Assessing the germination inhibition potential of compounds in pine (Pinus halepensis) needles using Bidens pilosa seeds

Abstract

Weeds are a major yield loss factor contributing up to 20 －30% of the losses farmers incur in most developing countries. This is attributed to shortage of labor or increasing labor cost due to rural-urban migration. Farmers have resorted to the use of synthetic herbicides to control weeds, but these have deleterious effects on human health and the environment. Fresh pine (Pinus halepensis) needles were evaluated for their allelopathic potential on black jack (Bidens pilosa) seeds through cultures in petri dishes. Such a bio herbicide can help farmers in Uganda and East Africa to avoid the adverse impacts of synthetic herbicides, lower the cost of production since pine needles can be obtained cheaply and still realize high agricultural output. The experiment was carried out at Makerere University, Department of Environmental Management lab. The needles of P. halepensis were collected from Kirinya village in Bweyogerere, Wakiso district in a private pine forest of about 5 years old. The seeds of test plant, B. pilosa were collected from a garden along Wampeewo, Gayaza road, Wakiso district, central Uganda. Two sets of experiments with varying concentrations were carried out. In experiment 1, 80g of ground pine needles were diluted in 500ml of water and after 12hr, 30ml, 60ml, 90ml, 120ml and 150ml were transferred into beakers and further diluted to 260ml. In experiment 2, 80g of ground pine needles were diluted in 500ml of water and after 12 hours, 30ml, 60ml, 90ml, 120ml, 150ml were transferred to beakers and further diluted to 360ml.The Petri dish culture study was laid in a completely randomized block design (CRBD) with three replicates and data (germination success) was collected over a period of three weeks. Results showed that for experiment 1 (260ml), there was increased allelopathic effect with increase in the concentration of the organic compound leading to 100% inhibition of germination in T6, 97% in T4 and T5, 95% in T3 and 82% in T2 (P-value <0.001). For experiment 2 (360ml), the allelopathic effect was also manifested with increase in the concentration of the organic chemical. T6 showed inhibition of 71.6%, T5 51.1%, T4 50.1% T3 26.2%, and T2 3.14% with a P-value of 0.002. The results strongly suggested the allelopathic potential of the fresh pine needle tissue being more pronounced with the increase in the concentration of the pine needle extract onto bidens pilosa. This allellopathic effect should be evaluated and demonstrated on weeds growing on farms and the optimum concentrations determined.