Willame dos Santos Candido

Obtaining resistant lettuce progenies to downy mildew

Lettuce is the most consumed leafy vegetable in Brazil. Its production, nonetheless, is increasing in difficulties mainly due to the infestation of producing areas with Bremia lactucae. Thus, the use of horizontal resistant cultivars is the most viable alternative in controlling progress of disease. So, the objective of this study was to obtain resistant lettuce progenies to the races of downy mildew: SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 and SPBl:07. The breeding consisted of two stages: crossover of parentals to obtain the resistant lettuce progenies and endurance test of the progeny to B. lactucae races. The parentals used to obtain progenies with resistance factor R-18 and R-38 were: JAB 4-13-7 and JAB 4-13-7. The Pedigree method was used for obtaining the progeny, using as default selections the Hortencia cultivar and JAB 4-13-7genotype. After selection and selfing of the plants in the field, the resistance or susceptibility test was realized, by inoculation of the progenies from the crosses, with mixture of distilled water + sporangia of B. lactucae races SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 and SPBl:07 obtained from isolates collected in the years 2008-2010. Fifteen days after inoculation, the seedlings were selected as resistant or susceptible, discarding those presenting sporulation and necrotic spots caused by B. lactucae. Through the Pedigree method we found 69 progenies F 3 with good agronomic characteristics. However, after resistance or susceptibility test, only 19 showed all the plants resistant to downy mildew.

Resistência de linhagens de alface-crespa às raças de Bremia lactucae identificadas no Estado de São Paulo

ABSTRACT Under controlled conditions in a BOD chamber, eight lines of green leaf lettuce and the cultivar Solaris were evaluated by means of a latency index (IL) as a measure of downy mildew severity, while the resistance response was assessed based on the percentage of seedlings with sporangia (PE) when inoculated with nine races of Bremia lactucae alone and with one single mixture of all races. The IL and PE for the lines were inferior to those shown for the Tobar-Tosse, D.E.; Candido, W.S.; Marin, M.V.; Panizi, R.C.; Barbosa, J.C.; Braz, L.T. Resistance of green leaf lettuce lines to the Bremia lactucae races identified in Sao Paulo State. Summa Phytopathologica, v.43, n.1, p.55-57, 2017. cultivar Solaris, used as the susceptibility standard. The lines L 1 , L 2 , L 3 and L 4 were highly resistant when inoculated (PE = 0.0%) with the nine races/mixture; the lines L 5 , L 6 , L 7 and L 8 , depending on the inoculated race/mixture, showed high resistance level (PE = 0-4.6%) and incomplete resistance (PE = 6.0-15.1%), and the line L

Reaction of melon genotypes to Didymella bryoniae (Fuckel) Rehm

CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 76(1) JANUARY-MARCH 2016 7 7 The cult ivat ion of melon (Cucumis melo L.) in greenhouses has contributed to the increased incidence of fungal diseases, particularly gummy stem blight caused by Didymella bryoniae (Fuckel) Rehm. This disease is currently considered the main disease affecting this crop, causing conditions such as water soaked seedlings, and stem and fruit cankers, reducing productivity and fruit quality. Considering the importance of this disease, the aim of this study was to evaluate the reaction of different C. melo genotypes to D. bryoniae. Sixty-eight different melon genotypes were investigated. Two phenotyping assays were performed to investigate the resistance to the disease, following a randomized block design with four replicates. Subsequently, a new assay was conducted to validate the resistance of the genotypes selected in the previous step, using a randomized block design with three replicates. The plants were inoculated using the toothpick method, and resistance was evaluated according to a grading scale. Also, reaction classes and assay groups were used for classifying the resistance level of the genotype. The JAB-11 and JAB-20 strains were susceptible to the pathogen, as well as the commercial hybrids Louis F1 and Fantasy F1. The hits AC-29, C160, Charentais Fom 1, PI 420145, PI 482398 and PI 532830 were resistant to D. bryoniae, and could become an important gene source for the development of resistant cultivars.