Studies On Improvement Of Salt Tolerance And Fruit Quality By Arbuscular Mycorrhizal Fungi Inoculation On Strawberry

Soil salinization is becoming one of the most serious problems not only in China but also in the world. Strawberry(Fragaria×ananassa)is perennial herb and belongs to Fragaria genus of Rosaceae family. The fruit of strawberry is attractive and with good flavor. It also possesses abundant phenolic compounds and considerable nutritional value. Strawberry intake has been associated with anti-aging and lower incidence of various diseases. The yield and cultivation area of strawberry have been occupying first place in the small berries production. However, strawberry is sensitive to salinity and soil salinization limits the strawberry development. Therefore, how to improve the salt tolerance of strawberry, how to breed salt-tolerant varieties, how to use the large areas of saline soil efficiently, is receiving more and more attention in strawberry production.Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic association in the nature which can improve the plant resistance, such as drought, saline-alkali, low temperature, with natural, environment-friendly characteristics. Despite many studies on the contributions of AMF to field crops and vegetables under salt stress, very few studies has been done on strawberries. In this paper, three strawberry cultivars with different salt tolerance 'Jewel', 'Kent' and 'Saint-Pierre' were selected, and the experiments were conducted in the greenhouse of two locations in St-Jean-sur-Richelieu and L'Acadie, Canada. Three selected strawberry cultivars either inoculated or non-inoculated with AMF Glomus irregulare B?aszk., Wubet, Renker & Buscot DAOM 197198 were treated with 0, 30, 60 mmol/L NaCl solution. The objective of this study was to understand the mechanisms of AMF alleviation of salinity stress on strawberry. The main results were as follows:1) After six weeks of NaCl treatment, the salinity index increased with salinity levels. The leaves of'Kent'showed injury symptoms 5 d after NaCl treatment, leaves of 'Jewel' and 'Saint-Pierre' showed injury symptoms 9 d and 10 d after NaCl treatment, respectively. AMF alleviated the injury symptoms of salinity and promoted the growth of strawberry.2) Under 30 mmol/L and 60 mmol/L NaCl treatment, the leaf number of strawberry reduced, flower period delayed, average fruit weight decreased, leaf area depressed, relative water content decreased, water saturation deficit increased. But AMF inoculation increased the corresponding parameters. NaCl stress reduced the chlorophyll content (SPAD) of strawberry, while SPAD of inoculated strawberry increased by 11.2% compared to non-inoculated plants. The leaf polyphenol content of strawberry (Dualex) was first increased and then decreased with increasing concentration of NaCl, but Dualex of inoculated strawberries were 1.16, 1.08, 1.06 times of non-inoculated strawberry within the same NaCl concentration, respectively.3) This is the first report of AMF inoculation on root morphology in strawberry under NaCl stress. AMF colonization was reduced under NaCl stress. There was a significant negative correlation between AMF colonization and salinity (r =-0.995, p < 0.05). The root morphology of strawberry was changed by AMF under NaCl stress. Total root length, root surface area, root volume, root forks and root crossings were increased. No significant effect on average root diameter was observed. Compared with the non-inoculated strawberry, the percentage of fine roots (diameterφ≤0.5 mm) of inoculated strawberry reduced by 3.8%, however, the percentages of medium root (0.5 mm <φ≤1.5 mm) and coarse roots (φ> 1.5 mm) of inoculated strawberry were increased by 10.7 % and 19.6%, respectively, indicating that AMF changed the root structure and the proportion of coarse roots was increased. The biomass of shoot and root, root to shoot ratio and root activity were significantly improved by AMF inoculation under NaCl stress. Total root length of inoculated strawberry was increased by 44.2% than that of control.4) NaCl stress affected the mineral nutrition absorption of strawberry. Macro-elements including nitrogen, phosphorus, potassium, calcium and magnesium and micro-elements including copper, iron, manganese and zinc were decreased with the increasing salinity level, but the AMF inoculation significantly increased the content of these elements in strawberry leaves. Na+ was increased with the increasing salinity level, but the absorption of Na+ of non-inoculated strawberries reduced by 15.7%. Neither NaCl stress nor AMF infection had significant effect on boron absorption. After the symbiosis established, proline content of strawberry leaves was decreased and soluble sugar and soluble protein content were increased by AMF inoculation under NaCl stress. Thus osmotic balance was maintained, water supply was provided and the negative effects of salinity were reduced.5) H₂O₂, O2·– and malondialdehyde (MDA) of inoculated strawberry leaves were declined by 27.9%, 15.2% and 16.2% than non-inoculated strawberries under NaCl stress, while superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity were increased by 16.5%, 24.4% and 31.6% than control, indicating that AMF inoculation can alleviate the salt-induced oxidative stress damage to the strawberry.6) This is the first study of AMF inoculation on fruit quality, total phenolic content (TPC) and total antioxidant capacity (TAC) in strawberry under NaCl stress. The results showed that the effects of salinity on strawberry fruit quality, TPC and TAC varied with NaCl concentration. The soluble solids content (SSC), titratable acidity (TA), firmness, shelf life, ascorbic acid content, TPC, TAC and oxygen radical absorbance capacity (ORAC) were improved under 30 mmol/L NaCl treatment, but the strawberry fruit quality and TAC were significantly decreased with higher salinity level. AMF inoculation can improve the fruit quality and TAC of strawberries, but the ranges were smaller as the salt concentration increased. Both salinity and AMF inoculation increased phenylalanine ammonia-lyase activity (PAL) in strawberry fruit.7) From our results,'Saint-Pierre'was the most salt tolerant cultivar,'Jewel'was the second, and'Kent'was the most salt sensitive one.