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In Vitro Hardening of Red Raspberry by CO2 Enrichment and Reduced Medium Sucrose Concentration

1993; American Society for Horticultural Science; Volume: 28; Issue: 10 Linguagem: Inglês

10.21273/hortsci.28.10.1048

2327-9834

Ribo Deng, Danielle J. Donnelly,

Berry genetics and cultivation research

Micropropagated `Festival' red raspberry (Rubus idaeus L.) shoots were rooted in specially constructed plexiglass chambers in ambient (340 ± 20 ppm) or enriched (1500 ±50 ppm) CO 2 conditions on a medium containing 0, 10, 20, or 30 g sucrose/liter. Plantlet growth and leaf 14 CO 2 fixation rates were evaluated before and 4 weeks after ex vitro transplantation. In vitro CO 2 enrichment promoted in vitro hardening; it increased root count and length, plantlet fresh weight, and photosynthetic capacity but did not affect other variables such as plantlet height, dry weight, or leaf count and area. No residual effects of in vitro CO 2 enrichment were observed on 4-week-old transplants. Sucrose in the medium promoted plantlet growth but depressed photosynthesis and reduced in vitro hardening. Photoautotrophic plantlets were obtained on sucrose-free rooting medium under ambient and enriched CO 2 conditions and they performed better ex vitro than mixotrophi plantlets grown with sucrose. Root hairs were more abundant and longer on root tips of photoautotrophic plantlets than on mixotrophic plantlets. The maximum CO 2 uptake rate of plantlet leaves was 52% that of greenhouse control plant leaves. This did not change in the persistent leaves up to 4 weeks after ex vitro transplantation. The photosynthetic ability of persistent and new leaves of 4-week-old ex vitro transplants related neither to in vitro CO 2 nor medium sucrose concentration. Consecutive new leaves of transplants took up more CO 2 than persistent leaves. The third new leaf of transplants had photosynthetic rates up to 90% that of greenhouse control plant leaves. These results indicate that in vitro CO 2 enrichment was beneficial to in vitro hardening and that sucrose may be reduced substantially or eliminated from red raspberry rooting medium when CO 2 enrichment is used.