| Apple is one of the most important table and processing fruits in the world. In China, apple ring rot disease (ARRD), which results from the infection of Botryosphaeria berengeriana. f. sp. piricola to barks and fruits, generates the most serious and prevalent harm, and becomes an outstanding problem in apple productions. In order to utilize our ARRD-resistant apple resources better to breed new ARRD-resistant cultivars, in this study, the ARRD-resistance of apple genetic resources to ARRD was evaluated with vaccination approach. Furthmore, the segregation rule of ARRD resistance was analyzed with several cross populations. In addition, the defensive responses and gene screening for different apple materials infected with ARRD were investigated. The results were shown as follows.1. Evaluation and screening of ARRD-resistant apple genetic resourcesWith vaccination approach, 51 wild apple resources, 24 widely used rootstocks, and 95 apple cultivars were evaluated in their resistance to ARRD. One immune and 14 high-resistant genetic resources were obtained.2. Genetic rules on ARRD resistance in appleA total of 1082 seedlings for bark disease and 318 seedlings for fruit disease from 6 cross combinations of Fuji apple as one of parents were used to analyze the inheritance of ARRD resistance in apple. The results showed that the resistance both to fruit and bark ARRD of progenies were controlled by a limited number of nucleic loci, and that there was no relationship to cytoplasmic locus.3. Induction of defensive responses against the infection with ring rot fungi by four elicitors of SNP, MeJA, SA, and CaCL2 in harvested'Fuji'apple fruitARRD fungi were vaccinated on apple fruit (Malus×domestica. cv. Fuji) after treatments with methyl jasmonate (MeJA), sodium nitroprusside (SNP), salicylic acid (SA), and calcium chloride. The results showed that all treatments with elicitors were conducive to inhibit the infection and spreading of ARRD fungi. Both decay fruit ratio and decay area were decreased significantly compared with the control. In addition, apple fruits treated with each of four elicitors showed enhanced enzyme acitivity for phenylalanine ammonia lyase (PAL), peroxidase (POD), superoxide dismutase (SOD), and polyphenol oxidase (PPO), with the highest activity in MeJA and SNP treatments.4. Involvement of nitric oxide (NO) in ARRD elicitor-induced defensive responses in apple suspension cellsARRD elicitor induced apple suspension cells to produce NO, which, however, was inhibited either by L-NAA or PTIO treatment in cells. Furthermore, elicitor also increased the level of H2O2, while SNP treatment did not. It was indicated that elicitor acted together with NO to trigger the production of H2O2 in suspension cells, and that NO lead to increased PAL activity as well as phytoalexin and MDA contents.5. Methyl Jasmonate-induced defensive responses of apple suspension cellsMeJA-treament remarkably induced the production of signal moclecules NO and H2O2, while the SNP treatment did not trigger H2O2 production. Either L-NAA or PTIO treatment inhibited the production of NO, PAL and MDA. The results indicated that MeJA induced the NO generation, and that MeJA worked together with NO to increase the H2O2 level in suspension cells. In addition, the increase in phytoalexin and MDA contents as well as PAL activity was mainly induced by NO.6. Differential expression of genes responsive to ARRD injection as revealed by SSHARRD-sensitive and -resistant progenies were chosen from a cross'Jinhong'×'Fuji'. Sensitive and resistant gene pools were constructed with 1-year-old branches infected with ARRD fungi for SSH assay. The result showed that SSH discovered 151 positive colonies, of which 11 colonies were false positive confirmed by reverse Northern blot. Furthermore, sequence alignment was conducted with BLASTx and BLASTn. The results showed that 21 genes known to be implicated into disease resistance in resistant library were related with stress response and signal transduction, hormone regulation, primary and secondary metabolism, cell division and growth. In parallel, 47 genes obtained from sensitive library were known to be correlated with disease resistance, and involved in primary and secondary metabolism, cell division and growth, stress response and signal transduction, and hormone regulation.
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