Phytotoxic potential of selected medicinal plants on germination of Lactuca sativa seeds

Medicinal plants are best sources to treat various illnesses with them. So they might prove be a good source of developing novel herbicides. The aim of the present study was to investigate the potential inhibition effects of Cucumis sativus, Portulaca oleracea, Malus baccata, Saxifraga flagillaris, Geranium wallichianum and Monotheca buxifolia powdered material on germination of Lactuca sativa seeds. Sandwich method was used for determining phytotoxicity of these plants in terms of radicle and plumule length of Lactuca sativa seeds with different amounts of 10, 20, and 40mg of powdered plant material. Cucumis sativus and Monotheca buxifolia were found the most phytotoxic among the selected medicinal plants at all concentration. The results can be sum off as Monotheca buxifolia > Cucumis sativus > Malus baccata > Saxifraga flagillaris > Geranium wallichianum > Portulaca oleraceae. From the results it can be assumed that the phyto-toxic effects of the aforementioned plants could be helpful in searching and development of new pharmaceuticals that can be used as positive sources for the development of new weedicides. 
Keywords: Allelopathy; Lactuca sativa; Medicinal Plants; Phyto-toxic Potential 
http://dx.doi.org/10.19045/bspab.2019.80103


Introduction
Plants of toxic nature can be used as natural herbicides or these phyto toxic components of interest can be extracted from the plants for developing new herbicides. A variety of plant's metabolites used to inhibit or stimulate the growth and development of other plants. These chemicals are called allelochemicals which exudated out, leached from different parts of plant or volatiled or plant residues present in the environment [1].
The effect of allelochemicals is called allelopathy which is the effects of donor plant, on recipient plant by the discharge of chemicals in the environment. This activity influences the growth and development of other plants either by inhibiting or stimulating the bio-physiologic processes of recipient organism. These activities are concentration dependent and might inhibit the growth of one plant at one concentration and might stimulate the growth at other concentration. Such chemical are present in different plant parts in high amounts at specific environmental conditions [2]. Environmental conditions are responsible for differences in concentration of these metabolites [3]. Germination of seeds and plant development is altered by allelopathy and therefore germination is important way for the learning of allelopathy. Allelopathy has a significant part in agriculture and disturbs the progress and magnitude of the crops by the exchange of chemicals among crops, weeds and trees. Allelochemicals secreted by unknown plants significantly affect the intrinsic plants regardless of native species secreted allelochemicals or not [4]. Allelochemicals can alter the contents of plant growth hormones or make inequalities in many phyto-hormones, which hinders plant growth and development, for instance, with respect to germination of seed and sapling growth.

Materials and methods
Allelopathic study was carried out using sandwich method of Fujii et al. [6, 7] with slight modification. In this method 15g agar was dissolved in 1liter of distilled water and was autoclaved. The agar solution was left to cool at room temperature but before to solidify completely, the agar solution was poured into sterilized petriplates kept to solidify. Dehydrated plant material of each selected medicinal plant of 10mg, 20 mg and 40 mg were placed on the agar in petriplate and again a layer of agar was spread over it. After complete solidification, ten seeds of lettuce (Lactuca sativa L.) were employed on agar-gel in petriplate. Petriplates were wrapped with plastic-tape and nurtured for 72 h at 24ºC in dark environments. The sizes of radicle and plumule were noted in (cm). Only agar without any plant material was used as a seed bed for lettuce seeds in control set of petriplates.
Each treatment was repeated three times. Means of radicle and plumule lengths for each medicinal plant were measured by relating to that of control. The data was evaluated statistically for the 10 mg, 20 mg and 40 mg of plant materials with radicle and plumule lengths of selected medicinal plants.

Results and discussion
Medicinal plants have inhibitory or stimulatory effects on selected whether cultivated or weeds and it's their allelochemicals inhibiting or promoting the plant growth. It is easy to separate allelopathic plants from medicinal plants due to their capability of accumulation of specific metabolitess which can cure numerous infections of manhood [15][16][17]. Plants possess toxic metabolites can be potential bases bio-herbicides. Climatic and various ecological conditions may alter the plant metabolites and ultimately their synthesis of these components [18]. The use of cultivated crops as soil cover have many possible profits such as increasing oil fertility, upgrade soil inclination, enhanced nitrogen fixing ability, reducing corrosion, stop leakage of nutrients and clamping down the weed production. Chemicals are used to reduce growth of weeds which inversely affect the crop production. Struggle for nutrients and production of biochemicals by the crops can reduce the weed density and enhances the growth of crops because these chemicals have adverse effect on weeds. Releasing allelopathic Chemicals and production of primary or secondary metabolites by the crops over weeds, these chemicals interfering growth properties of the weeds which in turn either proved toxic or stimulate their growth.  (Table 1). At 10mg dose seeds of Lactuca sativa were very susceptible to leaves fragments of Monotheca buxifolia with radicle length of 0.18cm, followed by Cucumis sativus seeds powder with radical length of 0.26cm and Malus baccata with radicle length of 0.64cm. Portulaca oleracae and Geranium wallichianum showed stimulatory effect on seeds of Lactuca sativa (Fig.1). Libralato et al. [24] reported the Phytotoxicity of zerovalent iron on Lepidium sativum, Sinapis alba and S. saccharatum, their results showed bio stimulation effects as increased seedling length and high biomass. At 10mg concentration plumule growth was also inhibited by Cucumis sativus (0.22cm), Monotheca buxifolia (0.24cm) and Malus baccata with 1.18cm length of plumule. Saxifraga flagillaris, Portulaca oleraceae and Geranium wallichianum showed stimulatory effects (Fig. 2). It is also reported that the chemicals of different part of the same plant can showed phytotoxic, inhibitory or stimulatory effects on other recipient plants. Mehmoodzadeh et al. [25] reported the allelopathic effect of Cannabis sativa shoot and root extract where shoot showed inhibitory effects while root gave stimulatory effects on seeds of Lactuca sativa. Present study showed that at 20mg radicle length of Lactuca sativa was least with Monotheca buxifolia (0.12), followed by Cucumis sativus (0.14) and Malus baccata (0.63). Portulaca oleracae, Geranium wallichianum and Saxifraga flagillaris showed 1.74, 1.82cm and 2.38cm length of radicle respectively (Fig. 3). Naz and Bano [26] reported that leaf extracts of R. communis and L. camara inhibit the growth of maize seedlings. Similar studies was conducted by Algandaby and Salama [17] where medicinal plants showed good phytotoxic or allelopathic effect. Devkota and Sherma [27] also screened allelopathy of rhizome and leaves of justice adhatoda where they reported inhabited germination of wheat and pea seeds. The present findings showed at 20mg conc. Malus baccata reduces Plumule length and was 0.03cm, followed by Monotheca buxifolia with 0.13cm and Cucumis sativus with 0.16cm. Saxifraga flagillaris, Portulaca oleraceae and Geranium wallichianum showed 1.54, 2.47 and 2.69 cm length of plumule respectively (Fig. 4). Monotheca buxifolia inhibited the growth of Lactuca sativa might be due to the presence of flavonoids present there in. Macdonald et al. [28] reported that Ocimum gratissimum flavonoids are phytotoxic. Jan et al. [29] reported the presence of flavonoids in Monotheca buxifolia. Same results were reported by Saadullah et al. [30]. At 40mg, radicle length of Lactuca sativa seeds was least Monotheca buxifolia (0.12), followed by Cucumis sativus (0.14) and Malus baccata (0.63). Portulaca oleracea, Geranium wallichianum and Saxifraga flagillaris showed 1.74, 1.82cm and 2.38cm length of radicle respectively (Fig. 5) while plumule length at 40mg was least (0.09cm) with Cucumis sativus, followed by Monotheca buxifolia (0.15cm) and Malus baccata (0.66cm). Portulaca oleraceae, Geranium wallichianum and Saxifraga flagillaris showed 1.82, 1.15cm and 2.30cm respectively (Fig. 6). These plants use in present study are commonly used for treating various illnesses but their allelopathic potentials are not reported yet. It is reported that medicinal plants can also be good