Screening of Castor (Ricinus communis L.) Genotypes for Resistance to Root Rot Caused by Macrophomina phaseolina under Pot Conditions

Abstract

Aims: Castor (Ricinus communis L.) is one of the oldest cultivated non-edible oilseed crops belonging to the family Euphorbiaceae. India stands as the leading producer and exporter of castor oil, accounting for approximately 68 per cent of the world's castor cultivation area and 76 per cent of global production. During 2024–2025, castor was cultivated over 7.87 lakh hectares in India, with a total production of 15.53 lakh tonnes and an average productivity of 1.93 t ha−1. Gujarat remains the dominant producer, accounting for more than 70% of the national output, with a productivity level (2.27 t ha−1) exceeding the national average, followed by Rajasthan, Andhra Pradesh, Karnataka, Tamil Nadu and Telangana (Indiastat, 2025). The present study was undertaken to identify potential sources of resistance to M. phaseolina under standardised pot conditions. Study Design: CRD. Place and Duration of Study: Department of Plant Pathology, ICAR-IIOR, Rajendranagar. The study was conducted from January to May 2026. Methodology: A total of 22 castor genotypes were evaluated using three replications. Genotypes were categorised according to the disease reaction scale of Mayee and Datar (1986). The experiment was conducted using three pots per genotype as replications, with 10 plants maintained in each pot, resulting in 30 plants evaluated per genotype. For artificial inoculation, M. phaseolina was multiplied on sorghum substrate and the colonised inoculum was incorporated into the potting soil at a standardised rate of 35 g kg⁻¹ soil. Disease development was monitored under pot conditions, and disease incidence was recorded at 45 days after sowing (DAS). Results: Considerable variation in disease response was observed among the genotypes, with percentage disease incidence ranging from 5.41 to 58.97% and an overall mean of 25.35%. Four genotypes, namely ICH 1916 (5.41%), JI 449 (5.88%), ICH 1928 (7.69%) and ICH 1930 (8.82%), were classified as resistant, recording less than 10% disease incidence. Five genotypes were moderately resistant, six were moderately susceptible, five were susceptible and two were highly susceptible. The highest disease incidence was recorded in GCH 4 (58.97%), followed by ICH 1897 (58.62%), and both were classified as highly susceptible. The substantial variation observed among the genotypes demonstrates the presence of exploitable genetic variability for resistance to M. phaseolina root rot in the evaluated material. Conclusion: The resistant genotypes identified in the present study may serve as promising sources for further validation under sick-plot and field conditions and for utilisation in castor breeding programmes aimed at developing root-rot-resistant cultivars. Note: Review paper may have different types of subsections.