| Tomatoes(Solanum lycopersicum L.)from South America,belonging to Solanaceae Lycopersicon,is an important worldwide economically crop.Tomato is a warm-like vegetable crop,which is sensitive to high temperatures.Along with the increasing of global temperature,high temperature has considered as a common abiotic stress,which has a serious effect either on normal growth or fruit quality of tomato.Different tomato germplasms have distinctive sensibility under high temperature.At present,natural identification in the field artificial analogue and indirect identification are the main heat tolerant evaluation methods.However,the workload is heavy and the procedure is tedious.The comprehensive evaluation has been proved to be more accyrate and quick to evaluate the heat tolerance of different plants.But there is no report about using this method to evaluate the heat tolerance of tomato.Besides,the sensitivity of tomatoes at different growth stages to high temperature is different.The current research on the heat tolerance of tomatoe is mostly in the seedling stage while the anthesis stage is few.The relationship of heat tolerance between seedling and anthesis stage is not clear.Studies have shown that the reproductive stage of plants is more sensitive to high temperature stress than the vegetative stage and pollen development and fertilization are the most sensitive periods under high temperature.The heat tolerance of tomato at anthesis stage is closely related to the production rate,so it is necessary to explore the most sensitive period of tomato at anthesis stage under high temperature and make the mechanism of heat tolerance clear.It is meaningful for improving the yield and quality of tomato,which will provide theoretical basis for high-quality and efficient production of tomato.In this study,we evaluated the heat tolerance of different tomato germplasm at seedling stage and anthesis stage and selected the germplasms with different heat tolerance in two growth stages.According to different heat-tolerant varieties' cluster analysis of seedling stage and florescence,we discussed the heat tolerance consistency of tomato seedling stage and anthesis stage.The main findings are as follows:1.Evaluation of the heat tolerance of 40 tomato germplasms at seedling stage:After high temperature stress treatment(40?/30? day/night,12/12h)for 7d at seedling stage,we measured 3 physiological indexes of seedling leaves including malondialdehyde(MDA)content,chlorophyll content and chlorophyll fluorescence parameter(Fv/Fm)as well as 6 growth indexes including plant height,stem diameter,fresh weight and dry weight of plant,fresh weight of shoot/root biomass and dry weight of shoot/root biomass.In addition,we calculated the heat tolerance coefficient of each indexes.Principal component analysis,subordinate function method and cluster analysis were applied to make comprehensive evaluation and classification of tomato heat tolerance in the vegetative growth stage.Based on the result of seedlings' heat tolerance,40 tomato materials were divided into 3 groups.There were 7 heat resistant materials,15 moderate materials and 18 heat sensitive materials.2.Evaluation of the heat tolerance of 40 tomato germplasms at anthesis stage.A total of 7 physiological indexes were measured under the field natural high temperature(day temperature 37-43 ?,night temperature 24-30?)7d at anthesis stage,including pollen germination rate,pollen tube length,sepal length,petal length,pistil length,stamen length and fruit setting rate.The heat tolerance coefficient of each index were calculated.Based on it,the heat tolerance of tomato florescence was comprehensively evaluated by principal component analysis,subordinate function method and cluster analysis.The 40 tomato germplasms were divided into 3 groups according to their heat tolerance with 15 heat resistant materials,22 moderate materials and 3 heat sensitive materials.3.Use correlate analysis to evaluate the consistency of heat tolerance between seedling and anthesis stages:The result indicated that there is significant correlation(r=0.386*,P<0.05)between the comprehensive evaluation value of the seedling and anthesis stage of tomato,what confirmed the heat tolerance of tomato at seedling stage is related to anthesis stage.The plant height,stem diameter and fresh weight of seedlings were significantly positive correlated with the pollen germination rate and pollen tube length of florescence.However,only fresh weight was identical to that of the anthesis stage.In this study,15 germplasm resources in 40 showed complete consistency of the heat tolerance between the seedling stage and anthesis stage.Heat tolerance evaluation of tomato at seedling stage can reflect the heat tolerance at anthesis stage to some degree.4.Heat tolerant,medium heat tolerant and heat sensitive tomatoes at anthesis stage were used in this experiment.We study the differences of flower bud differentiation,floral organ development and pollen formation under control(daytime temperature of 25-30 ?,night temperature of 15-20?)and high temperature(daytime temperature of 37-43 ?,night temperature of 24-30 ?),as well as the fruit set survey.The results showed that compared with the heat sensitive tomato,high temperature accelerated the process of flower bud differentiation of heat tolerant tomato,however it had little impact on pollen germination rate,pollen tube length,pollen morphology and the degree of stigma exposure.Heat tolerant tomato sustained a high fruit setting under heat stress conditions.It showed that pollen formation was the most sensitive period under high temperature stress,and normal of floral organ development made higher fruit setting under high temperature. |
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