Abstract
To determine the influence of plant density and powdery mildew infection of winter wheat and to predict grain yield, hyperspectral canopy reflectance of winter wheat was measured for two plant densities at Feekes growth stage (GS) 10.5.3, 10.5.4, and 11.1 in the 2009–2010 and 2010–2011 seasons. Reflectance in near infrared (NIR) regions was significantly correlated with disease index at GS 10.5.3, 10.5.4, and 11.1 at two plant densities in both seasons. For the two plant densities, the area of the red edge peak (Σdr 680–760 nm), difference vegetation index (DVI), and triangular vegetation index (TVI) were significantly correlated negatively with disease index at three GSs in two seasons. Compared with other parameters Σdr 680–760 nm was the most sensitive parameter for detecting powdery mildew. Linear regression models relating mildew severity to Σdr 680–760 nm were constructed at three GSs in two seasons for the two plant densities, demonstrating no significant difference in the slope estimates between the two plant densities at three GSs. Σdr 680–760 nm was correlated with grain yield at three GSs in two seasons. The accuracies of partial least square regression (PLSR) models were consistently higher than those of models based on Σdr 680760 nm for disease index and grain yield. PLSR can, therefore, provide more accurate estimation of disease index of wheat powdery mildew and grain yield using canopy reflectance.
Highlights
Wheat powdery mildew, caused by the obligate fungi Blumeria graminis f. sp. tritici (Bgt), is a worldwide destructive foliar disease of wheat
There were some reports on the relationships between canopy reflectance and yield when diseases occurred, including peanut-late leaf spot [28], alfalfa-leaf spot [29], and Asian soybean rust [30]. These reports indicated the potential of canopy reflectance in grain yield prediction. All of these studies on wheat powdery mildew detection or monitoring were focused on wheat planted at the same densities, previous work has shown that reflectance at near infrared (NIR) ranges was highly correlated with plant density and vigor [31,32]
A wide range of powdery mildew disease indexes was obtained across plots for the two plant densities at each assessment date in two seasons (Fig. 1)
Summary
Wheat powdery mildew, caused by the obligate fungi Blumeria graminis f. sp. tritici (Bgt), is a worldwide destructive foliar disease of wheat. Cao et al [23] used canopy hyperspectral reflectance to detect wheat powdery mildew in two winter wheat cultivars, and found that spectral indices at growth stage (GS) 10.5.3 (flowering over at base of ear), 10.5.4 (flowering over, kernel watery ripe) and 11.1 (milky ripe) were significantly correlated negatively with disease index. These reports indicated the potential of canopy reflectance in grain yield prediction All of these studies on wheat powdery mildew detection or monitoring were focused on wheat planted at the same densities, previous work has shown that reflectance at NIR ranges was highly correlated with plant density and vigor [31,32]. This study was conducted to (i) develop models relating spectral indices to the severity of wheat powdery mildew at two pant densities; (ii) to compare the performance of spectral indices and PLSR for estimating powdery mildew of winter wheat; and (iii) to predict grain yield of wheat using canopy reflectance
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