Desenvolvimento de métodos de detecção precoce de infecções quiescentes de Colletotrichum spp. em mamão / Development of early detections methods of quiescent infections of Colletotrichum spp. on papaya fruits

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

The objetives of this study were to evaluate the methods, maturation age, temperature effect, distribution and sample size to detect quiescent infection of Colletotrichum spp. (Glomerella cingulata) on papaya fruits. At first, different methods to detect quiescent infections on immature fruits were assessed: sodium hipoclorite (1,5%), paraquat (6 ml/L a.i.), ethanol (70%) and ethrel (1,2 ml/L a.i.). Compared to the standard method (mature fruits at harvest stage), the Paraquat and Ethrel methods were similar to or superestimated the probability of detection of chocolate spot and stem-end rot in papaya fruits. For anthracnose, only the Ethrel method resulted in similar disease incidence values as observed with the standard method. The effects of fruit maturation stage (age), 3, 4, 5, or 6 weeks before the harvest maturation stage and fruits at the harvest stage were assessed on the efficacy of the Paraquat and Ethrel methods. Only chocolate spot and stem-end rot were evaluated because anthracnose infection was not detected in the assessed areas. The incidence of chocolate spot in imature fruits harvested 3 weeks before full maturation stage did not differ from that of fruits harvested at the mature stage. Stem-end rot was detected in fruits of all ages at similar intensity as those recorded in fully mature fruits. After selecting suitable methods and fruit age, the Ethrel method was used to assess the effects of temperature on the detection. Imature and mature fruits were incubated at 22, 25, 28, 31, and 34oC, for 8 days. Temperature influenced the efficiency of the method. The use of Ethrel in fruits kept at 25 to 31 oC, for 8 days was the best detection procedure. Based on dispersion indices, spatial distribution of the diseases was studied in the rainy and dry seasons. The Poisson, Negative binomial and Betabinomial distribution were fit to the data by the maximum likelihood method. The sample size was calculated based on the coefficient of variation and probability of detection. The spatial pattern of both chocolate spot and anthracnose was aggregated. The aggregation was higher for anthracnose. Sample sizes for studies conducted during the dry season were greater than those estimated for the rainy season. In summary, Ethrel was the best detection method of Colletotrichum spp. quiescent infections in papaya fruits. Quiescent infection can be detected in imature fruits 3 weeks before harvest and the temperatures from 25 to 31oC are more suitable for detection. Sample size varies with the disease and growing season.

ASSUNTO(S)

fitopatologia quiescência detecção amostragem colletotrichum mamão quiescence detection sampling colletotrichum papaya fruits

ACESSO AO ARTIGO

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