Bridge grafting is widely applied in trunk-wounded apple trees. In this study, we carried out semigirdling and ring girdling on the trunk of 'Nagafu 2'/Malus baccata (L.) Borkh apple trees to simulate trunk injury. We then bridge grafted a M9 self-rooted rootstock on the injured trunks to study the effects of bridge grafting on flowering, fruitset, tree vigor, and fruit characteristics in 'Nagafu 2' apple. The results showed that both semigirdling and ring girdling due to the large wounded area caused significant decrease in flowering, fruit-set, and tree vigor (estimated by measuring leaf area, leaf gas exchange, tree height, and shoot growth); in addition, ring girdling increased flesh and peel firmness. However, bridge grafting of M9 self-rooted rootstock on semigirdling and girdling apple trees resulted in partial recovery of tree vigor (leaf area and photosynthesis) and maintaining the reduction of vegetative growth, thereby increasing flowering, fruit-set, yield, fruit weight, and peel firmness.

BACKGROUND:Dickeya zeae is the causal agent of maize and rice foot rot diseases, but recently it was also found to infect banana and cause severe losses in China. Strains from different sources showed significant diversity in nature, implying complicated evolution history and pathogenic mechanisms.RESULTS:D. zeae strains were isolated from soft rot banana plants and ornamental monocotyledonous Clivia miniata. Compared with D. zeae strain EC1 isolated from rice, clivia isolates did not show any antimicrobial activity, produced less extracellular enzymes, had a much narrow host ranges, but released higher amount of extracellular polysaccharides (EPS). In contrast, the banana isolates in general produced more extracellular enzymes and EPS than strain EC1. Furthermore, we provided evidence that the banana D. zeae isolate MS2 produces a new antibiotic/phytotoxin(s), which differs from the zeamine toxins produced by rice pathogen D. zeae strain EC1 genetically and in its antimicrobial potency.CONCLUSIONS:The findings from this study expanded the natural host range of D. zeae and highlighted the genetic and phenotypic divergence of D. zeae strains. Conclusions can be drawn from a series of tests that at least two types of D. zeae strains could cause the soft rot disease of banana, with one producing antimicrobial compound while the other producing none, and the D. zeae clivia strains could only infect monocot hosts. D. zeae strains isolated from different sources have diverse virulence characteristics.

Minimally processed fresh apple juice is a popular processed food product as it preserves the fruit's flavor and nutrients. To better understand the genetics of traits related to the quality of freshly squeezed apple juice (FS) in apple cultivars, we phenotyped hybrids derived from five biparental crosses of Malus asiatica 'Zisai Pearl', and M. domestica 'Red Fuji', 'Golden Delicious' and 'Jonathan' for a total of individuals 2575 in the year 2015 and 2023 in the year 2016. We also studied the inheritance of these traits with a quantitative trait loci (QTLs) analysis. Our results indicate that fruit juice yield, total soluble solid content (TSSC), pH value, light transmittance (TRA), and color traits (CIE coordinates, L*, a*, and b*) segregated quantitatively. We measured the average broad sense heritability and coefficient of variance to be 32.1-68.9% and 8.11-132.22%, respectively. Results from an untrained sensory evaluation panel indicated that FS with sour-sweet flavor, golden yellow color, moderate clarity and green apple aroma were most preferred. The overall sensory scores were closely related to TSSC, titratable acids (TA) and L* value. FS acidity (TA or pH) correlated with all physiochemical parameters except for poly phenol contents. We detected thirteen QTLs for juice yield, pH, TRA and b*, while QTLs for pH value co-localized with TRA and b* on linkage group 16 of both 'Zisai Pearl' and 'Red Fuji'. In summary, juice acidity, affecting juice flavor, color, clarity and the overall sensory scores, is an important breeding objective for FS specific apple cultivars.

Valsa canker is a destructive fungal disease for the apple industry, especially in Asian regions. Here, individuals in “Jonathan” × “Golden Delicious” hybrid population were phenotyped by off situ inoculation with Valsa mali isolates 03‐8 and xc56 from 2012 to 2015. Thirty‐one QTL s for the resistance were detected using high‐density genetic maps. Based on year‐stable and isolate‐robust QTL s, resistant loci G13‐1 and G13‐2 were mapped on chromosome 13 of the male parent, meanwhile locus J15‐1 was mapped on chromosome 15 of the female parent. Using the parental whole‐genome resequencing SNP databases, eighteen SNP s that could change predicted cis‐elements of gene or led to non‐synonymous substitution were screened in the three loci. After segregation analysis in hybrids and gene expression verification, three SNP s in an RNA ‐binding protein gene, a serine/threonine‐protein kinase gene and a MYB transcription factor gene showed a close relationship to Valsa canker resistance in apple. These results will be useful for the application of marker‐assisted selection for Valsa canker resistance in apple.