Bioecology of Spodoptera frugiperda (Smith, 1757) in different cover crops.

The objective of this work was to evaluate the biological variables of Spodoptera frugiperda on species of cover crops. The experiments were conducted in laboratory and greenhouse using the following species: sunflower (Helianthus annuus), sun hemp (Crotalaria juncea), brachiaria (Urochloa decumbens e Urochloa ruziziensis), millet (Pennisetum americanum), black oat (Avena stringosa), white lupin (Lupinus albus), forage turnip (Rafanus sativus) and maize (Zea mays). In laboratory the S. frugiperda larval survival varied from 57%, on L. albus, to 93% on H. annuus and the survival of the pre-imaginal phase varied from 45% on U. decumbens to 81.6% on Z. mays. On C. juncea the larval biomass was lower and the development period of the young and larval stage was higher. The adaptation index was less on C. juncea in greenhouse and laboratory. In greenhouse the larval survival at 14 days was similar for all plants and at 21 days was the lowest on C. juncea. There was less accumulation of biomass at 14 days on C. juncea and at 21 days on C. juncea and A. stringosa. Regarding damage, C. juncea presented less susceptibility to Spodoptera frugiperda attack, which together with the other evaluated parameters, indicated this plant as the most appropriate for soil cover before cultivation of maize.

Utilization of nitrogen (15N) from urea and green manures by rice as affected by nitrogen fertilizer rate.

The use of green manures (GMs) in combination with nitrogen (N) fertilizer application is a promising practice to improve N fertilizer management in agricultural production systems. The main objective of this study was to evaluate the N use efficiency (NUE) of rice plant, derived from GMs including sunn hemp (Crotalaria juncea L.), millet (Pennisetum glaucum L.) and urea in the greenhouse. The experimental treatments included two GMs (sunn hemp-15N and millet-15N), absence of N organic source (without GM residues in soil) and four N rates, as urea-15N (0, 28.6, 57.2 and 85.8 mg N kg-1). The results showed that both rice grain and straw biomass yields under sunn hemp were greater than that of millet or without the application of GM. The NUE of rice under sunn hemp was greater than that under millet (18.9 and 7.8% under sunn hemp and millet, respectively). The urea N application rates did not affect the fertilizer NUE by rice (53.7%) with or without GMs. The NUE of GMs by rice plants ranged from 14.1% and 16.8% for root and shoot, respectively. The study showed that green manures can play an important role in enhancing soil fertility and N supply to subsequent crops.

Biological and molecular characterization of a highly divergent johnsongrass mosaic virus isolate from Pennisetum purpureum.

2016

Influência da temperatura na germinação de sementes de Digitaria insularis, Leptochloa virgata, Pennisetum setosum e Sorghum halepense

Objetivou-se com este trabalho avaliar a influência de temperaturas constantes na germinação de sementes de espécies de plantas daninhas da família Poaceae que apresentam ocorrência em áreas de pastagem, para isto, foram analisadas as sementes de Digitaria insularis, Leptochloa virgata, Pennisetum setosum e Sorghum halepense coletadas manualmente de diversas plantas em áreas de pastagem. As sementes foram dispostas em caixas gerbox sobre folha dupla de papel "germitest", umedecido com água destilada equivalente a 2,5 vezes a massa do papel seco. As caixas foram incubadas em três germinadores verticais tipo MANGELSDORF com as temperaturas de 25ºC, 30ºC e 35ºC e fotoperíodo de 12 horas. As avaliações foram realizadas, efetuando-se a contagem diária das ocorrências germinativas, a partir da protrusão da radícula, durante 28 dias após o início do estudo. Os parâmetros avaliados foram porcentagem e índice de velocidade de germinação (IVG), efetuando-se a análise estatística pela análise de variância com comparação de médias pelo teste de Tukey a 5% de probabilidade e transformação dos resultados de porcentagem de germinação. As temperaturas que proporcionam os melhores resultados de porcentagem e velocidade de germinação são 30 e 35°C, para as espécies de D. insularis, L. virgata e S. halepense, por outro lado, a espécie de P. setosum não apresenta germinação em nenhuma das temperaturas avaliadas (25º 30º e 35ºC) não são adequadas para a sua germinação.