Preliminary Study On Heat Tolerance Of Spinach (Spinacia Oleracea L.)

The spinach (Spinacia oleracea L.) has cold resistance but cannot tolerate high temperaturewhich is the main factor that limits Spinach production in summer. To cultivate Spinach in summer, we have to select and breed heat-tolerant Spinach varieties, and improve the cultivation methods. Therefore it is necessary to study on the heat tolerance of Spinach. In this study, 14 Spinach varieties, which are commonly cultivated and from different places in the world, were treated under 15℃, 30℃,35℃to identify the heat tolerance at the germinationand 5-leaves stage. In addition, we chose 4 typical varieties and studied on thephysiological and biochemical characteristics of their seedling under 35℃/25℃.The main results were as follows:1. The suitable temperature for seeds germination was 15℃. High temperature significantly reduced the germination rate, germination potential, germination index and vigor index of different varieties, but the effect of high temperature on germination days was different from variety to variety. 30℃is the suitable heat tolerance identification temperature. The 14 Spinach varieties can be divided into 3 classes (high, medium and low). While"Space","Saint Firmin","Quinto","Zhizunbao"and"TokyoGreen"showed high heat tolerance, half of these 14 Spinach varieties failed to resist high temperature.The suitable temperature for Spinach seedling growth was 15℃. The heat injury index increased as the temperature and treat-days increased. 35℃was the suitable seedling heat tolerance identification temperature. The 14 Spinach varieties can be divided into 3 classes (high, medium and low). While"Qiangsheng","Bandolero"and"JewelryHonour"had high heat tolerance,"Chiyehuer","Quinto"and"Zhizunbao"had low heat tolerance, the rest of these Spinach varieties had medium heat tolerance.There was no significant correlation between the heat tolerances at the germinationand seedling stage.2. The accumulation of biomass - slowed down under heat treatment. The effect of high temperature to plant biomass was most significant in root fresh weight, and the main reason of fresh weight decrease was the water loss of the plant. The plant material accumulation at high temperatures was mainly used for height growth, resulting in expansive growth phenomena. The roots morphology indexes under high temperature were lower than those treated under 15℃. The root activity mainly decreased under high temperature and increased after recovery processing.SOD and POD activity of spinach increased at first and then decreased. However under the recovery treatment, they increased again. As the days of treatment prolonged, the relative conductivity and MDA content increased and decreased after 2d recovery treatment.High temperature can cause a decline in soluble protein content and free amino acids, and an increase in proline content of spinach. The varieties with high heat-tolerance had a high level of soluble protein and proline content, low level of free amino acids content. Soluble sugar content of"Qiangsheng","Bandolero", and"Quinto"increased under high temperature, while"Chiyehuer"showed a downward trend, which suggested the consumption was greater than the accumulation of soluble sugars.High temperature had different effects to chloroplast pigment content of different varieties of spinach;Pn decreased under high-temperature treatment of spinach and showed a slight increase under recovery treatment, and Gs, Ci, and E of all varieties tended to increase as the number of treat days grew. That means non stomatal factor caused the decrease of Pn.Fm generally dropped after the first rise, and changed differently from variety to variety after recovery treatment. Fv/Fm andΦPSII mainly showed downward trend at high temperature and had a slight increase in recovery treatment, but did not reach the level before treatment; qP in the whole process showed increasement at first and then decreased.3.The varieties with high heat-tolerance didn't have expansive growth phenomena; after the recovery treatment, the root activity of varieties with high-heat tolerance recovered soon; SOD activity increased faster and longer, SOD activity was significantly higher in varieties with high heat-tolerance than that in those with low heat-tolerance; POD activity and MDA content of varieties with high heat-tolerance was higher than varieties with low heat-tolerance at the 6th day; the varieties with high heat-tolerance had a high level of soluble protein and proline content, low level of free amino acids content.Meanwhile, Soluble sugar content of the least heat-resistant varieties of"Chiyehuer"showed a downward trend, which suggested the consumption was greater than the accumulation of soluble sugars, Pn and Fm of"Chiyehuer"was also significantly lower than other varieties.At the same time,Chloroplast pigment content under high temperature and recovery treatment showed no significant correlation to heat tolerance, and there was no significant difference between Fv/Fm,ΦPSII and qP of spinach varieties with different heat tolerance.4. Seeds germination of spinach was highly inhibited under high temperature of 30℃and 35℃,however, tolerance to high temperature of spincah seedlings was relatively higher than that of seeds, so it means that accelerating germination and seedling cultivation are especially important to spinach production in summer and we advise that accelerate seeds germination and breed seedlings under temperature below 30℃before outdoor cultivation. Meanwhile, there was no significant correlation between theheat tolerances at the germination and seedling stage, so we should reinforce the breeding of spinach cultivars with high heat tolerance at seedling stage under the premise of realization of indoor breeding.