Verticillium dahliae in soil, roots and stems of green manure crops
D. L. WHEELER (1), D. A. Johnson (1). (1) Washington State University, Pullman, WA, U.S.A.
Green manure crops are planted in rotation with crops susceptible to <i>V. dahliae</i> (<i>Vd</i>) to reduce wilt expression. However, asymptomatic infections of green manure crops may result in formation of microsclerotia that serve as inoculum for subsequent crops. The objective of this study was to quantify <i>Vd</i> pathotypes of potato and mint from soil, roots, and stems of potato, mints and selected green manure crops grown under greenhouse conditions. <i>Brassica juncea</i> ‘ISCI 199’, <i>B. juncea</i> ‘Pacific Gold’, <i>Sinapis alba</i> ‘Martigena’, <i>Sorghum bicolor sudanense</i> ‘Piper’, <i>Zea mays ‘</i>Marvel<i>’, Triticum aestivum</i> ‘Alpowa’, <i>Solanum tuberosum</i> ‘Norkotah’, <i>Mentha x piperita</i> ‘Black Mitchum’, and <i>M. spicata</i> were planted in soil infested with <i>Vd</i> pathotypes of potato and mint, grown to maturity, and harvested. <i>Vd</i> was quantified from soil, roots and stems on semi-selective media. Significantly greater colony-forming units (CFUs) of the mint pathotype were detected in soils from all crops except <i>Z. mays</i>, where the potato pathotype was greater and <i>M. spicata</i> where no difference was observed. Greater CFUs/g of soil were detected from asymptomatic hosts, <i>B. juncea</i> ‘Pacific Gold’ and <i>M. spicata</i>, soil relative to soil where symptomatic hosts were grown. Fewer CFU/60 cm of root tissue of both pathotypes were detected from green manure roots than <i>S. tuberosum</i>. Differential microsclerotia formation of <i>Vd</i> potato and mint pathotypes were observed in soil, roots and stems of asymptomatic and symptomatic hosts.
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