Host Specificity and Seed Stimulant Responses of Orobanche minor Infesting Clover and Leguminous Forage Crops

Abstract

Parasitic weed Orobanche minor poses a significant threat to clover and leguminous forage production systems due to its obligate dependence on host-derived chemical cues for germination and establishment. Studies were conducted to evaluate host specificity and seed germination responses of O. minor to root exudates of selected clover (Trifolium spp.) and other leguminous forage crops under controlled laboratory and pot conditions. Germination assays were performed using conditioned seeds exposed to aqueous root exudates and synthetic germination stimulants to determine differential responsiveness. Results indicated strong host-dependent variation in seed germination stimulation, with higher germination rates observed in response to clover species compared with non-preferred legume hosts. Root exudates of susceptible hosts effectively triggered germination through the release of strigolactone-like compounds, while tolerant or non-host species exhibited weaker stimulatory effects. Seedling attachment and haustorial initiation were also significantly influenced by host identity, confirming selective parasitic establishment. Pot experiments further demonstrated that infection severity was highest in clover-based systems, leading to reduced biomass accumulation, suppressed nodulation, and decreased forage yield. In contrast, non-preferred legume hosts showed limited parasitism and reduced impact on growth parameters. Environmental factors such as soil moisture and nutrient availability influenced parasite emergence and attachment success, with optimal conditions favoring rapid infection. The results highlight the strong host specificity and chemically mediated germination strategy of O. minor in forage systems.