Agroforestry is a dynamic system. It is ecologically-based natural resources management system. The integration of trees on farmlands diversifies and sustains production for increased social, economic and environmental benefits to the farmers. In India, agroforestry systems have been adopted as alternatives to traditional farming system. Agroforestry systems allow the intensification of production through the integrated management of natural resources without environmental degradation.

Allelopathy refers to any process involving secondary metabolites produced by plants, algae, bacteria and fungi that influence the growth and development of agricultural and biological systems which can play an important role in crop productivity, conservation of genetic diversity and maintenance of ecosystem stability (Anaya 1999, Khalid et al 2002).

Teak (Tectona grandis) is a large deciduous tree belonging to the family Verbenaceae. It grows up to 40 m in height. Teak is recognised as one of the most valuable timber species (Nidavani and Mahalakshmi 2014). Although native to south and southeast Asia, the significant economic potential of teakwood led the species to be introduced into the agroforestry systems of many countries across tropical Asia, Africa and Central and South America (Pandey and Brown 2000, Healey and Gara 2003, Kenny et al 2014, Newby et al 2014, Udayana et al 2020).

Teak is one of the most important trees in home gardens of south Asia because it is a very precious wood species and important in folk remedies (Kumar et al 1994, Peyre et al 2006, Lakshmi and John 2015). It has also been used as an important plant in Ayurvedic treatments. Hot water extract of teak bark is applied for the treatment of bronchitis, biliousness, hyperacidity, diabetes, dysentery and leprosy. Water extract of teak leaves is used in pruritus, stomatitis, ulcers and wounds. Hot water extract of teak roots is applied for anuria treatment. Oil extract of the flowers is useful for scabies and hair growth (Nidavani and Mahalakshmi 2014, Vyas et al 2019). Evidence of the pharmacological properties of teak plant has been accumulated over the past decades. Ethanol extract of teak leaves has shown significant wound healing activity (Varma and Giri 2013). Ethanol extract of teak roots has hyperglycemic activity (Varma and Jaybhaye 2010). Many compounds with pharmacological activities were also isolated from various parts of teak plant (Nidavani and Mahalakshmi 2014, Vyas et al 2019, Degbe et al 2018). Some plants have shown excellent weed control abilities as soil additives and/or in intercropping due to their characteristics of allelopathy (Semidey 1999, Caamal-Maldonado et al 2001). Plants produce hundreds of secondary metabolites. Some of these compounds are released into the surrounding environment through root exudation, volatilization, leaching and decomposition of the plants.

Those compounds with allelopathic activity are able to inhibit the growth and germination of neighboring plant species (Field et al 2006, Bais et al 2006, Belz 2007). The teak leaf extract exhibited inhibitory effects on germination and/or on seedling growth of Casuarina equisetifolia (Balasubramanian and Ravichandran 1996), Vigna unguiculata (Jadhav and Gaynar 1994, Mandal and Brahmachary 1998) and sorghum (Channal et al 2002). The inhibitory effect on the germination and growth of wheat seedlings increased with an increase in leachate concentration of teak (Patil et al 2003). Some of the phenolic acids viz salicylic acid, p-hydroxy benzoic acid, chlorogenic acid, tannic acid, caffeic acid and vanillic acid have been reported to occur in teak as inhibitory or stimulatory bioactive allelochemicals (Mandal and Brahmachary 1998, Tripathi et al 1999).

Rice is staple food of India as well as Asia, Latin America, part of Africa and the Middle-East. In India, rice cultivation is taken below sea level (Kerala) up to altitude of 2,000 m amsl (Kashmir). It plays vital role in national food security and it is means of livelihood of millions of people. It is the most important crop for human nutrition and calorie intake providing more than 1/5^th of the calories consumed.

Rice thrives in all types of soils ranging from pH 5 to 8 and can be grown under different environmental conditions (Shinde et al 2018). Globally, the highest area under rice is in India (43.86 million ha) followed by China (30.16 million ha) However, highest production of rice is in China (144.85 million tonnes) followed by India (104.80 million tonnes). This is due to higher productivity of rice in China (6.86 tonnes/ha) than India (3.77 tonnes/ha) (Anon 2017).

In Maharashtra, rice is cultivated on 15.56 lakh ha area in all four regions viz Vidarbha (8.15 lakh ha), Konkan ( 3 .69 lakh ha), western Maharashtra (3.55 lakh ha) and Marathwada (0.156 lakh ha). The highest productivity of rough rice is in Konkan region (4.25 tonnes/ha) followed by western Maharashtra (3.5 tonnes/ha) and Vidarbha (3.4 tonnes/ha) (Anon 2017). It is reported to possess allelopathic properties in its root, shoot and leaf exudates.

In the present study, the teak leaf extract was tested on germination and seedling growth of rice.

The experiment was conducted in the laboratory of College of Forestry, Dr Balasaheb Sawant Konkan Krishi Vidyapeeth, Dapoli, Maharashtra (latitude 17° 452 N, longitude 73° 122 E, altitude 250 m amsl) in the month of March 2021. Dapoli is located in the Konkan region of Maharashtra and is confined in between Sahyadri hills in the east and Arabian sea in the west. Dapoli represents more or less tropical climate having average humidity of 78 per cent throughout the year. The climate is hot and humid with well-expressed three seasons viz summer (March to May), rainy (June to October) and winter (November to February). The average minimum and maximum temperature is 18.5 and 30.8°C respectively with an average annual precipitation 3,500-4,000 mm which is generally received from June to October.

Data on the effect of various concentrations of T grandis leaf aqueous extract on germination and seedling growth parameters of rice have been presented in Table 1. Among different concentrations, significantly higher germination was recorded in control (99.00%) and 2 per cent concentration (95.00%) which were at par and minimum in 15 per cent (87.00%), 10 per cent (89.00%) and 5 per cent (91.00%), the three being at par. Higher collar diameter was recorded in control (0.97 mm) as compared to all other treatments which were at par. Lower shoot length of 6.21 and 6.51 cm was recorded in 10 and 15 per cent concentrations respectively which were at par as compared to control (7.24 cm). Root length was significanttly lower (7.25 cm) under 15 per cent concentration as compared to control (8.61 cm), however, former treatment was at par with all other treatments. The root-shoot ratio varied from 1.14 (10%) to 1.25 (2%), but there were no significant differences among the treatments. Higher vigour index was recorded in control (1,570.00) and 2 per cent concentration (1,440.00) which were at par and lower in 15 (1,173.00) and 10 (1,238.00) per cent concentrations, the two being at par. The sturdiness ranged from 164.10 (control) to 178.40 (2%) but there were no significant differences among all the treatments tested for this trait.

Present investigations indicated that the aqueous leaf extract of teak inhibited the germination, vigour index, shoot length, root length, total dry weight and Dickson quality index of rice which is supported by earlier works of Jayakumar et at (1987), Macias et al (2000), Sahoo et al (2007), Lalmuanpuii and Sahoo (2011) and Das et al (2012).

The phenolic compounds have been reported to possess inhibitory effect on the germination of the seeds of other plants (Chaves and Escudero 1997) due to their physiological effect on membrane functions, membrane potential, mineral absorption and plant water relations (Harper and Balke 1981, Barkosky and Einhellig 1993, Einhellig 1995). Phenolic acids are considered as one of the major allelochemicals responsible for herbicidal bioactivity (Lin et al 2004, Batish et al 2006) in many plants. But allelopathic inhibition typically results from the combined action of a group of allelochemicals which collectively interfere with several physiological processeses through joint action of allelochemicals (Einhellig 1996). The herbicidal bioactivity observed in the leaf extract of teak and its various fractions can be attributed to the occurrence of the combination of phenolic acids (salicylic acid, phydroxy benzoic acid, tannic acid and chlorogenic acid) which might have been at the optimum level in F4 and disintegrated due to further fractionation (PlP4). The ratio of these phenolic acids present in the active fraction may be useful for future development of bio-herbicides. The chlorofonn fraction of methanol extract of teak deciduous leaves may be considered as a potential pre-emergent allelopathic herbicide for controlling the weed jungle rice in rice field. The allelopathic herbicidal activity can be assigned due to the presence of phenolic acids in various combinations (Kole et al 2011)

This preliminary study was carried out to investigate the allelopathic effect of teak on germination and growth of rice. Germination and all the growth parameters of rice were reduced significantly in leaf aqueous extract. The present study revealed that the allelopathy may not be a universal explanation for regeneration failures, delayed seed germination, retarded seedling growth and reduction in productivity but is also not an ignorable phenomenon. The allelopathy could have a pronounced effect on simultaneous and release of chemicals continuously into the environment which directly or indirectly affect the companion crops. Considering the foregoing results, it can be concluded that teak plant has some allelochemicals which inhibit seed germination and seedling growth (both length and mass) of rice. However, long term field-based studies need to be carried out on the allelopathic effects of teak on valuable crops growing in different regions before selecting teak for large scale plantation.

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