Caracterização morfofisiológica e severidade de Cephaleuros virescens em mangueira

Abstract

The mango is one of the most important tropical fruit grown in the world, in which Brazil is the seventh world producer. However, there are many problems in this culture as the algal leaf spot, caused by Cehaleuros sp., that after install in mango cause leaf spots and tend to expand and, as consequence there is a reduction in the photosynthetic area of leaves. There are few studies about morphological characteristics, isolation and epidemiology of this microorganism. The objective of this work was the taxonomic characterization of the causal agent of the algal leaf spot in mango, its isolation in culture medium, study their in vitro physiology and distribution of lesions in the field. For this, was performed the characterization in light microscopy of pathogen structures and isolation was evaluated in various culture medium (with and without added hormones), with subsequent growth assessment and observation of the genesis of reproductive structures. To estimate the incidence and severity, a total of ten plants (5 x 5 m) from the orchard of the University State of Goiás (UEG) were evaluated along five days. Thus, with respect to symptoms, have been observed foliar lesions rounded and coalescing format, orange color, with velvety texture, especially in the upper side. The dimensions obtained for sporangiophores and sporangia were 245.5 - 545.6 x 10.5 - 19.1 μm and 21.4 - 34.2 x 16.3 - 24.7 μm, respectively. The isolation of the algae from tissue fragments on solid medium was not possible, but only in liquid medium Trebouxia. However, after isolation in liquid medium, was possible cultivation in solid medium, where vegetative and reproductive structures could be visualized, with or without added hormone, depending on the culture medium. In the field evaluation, the incidence of the disease in plants was 80 - 100% (mean 92.25%) with no statistical difference between plants; while for the severity, half of the plants exhibited 4.68 to 7.31% of leaf area covered with stain symptoms of algae (afcsma) and the other half positioned itself in a higher range (9.37 to 15.06% of afcsma). Unlike incidence, the severity showed plants in greater attack than the others. Thus it is concluded that: (1) Based on the descriptions of the symptomatology, combined with the micromorphological characteristics, indicated that the algae found in mango is Cephaleuros virescens; (2) The size of the sporangiophore is a safer character to differentiate C. virescens x C. parasiticus; (3) Germination of reproductive structures is required to give vegetative stem in vitro; (4) The addition of the hormone to the culture medium, individually, is not related as promoter of in vitro gametogenesis process in Cephaleuros; (5) As opposed to the incidence, the severity enables show plants with greater degree of attack than the others and; (6) Plants with higher shading present higher severity.