Improvement Of Drought Tolerance Of Processing Tomato By Molecular Marker Assisted Selection

Tomato（Solanum lycopersicum）is a vegetable crop with high economic value,whose fruit is delicious and highly nutritional.The processing tomato industry is a dominant industry in Xinjiang,but Xinjiang is located in arid and semi-arid areas,which is seriously threatened by water shortage.Therefore,it has become an important target for breeding drought-tolerant processing tomato cultivars.There are many obstacles in traditional breeding to develop drought-tolerant crop varieties,such as complicated phenotyping,high cost and time consuming.Molecular breeding technology can greatly improve breeding efficiency and shorten breeding years.The emergence of molecular breeding technology has greatly reduced the difficulty of drought-tolerant breeding and shortened the breeding time.The combination of marker-assisted selection（MAS）and conventional breeding will be an inevitable choice for drought-tolerant breeding.Previously in our lab,quantitative trait loci（QTLs）of drought tolerance were mapped using a subline population of IL2-5 and M82,in which IL2-5 is an introgression line derived from the wild tomato S.pennellii.A molecular marker ID68 was developed to track the major drought-tolerant QTL.With the assisted section of this marker,the backcrossing lines M3BC₃F₂ and 87-5BC₃F₂ were obtained by crossing M1040 with two processing tomato lines M3 and 87-5,and backcrossing using them as recurrent parents.In this study,MAS was used to further screen the backcross and selfing generations.The improvement of drought tolerance and the recovery of M82 genetic background of the backcross inbred lines（BILs）were evaluated through drought tolerance characterization and trait investigation.Therefore,two breeding lines M3D and 87-5D with improved drought tolerance were obtained.The main results are as follows.1.Further backcross and selfing generation between M3BC₃F₂,87-5BC₃F₂and their corresponding recurrent parent M3 and 87-5 were conducted,and ID68 marker screening was used to obtain the BIL lines M3D and 87-5D.2.The drought tolerance of the BILs and recurrent parent seedlings was evaluated under severe or moderate drought stress,followed by rehydration treatment.Under severe drought,the survival rate of BIL line was significantly higher than that of the recurrent parent,and the drought injury index was lower than that of the recurrent parent.Under moderate drought stress,the impact of drought on plant height,stem diameter and leaf area of the BIL lines was less than that of recurrent parents.The leaf relative water content was decreased,while the content of osmo-protectants proline and soluble sugar was significantly increased in all lines.These indicators in the BIL lines were significantly higher than those in the recurrent parents.The stomatal conductance and transpiration rate of the BIL lines were higher.Drought reduced the photosynthetic rate of plants,and the photosynthetic rate of BIL lines was significantly higher than that of the recurrent parents,while the chlorophyll content was lower than that of recurrent parents.Under moderate drought stress,Fv/Fm,φPSII and q P decreased,while NPQ increased.The Fv/Fm,φPSII and q P of BIL lines were significantly higher than those of the recurrent parents,whereas NPQ of BIL lines was significantly lower than that of the recurrent parents.Regarding redox homeostasis,moderate drought increased MDA and H₂O₂ contents and activities of the antioxidant enzymes POD,SOD,CAT and APX.The MDA and H₂O₂ contents of the BIL lines were significantly lower than those of the recurrent parents,and the activities of the four antioxidant enzymes were significantly higher than those of the recurrent parents.Therefore,for the BIL lines,the sensitivity to water stress is reduced,water retention capacity is improved,the damage of reactive oxygen species to cells is alleviated,and the physiological activities under drought stress are better maintained.3.The agronomic traits of the BIL lines were investigated.The results showed that there were obvious differences between the BIL lines and their donor parent on growth morphology,leaf,inflorescence and fruit,but no substantial differences between the BIL lines and their corresponding recurrent parent,indicating that the BIL lines largely recovered to the genetic background of the recurrent parent.