Progresso temporal e escala diagramática da ferrugem da figueira

Abstract

Fig tree (Ficus carica L.) is considered one of the most important fruit species cultivated worldwide. Turkey is the largest producer of figs in the world, followed by Egypt, Morocco, Algeria and Iran. Brazil is 9th in ranking of the most producing countries. In the states, production stands out in Rio Grande do Sul, São Paulo and Minas Gerais. In subtropical regions, fig tree is explored to supply the market for fresh fruit or for the production of sweets and jams. However, some diseases affect the fig trees in the tropics. The fig rust [Cerotelium fici (Cast.) Arth.] has been detected in the country more than 90 years ago and is present in all cultivated areas, constituting a serious and constant threat. In severe infections the leaves fall prematurely, reducing the accumulation of carbohydrates and compromising the growth of fruits and the next productive cycle. Considering the absence of epidemiological studies and standardized methods to quantify the severity of the rust, the objective of this work was to create a method to quantify the severity of the disease on field and to observe its temporal progress for 11 months. Initially, a diagrammatic scale was developed with 6 notes and percentage intervals: 0 (0%); 1 (0.1-5.0%); 2 (5.1-15.0%); 3 (15.1-25.0%); 4 (25.1-50%) and 5 (> 50%), based on the frequency ranges found in the field. The use of the scale provided good levels of accuracy, precision, repeatability and reproducibility of the evaluators. Subsequently, using the developed scale, the progress of the disease was evaluated for 18 cultivars of F.carica L. in the experimental field of the Federal University of Lavras. Disease monitoring was done weekly from August 2017 to July 2018. The result referring to the mean of the disease’s severity in the plots was plotted on the graph of the disease progress curve (AACPD) of the representative cultivar together with the means of the climatic variables maximum, medium and minimum temperatures (ºC), relative humidity of air (%) insolation (h), and the cumulative precipitation (mm). A test for average AACPD values was performed to group the cultivars with higher and lower indexes, and the correlation between the climatic conditions and the rust progress was evaluated. The rust occurred throughout the evaluation period of the experiment in all plots. It was observed incidence of rust in all cultivars, but there was a variation in the average disease severity between treatments. For some cultivars, in the plots without fungicide applications, the maximum severity index (100.0%) was reached faster compared to the sprayed plots. There was a significant correlation between the mean of the disease’s severity and the climatic variables for the two treatments. There was a significant difference for AACPD between the treatmentsand the 'Troiano' presented the lowest index of treatment with fungicide application. Thus, it can be concluded that the ‘Troiano’ shows some degree of resistance to the fig rust, being an alternative to the diversification in the tropical orchards.