Reação de Cafeeiros (Coffea canephora) ao Nematoide-das- Galhas Meloidogyne incognita (Est I2) sob condições controladas de inoculação

Abstract

Brazil is the leading producer and exporter of coffee world. The use of resistant coffee cultivars is one of the most economical ways to control the Root-knot nematodes Meloidogyne spp. However, studies are needed to demonstrate the best methodologies used in resistance tests of coffee to the gnath nematode to be Possible to reduce experimental errors and to standardize test facilities so that the results of different jobs can be compared with confidence. Therefore, the objective of this work is to analyze the effects of adjusting the inoculum concentration and evaluation period on the reaction of Coffea canephora and weed clones to Meloidogyne incognita (Est I2) in Rondônia, as well as to evaluate the reaction of 56 clones as resistance to the Root-knot nematodes M. incognita. For this, three experiments were conducted separately. Firstly, samples of coffee roots were collected in five producing areas of the municipality of Cacoal and sent to the biochemical characterization by esterase enzyme (Est) of the species (s) of Meloidogyne spp., where a single pattern of Meloidogyne incognita (Est I2) in all samples. One of them was used to obtain a pure nematode population of M. incognita and multiplied in cv. Saint Clara. The first experiment was set up as follows: Six-month-old seedlings of C. canephora "194", "125" and "750" clones, as well as of the Obatã variety of C. arabica, from the germplasm bank of Embrapa Rondônia, were transplanted to 8-liter vessels containing 2: 1: 1: 1 sterilized substrates (natural soil, vermiculite medium texture, sand and organic compost, respectively). As a susceptible control, tomato plants (Solanum Iycopersicum L.) cv Santa Clara were used to verify the viability of the inoculum of M. incognita used in this experiment. After fifteen days of adaptation of the coffee tree seedlings in the pots, six plants of each one of the coffee genotypes was inoculated with different concentrations of M. incognita, being 1000, 5000, 10000 and 20000 eggs + J2 per plants, constituting 11 treatments with six replicates. However the seedlings of the susceptible control, the tomato, were inoculated with 5000 eggs of the nematode/plant. After the inoculations the treatments were arranged in a completely randomized design in the shelter. Evaluations were performed at 5 and 8 months after inoculation. It was observed that the lowest concentrations of inoculum (1000 and 5000 eggs / pot) were the most efficient for nematode establishment and reproduction in both coffee genotypes. In the second experiment, clones of C. canephora of the BRS Ouro Preto variety, 8 months old were transplanted to vessels containing autoclaved soil and inoculated with 5,000 eggs + juveniles of the second stage (J2) of the nematode (first trial). The design was completely randomized, with six replicates for each genotype tested. Tomatoes cv. Santa Clara represented the positive witness and coffee clones Apoatã the negative witnesses, inoculated with the same level of inoculum of the others. After 148 days of inoculation the plants were removed from the vases and the roots separated from the aerial part, washed, weighed and evaluated for number of galls (NG). Then, the number of eggs of M. incognita (NO) from the roots was extracted and counted, obtaining the breeding factor (FR) of the nematode (FR = final population / initial population) in each tested plant. Considering immune genotypes with FR = 0.00; Resistant, FR <1.00; And, susceptible, FR> 1.00. The M. incognita NG and FR values were submitted to ANOVA and the means were compared by the Scott Knott test (1974) at 5% probability. The results showed that only clone 750 was susceptible to M. incognita. Apoatã clones obtained FR = 0, being considered non-hosts. The clones of the cultivar BRS Ouro Preto behaved as resistant to M. incognita. The second assay was installed on July 2, 2015, in order to evaluate the reaction of thirty - two clones of C. canephora to M. incognita, using the same methodology of the first assay, being evaluated on 02/11 / 2015. At 150 DAI the C. canephora clones of the botanical variety Conilon 694, 160, 837, 46, 909, 890 and the hybrid materials 844, 1005, 169, 543, 453, 120, 193, 636, both with early ripening cycle, Have behaved as resistant to M. incognita and can be used in breeding programs to obtain nematode-resistant precocious coffee cultivars under soil and climate conditions in Rondônia.