The Vascular Pathogen Verticillium longisporum Does Not Affect Water Relations and Plant Responses to Drought Stress of Its Host, Brassica napus

Abstract

Verticillium longisporum is a host-specific vascular pathogen of oilseed rape (Brassica napus L.) that causes economic crop losses by impairing plant growth and inducing premature senescence. This study investigates whether plant damage through Verticillium stem striping is due to impaired plant water relations, whether V. longisporum affects responses of a susceptible B. napus variety to drought stress, and whether drought stress, in turn, affects plant responses to V. longisporum. Two-factorial experiments on a susceptible cultivar of B. napus infected or noninfected with V. longisporum and exposed to three watering levels (30, 60, and 100% field capacity) revealed that drought stress and V. longisporum impaired plant growth by entirely different mechanisms. Although both stresses similarly affected plant growth parameters (plant height, hypocotyl diameter, and shoot and root dry matter), infection of B. napus with V. longisporum did not affect any drought-related physiological or molecular genetic plant parameters, including transpiration rate, stomatal conductance, photosynthesis rate, water use efficiency, relative leaf water content, leaf proline content, or the expression of drought-responsive genes. Thus, this study provides comprehensive physiological and molecular genetic evidence explaining the lack of wilt symptoms in B. napus infected with V. longisporum. Likewise, drought tolerance of B. napus was unaffected by V. longisporum, as was the level of disease by drought conditions, thus excluding a concerted action of both stresses in the field. Although it is evident that drought and vascular infection with V. longisporum impair plant growth by different mechanisms, it remains to be determined by which other factors V. longisporum causes crop loss.

Suppression of abscisic acid biosynthesis at the early infection stage of Verticillium longisporum in oilseed rape (Brassica napus)

“…The increase in ABA in the leaves of oilseed rape and Arabidopsis likely results from side effects, provoked by the fungal invasion into the roots and growth in the xylem, which could lead to an initially reduced water supply within the leaves. However, Reusche et al () reported that at 7 dpi V. longisporum triggers de novo xylem formation that can compensate for compromised water transport in brassicaceous host plants, which can explain why this vascular pathogen does not affect drought stress responses in oilseed rape (Lopisso et al , ). Furthermore, the increased ABA levels in Arabidopsis might contribute to an increased drought stress tolerance that has been observed for V. longisporum ‐infected plants (Reusche et al , ).…”

Variable impact of Verticillium longisporum on oilseed rape yield in field trials in the United Kingdom

“…Furthermore, rainfall was over twice as much during Verticillium stem striping, and further research is needed to reveal putative relations on the yield impact of this disease. However, watering regimes were previously shown not to impact V. longisporum disease levels if grown under controlled greenhouse conditions (Lopisso et al, 2017b).…”

The Diurnal Rhythm of Brassica napus L. Influences Contents of Sulfur-Containing Defense Compounds and Occurrence of Vascular Occlusions during an Infection with Verticillium longisporum

“…In order to detect an infection with V. longisporum, the DNA content of the pathogen was carried out using qPCR analysis (Table 1). In case of artificial inoculation under laboratory conditions, there is no resting phase for the host plant as well as for the fungus, therefore colonization of the vascular system is probably more rapid [52] and disease symptoms are different compared to plants growing in field conditions [53]. Using the entire plant (without roots) shows a more realistic picture of the state of infection of B. napus compared to analysis of only the hypocotyls of the plant.…”