Abstract
The objective of this study was to analyze the effects of nitrogen rates and sowing dates on the severity of white spot disease (WSD) in first season maize hybrids, and their correlation with relative chlorophyll content, thousand grain weight and yield. The experiment was set in a randomized block design with treatments arranged in split-split plots. Two hybrids were tested in the main plots: AG9025 PRO3 (super early) and 30F53 VYH (early). Two sowing dates were evaluated in the split plots: preferential (9/20/2016) and late (12/05/2016). Four nitrogen rates were applied in the split-split plots. Nitrogen rates were top-dressed at the V4, V8 and V12 vegetative stages. The relative chlorophyll content reading was performed at VT stage. The quantification of WSD severity was made at R6, using diagrammatic scale. The AG9025 PRO3 hybrid showed higher average WSD severity (17.7%) than the 30F53 VYH (9.3%). The preferential sowing date showed lower severity (2.2%) compared to the late sowing date (31.4%). There was a significant positive correlation between the disease severity and the relative chlorophyll content, thousand grain weight and grain yield, except for the 30F53 VYH hybrid on the late sowing date. The hybrid AG9025 PRO3 showed increase in WSD severity when the highest nitrogen rates were applied, on both sowing dates. The effect of N rates on WSD was not significant for the 30F53 VYH hybrid. The late sowing time generates greater disease severity. The AG9025 PRO3 hybrid is more susceptible and the severity of its white spot is increased with the increment in N doses. There is a positive correlation between the relative chlorophyll content, disease severity, yield and thousand grain weight.
Highlights
White spot disease (WSD) is one of the most important leaf diseases in maize crop
The relative chlorophyll content (RCC) values showed a linear behavior on preferential sowing date (PSD) and a quadratic behavior on late sowing date (LSD) (Figure 2a)
Late sowing of maize increases the severity of white spot disease
Summary
White spot disease (WSD) is one of the most important leaf diseases in maize crop. Its main damages include the reduction of the leaf area and plant photosynthetic capacity (Godoy et al, 2001). Sowing (August-September) and preferential sowing time (September-October) are usually less prone to the disease attack in the south of Brazil, as the plants are exposed to lower inoculum density and the crop reproductive stage does not coincide with favorable weather to the pathogen. Infection is favored by night temperatures between 14 and 20oC, and relative humidity above 60% (Sabato et al, 2013) These conditions are frequently found in the crop reproductive period at late sowings due to the reduction of the photoperiod, the smaller availability of solar radiation and temperatures from February onwards.
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