasma e da cigarrinha vetora. / Maize bushy stunt, caused by a phytoplasma, was reported in Brazil in the beginning of the seventies, and it was considered as not important for corn. Since the middle of the eighties decade, when the later planting practice and irrigation were adopted, the disease became relevant. Currently, maize bushy stunt represents one of the most important diseases and has caused significant losses. In some conditions the disease can limit the production, especially in relation to the region, used hybrids and crop season. A critical point to disease control is the lack of about survival of pathogen and vector, during the absence of corn crop on the field. This kind of information can be useful to promote the reduction of the initial inoculum, aiming a more efficient disease control. Thus, the objective of the present study was to evaluate some grasses and weeds species as potential alternative hosts of the maize bushy stunt phytoplasma and its vector Dalbulus maidis. Thirteen botanical species were experimentally inoculated with the phytoplasma by using infective leafhoppers. Evaluations were based upon symptom observation, molecular detection of the phytoplasma in tissue of inoculated plants and the of number of insects present in the plants. Detection was conducted by nested PCR and phytoplasma identification by RFLP analyses, using AluI, RsaI, KpnI and MboI as restriction enzymes. Phytoplasma was detected in three species, Panicum maximum, Brachiaria plantaginea and Brachiaria decumbens based on amplification of 16S rDNA, visualized as specific band in agarose gel. Insects remain on alive on the plants belonging to those three species up to the end of the assays. Thus, the present study showed the possibility of those species as potential alternative hosts to the pathogen and its vector, under natural conditions. The results can contribute for new investigations, in order to understanding the epidemiology of the disease, especially in relation to phytoplasma and vector survival.