IAP: Agronomic parameter of the inoculated plants; LSD: Least significant difference; LWI: Leaf Wilting Index; Ndl: Number of wilted leaves; NTl: Number of total leaves; PSA: Potato sucrose agar; RPAP: Percentage reduction of each agronomic parameter; SCc: Surface colonized by the fungus; STr: Total surface of the rhizome slice.

Iris germanica L. (Iridaceae), commonly known as bearded iris, is a perennial herbaceous plant. Widely cultivated across the world for its large, vividly colored flowers and strong ornamental appeal, this species is extensively used in landscaping, botanical gardens, and horticultural hybridizations. Its vegetative rhizome multiplication makes it particularly appreciated for its phenotypic stability and hardiness (Rønsted et al. 2012; Mazaheri et al. 2021). Beyond its aesthetic significance, I. germanica also possesses notable medicinal properties. Extracts from its rhizomes have shown antioxidant, diuretic, and anti-inflammatory properties, justifying their use in some traditional medicines (Kumar et al. 2015; Morning et al. 2017).

However, I. germanica is also exposed to numerous biotic threats, particularly soil-borne fungal infections, that severely compromise its growth, health, and propagation capacity. Among the most destructive pathogens are species of the genus Fusarium Link, a group of ubiquitous filamentous fungi responsible for severe diseases in a wide range of plant species. Several Fusarium species are known to cause ornamental diseases (Hembrom et al. 2019), with Fusarium oxysporum and Fusarium solani frequently reported to be responsible for rhizome rot in Iris germanica (Baayen et al. 1998; Mazaheri et al. 2020). These fungi often penetrate through mechanical or natural wounds and colonize vascular or cortical tissues, causing necrosis, wilting, reduced vegetative vigor, and even rapid plant death (Di Pietro et al. 2003).

In Morocco, iris cultivation is experiencing recent but promising growth, especially in the production of rhizomes (iris roots or 'orris roots') mainly used for the cosmetic industry and luxury perfumery (Khatib et al. 2022). The isolation, identification, and characterization of these phytopathogenic fungi are therefore essential to understand their pathogenicity, adapt cultural practices, and implement effective and sustainable control strategies. In this context, the objective of this study was to investigate the pathogenicity of different Fusarium spp. isolates via rhizome inoculation, with emphasis on symptom development, isolate aggressiveness, and consequent damage to the host plant.

Thirteen isolates belonging to the genus Fusarium were obtained from rhizomes and roots of Iris germanica plants collected from the Muslim cemetery in Taza, North-east (Achajri et al. 2025) (Table 1). Among these, isolates SP14, SP21 and RIZ2B were assigned to Fusarium oxysporum, while S4 and R33 were attributed to F. solani, according to their morphological characteristics. Species discrimination was based on macroscopic features observed on PSA: F. solani typically developing cream to white, woolly colonies with a pale reverse, whereas F. oxysporum produced cottony to floccose colonies often showing violet pigmentation, as well as on microscopic traits. F. solani was characterized by robust, thick-walled macroconidia (39–75 × 5–9 µm, with 3–5 septa), cylindrical microconidia (5–12 × 2–4 µm), and abundant, coarse-walled chlamydospores (7–12 µm). Conversely, F. oxysporum displayed more delicate and slightly curved macroconidia (27–39 × 3–5 µm), smaller oval microconidia (5–12 × 2–3 µm, generally aseptate), and chlamydospores occurring singly or in pairs (7–11 µm) (Fig. 1). These diagnostic elements are in agreement with the identification criteria outlined by Leslie and Summerell (2006).

Fig. 1. Morphological characterization of Fusarium oxysporum isolates SP14 and SP21. (A–B) SP14: abundant hyaline, mostly non-septate microconidia with regular oval to cylindrical profiles. (C–D) SP21: representative microconidia exhibiting similar morphology. Observed traits align with the species description of F. oxysporum. Scale corresponds to ocular micrometer calibration.

Table 1. Fusarium spp. isolates from Iris germanica rhizomes and roots native to Taza, Morocco.

The plants grown from these inoculated rhizomes showed leaf wilting and necrosis in the root system. Additionally, there was a decrease in various agronomic parameters (total number of healthy leaves; mean leaf area; number of newly formed rhizomes; plant weight) compared to the control.

This allowed for an evaluation of disease severity in Iris plants. The isolates RZ32, RIZ21, SP21, and SP14 were the most virulent, causing wilting and leaf drop (Fig. 2), with wilting leaf indices of 50%, 33.33%, 30.55%, and 21.81%, respectively. All other isolates caused only minor or no leaf wilting, ranging from 15.5% to 0% (Fig. 3).

Fig. 2. Symptoms of various strains in leaves. (A) Control. (B–C) Strain SP14. (D) Strain SP21.

Fig. 3. Percentage of leaf wilting in Iris plants caused by different Fusarium isolates. Two values do not differ significantly at the 5% level if followed by the same letter.

Furthermore, deep brown necrosis was observed on the rhizomes and roots of inoculated plants. The highest rhizome and root rot scores were seen in plants inoculated with RIZ2B, which scored a 3. This was followed by RIZ21, RIZ31, RZ32, RZ26, SP14, R33, and SP21, all of which scored a 2. A score of 1 was given to RZ41. Meanwhile, plants inoculated with other isolates showed no symptoms (Fig. 4). Necrosis symptoms appeared on the rhizomes (Fig. 5), along with deterioration of the root system in the most severe cases (Fig. 6).

Fig. 4. Rhizome and root rot scores in iris plants inoculated with different Fusarium spp. isolates. Two values do not differ significantly at the 5% level if followed by the same letter.

Table 1 (severity scale). Rhizome and root rot severity scale used for disease assessment.

The pathogenicity of Fusarium isolates caused significant changes in several agronomic traits of Iris germanica, indicating major physiological stress. Fusarium spp. significantly affected key parameters such as total leaf count, average leaf area, plant fresh weight, and rhizome number (Fig. 7). Data analysis revealed a substantial reduction in the number of leaves, reaching up to 73.89% with RZ32, 65.27% with R'12 and RZ'1, S4, and RIZ21, 60.83% with SP21, and 52.20% with R33. Conversely, isolates SP14, RIZ31, RIZ2B, RZ41, RZ'2, and RZ26 did not affect leaf formation (Table 2).

Fig. 5. (A–B) Necrosis symptoms seen in rhizomes after inoculation.

A marked decrease in average leaf area (50.88%) was observed in plants inoculated with Fusarium solani R33 (35.41 cm²), followed by RIZ21 (36.58 cm²) and RZ41 (43.4 cm²), representing reductions of 46.34% and 36.58%, respectively, from the control's 68.03 cm². The other isolates resulted in moderate reductions, with leaf areas ranging from 49.75 to 57.97 cm², not exceeding 26.87% (Table 2).

Fig. 6. (A–B–C) Necrosis observed in roots inoculated with the isolate RIZ2B of Fusarium oxysporum.

Additionally, there was a significant decrease in new rhizome production in plants inoculated with RIZ31, RZ'2, RZ41, and SP14, with reductions of over 75%. The number of rhizomes per plant dropped by 93.86% to 75.04%, leaving about one rhizome. RZ26 and RIZ2B followed, each with around 2 rhizomes per plant. In contrast, other isolates maintained the same or even higher number of rhizomes than the control (averaged 5.33), with some plants producing up to 10 rhizomes, such as RZ32 and R33 (Table 2).

A significant reduction of over 46% was observed in the total fresh biomass of inoculated plants with isolates SP14, S4, and RIZ31 (53.83 g, 53.80 g, and 51.8 g, respectively) compared to healthy controls at 100.5 g. The biomass with RIZ2B was 66.6 g. Conversely, RZ32 and R33 (F. solani) retained relatively high plant mass at 84.28 g and 81.26 g, respectively, indicating lower virulence for this trait (Fig. 7).