Root Morphology, Allometric Relations and Rhizosheath of Ancient and Modern Tetraploid Wheats (Triticum durum Desf.) in Response to Inoculation with Trichoderma harzianum T-22

Abstract

Early root traits and allometrics of wheat are important for competition and use of resources. They are under-utilized in research and un-explored in many ancient wheats. This is especially true for the rhizosheath emerging from root-soil interactions. We investigated root morphology, root/shoot relations and the amount of rhizosheath of four tetrapoid wheat seedlings (30 days after emergence): the italian landrace Saragolle Lucana and modern varieties Creso, Simeto and Ciclope, and tested the hypothesis that inoculation with Trichoderma harzianum T-22 (T-22) enhances rhizosheath formation and affects wheat varieties differently. Overall growth of non-inoculated plants showed different patterns in wheat varieties, with Saragolle and Ciclope at the two extremes: Saragolle invests in shoot rather than root mass, and in the occupation of space with highest (p < 0.05) shoot height to the uppermost internode (5.02 cm) and length-to-mass shoot (97.8 cm g−1) and root (more than 140 m g−1) ratios. This may be interpreted as maximizing competition for light but also as a compensation for low shoot efficiency due to the lowest (p < 0.05) recorded values of optically-measured chlorophyll content index (22.8). Ciclope invests in biomass with highest shoot (0.06 g) and root (0.04 g) mass and a thicker root system (average diameter 0.34 mm vs. 0.29 in Saragolle) as well as a highest root/shoot ratio (0.95 g g−1 vs. 0.54 in Saragolle). Rhizosheath mass ranged between 22.14 times that of shoot mass in Ciclope and 43.40 in Saragolle (different for p < 0.05). Inoculation with Trichoderma increased the amount of rhizosheath from 9.4% in Ciclope to 36.1% in Simeto and modified root architecture in this variety more than in others. Ours are the first data on roots and seedling shoot traits of Saragolle Lucana and of Trichoderma inoculation effects on rhizosheath. This opens to new unreported interpretations of effects of Trichoderma inoculation on improving plant growth.

Seed Coating with Trichoderma harzianum T-22 of Italian Durum Wheat Increases Protection against Fusarium culmorum-Induced Crown Rot

“…The production of growth-stimulating hormones and secondary metabolites, and the modifications of the root architecture induced by T-22 through seed coating are also suggested by our results of the evident effects on the shoot height and main root length in all the varieties (Table 4). In particular, the effect on the shoot height in Saragolle Lucana and the main root length in Ciclope and Simeto confirmed the recent assessment reported by [19]. It was demonstrated that T. harzianum spp.…”

“…On this basis, our previous results regarding seedling growth, with the best performance shown by Simeto, suggest that this variety can modify its root architecture by increasing the amount of rhizosheath more than other varieties when T-22 is provided as a seed coating [19]. Hence, this specific T. harzianum T-22 inoculation method resulted in root colonization that was characterized by a less dense coiling (see Figure 3) and by the possible production of root exudates and/or specific secondary metabolites that are able to alleviate the oxidative stress induced by F. culmorum [28] and affect T-22-Simeto-pathogen interaction.…”

“…Italian tetraploid wheats (Triticum durum Desf. ), specifically, three modern durum wheat varieties released in different years (Ciclope, Creso, and Simeto) and an ancient wheat landrace (Saragolle Lucana), were used [19], as summarized in Table 1. They are characterized by a sensitivity to Fusarium spp.…”

“…A mixture of a T. harzianum T-22 suspension at a concentration of 1 × 10 6 spores mL −1 , or water as a control, was used to coat seeds in 4 µL seed −1 Tween-20, and a homogeneous distribution was obtained by continuous rotation until complete adhesion and absorption, according to [19]. The presence of T-22 as the only microorganism on the coated seed of each variety was verified by fungus re-isolation on PDA medium.…”

“…In a previous study, we reported the different effects of seed coating with Trichoderma harzianum T-22 on the seedlings of four tetraploid durum wheats (Saragolle Lucana and the modern varieties Creso, Simeto, and Ciclope) in terms of the root morphology, root/shoot relations, and the amount of rhizosheath formation [19]. Apart from potential effects on the rhizosheath, the possible biocontrol efficiency in durum wheat infected with F. culmorum represents a prominent issue to be considered.…”