Abstract
Tar spot complex (TSC), caused by at least two fungal pathogens, Phyllachora maydis and Monographella maydis, is one of the major foliar diseases of maize in Central and South America. P. maydis was also detected in the United States of America in 2015 and since then the pathogen has spread in the maize growing regions of the country. Although remote sensing (RS) techniques are increasingly being used for plant phenotyping, they have not been applied to phenotyping TSC resistance in maize. In this study, several multispectral vegetation indices (VIs) and thermal imaging of maize plots under disease pressure and disease-free conditions were tested using an unmanned aerial vehicle (UAV) over two crop seasons. A strong relationship between grain yield, a vegetative index (MCARI2), and canopy temperature was observed under disease pressure. A strong relationship was also observed between the area under the disease progress curve of TSC and three vegetative indices (RDVI, MCARI1, and MCARI2). In addition, we demonstrated that TSC could cause up to 58% yield loss in the most susceptible maize hybrids. Our results suggest that the RS techniques tested in this study could be used for high throughput phenotyping of TSC resistance and potentially for other foliar diseases of maize. This may help reduce the cost and time required for the development of improved maize germplasm. Challenges and opportunities in the use of RS technologies for disease resistance phenotyping are discussed.
Highlights
Tar spot complex (TSC) is a major foliar disease of maize in many regions of Latin America
This explained the strong relationship between the yield and area under the disease progress curve (AUDPC) (Table 2) in the non-fungicide treatment (R2 = 0.84)
Our results suggest that potential yield losses from TSC in maize hybrids may be as high as 58% in susceptible genotypes under strong disease pressure
Summary
Tar spot complex (TSC) is a major foliar disease of maize in many regions of Latin America. While P. maydis is an obligate parasite, M. maydis is thought to be an endophyte or facultative parasite, causing extensive chlorosis in Phenotyping Tar Spot Complex of Maize the presence of P. maydis (Dittrich et al, 1991; Hock et al, 1992). It is not known whether M. maydis and P. maydis can be present as pathogens in a plant independently, or if infection in maize is triggered only by their simultaneous co-occurrence. It was suggested that optimal temperature for the development of the disease is 16– 18◦C (± 5–7◦C) with a monthly average rainfall of 150 mm and 10–20 foggy days per month (Hock et al, 1989)
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