Application of sugarbeet pure and crude extracts containing glycinebetaine affects root growth, yield, and photosynthesis of tomato grown during summer

The effects of the exogenous application of glycinebetaine (1mM) as a drip fertigation on the root growth, fruit yield, leaf photosynthesis, stomatal conductance and chlorophyll content of glasshouse-grown tomatoes (Solanum lycopersicom L.) were compared using a crude extract (CE) and pure extract (PE) from sugarbeet in different growing seasons (ES, early summer from June to July; and LS, late summer from August to September). The average air temperatures in the glasshouse were 24.5±3°C and 28±3°C in the ES and LS growing periods, respectively. The CE and PE application significantly increased and maintained the total yield of fruits, respectively, harvested in LS compared to ES. In contrast, the total yield was significantly decreased by a high incidence of blossom-end rot (BER) fruits in LS without glycinebetaine application. The CE application effectively inhibited BER and increased both the fresh weight and number of large fruits grown at a high temperature, resulting in an increase in the total yield by more than double compared to the control. The CE application also significantly enhanced root growth (both thick roots and rootlets) only in ES, whereas the PE application did not enhance root growth in either growing period. The CE-treated plants maintained photosynthesis in mature leaves at the maximum rate for approximately one month in LS, whereas the PE-treated and control plants showed significant reductions in the photosynthetic rates at the same leaf ageing. Stomatal conductance began to decrease significantly at the stage of leaf expansion at the high temperature in all of the treatments. These results indicated that CE and PE had different effects on the root growth, inhibition of BER, photosynthetic rate and stomatal conductance. CE application appears to delay leaf senescence, as based on both the significantly high values of photosynthetic O2 evolution and chlorophyll content in the leaves. By preventing BER, the CE application proved to be better than PE in improving root growth, leaf photosynthesis, chlorophyll content and yield. Thus, at low concentrations, CE can be used as an effective and low-cost organic liquid fertilizer to enhance root growth and prevent BER of fruits in glasshouse tomato production under high-temperature conditions in summer.