Allelopathic Effects of Guizotia Abyssinica On Seed Germination of Horse Gram

The term allelopathy involves both harmful and beneficial biochemical interactions between crop plants and weeds, through the release of chemicals from plant parts by different ways such as leaching, volatilization, root exudation, residue decomposition and other processes in both natural and agricultural systems. In this system the donor plant is benefitted, and the receiver plant is affected. This type of chemical signalling or interactions are widely known in different plant groups ranging from algae, lichens, and crops as well as annual and perennial weeds (Valcheva et al., 2019)¹. Allelochemical secreted by weeds reduced the growth and development of crop, cause economic loss. Thus, weed control measures become inevitable to get income gain (Knap and Kundu, 2019)². The main objective of the present study is to study crop – crop interaction of Niger crop and horse gram crop. We studied the allelopathic effect of Niger plant aqueous extracts on seed germination of horse gram.

For the present study we selected Niger plant (Guizotia abyssinica) to test its allelopathic effect on seed germination of crop plant Horse gram. Niger plant is a herbaceous plant belongs to the family Asteraceae, cultivated for edible oil obtained from its seed. Horse gram [Scientific name: Macrotyloma uniflorum (Lam.) Verdc.] is one of under exploited legume crop with great potential in sustainable agriculture. Horse gram having better yield potential, quality of produce, adaptability, tolerance to biotic and abiotic factors and also adopting proper nutrient management practices (Rathiya and Neelam, 2021)³.

MATERIALS AND METHODS

Plant material

The seeds of crop plant Guizotia abyssinica were procured from Andhra Pradesh Seed Development Corporation, Ananthapuramu. The plant material was collected from the field grown G. abyssinica, surface sterilized with 0.1% mercuric chloride and air dried in the laboratory. Dried plant material was separated into roots and shoots, chopped into fine pieces and stored in air tight containers at 4 ºC.

Preparation of Aqueous Extract

The extracts were prepared by taking 10 g of chopped part in 100ml distilled water in sterilized beakers. The beakers were kept for 72h at 10 – 15 ºC. Aqueous extracts thus obtained were filtered through Whatman No.1 filter papers and the volume was made up to 100 ml. This was labelled as pure extracts or stock solutions. A part of this stock solution was further diluted (0.1, 10 times) with distilled water to get 10, 5 and 1 per cent solutions.

Presowing Hardening

The hardening treatment of consisted of soaking of horse gram  in solutions of different concentrations of root and shoot extracts of G. abyssinica plant for 6h, 12h and 24h. Seeds soaked in distilled water served as controls. After completion of the treatment the seeds were washed with distilled water and placed in sterilized petri dishes of 10cm diameter which were lined with double layer of filter paper. All the petri dishes were moistened with distilled water for the germination of seeds. The percentage of seed germination was calculated.

Influence of Different Developmental Stages and Tissues types of Guizotia on test species

Three developmental stages of G. abyssinica plants such as vegetative, flowering and harvesting stages were selected for the present experiment. Plants of the three stages collected from population grown in departmental garden and plants of each stage were surface sterilized with 0.1 % mercuric chloride and air dried. The dried plants were separated into root and shoot and the water extracts were prepared as described earlier. Allelopathic effects were assessed by employing the extracts on seeds of horse gram.

Collection of Root Exudates

The collection of root exudates of G. abyssinica plant seedlings was done as per the method of [6]. A desiccator (20 cm – diameter) was autoclaved and 350 ml of sterilized distilled water was added to bring the water level to the bottom of the perforated porcelain disk that conventionally hold samples above the desiccant. A layer of sterile moist cheese cloth was placed on top of the porcelain disk and seeds of G. abyssinica which had been surface-sterilized were eventually distributed on top of the cheese cloth where the perforations on the disk were made. The lid was placed on the desiccator and it was located under fluorescent light approximately 150wm^-2 and at 27±5 ºC temperature. As G. abyssinica seeds germinated, they were allowed to grow for 15 days to a height of 9-10 cm with roots of 5-6 cm length protruding into the water. The water was withdrawn from the desiccator at respective intervals 5, 10 and 15 days from the day of germination. Water collected from desiccator was concentrated on a rotor evaporator to a volume of 30 ml and a part of this concentrate was tested for Allelopathic activity against germinating horse gram seeds in petri dish assays. Distilled water was used as control.

Residue Incorporation Studies

For the residue incorporation studies earthen pots (6.5” x 5.5” size) containing 1 kg of sterilized silica sand and 5, 2.5 and 1 % of finely ground root and shoot residue of niger seed were maintained under natural photoperiod of about 12-14h with a temperature of 28± 4 ºC in the botanical garden. A control was maintained without residue. The pots were irrigated once a day with distilled water. The pots were incubated for 15 days for decomposition of the residues. The seeds of horse gram were surface sterilized and raised in pots. After the seedlings emerged, the plants were thinned to 3 per pot and the plants were maintained for 45 days from the day of seeding emergence. The pots were irrigated once a day with distilled water and twice a week with Hoagland’s nutrient solution (Hoagland and Arnon, 1950)⁴. Maximum care was taken to ensure that the amount of water added was slightly less than field capacity. The pots were arranged in a randomized complete block experimental design with three triplicates to avoid drainage of leachates during experimentation.

All the plants were harvested at an interval of 15 days. The pots were flooded with water, the sand was loosened slowly and the plants were uprooted carefully. After each harvest (i.e. 15, 30 and 45 day – old plants), the plants were thoroughly washed with water and separated into root and shoot. Prior to this, seed germination was recorded. Morphological parameters such as seedling growth (root and shoot length) leaf area, dry mass production and some physiological parameters were studied. The results were averaged of three replicates.

RESULTS AND DISCUSSION

Allelopathic potential of a plant may vary with the phase of the development of the other plants growing around it. Many Angiosperm plants were reported to retard the germination and growth of their neighbouring species. The aim of the present study is to evaluate allelopathic effects Guizotia abyssinica aqueous extracts on seed germination of horse gram using different methods such as soaking method, root exudates and different stages of plant and plant residues.

In results we observed that the per cent germination of horse gram seeds is significantly inhibited by 10% and 5 % concentrations of G. abyssinica root and shoot extracts. Shoot extract was found to be more potent that root extracts. However, the per cent germination was not so much affected by lower concentration (1%) of all the extracts, but it stimulated the germination of seeds. The initial toxicity observed on 1^st day was alleviated by the end of 4^th day. The inhibitory effect of all the extracts was thus found to be concentration dependant. All the concentrations of shoot extracts absolutely inhibited the germination of horse gram on 1^st day. The degree of inhibition was alleviated gradually with increasing days of incubation. Shoot extracts was found to be more potent (Fig. 1). Allelopathic effect of root and shoot extracts on seed germination was studied by several authors (Seifu et al., 2023 and Seemi and Syed, 2014)^{5, 6}.

Figure 1: Effect of aqueous extracts of Guizotia abyssinica on seed germination of horse gram

Seeds of horse gram were soaked in root and shoot extracts of Guizotia for different time intervals and the per cent germination was considered as the primary criterion for toxicity. Figure 2 demonstrated that 10 and 5 % concentrations of the Guiotia decreased the per cent germination after 6h, 12h and 24 h and the inhibition was alleviated by the end of 4^th day. Among the three treatments, seeds soaked for 6h stimulated the growth of seeds. Seeds soaked for 24h period affected the germination to a higher degree followed by 12h (Figure 2). To evaluate the most potent stage of donor plant, the aqueous extracts of vegetative, flowering and mature stages of Guizotia were prepared and their effect was studied on horse gram. Among the three stages, the extracts prepared from mature plants showed significant inhibition in both plants to varying degrees. The higher concentrations (10 & 5 %) of all treatments inhibited the per cent germination, whereas lower concentration (1%) of root extracts prepared from the vegetative and flowering stages stimulated the germination on l and 2days of observation in horse gram (Figure 3). The present study observed that extracts from mature plants showed maximum inhibitory activity towards the germination of horse gram agree with observations made by Kanchan and Jayachandra (1979a) ⁷ and Wardle et al., (1993)⁸ regarding the most potent developmental stage of donor plant. Similarly, allelopathic effect of vegetative and flowering stage of sunflower on Lettuce was studied (Ravlic et al., 2022) ⁹.

Figure 3. Influence of different stages of Guizotia abyssinica extracts on per cent germination of horse gram

The root exudates of Guizotia were collected at the time intervals of 5, 10, 15 days. The solutions were collected and used to test their effect on germination and also to evaluate the most effective root exudate on horse gram seeds. Root exudates from 15^th and 10 day old plants showed significant inhibition on 1^st, 2^nd, and 3^rd day seeds. No significant inhibition of germination was observed with root exudates collected from 5- day old plants. On the contrary root exudates from 5-day old plants stimulated the germination on 1^st day in horse gram seeds (Fig. 4). The effect of root and shoot residue of Guizotia were tested on some toxicity criteria in horse gram. We observed that higher concentrations (2.5 and 5 %) of root and shoot residues inhibited the germination significantly to varying degrees of inhibition on all days of observation. The lower concentration (1%) stimulated the germination in some cases. The inhibitory effect was observed to be concentration dependant, which was alleviated by the end of 8^th day from 3^rd day of sowing. Shoot residue was found to be more effective. It is significant to note that 5% of shoot extract absolutely reduced the germination of horse gram on 3^rd, 4^th, and 5^th day of from 3^rd day of sowing (Fig. 5).

Figure 5. Effect of Guizotia abssinica residue on germination of horse gram from 3^rd day of sowing