Successive harvests affect the aromatic and polyphenol profiles of novel catnip (Nepeta cataria L.) cultivars in a genotype-dependent manner

INTRODUCTION: Catnip (Nepeta cataria L.) produces volatile iridoid terpenes, mainly nepetalactones, with strong repellent activity against species of arthropods with commercial and medical importance. Recently, new catnip cultivars CR3 and CR9 have been developed, both characterized by producing copious amounts of nepetalactones. Due to its perennial nature, multiple harvests can be obtained from this specialty crop and the effects of such practice on the phytochemical profile of the plants are not extensively studied. METHODS: In this study we assessed the productivity of biomass, chemical composition of the essential oil and polyphenol accumulation of new catnip cultivars CR3 and CR9 and their hybrid, CR9×CR3, across four successive harvests. The essential oil was obtained by hydrodistillation and the chemical composition was obtained via gas chromatography-mass spectrometry (GC-MS). Individual polyphenols were quantified by Ultra-High-Performance Liquid Chromatography- diode-array detection (UHPLC-DAD). RESULTS: Although the effects on biomass accumulation were independent of genotypes, the aromatic profile and the accumulation of polyphenols had a genotype-dependent response to successive harvests. While cultivar CR3 had its essential oil dominated by E,Z-nepetalactone in all four harvests, cultivar CR9 showed Z,E-nepetalactone as the main component of its aromatic profile during the 1(st), 3(rd) and 4(th) harvests. At the second harvest, the essential oil of CR9 was mainly composed of caryophyllene oxide and (E)-β-caryophyllene. The same sesquiterpenes represented the majority of the essential oil of the hybrid CR9×CR3 at the 1(st) and 2(nd) successive harvests, while Z,E-nepetalactone was the main component at the 3(rd) and 4(th) harvests. For CR9 and CR9×CR3, rosmarinic acid and luteolin diglucuronide were at the highest contents at the 1(st) and 2(nd) harvest, while for CR3 the peak occurred at the 3(rd) successive harvest. DISCUSSION: The results emphasize that agronomic practices can significantly affect the accumulation of specialized metabolites in N. cataria and the genotype-specific interactions may indicate differential ecological adaptations of each cultivar. This is the first report on the effects of successive harvest on these novel catnip genotypes and highlights their potential for the supply of natural products for the pest control and other industries.