Development of a Technical Itinerary for the Production of Avocado (<i>Persea américana</i> Mill.) Seedlings with Biofertilizers

Abstract

The cultivation of fruit trees generally requires a nursery phase during which the young seedlings are monitored and treated to improve their ability to adapt to the environment. This leads to the production of seedlings that are used to create orchards. It consists of four essential steps or operations: 1) The germination phase of the seeds in germinators for the production of rootstocks; 2) Transplanting into pots or bags; 3) Fertilisation in order to obtain seedlings of a satisfactory vigour (stem diameter) ready for grafting. The nursery phase requires a good understanding and mastery of plant regeneration and fertilisation techniques. In Cameroon, the demand for avocado (Persea americana) fruits is increasing, but the supply is not keeping up with this demand. After a summary monograph on the production practices of avocado seedlings in the Yaounde area, this work aims to optimise the aforementioned three steps in order to obtain seedlings of sufficient sizes for grafting. Three factors are considered in this study: 1) The substrate (Substrate), whose effects are evaluated by the germination rate (GR), the daily average germination (DAG) and the root volume of seedlings (RootV). 2) The transplanting date (TransD), determined by considering three dates including 40 (Trans40), 65 (Trans65) and 75 (Trans75) days after sowing, and 3) Fertilisation using biological fertilisers, evaluated by testing four fertilisation levels, Fert1 (10 gr of 20-10-10 plus 10 gr fowl droppings), Fert2 (Acaulospora tuberculata), Fert3 (Gigaspora margarita) and Fert4 (Mixed mycorrhizal strains of Gigaspora margarita and Acaulospora tuberculata). This third factor is evaluated by growth parameters including leaf area (LeafA), chlorophyll index (ChlorInd), gain in Plant height (GainPltH) and plant diameter (GainPltD). The trial took place in the First Seed company, a seed production unit located in the Simbock district of Yaounde for the field phase, and the Biological Control Laboratory of the Institute of Agricultural Research for Development (IRAD), Nlolbisson, Yaounde. Two trials were conducted, the first with the objective of determining the best substrate with a completely randomized block design in 2 replications, three substrates/replication. The second trial was done with a factorial design (Split plot) with three replicates, the main factor being the Transplanting Date (TransD) and the second factor the biological fertilizer. Data were separated using least significant difference at 5% treshhold. Results indicate a highly significant effect of substrate on RootV (p = 5.00E-03). This effect translated by an increase of 49.42% and 19.53% of root volume on sawdust respectively to sand and soil. Sawdust (100%) and soil (98%) affect germination by 8 days reduction over sand and the germination rate on these two substrates is higher than the one on sand (92%). The early transplanting (TransD40) allows a better growth of the seedlings in terms of stem length and the collar diameter. The only observation variable that stands out for the early nursery stage fertilisation is leaf area, which shows significant differences between the 4 fertilisation formulae tested. The chlorophyll index and leaf area are also strongly correlated with the seedling growth parameters. Our results show that the early transplanting stage (40 days after planting) combined with a germination on white sawdust should be proposed to reduce the production cycle of grafted seedlings in association with early application of biofertilisers or organic fertilizer.