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Identification and characterization of Phytophthora isolates from citrus orchards of South Texas
Shima Chaudhary: Texas A&M University; Veronica Ancona: Texas A&M Kingsville Citrus Center; Christopher Barbola: Texas A&M University-Kingsville, Citrus Center
<div>Foot rot and root rot caused by <i>Phytophthora</i> species are prevalent diseases in commercial citrus orchards of South Texas. There is a need for comprehensive study to identify and characterize <i>Phytophthora</i> isolates in the orchards. Ninety four isolates, were collected from soil and infected roots from 30 citrus orchards located across the three citrus producing counties in the Lower Rio Grande Valley of Texas. ITS sequence generated based on primers ITS4 and ITS6, exhibit 98 to 100% identity to <i>Phytophthora nicotianae </i>for all the isolates tested. This was also supported by morphological characteristics such as colony motif, sporangium and oogonium shape and size. Thirty Isolates were tested for mating type with known A1 and A2, <i>P.nicotianae</i> testers. Twenty two and eight isolates were identified as A2 and A1 mating type respectively. Thirty isolates of <i>P. nicotianae</i> were also screened for sensitivity to mefenoxam on 10% clarified V8 agar at 1 a.i.µg mL <sup>–1</sup>. Six isolates were inhibited less than 50%, twenty-two isolates were inhibited 50% to 90% and two isolates were inhibited more than 90% and were marked as insensitive, intermediate sensitive and sensitive respectively. We conclude from this study that prevalent species in the commercial citrus groves is <i>P.nicotianae</i> and most of the isolates tested, are intermediate or insensitive to mefenoxam at 1 a.i.µg mL <sup>–1</sup>. Occurrnce of both mating types in the orchards, can have an implication for the management of the <i>Phytophthora </i>diseases in the region.</div>

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