Moringa oleifera leaf extract affects avocado (Persea americana) seed phenolics, sugars and starch as well as germination

Avocado (Persea americana) seedlings, obtained from commercial avocado seeds, are used as 'nurse seed' to graft the clonal rootstock, that is subsequently combined with the cultivar. A healthy nurse seed, growing into a vigorous seedling is, therefore, of paramount importance. This experiment was carried out on avocado seeds of different maturity stages to determine, if moringa leaf extract (MLE) application can enhance seed germination. The experiment was laid out in a completely randomized factorial design with MLE applied at various concentrations (0, 2.5, 5.0 and 7.5% w/v MLE) over different periods (0, 10, 30 or 120 min) of soaking. Thereafter, seeds were placed onto agar to monitor germination and radicle development daily. Additionally, phenolic compounds and starch, as well as sugar concentrations were determined after the 2-h soaking period. Seed germination occurred from 18 to 23 days; this event was not influenced by MLE application. There is a significant positive relationship between low seed coat phenolics and a higher germination percentage, (r=0.23), (p.0.008), particularly at MLE 2.5 and 5.0%. Cotyledonal sugar and starch concentrations were neither affected by MLE concentration nor by soaking duration. Application of MLE at high concentration (7.5% w/v) had an inhibitory effect on germination and resulted in lowering cotyledonal starch levels. Germination percentage was positively influenced by all MLE applications, but phenolic compounds, sugar and starch concentrations were neither affected by MLE concentration nor soaking time. The MLE effect on germination velocity subsided with seed age (lowering from April to May to June). Application of 2.5 or 5% MLE could therefore, be developed as a viable pre-treatment of nurse seed in the avocado industry, particularly for seed from the early season.