Scientific Method Experiment

The allelopathic effects of the Pinus Rigada on Raphanus Sativus

A. Student

October 22, 2015

Georgia Military College

Introduction

In a garden, Raphanus sativus were planted near other vegetables that were considered “companion plants”, but the R. sativus plant was not exhibiting any real growth. Overhead Eastern pitch pine trees (Pinus Rigida) were growing and knowing that pine trees typically exhibit allelopathic tendencies, determining whether P. rigida was to blame or whether there was another contributing factor was important in getting to the root of the problem. To discover if the P. rigida were possibly inhibiting the growth, a study was done to determine if there was any connection between the stunted growth of the R. sativus and the P. rigida. The primary goal of this study was to gather and analyze data on the effects of the P. rigida on the growth of R. sativus. This was done to determine whether P. rigida exhibited allelopathic traits towards the seeds of R. sativus.

The R. sativus is a cultigen, meaning it has been altered by humans and is the result of artificial selection. They belong to the Brassicaceae family, which includes turnips (Brassica rapa), cabbage and relatives (Brassica oleracea) and horseradish (Armoracia rusticana). The name Raphanus refers to the radishes ability to rapidly germinate and is derived from the greek language: ra, meaning quickly and phainomai, meaning to appear. (Plants & Fungi)

Allelopathy is the secretion of chemical substances by plants that inhibit the growth of a competing species. (Allelopathy) A study was done on Pinus halepinsus and the possible allelopathic effects of its needles. In growth chambers, plastic pots consisting of 6(g), 8(g), and 12(g) of pine needle tissue and screened perlite were used to perform this study. Three different physiological stages of pine needles were collected from the P. halepinsus; fresh, senesced, and decaying. The pots containing the pine needle tissue were then seeded with tall fescue, Bermuda grass, or oat at 20, 20, and 3 seeds per pot. The needles tissue of the P. halepinsus in the perlite substrate reduced growth and development of the tall fescue and Bermuda grass. This suggests that toxic chemicals were excreted through the pine needle tissue. Growth inhibition was dependent on the type of pine and the amount incorporated into the pot. From the results, it was concluded that inhibitory compounds were within the pine needle tissue and were more apparent in fresh needles than senesced and decaying needles. (Nektarios, 2005)

The Eastern P. rigidia is from the same family of trees as P. halepinsus called Pinaceae. Being from the same family, it is possible that they exhibit the same allelopathic traits. The inhibited growth of the R. sativus may be caused from possible allelopathic effects of the pine needles from the P. rigidia. If radish (R. sativus) seeds are exposed to extracts from the pitch pine tree (P. rigidia), then they will have less growth than the seeds that are not exposed to extracts from the pitch pine tree (P. rigidia).

Methods

Fresh pine needles from a Pinus rigida were collected and rinsed with a 3% hydrogen peroxide solution to prevent any microbial growth. They were then rinsed with water, cut into small pieces (about ½ inch), and placed into a mason jar containing water. More pine needle matter was placed into the mason jar than water. The jar was labeled with the type of pine needle, the name of the tree the needles came from, and the date they were placed into the mason jar. The lid was placed on the mason jar and the needles were stirred with a spoon several times a day for three days, at the same time each day. Raphanus sativus seeds were used to test for possible allelopathic traits of the P. rigida needles. Five R. sativus seeds were first rinsed with a 3% hydrogen peroxide solution to prevent any microbial growth. They were then rinsed with water, folded up into separate, plain paper towels, free of ink printed designs, along with 1 tablespoon of the pine needles matter, and 1 tablespoon of water mixture from each mason jar. An equal amount of control seeds were folded up into separate paper towels, also free of ink printed designs, with only water. Each paper towel that enclosed a single seed with either pine needle matter or water only, were then placed into separate plastic bags and labeled control seed 1-5 or experimental seed 1-5 and then placed into in a dark room for 10 days. After the 10 days had passed, the bags and paper towels containing the seeds were opened and the growth of the seeds were analyzed.

Results

The seed with the most growth was not exposed to the needles of P. rigida. The other three of the five seeds exposed to the needles had no growth at all, whereas all of the control seeds had a significant amount of growth. These results indicate that the pine tree, P. rigida, is allelopathic towards the R. sativus seed.

Table 1: The amount of growth (cm) of each R. sativus seed after 10 days

Fig. 1: The growth (cm) of each R. sativus seed after ten days.