Histochemical marker: dissecting phenylpropanoid pathway for identifying dry root rot resistant sources in cowpea

Abstract

Cowpea [Vigna unguiculata (L.)] is one of the important grain legumes of arid and semi-arid agroclimatic zones, mostly grown as food for humans and feed for cattle. However, its production has plateaued due to its cultivation in low-input conditions, such as low-fertility soils in rainfed areas. Additionally, climate change exacerbates various biotic stresses affecting plants. One significant biotic stress is dry root rot, caused by Macrophomina phaseolina (Tassi) Goid., which has emerged as a major threat, especially in the era of climate change like erratic rainfall patterns and prolonged dry spells. Extended periods of moisture stress combined with high temperatures increase the incidence of dry root rot in cowpea. Thus, the current study was conducted to identify the dry root rot resistant genotypes of cowpea. For that, twenty four genotypes of cowpea were screened in field during summer and rainy season of 2023 and only four entries, viz., DC 18 − 1, GC 2105, RC 101 and Pusa Falguni showed resistant reactions in both seasons. Further, in vitro testing was done to confirm the durability of the resistance. Leaves of resistant (DC 18 − 1, GC 2105, RC 101, and Pusa Falguni), susceptible (PGCP 82, Pant lobia-7) and highly susceptible (CPD-331, GC 2006) inoculated genotypes showed higher levels of enzyme activity of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO). A significant increase in the phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) in the inoculated genotypes was observed after the invasion of pathogen. In contrast, in the case of hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) three inoculated resistant genotypes (DC 18 − 1, GC 2105, RC 101), one susceptible and highly susceptible inoculated genotypes (CPD-331 and PGCP 82) significantly recorded a higher level of hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) than the uninoculated genotypes. In lignin deposition, the resistant genotypes (DC 18 − 1, GC 2105, RC 101, and Pusa Falguni) had a higher level of lignin deposition than susceptible and highly susceptible genotypes. Thus, the histochemical dissection of the plant defense mechanism would be an important approach for the differentiation of the root rot-resistant and susceptible genotypes of cowpea and further selection of resistant genotypes. © The Author(s) under exclusive licence to Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2025.