Table 2.

The screening methods usually used to detect allelopathic potential in rice.

Sl. No	Name of method	Short description	Receiver plant	References
1.	Relay seeding technique	• First rice seeds are sprouted in Petridish with moistened filter paper, after 11 days, the receiver weed seeds are placed near to germinating rice seeds, which release allelochemicals in the growth medium. Effects are measured by estimating loss in root, shoot and biomass of the weed in comparison to control.	Barnyard grass	Mazid et al., 2018
2.	Sandwich method	• Between two layers of agar solution, some crushed rice leaf, stem, husk, and other rice debris are kept uniformly and 20 test weed seeds are put on agar medium close to smashed rice seeds. After ten days, different seedling traits are measured as mentioned above.	Barnyard grass	Yoshiharu Fujii et al., 2003
3.	Leaf, root and hull extracts bioassay	• Leaf and hull extracts of rice are used in a growth medium in the laboratory (e.g. petridish) where the test weed seeds are placed for germination. After 10 days the seedling parameters as mentioned early are measured. Sometimes root extracts of the rice varieties are collected and tested in the laboratory for phytotoxicity. This technique is usually done first to identify allelopathic potential and then to identify the most active chemical responsible for allelopathic action by column fractioning of different allelochemicals followed by testing with weed species.	Barnyard grass	Chung et al., 1997
4.	Pot culture bioassay with plant extracts	• A greenhouse pot is filled with soil along with an appropriate amount of N, P, K, Ca, Mg, Fe etc. Seven pre-germinated receiver test weeds are sown in the pot. An amount of 250 ml of 10% aqueous solution of rice leaf is added to the weed seedlings at a 3-leaf stage in the pot. Ten days after the addition of extracts the weeds are harvested for measurement of weed parameters.	Barnyard grass	Masum et al., 2016
5.	Equal compartment agar bioassay	• An agar solution (0.3%) is autoclaved and then solidified in a beaker. Six pre-germinated rice seeds are placed in one half of the agar cycle. After seven days, the other portion of the agar surface is covered with 10 pre-germinated re-receiver weed seeds. The beaker is crossed in the middle and the middle of a piece of whiteboard is placed, keeping the board 1 cm above the surface. Again after 10 days, the seedling parameters are assessed.	Lettuce, Cress, Radish,E. coli,Jungle rice	Masum et al., 2016
6.	Plant box method	• This technique involves transplanting rice seedlings into a root-separating cellulose tube occupied with 0.5% water agar medium, which is then positioned in the middle of one side of a sterilized square plastic box that has been filled with 1 lit of 0.5% water agar solution. A highly engineered holding structure holds the dialysis tube. Receive weed seeds are sterilized and then arranged in rows close to the dialysis tube on the agar surface. The allelochemicals released by the rice plants move to weed seedlings and affect the growth of the weed.	Lettuce andBarnyard grass	Azmi et al., 2000
7.	Field screening following additive technique	• Rice seedlings are raised in seedling boxes and 45 days old seedlings are transplanted in the well-prepared field in five 30 cm rows with a 15 cm spacing between rows (30 x 15 per 3.3 m2). Forty days old seedlings of receiver test weed (barnyard grass) raised in seedling boxes, are planted in five rows across the rice rows two weeks after they are planted. Recommended N, P, K, Ca, Mg, Fe etc. are applied and no herbicide is sprayed. The allelopathic effects of rice on the weed are evaluated after 67 days of rice planting based on per cent loss in weed parameters.	Barnyard grass	Ahn et al., 2005
8.	24-well plate bioassay	• Twelve-day-old rice seedlings are placed in the 10 cm apart holes in a Styrofoam float which is placed in a 24 L pail that is filled with hydroponic solution. The float allows the rice roots to submerge in the hydroponic solution. The solution is replaced after every 2.5 days and the pH is maintained at 5.5. After one month of growth, the roots are separated, dried and powdered. The powdered root mass is mixed with methanol (50:50) to prepare root extract. The extract is dissolved in acetone to make 10% strength and is tested for selected weed species.* Five weed seeds are placed on the filter paper which is set at the bottom of the well containing 20 µLof the extract. The plate is sealed with parafilm and placed in a growth chamber at 25 0C and 16 hrs photoperiod for four days. After that, the measurement of the shoot and root lengths is done and the per cent reduction in comparison to control is estimated.	Barnyard grass	Rimando et al., 2001
9.	Root exudation bioassay	• Hydroponically grown 15 days old 51 rice seedlings are bound to an urethrane foam which is placed at the top of 100 mL paper cups containing 100 mL of sterile deionized water. The cups are aerated continuously with a vinyl chloride tube connected to an air pump and are replaced every week. The root exudate solutions are collected from the cups and are filtered using appropriate filter papers. The seeds of test weeds are placed in a petridish for germination and the exudation solutions are added to the germinating medium. The measurement of allelopathic effects is done by estimating the percent loss in root and shoot parameters as mentioned early in comparison to control.	Barnyard grass	Tawaraya et al., 2018