Mechanical Mechanism Of Irrigation-induced Cracking To Tomato Fruit In Greenhouse

Tomato is one of the important fruits and vegetables in human diet.The area grown,yield and consumption of tomato in China all rank among the front ranks of the world.However,fruit cracking in the process of tomato planting and production will lead to poor appearance and quality of fruit,increase the risk of mold invading the inner pulp from cracks,accelerate fruit decay,lose commodity value,and bring serious economic losses.Many studies have shown that fruit cracking is mainly affected by environmental factors,among which water is the main environmental factor leading to fruit cracking during tomato planting in greenhouse.Unreasonable irrigation during tomato fruit growth and development will increase the probability of tomato fruit cracking.The lack of research on the mechanical mechanism of tomato fruit cracking caused by irrigation limits the use of gene breeding and irrigation management strategies to reduce fruit cracking.In order to solve this problem,this investigation took tomato fruit as the research object,through the irrigation experiment of tomato plants in solar greenhouse,and the cracking characteristics of tomato fruit was observed and recorded,and the mechanical properties,chemical composition and structure of the pericarp were measured and analyzed.Based on the experiment by using finite element analysis software ABAQUS and the discrete element EDEM from the micro-mesoscopic-macro level to build simulation model of tomato fruit different organizational structures investigation of mechanical mechanism of fruit cracking,according to the simulation results predicted regression model,to prevent and reduce fruit cracking behavior to provide the theoretical basis and technical support.The main research contents and results are as follows:(1)In order to investigate the influence of different irrigation methods on the texture and mechanics of multiscale crack resistance,the phenotypic indexes with differential effect on the texture and mechanics of fruit crack resistance were selected.In this study,tomato plants were treated with different irrigation methods.In this study,tomato plants were treated with different irrigation methods.The results showed that proper water shortage irrigation could reduce the cracking rate of tomato fruit,and the lowest cracking rate was 8.75%when the irrigation frequency was 1 time/interval of 5 d,and the irrigation amount was 50%ET_c.Too high or too low irrigation amount and irrigation frequency were easy to increase tomato fruit cracking rate.According to the mechanical characteristics of the pericarp,uncracked area and uncracked fruit,the fracture stress,fracture strain,elastic modulus and fracture energy of tomato pericarp were 0.45-4.50 MPa,0.13-0.21%,3.65-8.58 MPa and 1.52-4.73 m J/mm~2,respectively.The change ranges of fracture stress,fracture strain,elastic modulus,and fracture energy of the mesocarp were 0.14-0.45 MPa,0.12-0.21%,0.09-0.28 MPa,and 0.068-0.186 m J/mm~2,respectively.Through ANOVA,it was found that the phenotypic indicators that had the effect of irrigation mode on the mechanics of the fracture resistant texture of the fruit were fracture stress and elastic modulus,while there was no significant difference between fracture strain and fracture energy.(2)In order to investigate the effect of irrigation methods on the composition and structure of tomato pericarp,the content of cell wall components and the change of polysaccharide structure,the content of cell wall polysaccharide in the pericarp tissue of the tomato fruit dehiscence area was extracted and measured and its structural characteristics were analyzed.The results showed that different irrigation treatments had important effects on the content and existence of pectin in the cell wall of tomato fruit,but had little effect on the content of hemicellulose and cellulose in the cell wall.When the total pectin content of the tomato pericarp cell wall,the higher the WSP/NSP+CSP ratio was 0.08,the lower the cracking resistance of the tomato fruit;while the content of hemicellulose and cell wall residue(mainlyα-cellulose)has no significant effect on the fruit cracking.FTIR and XRD were used to characterize the structural characteristics of pectin and SEM morphology in tomato peel cells,and it was also found that the peel cells of tomato fruits under different irrigation treatments contained naturally occurring pectin characteristic functional groups.The diffraction peaks of tomato exocarp and mesocarp pectin in the A1 experimental group were small,wide,and flat,and amorphous structure,while the diffraction peaks of tomato exocarp and mesocarp pectin in the B1,D1 and E1 experimental groups fluctuated high and low,without much fluctuation,and the pectin had a certain definite structure.Compared to the relatively compact,complete,and smoother surface of pectin observed in the C1 test group,the pectin surface morphology in the A1 test group showed rougher,potholes,and more cracks.This indicated that the higher the frequency of irrigation and the greater the amount of irrigation,the greater the influence on the peel structure and cell wall component content of tomato fruit,and it was more likely to lead to cracking of tomato fruit.The pectin substance in the C1 test group had a crystalline qualitative structure,which was more stable and not easy to crack.(3)In order to investigate the fruit growth and development in the process of fruit macroscopic crack is caused by irrigation cells increased inflation pressure in the microscopic scale,the finite element model of single cell and mesocarp block discrete element model were established,the finite element model to predict the single-celled during compression deformation to 11%internal peak turgor pressure of 12.9 k Pa,the average relative errors of single cell finite element model and mesocarp tissue block discrete element model were 5.8%and 9.5%,respectively.Simulation and regression analysis showed that turgor pressure was the most important factor affecting cell mechanics,followed by cell shape and elastic modulus of cell wall.The apparent elastic modulus of cells is the most important factor affecting the tissue mechanics of mesocarp,followed by the number and shape of cells.Finally,the relationship between elastic modulus of mesocarp and turgor pressure of mesocarp was quantitatively described and determined by establishing mathematical model.(4)In order to investigate the information of macroscopic crack generation and crack propagation caused by the change of turgor pressure in tomato fruit caused by irrigation,the quantitative correlation between crack behavior and its physical and biomechanical properties was established.,the XFEM model was constructed to simulate the internal swelling pressure change of tomato fruit by use the extended finite element method(XFEM).The results showed that the model could reproduce the macroscopic crack propagation behavior of tomato peel cracking caused by irrigation.According to the simulation test and the crack length and shape of fruit cracking caused by irrigation,the peak expansion pressure inside the fruit was predicted to be 3.5 MPa.The results of numerical simulation and covariance mathematical model analysis showed that the factors affecting fruit cracking depend on pericarp thickness,internal peak turgor pressure,crack position,fruit surface crack number,pericarp elastic modulus and failure stress,and demonstrate that the linear mathematical function was suitable to quantitatively describe the relationship between fruit crack information(extended length and volume)and pericarp thickness,internal peak turgor pressure,crack position,fruit surface crack number,pericarp elastic modulus and failure stress.An objective understanding of the mechanical mechanisms by which irrigation caused tomato fruit cracking at a macro-level could help to develop strategies to prevent fruit cracking through a combination of genetic breeding and irrigation management techniques.