Allelopathic potential of some tropical trees of Ecological Reserve El Eden, Quintana Roo, Mexico

We investigated the allelopathic potential of leaves of six tropical trees (Jatropha gaumeri, Pedilanthus tithymaloides, Sebastiania adenophora, Zuelania guidonia, Zanthoxylum caribaeum and Heliocarpus sp.)from the Ecological Reserve El Eden, Quintana Roo, Mexico. Aqueous leachates from dry leaves (1 percent)were tested in vitro on the root growth of 7 test plants [Echinochloa crus-galli, Lolium multiflorum, Zea mays, Amaranthus hypochondriacus, Lycopersicon esculentum, Phaseolus vulgaris and Cucurbita pepo (ungerminated and pre-germinated)] and the diameter growth of 3 phytopathogenic fungi [Alternaria sp., Fusarium oxysporum and Helminthosporium sp]. Aqueous leachates of P. tithymaloides, S. adenophora, Z. caribaeum, J. gaumeri and Heliocarpus sp. were most phytotoxic. S. adenophora and Heliocarpus sp. aqueous leachates inhibited the growth diameter of all phytopathogenic fungi. We did two greenhouse pot experiments in soil amended with leaves (2 percent w/w)of 3 highly phytotoxic species (J. gaumeri, S. adenophora and Z. guidonia), and tested their decomposition effects on the (i)emergence of weeds in pots, (ii)the growth of bean and tomato, (iii)the colonization of arbuscular mycorrhizal (AM)fungi in roots of both crops and (iv)the development of Rhizobium nodules in bean roots. The dicots weeds were more abundant than monocots in bean and tomato pots. The weeds were less in bean pots than tomato pots. In bean pots, dicotyledon weeds were more abundant with J. gaumeri and S. adenophora amended leaves. Beans dry weight was not affected by any treatment, but tomato was significantly reduced in all treatments. Colonization of AM fungi in bean roots was less than control, but contrarily, S. adenophora leaves significantly stimulated them in tomato roots. All treatments significantly stimulated the Rhizobium nodules in bean roots.