Genotypic variation in resistance of roselle (Hibiscus sabdariffa L.) to the foliar beetle Monolepta thompsoni Allard, and its consequences for yield in Nigeria’s Southern Guinea Savanna

Abstract

Monolepta thompsoni Allard is a major foliar beetle that limits roselle (Hibiscus sabdariffa L.) production in Nigeria through severe leaf defoliation and yield losses. However, information on genotypic field resistance to this pest remains scarce. This study evaluated the field resistance of eight roselle genotypes under natural M. thompsoni infestation at Makurdi (Benue State) and Bali (Taraba State) during the 2023 cropping season. The experiment was laid out in a randomized complete block design with four replications at each location. Beetle population density was assessed at 3, 6, 9, and 12 weeks after sowing (WAS), and leaf defoliation, functional leaf area, yield components, and dry calyx yield were determined. A Composite Field Resistance Index (CFRI) integrating standardized beetle population, leaf defoliation, functional leaf area and dry calyx yield was developed to rank genotypes. Significant genotypic differences (P < 0.001) were observed for all measured traits. Beetle populations peaked at 9 WAS, with Jalin-White recording the highest infestation (12.78 insects plant?¹), greatest leaf defoliation (57.84%) and lowest dry calyx yield (8.23 g plant?¹), whereas Kona White G01 and MKD-Red (Local) exhibited the highest CFRI values (0.907 and 0.854, respectively). Beetle density was strongly correlated with leaf defoliation (r = 0.94, R² = 0.88; P < 0.001). The results demonstrate substantial genetic variation in resistance to M. thompsoni and identify Kona White G01 and MKD-Red (Local) as promising sources of resistance for breeding and sustainable pest management.