The use of silicon (Si) in agriculture has attracted a great deal of interest from researchers because of the numerous benefits of this element to plants, especially when they are submitted to abiotic and/or biotic types of stress. The host's increased resistance to diseases, promoted by Si, is mainly associated with the deposition of this element in the tissues and the potentiation of defence mechanisms. However, the mechanisms involved in Si-mediated host resistance need to be further investigated. Thus, this study aimed to microscopically and biochemically elucidate the resistance of sorghum to anthracnose. In the leaves of plants supplied with Si, in addition to a greater deposition of Si at the infection sites, the acervuli were smaller in number compared to the leaves of plants not supplied with Si. Additionally, the activities of the defence enzymes peroxidases and polyphenoloxidases and the concentration of anthocyanins were higher in the leaves of plants supplied with Si. It can be concluded that Si, in addition to participate in the physical barrier that slows or prevents Colletotrichum sublineolum penetration in sorghum leaves, also plays a role in the biochemical aspect of sorghum resistance to anthracnose.

The instability of heliconia flower stem production may be related to climatic variation. Therefore, that information is very important for planning the species production throughout Brazil, mainly in northeast region. The objective of this work was analyzed the previous effects of photoperiod, air temperature and precipitation in the flower stem production of Heliconia psittacorum cv. Red Opal, H. psittacorum x H. spathocircinata cv. Golden Torch, H. stricta cv. Fire Bird and H. rauliniana, and the monthly temporal stability. The flower stems with two to three open bracts were harvested twice a week between May, 2004 and March, 2012 from a field in Camaragibe – PE, Rain Forest Zone of Pernambuco, Brazil. Pearson’s linear correlation demonstrate flower stem production occur in response to the environment stimulus. H. rauliniana inflorescence initiation response mainly to the shortest photoperiod and cv. Fire Bird to highest photoperiod. Production of the cv. Golden Torch was more stable in April, with reduction in September (39.46%) and an increase in December (87.02%), compared with the annual average. The cv. Red Opal produced more in September (31.43%), with a reduction in February (44.8%) and stable in July. H. rauliniana production was stable in September and increase in November (274.8%). The cv. Fire Bird production was stable in April, with the lowest production in November and the highest in March (65%). With this information is possible to predict the cultivar production in the Rain Forest Zone of Pernambuco State, Brazil

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