Growing vegetables
Parastoo Molaei; Fatemeh Nekounam
Abstract
IntroductionLettuce (Lactuca sativa L.) from the Asteraceae family is one of the most important vegetables due to its rapid growth and commercial value. Currently, the market share of organic vegetables is constantly increasing due to customer demand for safer and healthier food. Excessive use of pesticides ...
Read More
IntroductionLettuce (Lactuca sativa L.) from the Asteraceae family is one of the most important vegetables due to its rapid growth and commercial value. Currently, the market share of organic vegetables is constantly increasing due to customer demand for safer and healthier food. Excessive use of pesticides and chemical fertilizers threatens the environment and leads to the production of unsafe food products. Therefore, it is important to find alternatives instead of using pesticides chemical methods to manage powdery mildew. Generally, biotic and abiotic stresses are among the factors that have a destructive effect on growth and development, performance, and production of plant biomass. Fungicides can be the most effective method of controlling the powdery mildew disease, but this pathogen can develop resistance to fungicides. Rhizosphere bacteria are among the living agents that, by producing some allelochemicals, cause the dissolution of soil nutrients, increase the availability of nutrients, and induce plant resistance to biotic and abiotic stresses. In addition, they enhance host plant growth through an indirect mechanism, including the inhibition of disease-causing pathogens by releasing some allelochemical substances. The biological control of powdery mildew disease with the use of rhizospheric bacteria in lettuce and zucchini has been reported. Material and MethodsTo evaluate the biological control of powdery mildew fungus with plant growth promoting rhizobacteria (PGPR) and effects on yield and quality of New Red Fire greenhouse lettuce, an experiment was carried out in a completely randomized design with three replications in the Research greenhouse of University of Zanjan during 2020. Experiment treatments consisted of five levels of PGPR (Pseudomonas vancouverensis- VPM, Pseudomonas Koreensis- KPM, Pantoea agglomerans- PAPM, Pseudomonas putida- PPM, and one level of combined bacteria (Pantoea agglomerans+ Pseudomonas Koreensis+ Pseudomonas putida+ Pseudomonas vancouverensis- MBPM, one level of chemical fertilizer 100% N, P and, K according to soil test results- NPK, and two control treatment without powdery mildew condition (C) and under powdery mildew conditions (CPM).The “New Red Fire” lettuce seeds were surface sterilized with 0.5% (v/v) sodium hypochlorite for 10 min and germinated at 20ºC. After germination, seedlings with similar size were transplanted into pots. Plants were grown under greenhouse condition with 60/70 % (day/night) relative humidity, 15/18 °C (day/night) temperature. Inoculation of pathogenic fungi was done 40 days after seed germination. Plants were harvested after 75 days. The chlorosis and necrosis spots number on each plant, plant fresh weight, plant dry weight, leaf number, total chlorophyll, total phenol and flavonoids contents, antioxidant activity, anthocyanin content, and catalase and peroxidase enzyme activity were measured. ResultsThe results showed that the application of potassium and phosphorus solubilizing bacteria and NPK fertilizer significantly increased plant growth compared to control plants under the stress of powdery mildew fungus. The highest plant fresh weight, percentage of plant dry weight, and leaf number were obtained with the application of combined potassium and phosphorus solubilizing bacteria treatment and 100% N fertilizer under the biostress. The maximum total chlorophyll was obtained with the application of Pseudomonas koreensis and Pantoea agglomerans bacteria. 100% reduction of necrosis spots was obtained by using the Pantoea agglomerans bacteria. The maximum of chlorosis spots (increase of 55.8%) and necrosis spots (an increase of 88.8%), total phenol (an increase of 52%), total flavonoids (an increase of 39.3%), catalase (an increase of 28.4%) and peroxidase enzymes activity (49.1%) were obtained with application of NPK fertilizer. No significant effect on antioxidant activity was observed with the application of chemical fertilizer and rhizosphere bacteria under the Biostress. The maximum anthocyanin contents were obtained with the application of Pseudomonas koreensis. ConclusionAccording to the results, the application of NPK chemical fertilizer and seed pretreatment of lettuce with PGPR increased the value of antioxidant compounds including total phenol, flavonoid, and anthocyanin contents and catalase and peroxidase enzymes activity under powdery mildew conditions. Inoculation of lettuce seeds with PGPR, in addition to improve plant growth under biological stress conditions, increased anthocyanin contents and induced the resistance of lettuce plants to powdery mildew. Seed pretreatment with PGPR reduced chlorosis and necrosis spots in leaves. Therefore, pretreatment of lettuce seeds with PGPR instead of chemical compounds (fertilizers, pesticides and plant growth regulators) is recommended to improve the yield and quality of lettuce under powdery mildew conditions.
Growing vegetables
Parastoo Molaei; Taher Barzegar; Mohammad BabaAkbari Sari; Fatemeh Nekounam; Zahra Ghahremani
Abstract
Introduction
Excessive use of chemical fertilizers threatens the environment and leads to production of unsafe food products. Currently, the market share of organic vegetables is constantly increasing due to customer demand for safer and healthier food. Therefore, it is necessary to find alternatives ...
Read More
Introduction
Excessive use of chemical fertilizers threatens the environment and leads to production of unsafe food products. Currently, the market share of organic vegetables is constantly increasing due to customer demand for safer and healthier food. Therefore, it is necessary to find alternatives instead of using chemical fertilizers in plant production.
Lettuce (Lactuca sativa L.), belongs to Asteraceae family is considered as one of the most popular salad vegetables as a cool season crop. It is also one of the most important vegetables due to its rapid growth and commercial value. Plant growth promoting bacteria promote plant growth directly by facilitating nutrient uptake through fixing nitrogen, solubiliszation of phosphorus, production of hormones and iron uptake. Arbuscular mycorrhizal fungi establish symbioses with plant roots which help to improve nutrient uptake by the host plant and alter its physiology to withstand external abiotic factors and pathogens. Arbuscular mycorrhizal fungi interactions with bacteria have been reported to enhance plant growth through phosphate solubilization, nitrogen fixation, increased AMF spore germination and colonization of plant roots. The potential of co-inoculation of these two organisms in promoting the growth of horticultural crops like tomato, strawberry, lettuce and spinach have also been reported.
Materials and Methods
In order to compare the effect of growth-promoting bacteria, mycorrhiza fungi and chemical fertilizers on morphological and physiological properties of lettuce (Lactuca sativa cv. New Red Fire), the experiment was carried out in a completely randomized design with three replications. Experiment treatments consisted of 14 treatments including three levels of potassium solubilizing bacteria (Pseudomonas vancouverensis, Pseudomonas koreensis, Pseudomonas vancouverensis + Pseudomonas koreensis) + 100% N and P, three levels of phosphorus solubilizing bacteria (Pantoea agglomerans, Pseudomonas putida and Pseudomonas putida + Pantoea agglomerans) + 100% N and K, and one level of potassium and phosphorus solubilizing combined bacteria (Pantoea agglomerans+ Pseudomonas koreensis+ Pseudomonas putida+ Pseudomonas vancouverensis) + 100% N, mycorrhiza fungi combination of three Glomus species (G. mosseae, G. etunicatum and G. intraradices) + 100% N and K and five chemical fertilizer levels (N100P100K100, N100P100K0, N100P0K100, N100P25K100 and N100P100K25) according to soil test results, and control treatment without bio-mineral fertilizers.
The “New Red Fire” lettuce seeds were surface sterilized with 0.5% (v/v) sodium hypochlorite for 10 min, and germinated at 20ºC. After germination, seedlings of similar size were transplanted singly into pots containing agricultural soil. Plants were grown under greenhouse condition of 60/70% (day/night) relative humidity, 15/18 °C (day/night) temperature. After a growth period of 75 days, plants were removed from the pots. The root system was separated from the shoot and washed to remove adhered soil. Root and shoot fresh weight, chlorophyll, vitamin C, anthocyanin, TA, TSS and nitrate contents were measured.
Results
The results showed that application of potassium and phosphorus solubilizing bacteria and mycorrhiza fungi significantly increased plant growth compared to control plant. The highest fresh shoot weight (increase of 42.3%) and crown diameter (increase of 14.4%) was obtained with application of combined potassium and phosphorus solubilizing bacteria treatment + 100% N fertilizer compared to control plants. Application of Pseudomonas koreensis + 100% N and P resulted in the maximum content of anthocyanin (increase of 62.2%) and total soluble solids (increase of 82.5%) compared to control plants. Ascorbic acid, a well-known antioxidant and organic compound, is an essential vitamin can be obtained from fruits and vegetables. The highest vitamin C content (32.3 mg 100 mL-1) was observed at plant treated with N100P100K100 fertilizer. The maximum titratable acidity content was obtained with application of Pseudomonas vancouverensis + 100% N and P, and combined potassium and phosphorus solubilizing bacteria treatment +100% N fertilizer. The nitrate content is an important quality index of leafy vegetables; low nitrate content is associated with enhanced quality. Application of chemical fertilizers significantly increased nitrate accumulation compared to biofertilizers and control plants, so that the minimum nitrate accumulation content was observed in control plant and combined potassium and phosphorus solubilizing bacteria treatment + 100% N fertilizer (21.14 µg g-1FW), respectively.
Conclusion
With continuous development of economy and society, people pay an increasing attention to the quality of fruits and vegetables. Improving the crop yield means that attention must also be given to improving vegetables quality, resulting in chemical fertilizer nutrition problem. To conclude, our study suggested that after the control treatment (without using any chemical fertilizers), which had the lowest accumulation of nitrate, application of growth-promoting bacteria and mycorrhizal fungi in combination with nitrogen fertilizer caused lower nitrate accumulation than chemical fertilizers treatments. So, the use of combined and pure bacteria treatments and mycorrhizal fungus treatment can be used to improve the growth, quality and antioxidant properties and increase the concentration of nutrients and also reducing nitrate accumulation in lettuce.
