ALLELOPATHIC EFFECT OF (Casimiroa edulisLlave et Lex.) LEAF EXTRACTS ON GERMINATION AND SEEDLING GROWTH OF MAIZE (Zea mays (L.) AND SORGHUM (Sorghum biocolor (L.)Moench)

Abstract

The changes over time of both composition and quantity of allelochemicals can either increase or decrease the phytotoxicity of decomposing plant litter. The present study was undertaken to investigate the allelopathic effects of leaf extracts of C. edulis on sorghum and maize seed germinations. The aqueous extract of white sapota(Casimiroa edulis L1ave & Lex) leaf samples were used as a source of allelochemicals. Data collection involved the germination and seedling growth parameters including Germination rate (GR); germination inhibition rate GIR); MGT: mean germination time (MGT); germination index (GI); Relative length of plumule (RLP); germination speed (v); relative length of radicle (RLR); plumule inhibition rate (PIR); radicle inhibition rate (RIR); allelopathic index (AI). The result indicated that highest concentration of the allelopathic extract (20 mg/L) has demonstrated significantly the highest germination inhibition rate (56.67 %) for sorghum; GIR (36.67 %) and MGT (3.90 days) for maize seeds. However, the least RLP (23.95%), RLR (10.38%) for sorghum seeds while RLP (43.21%) and RLR (19.92%) for maize seeds; thehighest PIR (76.05%) and RIR (89.60%) for sorghum, as PIR (56.79%), RLR (80.09%) for maize seeds. The allelopathic intensity was found to be the highest (50 %) for sorghum, and (36.67%) for maize seed germination. The negative allelopathic index (AI) for sorghum seed germination was sginficant and negatively correlated with GIR (-0.974), PIR (-0.942) and RIR (-0.913). The negative allelopathic index (AI) for maize seed germination was significant and negatively correlated with germination speed (-0.872), MGT(-0.870), RLP (-1.00) and PIR (- 0.930). For sorghum seed germination, the first principal component (PC1) has got high positive loads from germination rate (0.36), RLP(0.36), AI(0.36), RLR (0.35), and GI (0.31). However, in PC1 the highest negative component loads were recorded by GIR(-0.36), PIR (- 0.36) and radicle inhibition rate (-0.35). The second PC has got the highest positive load (0.67) from germination speed, but high negative load from MGT(-0.68). In allelopathic effect on maize seed germination, PC1 has got highest scores from AI (0.51), and Gi(0.51), but highest negative scores from relative length of plumule (-0.51). Similarly, PC2 has got high positive scores from germination speed (0.58), AI (0.28) and GI (0.27) while negative score from GR (-0.58) and GI (-0.27). The third principal component (PC3) has got high positive score from MGT (0.66) but highest negative score from GIR (-0.66). It can be concluded that the highest negative scores in PCs which is GIR indicate direct relationship between the negative allelopathic index and negative score factors. However, the highest positive scores in PCs indicate inverse relationship between allelopathic index and positive score factors in both sorghum and maize seed germinations