Effect of biostimulants on pod morphology and development of soybean (Glycine max L.) under charcoal rot disease conditions caused by Macrophomina phaseolina

Abstract

Charcoal rot, caused by Macrophomina phaseolina (Tassi) Goid, is a major soil-borne disease that severely affects soybean productivity by disrupting vascular flow, reducing photosynthetic efficiency, and limiting pod formation and filling. The present investigation was undertaken during Rabi 2023-24 and 2024-25 to evaluate the effect of biostimulants and stress modulators on pod morphology in soybean under charcoal rot conditions. The experiment was conducted in a factorial completely randomized design comprising two varieties—JS 20-29 (susceptible) and JS 20-98 (moderately resistant)—and twelve treatments, including untreated control, Trichoderma seed treatment (10 g kg⁻¹ seed), fungicide (Penflufen 13.28% w/w + Trifloxystrobin 13.28% w/w F8 @ 1 ml kg⁻¹ seed), plant extract (PE @ 50-200 ppm), Macrophomina fungal extract (MFE @ 50-100 ppm), and salicylic acid (SA @ 100-200 ppm). Results revealed that pod morphological traits were significantly influenced by treatments and varieties. The highest pod length (34.18 mm), girth (10.52 mm), and width (4.93 mm) were recorded in the non-inoculated control (T₁), which was statistically at par with Trichoderma (T₃) and fungicide (T₄) treatments, indicating effective disease suppression and physiological maintenance under stress. The lowest pod length (28.21 mm) and girth (8.54 mm) were observed in Macrophomina phaseolina fungal extract @ 100 ppm (T₁₀), confirming pathogen-induced inhibition of pod growth. Between varieties, JS 20-98 outperformed JS 20-29 in pod length (32.78 mm vs. 28.24 mm) and girth (9.36 mm vs. 8.94 mm), demonstrating greater tolerance and adaptability to pathogen stress. The application of Trichoderma and salicylic acid proved effective in mitigating disease severity by improving physiological balance and assimilate translocation during pod development. Thus, integrating biocontrol agents and resistance inducers represents a promising, sustainable approach for maintaining pod morphology and yield stability of soybean under Macrophomina-infested environments.