Early Recognition of Orobanche Cumana Parasitism on Sunflower Plants Using Physiological Measurements and Narrow-Band Spectral Signatures.

Broomrape (Orobanche and Phelipanche spp.) parasitism is a severe problem in many crops worldwide, including the Mediterranean basin. Most of the damage occurs during its sub-soil developmental stage. When broomrape shoots emerge above the soil surface, the damage to the crop is already done. One option to sense early parasitism is through physiological measurements. However, large scale of physiological measurements at the field, during growth, is complicated and not economical. To date, no agricultural method has been developed for understanding the spatial distribution of parasitism in the field – leading to excess- and indiscriminant-use of herbicides. Nonetheless, in the last decades, hyper-spectral tools were shown to have potential for fast, repetitive, inexpensive and non-destructive spatial mapping for agricultural purposes. In the current study, detection of pre-emerged O. cumana parasitism on sunflower plants was investigated. Susceptible and resistant sunflower plants were planted in infested soil (5, 10, 15 and 30 mg seeds kg-1). The plants were measured weekly for photochemistry and stomatal conductance midday. In addition, leaf samples were taken every week for mineral analysis. Narrow-band leaf signatures were simultaneously-taken with a contact field spectrometer. Physiological and spectral measurements revealed significant differences between infested and non-infested sunflower plants during early parasitism stages. Furthermore, by applying the partial least squares regression analysis, specific correlation was found between wavelength changes and mineral content changes in young leaves. These results demonstrate the potential of early stage detection of O. cumana parasitism on sunflower.