Aiming to evaluate an indirect screening approach for Ceratocystis wilt resistance, the leaf disc (LD) method, two assays were conducted to assess its efficiency in discriminating resistant/susceptible genotypes. The first one used five and the second 16 cacao clones. For each assay, 40 discs of 2month-old leaves were cut, wounded at the midrib, laid down in wet sterilized foam and inoculated (20 μL-3 × 10 4 CFU/ mL suspension of Ceratocystis cacaofunesta spores). The number of perithecia formed per leaf disc was assessed 4 days after inoculation (DAI). To assess the correlation between the LD method and field resistance, 16 branches of the same 16 clones were randomly selected and inoculated (30 μL/ 3 × 10 4 CFU/mL). The lesion length, width and area were measured 60 DAI. In both assays it was possible to distinguish resistant from susceptible clones. The clonal heritabilities were high (h 2 clo ≥ 77.19) for the assays in the lab and in the field, the highest estimate being obtained for perithecia number (h 2 clo = 95.82). The correlation of perithecia number with lesion width was positive and highly significant (r = 0.65, pvalue = 0.009). Therefore, high genetic gains on field resistance can be achieved by indirectly selecting through the LD method.

No abstract

Keywords: RESUMORosellinia pepo, uma nova doença do craveiro-da-índia no Brasil Palavras-chave:

Ceratocystis wilt is a lethal disease to several hosts. This study tested the isolation of Ceratocystis spp. from the leaf blade of cacao and other hosts showing yellowing and the isolates pathogenicity to their hosts. Leaves with yellowished and/or darkened areas were disinfested and placed between slices of unripe cacao pods, like a sandwich, in a BOD chamber (25 o C), for four days. Ascospores were transferred to Petri dishes containing PDA and their colonies were preserved. The presence of C. cacaofunesta in the leaf blade of cacao tree; C. paradoxa in coconut palm; and C. fimbriata in eucalyptus, rubber, soursop, custard-apple trees and coffee plants were confirmed. To test the isolates pathogenicity, culture discs or droplets of inoculum suspensions (3 × 10 4 i.u./mL) were applied in two points on leaves of each host, with and without wound, and evaluated in four to seven days. Chlorosis, lesions, mycelia and perithecia development were observed in the midrib and on blades of inoculated leaves. Therefore, an early method of detection of Ceratocystis spp. as well as another method to evaluate pathogenicity to various hosts using whole leaves of these hosts were described in this paper.

Ceratocystis wilt, a new disease of the cupuassu tree, in Brazil. The cupuassu tree (Theobroma grandiflorum), native of the Amazon region, is cultivated mainly in the states of Para, Amazonas, Acre and Bahia, Brazil. In Bahia, it has been planted in the same municipalities were cacao is grown, especially, in the region known as Baixo Sul. During fitossanitary inspections carried out in one area at the Cacao Research Center (CEPEC), in Ilheus, BA, cultivated with cupuassu, trees showing symptoms of wilting, chlorosis and leaf drying, in addition to canker and necrosis of the stem, were observed. Ceratocystis fimbriata was the fungus, predominately, isolated in PDA medium in all the attempts using necrotic tissues obtained from the stem. Histopathological studies, done at the optical microscope, showed the presence of mycelia and chlamydospores of the fungus in the xylem vessels. Three-and 8-month-old cacao and cupuassu seedlings inoculated with the fungus started exhibiting the disease symptoms 20 and 40 days later, respectively. The fungus was re-isolated from inoculated plants in all the attempts. This is the first record of ceratocystis wilt disease in cupuassu tree.