Reaction of sunflower material from IFVCNS to Orobanche cumana race F and a sensor-based initial approach for early detection of infections

Broomrape, caused by the root parasitic plant Orobanche cumana Wallr., is one of the main biotic constraints on sunflower oil production. Parasite races A to F, with increasing levels of virulence, have been described. These are controlled by incorporating resistance genes into the hybrids. The IFVCNS has an important collection of sunflower lines in its breeding program. These lines respond differently to biotic and abiotic stresses and are intended to obtain sunflower hybrids with resistance to broomrape race F eventually. According to previous research by our group, broomrape infections can be detected by multicolor fluorescence measurements under specific temperature conditions and in darkness. Additionally, symptoms of crop diseases caused by pathogens other than O. cumana can be detected through spectral indicators before visual symptoms appear. Our objectives were to: i) evaluate the reaction of IFVCNS entries to O. cumana race F, and ii) assess the effectiveness of different sensors for early infection detection. A greenhouse experiment was conducted from February to May 2025. Sixteen sunflower lines, along with control lines B117 (susceptible to all races) and NR5 (susceptible to race F, resistant to races <F), were included, using the O. cumana race F population Oc0115. Six individual seedlings (replications) of each genotype were inoculated by transplant to broomrape-infested soil and grown in a greenhouse at 23–27°C with a 14-hour photoperiod. Control plants were transplanted to non-infested soil and maintained under the same conditions. The number of emerged O. cumana stems per plant was assessed weekly until sunflower senescence. Nine weeks after inoculation (WAI), broomrape incidence (BI, percentage of sunflower plants with broomrape) and final degree of attack (FDA, number of nodules and stems per plant) were recorded. Genotype AZDO-2 was as susceptible as B117: FDA=1.5 nodules and stems/plant and BI=83%. Genotypes AB-OR-8, AR-KOR-5, BG-N-2, IMI-AB 24-PR, NS-KOD-4-PR-SU, and OD-DI-65-SU showed moderate susceptibility (averages FDA=0.3 nodules and stems/plant, and BI=22%). The remaining nine genotypes were resistant to the parasite. During the initial weeks of the experiment, up to 5 WAI (when parasite stems emerged aboveground), several devices were used to take weekly measurements on B117 and NR5 control and inoculated plants: porometer, fluorometer, spectrophotometer, and optical sensors to assess flavonoid, anthocyanin, and chlorophyll contents in leaves. Measurements were taken at the same time of day on shaded leaves. For each treatment, one leaf from each of the six plants was measured. Very low standard deviations in the averages confirmed that the protocol was robust and replicable. In our greenhouse conditions, the most effective devices for infection detection were those measuring chlorophyll fluorescence, leaf temperature, stomatal conductance, NDVI, and anthocyanin content. Infected plants also exhibited higher hyperspectral signature values.