Evaluation and selection of elite clonal genotypes of the sweet crop licorice (Glycyrrhiza glabra) in a new environment

The adaptability and vigour of exotic licorice,Glycyrrhiza glabra, as a source of sugar substitute in the subtropics of Papua New Guinea (PNG) was monitored from seed germination to 3-month in the greenhouse and to 12-month in the field. The germination potential of sulphuric acid-scarified seeds was significantly (p>0.01) higher than un-scarified. A total of 120 early-germinated seeds were selected and maintained in greenhouse for 3-month. In a stepwise manner, 65 plants with Biomass Fresh Weight (BFW) = average were initially selected, out of which 36 with Root Fresh Weight (RFW) = average were further selected, from which 12 plants with and Root Bulk Density (RBD) = average + SD were finally selected; namely P2, P5, P14, P23, P33, P37, P49, P58, P83, P94, P112 and P118. Clonal stock lines of the 12 selected genotypes (L2 to L118) were established by shoot culture. The agronomical vigour of the clonal genotypes was tested at four time points over 12-month under open field conditions and rainfall averaged 275 mm/month and frequent dry spills. Means of parameters measured increased over the growth period, where rootstock grew steadly, and then growth was directed to shoot recovery until reached a balance. Based on a novel value named Principle Selection Index, (PSI=RFW x RBD), three genotypes including L58 followed by L112 and subsequently L 33 were selected and multiplied to a clonal stockin vitro. No common direct relation was found between the vigour and physiological attributes to drought tolerance. However, the low stomata area of L33 and L58 may have played a role in their vigour, especially L58, which showed extremely low peroxidase activity, a characteristic of higher level of drought tolerance, compared to that of L33 and L112. The three genotypes were the lowest in chlorophyll “a” and “b” content showing no special evidence of better photosynthetic apparatus compared to the other genotypes. The agro-physiological advantages of the selected lines, especially L58 suggest their potential as a new crop, at least in the low land of PNG for its economically important rootstock as a source of sugar-substitute in dietary food.