Evaluation of the impact of small herbivores and fungal infection in the production of seedlings and in the establishment of the bioengineering halophyte grass of Spartina alterniflora marshes
Author: Ricardo Franco Freitas (Currículo Lattes)
Supervisor: Dr Cesar Serra Bonifácio Costa
Abstract
Aquaculture involves the cultivation of aquatic organisms including fish, crustaceans, mollusks and aquatic plants. These crops have as main objectives the production of food and other bioproducts for man. On the other hand, the cultivation of aquatic plants can also be used for the treatment of aquaculture effluents, the phytoremediation of contaminated soils or the creation / restoration of vegetated aquatic environments. Everglades plants, such as Spartina alterniflora, are among the higher plants most cultivated by man, aiming to contain natural erosive processes related to the relative rise in sea level. The production of seedlings in agricultural greenhouses and the establishment of seedlings in the intertidal environment are among the most critical stages for the success of everglades rearing / restoration projects.In addition, the cultivation of these plants, as well as for any other type of aquatic organism, needs care for greater productivity, thus avoiding pests (herbivores and fungi) and plant diseases. Therefore, knowledge of ecological mechanisms is essential for success in these types of projects. Thus, in an attempt to assess the impact of small herbivores and the subsequent fungal infection on seedlings caused by injuries to these herbivores, this Master's Thesis describes the development of 2 studies. In the first study, presented in Chapter 1, the effects of the herbivory of aphids Hysteroneura setariae on the development of S. alterniflora seedlings and on the infection of their leaves by fungi were evaluated. For the control of these pests,the efficiency of the separate and joint application of the insecticide Malathion 500 CE and the fungicide Daconil BR on the cultivation of these seedlings in an unheated greenhouse was also determined. The results obtained proved a great efficiency of the insecticide Malathion in protecting seedlings of S. alterniflora against the attack of aphids and fungi, in addition to improving the biometric and phytosanitary parameters of the plant. Regarding the development of the plant, it is important to highlight that the average tillering values of seedlings treated with insecticide were about 155% higher than those not treated with this insecticide. The use of the fungicide Daconil was not effective in reducing the damage caused by aphids and neither the fungal infection, facilitated during feeding and 2 secretion of sugary substances (honeydew) by these insects. So much so that the frequency of the occurrence of fungal spots on leaves sprayed with this fungicide had average values around 90%. Additionally, this fungicide has not been shown to cause acute effects on the growth / development of S. alterniflora seedlings. The second study, described in Chapter 2, was carried out in the intertidal zone of a newly established tide. In this study, the impacts of Neohelice granulata crabs and fungal infections facilitated by these herbivores on S. alterniflora were examined from 2 factorial experiments with the use of crab exclusion cages and the spraying of the fungicide Daconil BR. Through the results found, it was possible to verify a great impact of crabs on the development of seedlings. While 100% of S.alterniflora protected with exclusion cages survived, in hollow cages the survival of seedlings reduced to 65%. The leaves injured with fungicide and those without injuries and use of this pesticide had average values of fungal biomass up to 70% lower than those of the injured leaves. Finally, the fungicide and fungi did not affect the development and survival of S. alterniflora seedlings during the 2 experiments carried out.