Sobrevivência do fitoplasma do enfezamento vermelho do milho e de seu vetor >i<Dalbulus maidis>/i< (Delong & Wolcott) em algumas espécies forrageiras

Abstract

Sobrevivência do fitoplasma do enfezamento vermelho do milho e de seu vetor Dalbulus maidis (Delong & Wolcott) em algumas espécies forrageiras/ Felipe Franco de Oliveira.-versão revisada de acordo com a resolução CoPGr 6018 de 2011.-Piracicaba, 2019. 40 p. Dissertação (Mestrado)-USP / Escola Superior de Agricultura "Luiz de Queiroz". 1. Milho 2. Forrageiras 3. Cigarrinha do milho 4. Enfezamento vermelho I. Título Maize bushy stunt, associated with a phytoplasma of the group 16SrI, subgroup B, has been reported in Brazilian areas cultivated with corn since 1970s.The economic importance of the disease was expressed from 1980s, with the introduction of a cultivation system named "safrinha" maize. The pathosystem has long been explored, but failures of knowledge are yet significant. In the present work it was investigated the survival of the fitoplasma and its vector, the leafhopper Dalbulus maidis, in various forage species of high agronomic interest. So, five varieties of forage (Panicum maximum cv. Mombaça, P. maximum x P. infestum cv. Massai, Brachiaria bizantha cv Marandu, B. brizantha cv. Piatã e B. decumbens cv. Basilisk (popularly known by Decumbens) were used, which were inoculated with the phytoplasma via infective insects fed in corn plants infected by the pathogen. Assessment was conducted based on the detection of phytoplasma using PCR tecnique and daily counting of dead leafhoppers found in the inoculated forage plants. Tissues were collected for detection 28, 56, 84, 112 and 140 days after inoculation and plants were cut immediately after each sampling. In addition, an assay was conducted, in which insects were fed in infected plants belonging to all forage varieties and, subsequently, confined in healthy corn plants. The results allowed to detect the phytoplasma in all distinct forage varieties, 28 days after inoculation. Assesment made to the 56 days allowed to detect the pathogen in 66% of the plants of Marandu, in 50% of Massai, and 16% of plants of the varieties Decumbens, Mombaça and Piatã. In evaluations conducted to the 84, 112, and 140 days after inoculation, the phytoplasma was not more detected in the new tissues from forage plants. Concerning survival of leafhoppers, the different forage showed the same behavior, within each period corresponding to 24, 48, 72, 96 e 120 hours after confining of the insects in the plants; in the period of 120 hours, almost all insects were dead. In relation to the infection of corn plants by insects fed in forage plants infected with the pathogen, the analysis showed absence of the phytoplasma in all inoculated corn plants. These results pointed that, in natural conditions, probably the forages to serve as reservoir; however, they also suggested that these forages probably do not act as inoculum sources of the pathogen for corn plants. In addition, the results also demonstrated that none variety stood out as more favorable to survival of the leafhopper.

Análise da aplicação experimental de silício em plantas de milho visando a resistência ao enfezamento vermelho causado por fitoplasma

“…Esta previsão foi confirmada a partir da década de 1980 com a adoção generalizada do plantio do milho safrinha. Assim, a presença frequente do milho no campo, principalmente resultante do plantio de "safrinha", a sobrevivência do patógeno e do inseto vetor favoreceram a disseminação da doença (Oliveira et al, 1998).…”

“…Devido a ampla faixa de temperatura (17º a 35ºC) em que as cigarrinhas conseguem se desenvolver, a sua distribuição geográfica é bastante ampla (Waquil et al, 1999;Nieuwenhove et al, 2016), sendo encontradas em todas as regiões brasileiras (Oliveira et al, 2013b(Oliveira et al, , 2017. No Brasil, o pico populacional da cigarrinha é atingido nos meses de março e abril, coincidindo com o período em que ocorre o cultivo do milho safrinha; assim, a disseminação é favorecida, aumentando a incidência e intensidade da doença no campo (Waquil et al, 1997;Oliveira et al, 1998). A espécie é uma praga exclusiva da cultura do milho, porém durante a entressafra, na ausência de seu hospedeiro principal, a cigarrinha consegue sobreviver em hospedeiros alternativos pertencentes à família Poaceae (Nault, 1980;Summers et al, 2004;Oliveira et al, 2020).…”