Modeling the effects of mineral nutrition for improving growth and development of micropropagated red raspberries

- This study modeled the effects of in vitro minerals on the growth of raspberries.
- Increased meso nutrients improve the growth of micropropagated red raspberries.
- The ratio of ammonium to nitrate varies greatly for improving plant growth.
- This study establishes a systematic approach for developing growth media for Rubus.

In vitro propagation is important for rapid multiplication of a wide range of nursery crops, including red raspberries. The genetic variation of the many red raspberry cultivars makes it difficult to use one growth medium for all. Although some cultivars grow well on Murashige and Skoog (1962) medium (MS), others display stunting, hyperhydricity, discoloration, callus, leaf spots, or necrosis. This study used response surface methodology (RSM) to determine the effects of MS mineral salts on red raspberry growth and which of these mineral salts are critical for improving growth. In vitro growth of five red raspberry cultivars was determined by varying five factors that included NH4NO3, KNO3, mesos salts (CaCl2, KH2PO4 and MgSO4), minor elements (Zn-Mn-Cu-Co-Mo-B-I), and EDTA-chelated iron. The effects of these five factors on plant quality, multiplication, shoot length, leaf size, leaf area, leaf color, callus and leaf spots were determined. The effects varied by cultivar for some characteristics, but all cultivars had improved growth or appearance on some experimental treatments when compared to MS medium. Increased mesos was the most significant factor associated with plant quality, multiplication and shoot length in all cultivars. Increasing iron above MS levels decreased quality in all cultivars except 'Willamette'. Decreased KNO3 with increased mesos and low iron were required to improve shoot multiplication. Increased NH4NO3 resulted in greater shoot elongation only in 'Willamette'. Determining the driving mineral factors is the first step in improved medium formulations for micropropagated red raspberries.