Drought Stress Exacerbates Fungal Colonization and Endodermal Invasion and Dampens Defense Responses to Increase Dry Root Rot in Chickpea

Abstract

Drought plays a central role in increasing the incidence and severity of dry root rot (DRR) disease in chickpea. This is an economically devastating disease, compromising chickpea yields particularly severely in recent years due to erratic rainfall patterns. Macrophomina phaseolina (formerly Rhizoctonia bataticola) is the causal agent of DRR disease in the chickpea plant. The infection pattern in chickpea roots under well-watered conditions and drought stress are poorly understood at present. This study provides detailed disease symptomatology and the characteristics of DRR fungus at morphological and molecular levels. Using microscopy techniques, the infection pattern of DRR fungus in susceptible chickpea roots was investigated under well-watered and drought stress conditions. Our observations suggested that drought stress intensifies the progression of already ongoing infection by weakening the endodermal barrier and overall defense. Transcriptomic analysis suggested that the plant’s innate immune defense program is downregulated in infected roots when subjected to drought stress. Further, genes involved in hormonal regulation are differentially expressed under drought stress. These findings provide hints in terms of potential chickpea genes to target in crop improvement programs to develop climate change-resilient cultivars.

Combined Drought and Heat Stress Influences the Root Water Relation and Determine the Dry Root Rot Disease Development Under Field Conditions: A Study Using Contrasting Chickpea Genotypes

“…We compared the effect of individual and combined drought and DRR infection on plant water status at various stages of development in the two genotypes ( Supplementary Figure 13A ). Global transcriptome profile data ( Irulappan et al, 2022 ) was analyzed to study the molecular changes occurring under combined drought and DRR infection in chickpea. We observed differential regulation of genes related to water transport, root architecture, xylem modification (lignin deposition), and hormone response (auxin, ABA, and JA) under drought, pathogen, drought and pathogen stress treatments ( Supplementary Figure 13B ).…”

“…Macrophomina phaseolina also exhibits the ability to have sustained growth and better survival under osmotic stress conditions due to the de novo synthesis of osmolytes such as glycerol ( Baird et al, 2003 ) and variations in the lipid contents of both mycelium and microsclerotia ( Marquez et al, 2021 ). On the plant side, weakened endodermal barrier and suppression of overall host defenses can cause enhanced DRR severity under the water stress conditions ( Irulappan et al, 2022 ).…”

“…The plants were infected using the blotting paper method ( Irulappan and Senthil-Kumar, 2021 ). The number of attached microsclerotia clearly visible in the images were manually counted to estimate the extent of microslerotial attachment in the two genotypes ( Irulappan et al, 2022 ).…”

Does Abiotic Host Stress Favour Dothideomycete-Induced Disease Development?

“…In contrast, drought appears to play an important role in increasing the severity and incidence of dry root rot (DRR) in chickpea [117]. The soil-borne fungus, Macrophomina phaseolina (teleomorph unknown) is the causative agent for DRR and can infect over 500 plant species worldwide, including some important crops such as soybean, chickpea, maize, sorghum and oilseed rape [118,119].…”

“…M. phaseolina is also responsible for stem canker, seedling blight, charcoal rot, wilt, leaf blight, stem blight and pre-emergence and post-emergence damping-off [120]. Many studies mention that, especially under high temperatures and soil moisture below 60%, this fungus can cause substantial yield losses [117,118,121,122]. Although drought is known to play an important role in the development of M. phaseolina, as dry soil favours microsclerotia survival, drought-induced host stress also plays a role in disease development [121,123,124].…”