Effects of media and fruit ripeness on germination and transplanting of in vitro cultured embryos from low-chill peach and nectarine

Abstract

Embryo culture is used to improve seed germination of short fruit development period (FDP) peach genotypes thus allowing selection for early ripening of both male and female parents. To improve efficiency of embryo culture, two recognised Prunus embryo culture media, Smith-Bailey-Hough (SBH) and Woody-Plant Media (WPM), were used to germinate 4 low-chill peach and 2 low-chill nectarine genotypes at 2 stages of fruit ripeness. Cultured embryos were stratified in the dark at 4°C for 45 days then held at 16°C with continuous light. Germination was evaluated after 14 days and seedling development rated on a 0 (no germination) to 4 (strong radicle and hypocotyl development) scale. Seedlings were then transplanted into a greenhouse and rated for survival after 2 months. There was no significant effect on germination due to either media or ripeness. But there were significant differences in cultivar response to germination. Seedling development was significantly better on WPM than SBH with an average germination rating of 2.3 compared to 1.6 on the 0-4 rating scale. Cultivars also varied in their response to seedling development with Flordaking producing the most developed seedlings. A significantly higher proportion of seedlings survived transplanting from unripe fruit (68% compared to 57%). There was a significant cultivar by media interaction for the proportion of embryos that survived transplanting with all having higher survival on WPM except one cultivar that showed no difference for media type. Transplanting survival differed between genotypes ranging from the lowest combination 28% (White Opal on SBH) to highest 92% (Flordaking on WPM), which may be a direct result of the degree of seedling development.