High-density interspecific genetic maps of kiwifruit and the identification of sex-specific markers

Kiwifruit (Actinidia chinensis Planchon) is an important specialty fruit crop that suffers from narrow genetic diversity stemming from recent global commercialization and limited cultivar improvement. Here, we present high-density RAD-seq-based genetic maps using an interspecific F₁ cross between Actinidia rufa ‘MT570001’ and A. chinensis ‘Guihai No4’. The A. rufa (maternal) map consists of 2,426 single-nucleotide polymorphism (SNP) markers with a total length of 2,651 cM in 29 linkage groups (LGs) corresponding to the 29 chromosomes. The A. chinensis (paternal) map consists of 4,214 SNP markers over 3,142 cM in 29 LGs. Using these maps, we were able to anchor an additional 440 scaffolds from the kiwifruit draft genome assembly. Kiwifruit is functionally dioecious, which presents unique challenges for breeding and production. Three sex-specific simple sequence repeats (SSR) markers can be used to accurately sex type male and female kiwifruit in breeding programmes. The sex-determination region (SDR) in kiwifruit was narrowed to a 1-Mb subtelomeric region on chromosome 25. Localizing the SDR will expedite the discovery of genes controlling carpel abortion in males and pollen sterility in females.     

Effects of light, magnesium and sucrose on leaf anatomy, photosynthesis, starch and total sugar accumulation, in kiwifruit culturedin vitro

Shootlets of kiwifruit plants (Actinidia deliciosa) were culturedin vitro. Combinations of light intensity, Mg and sucrose in the cultures showed that an increase of light intensity resulted in a corresponding increase of the relative size of the leaf mesophyll cells and in a decrease of the numbers of chloroplasts and contained starch grains. The addition of sucrose to the substrate media negatively affected the size of the mesophyll cells under normal Mg concentration (35 mg l⁻¹), and positively under high Mg concentration (105 mg l⁻¹ ). Sucrose further resulted in an increase in the numbers of chloroplasts and contained starch grains. The photosynthetic capacity of leaves greatly increased when Mg concentration was enhanced and sucrose was excluded from the nutrient substrate. Total sugar accumulation in all treatments was favoured by normal light intensity and addition of sucrose.