Seed viability determination in parasitic broomrapes (Orobanche and Phelipanche) using fluorescein diacetate staining

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Abstract
Summary: Fluorescein diacetate (FDA) was investigated as a potential viability stain for seeds of holoparasitic broomrapes Orobanche and Phelipanche (Orobanchaceae), using four weedy and two non‐weedy taxa. FDA viabilities were compared with the currently used 2,3,5‐triphenyl tetrazolium chloride (TTC) test, and in vitro germination induced by the strigolactone analogue GR‐24. Viable FDA‐stained seeds were characterised by bright yellow–green fluorescence under 450–490 nm blue light. These viable seeds could be discriminated from non‐viable seeds, in which low levels of fluorescence, similar to non‐stained control seeds were observed. FDA viabilities were not significantly different from those obtained using the TTC stain; however, viability values for both stains were consistently higher than levels of artificially induced germination. Positive TTC‐staining showed continuous variation that was difficult to interpret. Nevertheless, the TTC test does not involve grinding seeds, and therefore probably remains a practical alternative to FDA for screening soil samples contaminated with Orobanche and Phelipanche seeds, which indicates different applications for the two viability tests. Interestingly, the strigolactone analogue GR‐24 only induced germination in O. crenata, P. ramosa and O. minor, suggesting a high specificity towards this germination inducer among the species investigated. We suggest that FDA‐staining provides a potential alternative to the currently used TTC test for seed viability assays for Orobanche and Phelipanche, and other parasitic weeds which are an obstacle to crop cultivation.

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