Texas ranks first in cotton production in the United States and accounts for approximately 40% of the total production. Most of the cotton production is concentrated in the Texas High Plains where cotton and peanut are commonly grown in rotation. With peanut being a legume crop, farmers routinely leave residue on the soil surface to improve soil fertility; however, V. dahliae can survive in the crop residue contributing inoculum to the soil. A microplot study was conducted to investigate the impact of peanut residue infested with V. dahliae on subsequent microsclerotia density in soil and Verticillium wilt development in cotton. The effects of infested peanut residue rate on percent germination of cotton seeds and on wilt incidence were monitored in 2008 and 2009. In both years microplots were planted with a susceptible cotton cultivar, Stoneville (ST) 4554B2RF. Increasing infested peanut residue rate was positively correlated with wilt incidence in cotton and negatively correlated with germination of cotton seeds. Density of microsclerotia in the soil increased significantly with increasing rates of infested peanut residue over time. Results indicate infested peanut residue serve as a source of V. dahliae inoculum, and removing infested residue can reduce disease development in subsequent cotton crops. 1. Introduction Verticillium wilt, caused by the soilborne fungus Verticillium dahliae Kleb., is an economically important disease of cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.). The pathogen has a broad host range of more than 400 plant species including field crops and most vegetables [1]. Several factors, including cultivar selection, pathogen aggressiveness, inoculum density, and environmental conditions, influence disease development [2, 3]. Cotton and peanut plants affected by Verticillium wilt show stunting and epinasty [4]. Their leaves exhibit interveinal chlorosis, necrosis, curling, and die back from the margins inward. Plants develop characteristic mosaic patterns on foliage, starting from the base of the plant and progressing towards the top [5]. Ramification of the fungus in the xylem vessels leads to a tan-to-brown discoloration, a decrease in hydraulic conductance, wilting, and eventually death [6]. In infested cotton, plants can appear stunted, defoliate prematurely, and have fewer fruiting positions; bolls may abscise or not open [7], whereas in peanut, pegs are formed in less numbers and have fewer seeds [8]. The fungus is capable of infecting plant roots directly or through wounds throughout the growing season
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