Federica Caradonia1*, Domenico Ronga1, Leonardo Setti1,Luca Laviano1, Enrico Francia1, Caterina Morcia2, Roberta
Ghizzoni2, Franz-W. Badeck2, Fulvia Rizza2, Valeria Terzi2
1Department of Life Sciences, University of Modena and Reggio Emilia, Via Amendola, n. 2, 42122 Reggio Emilia (RE), Italy.
2Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria - Centro di Ricerca per la Genomica e la Bioinformatica (CREA-GB), Via San
Protaso, 302, 29017, Fiorenzuola d'Arda, Italy.
Abstract
Arbuscular mycorrhizal fungi (AMF) are ubiquitous in the natural environment and interact with the roots of most plants providing a range of benefits to the host species. Therefore, the presence of AMF in the soil might improve the tolerance of horticultural crops like tomato to water deficit, and could be an interesting strategy in view of ongoing climate change. In this work, three processing tomato genotypes – Pearson (old), Everton (modern) and H3402 (modern) – were inoculated with two AMF – Glomus mosseae, Rhizophagus intraradices – to assess their responses to drought stress in a short-term growth chamber experiment evaluating physiological changes at seedlings stage. Data recorded during the stress show that tomato plants growth in presence of AMF – in particular Rhizophagus intraradices – have enhanced drought tolerance. The results obtained represent a first step towards the characterization of processing tomato-AMF interaction.
Keywords: drought stress, processing tomato, arbuscular mycorrhizae, sustainable agriculture Parole chiave: stress da siccità, pomodoro da industria, micorrize arbuscolari, agricoltura sostenibile Introduction
Tomato (Solanum lycopersicum L.), after potato, is the main cultivated horticultural crop in the world, and in 2014 ca. 16.9 M tons were produced in Europe, with Italy being one of the major producers of the region (FAOSTAT, 2017). Many abiotic stresses can threaten the tomato plant causing large production losses and drought stress is considered the most important one (Subramanian et al., 2006). During the growth season processing tomato needs large amounts of water (Patanè et al., 2011) ranging from 400 to 600 mm based on climatic conditions (Rana et al., 2000). Furthermore, the ongoing climate change could raise the frequency of drought stress events; hence, sustainable agronomical strategies aiming at increasing tomato tolerance to drought should be developed. Arbuscular mycorrhizal fungi (AMF) are ubiquitous in natural environment and interact with the roots of most of plants, providing a range of benefits to the hosts. The application of AMF has been reported to improve water and nutrient (P, K, Mg, N and micronutrients) uptake, enhance tolerance to soil-borne pathogens and environmental stresses, reduce sensitivity to heavy metals, and have positive influence on soil structural properties (Baum et al., 2015; Bernardo et al., 2017; Cavagnaro et al., 2012; Gosling et al., 2006; Hart et al., 2014; Subramanian et al., 2006; Zouari et al., 2014). Furthermore, Ruth and colleagues (2011) showed as AMF contributed to the direct and indirect total water uptake of the plants. Therefore, the use AMF could be an interesting solution to reduce yield losses due to growth in water limiting conditions. In this context, the aim of the present study was to assess the physiological responses during drought stress of three different processing tomato genotypes – Pearson (old), Everton (modern) and H3402 (modern) – inoculated with two AMF (Glomus mosseae and Rhizophagus intraradices) at seedlings stage.
Materials and Methods
The study was conducted in the CREA-GB growth chambers (Fiorenzuola d’Arda, Italy), following a fully randomised experimental design. The experiment was carried out in pots using three genotypes: Person (old), Everton (modern) and H3402 (modern). Seed was provided by ISI Sementi S.p.A. (Fidenza, Italy) and plants were grown in pots containing the same quantity of peat (pH 6, electrical conductivity 0.25 dS m-1, dry apparent density 110 kg m-3). Before transplanting, G.
mosseae and R. intraradices were mixed with peat 50g:500g (w/w) (1g of inoculum contained 10 propagules). AMF
inocula were obtained from MycAgro, LabTechnopôle Agro Environnement, Bretenière, France. The experiments had two level of irrigation: full (100%) and partial (65%).
Five tomato seedlings per treatment were cultivated in a growth chamber at 23°C day/17°C night with 14h photoperiod. Three weeks later, seedlings were subjected to drought stress for 3 weeks by withholding watering. Relative soil water
content (RSWC) was controlled gravimetrically weighing the pots every 3 days (Bernardo et al., 2017). Some morphological (height of plant, number of leaves, stem diameter, dry weight of leaves, stems and roots and the total dry weight) and physiological (chlorophyll, flavonoid and nitrogen estimation content, transpiration index) parameters were recorded at 3 timing during the stress: at start, in the middle, and at the end. Chlorophyll (Chl), flavonoids (Flav) and nitrogen content (NBI) were estimated on the youngest fully expanded leaf using Dualex 4 Scientific (Dx4) (FORCE-A, Orsay, France). The different parts of the plant (leaves, stems and root) were weighted and oven-dried at 65°C until constant weight to obtain the dry weight of single organs and the total dry weight.
Analysis of variance (ANOVA) was performed with GenStat 17.0th edition on data recorded at the end of drought stress.
Means were compared using Duncan’s test at the 5% level. Moreover, all recorded data during the experiment was analyzed by Principal Component Analysis (PCA) model (Jackson, 1991; Wold et al., 1987) to evaluate the relationships between the analyzed objects and the original variables, a biplot graph was used.
Results and Discussion
Irrigation regimes significantly affected all parameters investigated (Table 1). Plant growth was reduced as observed by plant height, number of leaves, steam diameter, and root and total dry weight. Noteworthy, chlorophyll content was apparently higher in seedlings under partial irrigation (+11%), probably because of an increase Chl concentration rather than greater accumulation. Partially irrigated seedlings, when inoculated with AMF, showed a higher value of flavonoids but also an interesting increase of plant height; furthermore, inoculation with G. mossae showed a higher stem diameter and plant height/stem diameter. On the other hand, inoculation with R. intraradices showed a higher number of leaves, stem diameter, root and total dry weight under stress, but also a lower ratio between water use and leaf fresh weight that might suggest a greater resistance to drought. Our data agree with the findings by Subramanianet al. (2006) who reported that AMF increased tomato shoot dry matter.
No significant differences in water use could be ascribed to AMF inoculation; however, Pearson was the genotype that showed the highest value (+3%) and R. intraradices showed the lowest water use/leaf fresh weight ratio.
Principal Component Analysis (PCA) explained 66.79% of the variability, with the first two PCs being 54.01% and 12.78%, respectively (data not shown). In general, seedlings inoculated with AMF, and in particular using R. intraradices, increased the growth in term of number of leaves, stems and total dry weights and the content of flavonoids showing similar trend among all genotypes. In addition, AMF improved Chl during the stress period. These results are in agreement with those showed by Ruiz-Lozano et al. (2016), who reported that AMF symbiosis alleviates drought stress by altering plant physiology in the host plant. As expected the highest physiological and morphological values were obtained without drought stress; however, the indications obtained in this first year of experiment show the sustainability of AMF inoculation in alleviating drought stress effects on processing tomato seedlings.
Conclusions
The present study provides some useful information on the application of AMF on processing tomato at seedlings stage during drought stress. The results showed how AMF could improve drought tolerance and enhance plant growth. Hence, a multidisciplinary approach to investigate the interaction between élite genotypes and AMF is being performed to obtain useful information that might promptly converted in agronomic practices to face future climate change.
Tab.1: Morphological and physiological data recorded at the end of drought stress.
Chlorophyll content = Chl; flavonoid content = Flav; nutrient balance index = NBI; water use = WU; leaves dry weight = LDW; steams dry weight = SDW; root dry weight = RDW; total dry weight = TDW; no arbuscular mycorrhizal fungi treatment = M-; G. mosseae treatment = MG+; R. intraradices treatments = MR+; not significant = n.s. Mean values (n=5) within a column followed by different lowercase letters are significantly different at p<.05, according to Duncan’s test.
Tab.1: Dati morfologici e fisiologici rilevati alla fine dello stress da siccità.
Contenuto in clorofilla = Chl; contenuto in flavonoidi = Flv; Indice del bilancio dell’azoto = NBI; acqua utilizzata = WU; peso secco delle foglie = LDW; peso secco dei fusti = SDW; peso secco delle radici = RDW; peso secco totale = TDW; nessun trattamento con fungi micorrizici arbucolari = -M; trattamento con G. mosseae = MG+; trattamento con R. intaradices = MR+; non significativo = n.s. I valori medi (n = 5) all'interno di una colonna seguita da diverse lettere minuscole sono significativamente diverse a p <0,05, secondo il test di Duncan.
Treatment Genotype Pearson 29.02 1.11 a 29.40 55.12 a 6.23 b 23.70 a 0.53 45.09 a 6.96 a 6.38 a 6.19 19.53 0.42 b 4.12 a Everton 28.09 0.97 b 31.20 53.15 ab 6.57 a 21.79 c 0.51 42.56 b 6.83 b 6.28 b 6.24 19.35 0.48 a 4.14 a H3402 28.61 1.02 ab 31.50 52.10 b 5.86 c 18.97 b 0.52 36.78 c 6.93 a 6.28 b 6.19 19.17 0.45 c 3.82 b Mychorrizae M- 29.41 0.92 b 34.40 53.81 6.15 20.77 b 0.51 b 41.00 ab 6.86 b 6.28 b 6.24 a 19.14 0.47 a 4.10 a MG+ 28.32 1.11 a 29.60 52.75 6.17 21.97 a 0.51 b 43.10 a 6.83 b 6.28 b 6.17 b 19.28 0.44 b 4.14 a MR+ 27.99 1.07 a 28.10 53.81 6.34 21.72 a 0.54 a 40.34 b 7.02 a 6.38 a 6.21 a 19.62 0.44 b 3.85 b Irrigation 100% 26.96 b 1.19 a 24.50 b 73.99 a 6.54 a 24.48 a 0.54 a 45.46 a 7.12 a 6.39 a 6.27 a 19.61 a 0.44 b 5.15 a 65% 30.19 a 0.87 b 36.90 a 32.93 b 5.90 b 18.49 b 0.50 b 37.50 b 6.70 b 6.24 b 6.15 b 19.09 b 0.46 a 2.91 b G n.s. <.05 n.s. <.05 <.001 <.001 n.s. <.001 <.01 <.001 n.s n.s. <.001 <.001 M n.s. <.001 n.s. n.s. n.s. <.01 <.05 <.05 <.001 <.001 <.01 n.s. <.001 <.01 I <.01 <.001 <.001 <.001 <.001 <.001 <.001 <.001 <.001 <.001 <.001 <.001 <.01 <.001 G*M n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s n.s. n.s. n.s. G*I n.s. <.01 n.s. n.s. n.s. <.001 <.01 <.001 <.001 <.05 n.s n.s. n.s. <.05 M*I n.s. n.s. n.s. <.01 n.s. n.s. n.s. n.s. n.s. n.s. n.s n.s. n.s. n.s. G*M*I n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s n.s. n.s. n.s. Leaves3 (no.) RDW3 (g) Chl3 Flav3 NBI3 WU3 TDW3 (g) Root Shoot -1 3WU LFW-13 Plant height3 (cm) Stem diameter3 (cm) Plant height Stem diamter-13 LDW3 (g) SDW3 (g)
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