Effects of aqueous leachates of multipurpose trees on test crops/agrometsanduses kasutatavate puude vesileotiste toime pollukultuuridele.
In traditional agroforestry systems of Garhwal Himalaya, farmers grow along with agricultural crops various multipurpose trees on boundaries between agricultural fields. With the increasing recognition of agroforestry as an alternative land use, many scientists have focused their attention on trees. These trees contribute to sustainability of food production and are essential for the survival of local population (Tripathi et al., 2000, Sachan, 2006). The goal of agroforestry is to maintain sustainable land use by incorporating woody species with agriculturally important crops that can help to decrease soil erosion while providing unique allelopathic benefits to the system. Temporal sequences and tactical spatial arrangements with respect to allelopathic contributions must be carefully considered to encourage both the production of food and sustainability of the land as a resource (Razvi et al., 1999). Agroforestry includes numerous land use systems, ranging from planting of trees on agricultural lands to those in which agriculture is practiced on forestlands without deforestation. Ficus subincisa, Bauhinia purpurea, and Toona hexandra are important multipurpose tree species in the traditional agroforestry system of the Garhwal Himalayan region, India (Bhatt & Verma, 2002). The suitability of these species in agri-silvicultural, silvi-horticultural, and silvi-pastoral practices is discussed in (Sachan, 2006). The phytotoxic substances exuded by agroforestry tree species retard the germination and growth of weed and crop species (Bhatt et al., 1997; Todaria et al., 2005; Singh et al., 2006). Chemicals released by plants might be beneficial or detrimental to the growth of receptor plants (Chou, 1989; Thapaliyal et al., 2007).
Allelopathy plays a significant role under both natural and managed ecosystems (Rice, 1984), mainly by adversely affecting seed germination and seedling growth. Although the research on allelopathy in cropping systems has increased in the last two decades, the allelopathic influences of multipurpose trees on crops in the traditional agroforestry system in Garhwal Himalaya have been little investigated. Hence, the present investigation was undertaken to assess the allelopathic potential of these three promising multipurpose agroforestry tree species on field crops in Garhwal Himalaya, Uttarakhand, India.
MATERIALS AND METHODS
The study was conducted in the experimental garden of the Forestry Department of H.N.B. Garhwal University, Srinagar Garhwal, (Chauras) Uttarakhand (long. 78[degrees]48' E, lat. 30[degrees]3' N, mean height about 530 m above sea level).
The study consisted of three factors: (i) three tree species, viz., Ficus subincisa Buch.-Ham. ex J. E. Smith, Bauhinia purpurea L., and Toona hexandra Wallich ex Roxb., (ii) two leachate types (leaf and bark leachate), and (iii) three test crops (Triticum aestivum L., Brassica campestris L., and Hordeum vulgare L.); local varieties were taken. For bioassay studies, leaf and bark were collected from fully-grown, mature trees of Ficus subincisa, Bauhinia purpurea, and Toona hexandra growing naturally in agroforestry systems.
The sun-dried leaves and bark of trees were ground separately in a mechanical grinder. By adding 1, 2, and 5 g of leaf and bark powder from each species to 100 mL double distilled cold water 1%, 2%, and 5% aqueous leachates were made separately for each component. The leachates were left for 24 h at room temperature (25[+ or -]2[degrees]C). The resulting leachates were filtered through three layers of Whatman No. 1 filter paper and stored in a dark and cool place in conical flasks. The effect of leachates on seed germination and radicle and plumule growth was tested by placing 100 seeds (five replications of 20 seeds each) of each test crop in petri dishes (9 cm diameter) containing three layers of Whatman No. 1 filter paper saturated with a particular leachate and kept at room temperature. A separate control series was set up using double distilled water. Moisture in the petri dishes was maintained by adding about 1 mL of leachate or distilled water as required. The number of germinated seeds was counted daily for up to 7 days because after this radicles and plumules in petri dishes normally start shrivelling at their tips. To assess the radicle and plumule growth, five seedlings of each leachate treatment in each of the five replicates were randomly measured with the help of a meter scaled in centimetres. All the data collected for germination and radicle and plumule growth were statistically analysed using Duncan's Multiple Range Test (Sharma, 1998).
The results on the allelopathic effect of leaf and bark (1%, 2%, and 5%) leachates of Ficus subincisa, Bauhinia purpurea, and Toona hexandra on the germination of test crops are shown in Figs 1 and 2. All treatments with both leaf and bark leachates had a negative effect on the germination of all test crops. The inhibition of germination was always the strongest in treatments with 5% extracts (except in B. campestris where 2% and 5% leaf leachates of B. purpurea and 2% and 5% bark leachates of F. subincisa had an almost equal effect). The negative effect of leaf extracts on the germination of test crops was the strongest in B. campestris where treatment with 5% extract of T. hexandra reduced germination by 38% with respect to control. The germination of H. vulgare was most notably inhibited by the leaf leachates of T. hexandra (18.4%) and B. purpurea (12.2%).
The 5% bark leachate of F. subincisa caused greatest reduction of the germination of T. aestivum and H. vulgare as compared to control. The inhibitory effect of the bark leachate of T. hexandra was the highest (23.0%) on the germination of T. aestivum.
Radicle and plumule growth
The radicle and plumule length of test crops were measured and compared with those of control. In radicle and plumule growth both inhibition and stimulation by leaf and bark leachate treatments were observed (Table 1). Ficus subincisa 2% leaf leachate inhibited the radicle length in B. campestris by 18.4% while 1% leaf leachate of the same species reduced most strongly (26.6%) the plumule length of T. aestivum.
The maximum stimulation of the radicle and plumule length (60.8% and 95.2%, respectively) was observed in B. campestris treated with 5% leaf leachate of F. subincisa. The 2% leaf leachate of B. purpurea was toxic for the growth of B. campestris while, interestingly, its 5% leachate caused maximum stimulation in the radicle and plumule length (48.7% and 58.1%, respectively) of B. campestris. The 2% T. hexandra leaf leachate caused maximum reduction in the radicle length of T. aestivum (33.9%) and the plumule length of B. campestris (58.1%) as compared to control. The 5% leaf leachate of T. hexandra stimulated most notably the radicles and plumules length (51.9% and 78.1%) of B. campestris.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Similarly, maximum reduction in the radicle and plumule length was observed in T. aestivum (26.6%) and in B. campestris (71.9%) in response to bark leachate (2%) of F. subincisa. In general, maximum stimulation in radicle and plumule length was observed in B. campestris (56.0% and 57.1%) by bark leachate (5%) of F. subincisa. The 2% bark leachate of B. purpurea caused maximum (14.6% and 31.9%) reduction of radicle and plumule length in T. aestivum as compared to control and other treatments. Interestingly, the 1 % bark leachate of B. purpurea caused maximum (81.0% and 96.8%) stimulation of radicle and plumule length of B. campestris as compared to control. The 1% T. hexandra bark leachate caused maximum reduction in the radicle length of T. aestivum (24.2%) and the plumule length of B. campestris reduced by 53.2% in 2% bark leachate of the same species as compared to control. The 5% bark leachate of T. hexandra stimulated most strongly the radicle and plumule growth of B. campestris (41.1% and 71.0%, respectively).
Most published work has revealed that foliage leachates are a potent source of toxic metabolites and their toxic effects are species specific (May & Ash, 1990; Bhatt et al., 1993; Todaria et al., 2005). In our study the acceptability of the trees studied decreased in the order Ficus subincisa, Bauhinia purpurea, and Toona hexandra. Our study revealed that both leaf and bark leachates of the multipurpose tree species tested significantly influenced the germination and radicle and plumule length of test crops. While the effect on germination was always inhibitory, in radicle and plumule growth both inhibition and stimulation were observed. Of the agricultural crops studied B. campestris was on average the most resistant to toxic effects of leaf and bark extracts of trees. Negi et al. (2007) reported that leaf and bark extracts of Ougeinia oojeinensis are equally toxic to the germination and plumule and radicle growth of Brassica campestris, Hordeum vulgare, and Triticum aestivum. The leaf and bark extracts of Terminalia bellirica, T. chebula, Aegle marmelos, and Sapindus mukorossi were also found to significantly inhibit the germination and radicle and plumule growth of test crops. Leaf extracts of these species are more toxic and influence more the germination and radicle growth of test crops as compared to bark extracts (Thapaliyal et al., 2007). Basotra et al. (2005) also reported an inhibitory effect of leachate from leaf and root/tubers of some medicinal plants on the germination and growth of food crops in Garhwal Himalaya. The present investigation shows that the three tree species studied have an allelopathic potential and contain water-soluble substances. Their effect on radicle and plumule length was inhibitory at lower concentrations but stimulatory at higher concentrations. Diverse allelochemicals such as phenolic acids, terpenoides, and alkaloids are leached from plants (Tukey, 1970; Inderjit, 1996; Blum et al., 1999). Gantzer (1960) reported that endogenous phenols possess only stimulatory properties and act as analogues of growth hormones and affect growth and physiological properties of plants. Singh et a1. (1980) reported that phenolic treatment of plants increases the grain yield of chickpeas. In the present study, the stimulatory effects of higher concentrations may be due to the presence of phenolics in leachates. Appel (1993) reported that plant phenolics influence nutrient cycling. Different inhibitory or stimulatory effects of various parts of the same plant are likely due to variability in the amount of phytotoxic compounds in different plant tissues (Rice 1974; Nishimura et al., 1982; May & Ash, 1990).
The results of this study reveal that allelopathic influences are (i) species-specific, (ii) have different effects on ermination and radicle and plumule growth, and (iii) the toxicity also depends on the concentration of allelochemicals in the medium. On average, the leaf leachate of T. hexandra was more toxic to the germination and radicle and plumule growth of H. vulgare and both its leaf and bark extracts inhibited T. aestivum while the leachate of F. subincisa was toxic to the growth of both these crops. The leaf and bark leachates of B. purpurea were the least toxic for the growth of the test crops. Among the test crops B. campestris was the most resistant and could be grown in association with all the tested tree species with least harmful effects.
The authors gratefully acknowledge the financial assistance received from I.C.A.R. New Delhi.
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Bhupendra Singh, Vivek Jhaldiyal, and Munesh Kumar [email]
Department of Forestry, H.N.B. Garhwal University, Srinagar Garhwal, Post Box-59, Uttarakhand-246174, India
[email] Corresponding author, firstname.lastname@example.org
Received 21 November 2008, revised 20 February 2009
Table 1. The effect of leaf and bark extracts of selected tree species on radicle (cm) and plumule (cm) growth of three food crops Tree species Extract Organ Leachate level, % 0 Test crop Triticum aestivum Ficus subincisa Leaf Radicle 8.80 (b) Plumule 8.40 (ab) Bark Radicle 8.80 (b) Plumule 8.40 (ab) Bauhinia purpurea Leaf Radicle 8.80 (bc) Plumule 8.40 (bc) Bark Radicle 8.80 (b) Plumule 8.40 (b) Toona hexandra Leaf Radicle 8.80 (ab) Plumule 8.40 (b) Bark Radicle 8.80 (ab) Plumule 8.40 (ab) Test crop Brassica campestris Ficus subincisa Leaf Radicle 3.70 (b) Plumule 3.10 (b) Bark Radicle 3.70 (b) Plumule 3.10 (ab) Bauhinia purpurea Leaf Radicle 3.70 (b) Plumule 3.10 (b) Bark Radicle 3.70 (b) Plumule 3.10 (b) Toona hexandra Leaf Radicle 3.70 (b) Plumule 3.10 (b) Bark Radicle 3.70 (bc) Plumule 3.10 (bc) Test crop Hordeum vulgare Ficus subincisa Leaf Radicle 9.20 (b) Plumule 8.90 (ab) Bark Radicle 9.20 (b) Plumule 8.90 (a) Bauhinia purpurea Leaf Radicle 9.20 (bc) Plumule 8.90 (b) Bark Radicle 9.20 (b) Plumule 8.90 (b) Toona hexandra Leaf Radicle 9.20 (ab) Plumule 8.90 (a) Bark Radicle 9.20 (ab) Plumule 8.90 (a) Tree species Extract Organ Leachate level, % 1 Test crop Triticum aestivum Ficus subincisa Leaf Radicle 7.45 (b) (-15.3) Plumule 6.17 (c) (-26.6) Bark Radicle 7.82 (bc) (-11.1) Plumule 6.32 (b) (-24.8) Bauhinia purpurea Leaf Radicle 10.87 (ab) (+23.5) Plumule 9.72 (ab) (+15.7) Bark Radicle l0.82 (a) (+23.0) Plumule 11.05 (ab) (+31.6) Toona hexandra Leaf Radicle 8.15 (b) (-7.4) Plumule 6.60 (bc) (-21.4) Bark Radicle 6.67 (c) (-24.2) Plumule 5.60 (c) (-33.3) Test crop Brassica campestris Ficus subincisa Leaf Radicle 3.45 (b) (-6.8) Plumule 2.90 (b) (-6.5) Bark Radicle 3.42 (b) (-7.6) Plumule 2.50 (bc) (-19.4) Bauhinia purpurea Leaf Radicle 4.06 (b) (+8.1) Plumule 2.37 (b) (-23.6) Bark Radicle 6.70 (a) (+81.0) Plumule 6.30 (a) (+96.8) Toona hexandra Leaf Radicle 4.80 (b) (+29.7) Plumule 4.07 (ab) (+31.3) Bark Radicle 4.12 (b) (+11.4) Plumule 3.30 (ab) (+6.5) Test crop Hordeum vulgare Ficus subincisa Leaf Radicle 9.20 (b) (-) Plumule 7.47 (bc) (-16.1) Bark Radicle 8.32 (bc) (+9.6) Plumule 7.22 (b) (-18.9) Bauhinia purpurea Leaf Radicle 9.86 (b) (+7.2) Plumule 8.27 (b) (-7.1) Bark Radicle 9.07 (b) (-1.4) Plumule 7.60 (bc) (-14.6) Toona hexandra Leaf Radicle 7.77 (c) (-15.5) Plumule 6.57 (b) (-26.2) Bark Radicle 7.87 (bc) (-14.5) Plumule 6.12 (b) (-31.2) Tree species Extract Organ Leachate level, % 2 Test crop Triticum aestivum Ficus subincisa Leaf Radicle 7.55 (b) (-14.2) Plumule 6.42 (bc) (-23.6) Bark Radicle 6.46 (c) (-26.6) Plumule 6.02 (b) (-28.3) Bauhinia purpurea Leaf Radicle 7.50 (c) (-1.3) Plumule 6.17 (c) (-26.6) Bark Radicle 7.52 (b) (-14.6) Plumule 5.72 (c) (-31.9) Toona hexandra Leaf Radicle 5.82 (c) (-33.9) Plumule 4.72 (c) (-43.8) Bark Radicle 7.15 (bc)(-18.8) Plumule 6.12 (bc) (-27.1) Test crop Brassica campestris Ficus subincisa Leaf Radicle 3.02 (b) (-18.4) Plumule 1.00 (c) (-7.7) Bark Radicle 2.95 (b) (-20.3) Plumule 0.87 (c) (-71.9) Bauhinia purpurea Leaf Radicle 2.97 (b) (-19.7) Plumule 1.75 (b) (-43.6) Bark Radicle 3.82 (b) (+3.2) Plumule 2.52 (c) (-18.7) Toona hexandra Leaf Radicle 2.72 (c) (-26.6) Plumule 1.30 (c) (-58.1) Bark Radicle 2.82 (c) (-23.8) Plumule 1.45 (c) (-53.2) Test crop Hordeum vulgare Ficus subincisa Leaf Radicle 7.85 (b) (-14.7) Plumule 6.72 (c) (-24.5) Bark Radicle 7.95 (c) (-13.6) Plumule 7.12 (b) (-20.0) Bauhinia purpurea Leaf Radicle 8.25 (c) (-10.3) Plumule 7.57 (b) (-14.9) Bark Radicle 8.32 (b) (-9.6) Plumule 6.30 (c) (-29.2) Toona hexandra Leaf Radicle 8.20 (bc) (-10.9) Plumule 6.92 (b) (-22.3) Bark Radicle 6.97 (c) (-24.2) Plumule 6.30 (b) (-29.2) Tree species Extract Organ Leachate level, % 5 Test crop Triticum aestivum Ficus subincisa Leaf Radicle 11.17 (a) (+26.9) Plumule 10.42 (a) (+24.1) Bark Radicle 11.40 (a) (+29.6) Plumule l0.37 (a) (+23.5) Bauhinia purpurea Leaf Radicle 11.75 (a) (+33.5) Plumule l0.90 (a) (+29.8) Bark Radicle 11.57 (a) (+31.5) Plumule 11.55 (a) (+37.5) Toona hexandra Leaf Radicle l0.90 (a) (+23.7) Plumule 11.35 (a) (+35.1) Bark Radicle 10.15 (a) (+15.3) Plumule l0.32 (a) (+22.9) Test crop Brassica campestris Ficus subincisa Leaf Radicle 5.95 (a) (+60.8) Plumule 6.05 (a) (+95.2) Bark Radicle 5.55 (a) (+56.0) Plumule 4.87 (a) (+57.1) Bauhinia purpurea Leaf Radicle 5.50 (a) (+48.7) Plumule 4.90 (a) (+58.1) Bark Radicle 5.62 (a) (+51.9) Plumule 4.57 (ab) (+47.4) Toona hexandra Leaf Radicle 5.62 (a) (+51.9) Plumule 5.52 (a) (+78.1) Bark Radicle 5.22 (a) (+41.1) Plumule 5.30 (a) (+71.0) Test crop Hordeum vulgare Ficus subincisa Leaf Radicle 11.6 (a) (+26.1) Plumule 10.62 (a) (+19.3) Bark Radicle 11.42 (a) (+24.1) Plumule 6.45 (b) (-27.5) Bauhinia purpurea Leaf Radicle 11.35 (a) (+23.4) Plumule 11.40 (a) (+28.1) Bark Radicle 11.57 (a) (+25.8) Plumule 11.50 (a) (+29.2) Toona hexandra Leaf Radicle l0.07 (a) (+9.7) Plumule l0.32 (a) (+16.0) Bark Radicle l0.00 (a) (+8.7) Plumule l0.57 (a) (+18.8) Values in parentheses indicate percentage stimulation (+) or reduction (-) as compared with controls. Means for radicle and plumule length of a test crop within a row having the same letter indicate non-significant statistical difference between treatments at p < 0.05.