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Invasion of Sugarbeet Leaf Blades by Larvae of Heterodera schachtii

Journal of Nematology
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Interrelationships of Meloidogyne Species with Flue-cured Tobacco Interrelationships of Meloidogyne Species with Flue-cured Tobacco 1 K. R. Barker 2, F. A. Todd 2, W. W. Shane 2, and L. A. Nelson 3 Abstract: Microplot and field experiments were conducted to determine relationships of popu- lation densities of Meloidogyne spp. to performance of flue-cured tobacco. A 3-yr microplot study of these interactions involved varying initial nematode numbers (Pi).and use of ethoprop to re- establish ranges of nematode densities. Field experiments included various nematicides at different locations. Regression analyses of microplot data from a loamy sand showed that cured-leaf yield losses on 'Coker 319' for each 10-fold increase in PI were as follows: M. javanica and M. arenaria-- 13-19%; M. incognita--5-10%; M. hapla--3.4-5%; and 3% for M. incognita on resistant 'Speight G-28' tobacco. A PI of 750 eggs and larvae/500 cmS of soil of all species except M. hapla caused a significant yield loss; only large numbers of M. hapla effected a loss. M. arenaria was the most tolerant species to ethoprop. Root-gall indices for microplot and most field-nematicide tests also were correlated negatively with yield. Relationships of Pi(s) and necrosis indices to yield were best characterized by linear regression models, whereas midseason numbers of eggs plus larvae (Pro) and sometimes gall indices vs. yield were better characterized by quadratic models. The relation of field Pm and yield was also adequately described by the Seinhorst model. Degrees of root galling, root necrosis, yield losses, and basic rates of reproduction on tobacco generally increased from M. hapla to M. incognita to M. arenaria to M. javanica. Key words: population dynamics, resistance, Nicotiana tabacum. Root-knot nematodes, Meloidogyne spp., have caused severe losses of tobacco for many years (5,17). As early as the 1940s, root knot was described as being so easily recognized that a detailed description was not

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