Fine Mapping Of Fruit Cracking-resistant Genes Cr3a And Cr4a In Tomato

Fruit cracking is a common problem in tomato cultivation,and it can cause serious economic losses.Fruit cracking usually occurs on the peel and pulp of the fruit before harvesting.In addition,some cracks appear in the post-harvesting phase,mainly due to the unsuitable storage conditions.Fruit cracks provide access to insects and fungi,which greatly reduces market competitiveness.At the same time,the water loss of the fruit is accelerated after the occurrence of cracks,which shortens the storage and transportation time and reduces the appearance quality.In the production,we can take some measures to avoid tomato cracking to some extent,such as supplying water evenly,regulating soil and air humidity and so on.But it is difficult to solve the problem of cracking radically.Therefore,mapping and cloning fruit resistance genes in tomato is of great significance for accelerating the breeding process of cracking-resistant tomato in China.The two lines of the S.pennellii LA0716 introgression group,14h616 and 14h597,both contain a fragment of LA0716 chromosome 3 and chromosome 4 with the genetic background of KR2R144,respectively,and contain the cracking-resistant genes Cr3a and Cr4a.In this study,14h616 and 14h597were hybridized with KR2R144 and then self-crossing for several generations to construct sub introgression groups of Cr3a and Cr4a.Through phenotypic identification and genetic analysis of the sub introgression groups,we will fine map fruit cracking-resistant genes Cr3a and Cr4a in tomato.At the same time,the cuticle thickness of the peeling,the number of epidermal cells,the hardness of the fruit and the water content of the fruit were studied between cracking-resistant fruit and cracking fruit to determine the relationship between them.The main findings are as follows:1.The introgression lines 14h616 and 14h597 were hybridized with KR2R144 and then continuously selfed.From the F₂ generation,molecular markers were used to screen out individual plants containing shorter chromosomes of S.pennellii LA0716.We conducted genetic analysis of the third,fourth,fifth,sixth,seventh generation of sub introgression groups with molecular markers,and the sub introgression groups were obtained by crossing 14h616 and 14h597 with KR2R144 respectively and then selfing.The 12 plants with the same genotypes as the cracking-resistant tomato and cracking tomato,and 12 plants with heterozygous genotypes were selected to construct sub introgression groups of Cr3a and Cr4a.And we did physiological experiments with strains containing genes Cr3a and Cr4a and strains easy to crack.2.The experiment results of cuticle thickness,epidermal cell layer,fruit firmness and fruit water content of cracking-resistant and non-cracking fruits showed that there was no significant difference in the thickness cuticle of the pericarp and the number and size of epidermal cells in every one of growth stage between the tomato containing gene Cr3a and cracking tomato.There was no significant difference in the hardness of the fruit during the red ripening period,but the water content of tomato Cr3a was significantly lower than that of cracking tomato,And the water content of fruit in the mature green period was extremely significant.There was no significant difference in fruit peel hardness,fruit water content in each period,fruit epidermal cell layer and cell size between tomato containing gene Cr4a and cracking tomato.However,there was a significant difference in the thickness of the cuticle between tomato containing gene Cr4a and tomato easy to crack,and the cuticle of the tomato peel containing the gene Cr4a was thicker.3.The results of genetic analysis indicated that the tomato resistance to cracking was not completely dominant.Through the genotypic analysis and phenotypic identification of the offspring identification population,the cracking-resistant gene Cr3a was located between the molecular markers3-ZY75 and 3-ZY43 of about 349 kb,and the cracking-resistant gene Cr4a was located between the molecular markers HP3365 and HP613 of about 1.99 Mb.4.47 genes were detected in the localized region of the gene Cr3a.For the 47 genes,the genes Solyc03g115420,Solyc03g115740,Solyc03g115750 and Solyc03g115850 were involved in the process of protein synthesis related to tomato cracking.Listed as candidate genes for the gene Cr3a.