The co-occurrence of drought and Fusarium solani f. sp. Phaseoli Fs4 infection exacerbates the Fusarium root rot symptoms in common bean (Phaseolus vulgaris L.)

Abstract

At this pace, global warming is expected to exacerbate drought spells now and forever. Being an integral part of the plant disease triangle, the effect drought might exerts on plant-pathogen interactions is a major subject of debates nowadays. The present study examined at how severe artificially-induced severe drought could affect the common bean and the root rot causing fungus; Fusarium solani Fs4 (F. solani Fs4) pathosystem at the morphological, physiological and biochemical levels. The results indicated significantly increased seedling susceptibility (2.08-folds; incidence = 61.8%) to fusarium root rot (FRR) upon severe drought imposition. It to be drought, F. solani Fs4-infection or their combined effects, 1.5 to 2-folds seedlings growth reduction were witnessed, with altered root growth and architecture. Further, as referred to their individual counterparts, the co-occurrence of both the stressors [F. solani + Drought] resulted in 1.23 and 1.5-fold drop in the specific activity of phenyl-alanine ammonia-lyase (PAL) and polyphenol oxidase (PPO), respectively. Meanwhile, the associative effect of the two stressors culminated at 2.3, 2.5 and 1.62-folds increase in the specific activities of peroxidases (POX), catalase (CAT), and proline content, respectively. The principal component analysis (PCA) and the Pearson correlation disclosed a negative and significant correlation between the tested defense-related enzymes PAL, PPO) and the biosynthesis of the studied de-stressing enzymes (SOD, APX, and CAT) and the osmo-protectants (proline, soluble protein). These outcomes strengthened the hypothesis of a repressive crosstalk of the Abscisic acid (ABA), the major abiotic stress mediator, on the expression of the defense-related phytohormones (Jasmonic acid and ethylene).