Ramularia leaf spot severity and effects on cotton leaf area and yield1

João Paulo Ascari,Dejânia Vieira De Araújo,Inês Roeder Nogueira Mendes,Vanessa Costa Da Silva

doi:10.1590/1983-40632016v4642781

João Paulo Ascari, Dejânia Vieira De Araújo + Show 2 more

Open Access

https://doi.org/10.1590/1983-40632016v4642781

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Abstract

ABSTRACT Cotton monoculture favors the development of diseases such as ramularia leaf spot, which causes early defoliation and boll rotting, thus decreasing yield. This study aimed at evaluating the severity of ramularia leaf spot and its effects on cotton leaf area and yield. The experiment was conducted in a triple (4 x 3 x 2) factorial design, consisting of four cultivars (FM940GLT, FM944GL, TMG42WS and TMG43WS), three thirds of the plant (lower, middle and upper) and two management conditions (with and without fungicide application). To the variable area under the disease progress curve, the lowest values were observed in the upper third of the TMG42WS and TMG43WS cultivars, with the lower and middle thirds presenting the highest severity. The condition managed with fungicide and the upper third showed the lowest values for area under the disease progress curve. The leaf area was negatively affected by the ramularia leaf spot. Concerning the seed and fiber yields, the highest averages were observed for the middle third and the condition managed with fungicide. There was no statistical difference for cotton yield loss.

Highlights

Cotton (Gossypium hirsutum L.) crops are very important for the Brazilian agribusiness
The results found for the TMG42WS and TMG43WS cultivars showed a correlation between yield and area under the disease progress curve, since these cultivars had lower values for severity and higher yield, even with low leaf area
Based on the results presented in this study, the ramularia leaf spot was related to the cotton crop yield, and the different levels of severity in the thirds of the plants may have contributed to the decrease of their leaf area

Summary

Introduction

Cotton (Gossypium hirsutum L.) crops are very important for the Brazilian agribusiness. The cotton fiber yield losses caused by this disease reached 36.8 % in the region of Tangará da Serra, Mato Grosso State, Brazil (Gilio 2014), and 68.7 % in India (Shlvankar & Wangikar 1992). These yield losses are due to the field conditions, which favor the fungus by the microclimate formed under the plant canopy, with high humidity and mild temperatures (±24 oC). These characteristics form a gradient of severity in the plant, with leaves in the lower third being more affected by the disease, which progresses to the middle and upper thirds of the plant (Aquino et al 2008b, Curvelo et al 2010)

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