Weeds as Hosts of Plant Parasitic Nematodes in Subtropical Agri-culture Systems

With a nearly year-round growing season, tropical and subtropical regions are plagued with a myriad of agronomic challenges, including near-continuous weeds and invertebrate pests including plant-parasitic nematodes (PPNs). A poor understanding of the presence and geographical distributions of these pests complicate their management, especially in organic farming systems. This work attempts to document the interaction of PPNs with the major weeds in the semi-arid region of south Texas. Five organically managed farms were surveyed for four weeds of regional agronomic importance including silverleaf nightshade (Solanum elaeagnifolium), common sunflower (Helianthus annuus), false ragweed (Parthenium hysterophorus), and London rocket (Sisymbrium irio). Soil and root samples were collected to determine the presence of economically important PPNs in the roots and rhizosphere of the selected weed species. Eight different nematode genera associated with the selected weed species, includingPratylenchus spp., Trichodorus spp., Criconemella spp., Helicotylenchus spp., Xiphinema spp., Dorylaimus spp., Aphelencoides spp., and Tylenchus spp. were recorded. Four of the major economically important nematode genera (Pratylenchus spp, Trichodorus spp., Criconemella spp., X iphinema spp.) were found in the rhizosphere of all four weeds. The two major PPN genera Helicotylenchus spp. and Pratylenchusspp., were largely associated with common sunflower, a major weed in the region. Our results indicate that these weed species can present additional challenges in agriculture, not only as direct competitors for resources to agronomic crops, but also as potential hosts for PPNs. Additional index words: plant parasitic nematodes, organic farming, subtropics, weedy plants _____________________________________________