Genômica comparativa e filogenia de espécies de fitonematóides e reação de genótipos de Psidium spp ao parasitismo de Meloidogyne enterolobii

Abstract

The main phytosanitary problem of the guava crop in our country is meloidoginose, caused by Meloidogine enterolobii Yang and Eisenback (= M. mayaguensis. Its incidence results in a marked drop in productivity and, in most cases, the death of plants in medium-term. In general, the best chances of success in the control of M. enterolobii are in the use of resistant materials, which can be obtained by genetic improvement. Several studies have already been carried out on the resistance of guava tree and araçá tree about this pathogen, in which a wide range of methods and criteria were used to classify the genotypes. However, up to the present no guava genotypes resistant to M. enterolobii have been found. In order to control the nematode in question, the objective of this research was to contribute to identify sources of resistance in guava Psidium guajava L., Psidium sp. and other species of the family Myrtaceae. The three scientific articles that compose this PhD thesis in the Graduate Program in Agronomy - Genetic Improvement of Plants, at UFRPE, they were developed with the intention of contributing to the identification of resistance sources in species of Myrtaceae that may serve in the future as rootstock for commercial guavas. The first article had as objective to evaluate different levels of inoculum of M. enterolobii, times of evaluation and to compare two levels of substrates, in screenings of Psidium spp. The evaluations occurred at 30 (E1), 60 (E2), 90 (E3), 120 (E4) and 150 (E5) days after inoculation, in two containers with different volumes (R1 and R2), four levels of inoculum I1, I2, I3 and I4) with six replicates. Each experimental plot consisted of one plant, totaling 240 plots which were delineated in DIC (completely randomized). According to the results obtained, it was concluded that the evaluation of parasitism tests of Meloidogyne enterolobii in Psidium spp can be carried out using a smaller number of inoculum (2000 eggs / plant) in a period of only three months, thus streamlining the results of the research with this pathogen. The second article had the following objectives: (1) To observe the organization and conservation of mitochondrial genomes of phytonematous species deposited in public databases; and (2) To carry out phylogenetic analyzes among species of phytonematodes based on sequences of mitochondrial genes (Cox1) and nuclear genes (rRNA 28s). it was concluded that the phylogenetic trees of the phytonematoid species showed consistency with the classification proposal at the family level. Based on the results of the phylogenetic analyzes, the inclusion of the species in the family Pratylenchidae or removal of species of the genus Radopholus and inclusion of these species in the family Hoplolaimidae is recommended. It is clearly observed the paraphyletic inside the genus Heterodera, which the markers used may not have sufficient resolution to base the classification of this group. The third article had as objective to evaluate the genotype response of the species Psidium guineense and Eugenia uniflora to the nematode parasitism M. enterolobii. At the end of the evaluation, one P. guineense genotype and all 10 E. uniflora genotypes showed resistance to the pathogen. This opens the possibility for its use as rootstock for commercial varieties or cultivation in infested areas for the reduction of the nematode population in the soil.