| Root-knot nematode (Meloidogyne spp.) is a pathogen which damaged worldwide cucumber cultivation, in our country, Meloidogyne incognita as the main harmful nematode specie. At present, in all of the cucumber resources, only find the introgression lines from interspecies cross progeny between Cucumis hystrix Chakr. (2n=24)and Cucumis sativus L. (2n=14) which is resistant to Meloidogyne incognita. Therefore, explicit the resistant inheritance regulation, explore the gola gene of resistant trait and relative resistant mechanism were important to the research of cucumber resistant to root-knot nematode. In the report, firstly, from the perspective of hormone mediate resistance signaling pathway and histopathology to analysis the defense mechanism. And the F2 population which derived from the resistant and susceptible Cucumis-hystrix introgression lines was used to discuss the resistance inheritance regulation and gene mapping.1. Histopathological Observation of Roots in Cucumis Sativus-hystrix introgression Line Resistant to Meloidogyne incognitaResistant Cucumis sativus-hystrix introgression line 10299FA and susceptible control cucumber cultivar ’Beijing jietou’ were used in the experiment to analyze the histological changes of cucumbers with different resistances infected by root-knot nematode Meloidogyne incognita. Root samples were collected after Meloidogyne incognita inoculation 3 d,6 d,9 d,12 d,15 d,22 d. The results shows:3 d after inoculation, the root tips of 10299FA and’Beijing jietou’ appeared hypersensitive response; 6 d after inoculation, root knots were found both in 10299FA and ’Beijing jietou’, the size and number of root knots between them were not significant; with the increase of inoculation days, the number of root knots in 10299FA was significantly less than’Beijing jietou’. To observe paraffin sections of the largest diameter root knots, It was found that the giant cells located in the parenchyma cell layer of 10299FA and vascular of’Beijing jietou’, and during the period of giant cells formation, the size and number of giant cells in 10299FA were smaller than ’Beijing jietou’. After inoculation 6 d, a large number of cells surrounding the giant cells appeared elongate and vacant in 10299FA; however, in’Beijing jietou’, there were a part of cells surrounding the giant cells initiated vacant after 9 d with inoculation, and formed cluster of root knots easily.2. Expression Analysis of Hormone Pathway Related Genes in Cucumis sativus-hystrix Introgression Line Resistant to Meloidogyne incognitaCucumis sativus-hystrix introgression line 10299FA which is resistant to Meloidogyne incognita, as well as susceptible control cucumber cultivar’Beijing jietou’. Real-time PCR was applied to analysis the expression of key genes about salicylic acid, jasmonate and ethylene synthesis pathway in root samples after inoculation 0 d,3 d,6 d,9 d,12 d and 15 d. The result shows:the salicylic acid and jasmonate synthesis pathway related genes PAL、 ICS、LOX、AOC were up-regulated in 10299FA continually and the expressions amount were significantly higher than’Beijing jietou’after inoculation in 9 d. However, Ethylene synthesis pathway key gene ACO gene expression level in 10299FA was extremely lower than’Beijing jietou’.3. QTL mapping of root-knot nematode Meloidogyne incognita in Cucumis sativus-hystrix introgression lineA F2 segregation population of 344 lines was developed from resistant Cucumis-hystrix introgression line 10299FA and susceptible Cucumis-hystrix introgression line 10299FC. Single plant of F2 population was infected with Meloidogyne incognita to calculate the plant disease index. It was indicated that the resistant trait was major-multiple mix heritability model.995 SSR makers were tested between parents firstly, then sleeted polymorphic makers to test the genotype of F2 population. Software JoinMap4.0 and MapQTL was used to analysis phenotype and genotype statistics of F2 population. It was indicated that the major QTL loci was located in chromosome 6 with 28.5% phenotype variation. |
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