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Abstract
Although the impact of Orobanche cumana Wallr. on sunflower (Helianthus annuus L.) becomes evident with emergence of broomrape shoots aboveground, infection occurs early after sowing, the host physiology being altered during underground parasite stages. Genetic resistance is the most effective control method and one of the main goals of sunflower breeding programmes. Blue-green fluorescence (BGF) and thermal imaging allow non-destructive monitoring of plant diseases, since they are sensitive to physiological disorders in plants. We analyzed the BGF emission by leaves of healthy sunflower plantlets, and we implemented BGF and thermal imaging in the detection of the infection by O. cumana during underground parasite development. Increases in BGF emission were observed in leaf pairs of healthy sunflowers during their development. Lower BGF was consistently detected in parasitized plants throughout leaf expansion and low pigment concentration was detected at final time, supporting the interpretation of a decrease in secondary metabolites upon infection. Parasite-induced stomatal closure and transpiration reduction were suggested by warmer leaves of inoculated sunflowers throughout the experiment. BGF imaging and thermography could be implemented for fast screening of sunflower breeding material. Both techniques are valuable approaches to assess the processes by which O. cumana alters physiology (secondary metabolism and photosynthesis) of sunflower.
Highlights
Sunflower (Helianthus annuus L.) oil is a major commodity in world trade mainly in Europe, where 60% of the total world production is obtained every year (FAOSTAT, 2016)
With the exception of a slight increase in the F520 signal in the first leaf pair (LP), that of the rest of leaves remained fairly constant throughout the experiment, and even a decrease was detected in the second LP in the last week (Figure 1)
Our results showed that the Blue-green fluorescence (BGF) emission of individual LPs of healthy sunflower increases in time
Summary
Sunflower (Helianthus annuus L.) oil is a major commodity in world trade mainly in Europe, where 60% of the total world production is obtained every year (FAOSTAT, 2016). The main biotic constraint for sunflower oil production in all the countries where sunflowers are grown with the only exception of the Americas- is broomrape, caused by the achlorophyllous parasitic plant Orobanche cumana Wallr. After parasite seed germination in the soil early after sowing, penetration of its intrusive cells into the host root tissues triggers their division, leading to the formation of a subterranean shoot that grows outside the root of sunflower. Parasite shoots emerge from the soil and form a flowering spike that rapidly produces a large amount of tiny seeds. Orobanche cumana parasitizes sunflower all through the crop growing season, and flowering of both, host and parasite, are coincident in time (Molinero-Ruiz et al, 2015)
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