Use of hydroponics-based evaluation for phenotyping tolerance/susceptibility to the aphid, Uroleucon compositae and inheritance analysis of aphid tolerance in a global germplasm collection of Carthamus tinctorius L. (Safflower)

Carthamus tinctorius L. (Safflower) is an important oilseed crop that is cultivated globally. Aphids are a serious pest of safflower and cause significant yield losses of up to 80% due to their ability to multiply rapidly by parthenogenesis. In this study, we report the identification of an aphid-tolerant accession in safflower following screening of a representative global germplasm collection of 327 accessions from 37 countries. Field-based screening methods gave inconsistent and ambiguous results for aphid tolerance between natural and controlled infestation assays and required ~ 3 months for completion. Therefore, we used a rapid, high-throughput hydroponics-based assay system that allows phenotyping of aphid tolerance/susceptibility in a large number of plants in a limited area, significantly reduces the time required to ~ 45 days and avoids inconsistencies observed in field-based studies. We identified one accession out of the 327 tested germplasm lines that demonstrated aphid tolerance in field-based natural and controlled infestation studies and also using the hydroponics approach. Inheritance analysis of the trait was conducted using the hydroponics approach on F₁ and F₂ progeny generated from a cross between the tolerant and susceptible lines. Aphid-tolerance was observed to be a dominant trait governed by a single locus/gene that can be mobilized after mapping into cultivated varieties of safflower. The hydroponics-based assay described in this study would be very useful for studying the molecular mechanism of aphid-tolerance in safflower and can also be used for bioassays in several other crops that are amenable to hydroponics-based growth.