Resistência à cochonilha do carmim em clones de palma forrageira

Abstract

This thesis’ objective is to identify the genetic variability among cactus clones and to demonstrate resistance to cochineal carmine for plants cultivated in vitro. Observations were made regarding the establishment of colonies on the cladodes of 20 clones of cactus, from a scale ranging from zero to five, zero being the absence of infestation and five the highest. We used the mixed model methodology for obtaining the Best Linear Unbiased Prediction (BLUP) of genotype effects and the process of Restricted Maximum Likelihood (REML) to estimate components of variance and genotypic parameters. The variance components and genotypic parameters were obtained by using the REML process. The selection of the best clones by the REM/BLUP methodology was efficient with high gain selection. High genetic variability was verified among the genetic material evaluated, as shown by the coefficient of genotypic variation (26,73%) and hereditary (72%). These coefficients indicate favorable conditions to clone selection, which can favor considerable genetic advances. The clones “Miuda” and “Orelha de Elefante” were selected and classified as resistants, with relative value above 95%. Explants from the clones of “Orelha de Elefante Mexicana” (Opuntia stricta), “IPA Sertânia” (Nopalea cochenillifera) and “Gigante” (Opuntia fícus-indica), originated from the sequential micro-propagation, were submitted to artificial infestation with Dactylopius opuntiae cochineal nymphs, in order to prove their resistance to this plague. After 150 days of growth, cultivation were removed from the in vitro condition and maintained in environmental conditions. The observations about the fixation of the insects on the explants were made at 7, 14, 21, 28 and 35 days after infestation. Explant samples were immersed on FAA 50 fixator, to produce histological blades. Epiderm and parenchyma areas were sized from the samples. It was found that no nymphs were present on the “Orelha de Elefante Mexicana” and “IPA Sertânia” clones, and that 65% of the explants of the “Gigante” clone were dead by 35 days because of the damage caused by the cochineals. There was no mortality of any explant from the considered resistant material. There were significant differences in epidermal thickness, with the clone “Gigante” having the highest thickness, which contradicts the theory that resistance to cochineal carmine is related to anatomy.