Germination and seedling growth of green gram was inhibited by various aqueous extracts used and the effect showed mixed results. No uniformity in inhibition was noticed due to various aqueous extracts of the same species and it differs with tree species/parts. Flower aqueous extracts of
Delonix had a more inhibitory effect on green gram while matured pod aqueous extracts of
Peltophorum showed higher inhibition. Inhibition is thought to be due to phytotoxins present in extracts, instead of osmotic inhibition because the use of 10 % extract ensures low osmolality
(Orwa et al., 2009b).
Easily visible effects including retarded germination rate
(Williamson et al., 1992), seeds darkening and swelling reduced radicle and shoot extension (
Turk and Tawaha, 2003;
Bhatt and Todaria, 1990), swelling/necrosis of root tips, discoloration, (Fig 3), lack root hairs, reduced dry weight
(Ayeni et al., 1997) were observed and such visible effects were proved and reflected in response index.
Inhibition was measured by RI with a range of 1 to 5%. The highest suppression was registered in germination (45.00 and 60.00%), shoot length (13.87 and 13.39 cm) and root length (4.27 and 10.49 cm) by the flower of
Delonix regia and a matured pod of
Peltophorum pterocarpum aqueous extracts respectively. Though flower aqueous extracts of
Delonix had high inhibition on germination, seedling growth, as against, it produced maximum fresh weight (354.65 mg) and dry weight (21.35 mg) of seedlings. But, matured pod aqueous extracts of
Peltophorum which had the highest supersession on germination and seedling growth of green gram continue to maintain the inhibitory effect and produced the lowest fresh weight (227.50 mg) and dry weight (15.80 mg) of seedlings (Table 1). Seed vigour index-I and II data revealed that
Delonix regia flower (624.15 and 960.75) and
Peltophorum pterocarpum matured pods (803.40 and 948.00) produced very weak seedlings with the lowest vigour index values respectively when compared to aqueous extracts.
The RI indicated the highest negative values of germination (-0.430 and -0.241), shoot length (-0.187 and -0.215) and root length (-0.753 and -0.394) for flower aqueous extracts of
Delonix regia and matured pod aqueous extracts of
Peltophorum pterocarpum respectively. Bark aqueous extracts
Delonix regia had negative RI (-0.053) for fresh weight and all other tree parts had positive RI of fresh and dry weight. Bark (-0.079) and fresh pod (-0.102) aqueous extracts of
Peltophorum pterocarpum registered negative RI and all other tree parts registered positive RI for the fresh and dry weight (Table 2). Considering cumulative effects, all aqueous extracts had affected germination and seedling growth and it was in the order of root length> germination>shoot length for
Delonix regia aqueous extracts and root length>shoot length>germination for
Peltophorum matured pods.
Among aqueous extracts of different tree parts of both species flower aqueous extracts of
Delonix regia and matured pod aqueous extracts of
Peltophorum pterocarpum had registered the lowest values of germination, shoot length, root length and highest negative values of RI (Fig 4).
Delonix regia flower aqueous extracts had a more inhibitory effect which may be occupied by a variety of allelochemicals (chlorogenic acid, 4-hydroxybenzoic, 3,4- dihydroxybenzoic, 3,5-dinitrobenzoic, L-azetidine-2-carboxylic 3,4-dihydroxybenzaldehyde, 3,4-dihydroxycinnamic and gallic acid) as reported by a team of scientists (
Chou and Leu, 1992;
Perveen et al., 2018). Similarly,
Peltophorum pterocarpum matured pod may contain more aliphatic alcohol, fatty acids, amino acids, terpenoids, phenolics, flavonoids, alkaloids, steroids chemicals as inferred by a group of scientists
(Shyamal et al., 2014; Taiwo et al., 2013).
Studying the qualitative and quantitative distribution of carotenoids in flowers of
Delonix regia indicated that flower petals contained 29 carotenoids
viz. phytoene, phytofluene, β-carotene, γ-carotene, lycopene, rubixanthin, zeaxanthin, lutein while flower sepals contained 18 carotenoids (phytoene, phytofluene, β-carotene, γ-carotene, lycopene,
etc), whereas filaments contain 20 (phytoene, β-carotene, γ-carotene, lutein, zeaxanthin, antheraxanthin, flavoxanthin, and other epoxy carotenoids) and anthers had the highest concentration of carotenoids with zeaxanthin accounting for 90 percent (
Jungalwala and Chama, 1962). Further, alkaloids, flavonoids, proteins, tannins, carbohydrates, phenols, triterpenes, and steroids were also found in flowers of
Delonix regia (Khursheed et al., 2012; Rahman et al., 2011;
Shanmukha et al., 2011;
Shiramane et al., 2011). The LC-MS studies characterized and confirmed the molecular structure of three major anthocyanins in water extract of
Delonix regia flowers. Cyanidin 3-O-rutinoside and pelargonidin 3-O-rutinoside were identified in a concentration of 10.7 and 0.9 mg/l respectively
(Adje et al., 2008) and GC-MS analysis of flower extract revealed the presence of benzenetriol, butyl-8-methylnonyl ester, lupeol, and vitamin E as major compounds
(Rani et al., 2011).
About eighty-three phytochemicals have been reported in
Peltophorum pterocarpum pods that include aliphatic alcohol, fatty acids, amino acids, terpenoids, phenolics, flavonoids, alkaloids, steroids (
Nathan et al., 2012) and matured pods had Quercetin, Rhamnetin, Rhamnetin, Meratin and Propelargonidin compounds
(Polasek et al., 2013; Menon et al., 1982).
Parafiniuk and Czerwiñska (2019) reported that bark aqueous extracts of eight tree species inhibited germination of maize, pigeon pea and sesame, with most inhibition in germination and radicle growth and plumule elongation in
Ailanthus excelsa, followed by
Acacia nilotica,
Dalbergia sissoo while
Swaminathan (1996) stated aqueous extracts of bark generally inhibiting the growth of sesame most and pigeon peas least. On the contrary same author
(Swaminathan et al., 1990) in his earlier studies observed that aqueous extracts
Parthenium hysterphorus weed has affected germination of four multi-purpose tree species
viz.,
Acacia leucophloea, Casuarina equisetifolia, Eucalyptus tereticornis and
Leucaena leucocephala and inhibition of germination and seedling growth is attributed to parthenin, an unsaturated lactone found in plant parts of weed species.
