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Studies show that once a suppressive effect has been established, a green manure treatment for a single season is sufficient to either maintain or to re-establish the control of Verticillium wilt of potato. Verticillium wilt, caused by Verticillium dahliae Kleb., was controlled on the first years of Russet Burbank potato cropping following 2-3 successive years of green manure treatments. Following this control, yields were increased with the first year of potato cropping, but were reduced during the second consecutive year of cropping with potato. In the second year of continuous cropping with Russet Burbank, total yields were reduced by 10% and U.S. #1 tubers by 40%, and these yield reductions were accompanied by increased soil populations of V. dahliae by >5-fold. Yet, with a single season of an earlier-used green manure treatment (e.g. Austrian winter pea, sudangrass, Dwarf Essex rape, Bridger rape, oats, rye, or sweet corn), Verticillium wilt was again controlled and yields of Russet Burbank were increased to higher levels or to levels that were equivalent to those initially observed following either 2 or 3 successive seasons of green manure treatment. Green manures also demonstrated significant effects on microbial activities, which were inversely related to the incidence of Verticillium wilt. More specific effects on microbial activity and soilborne ecology were shown with increased populations of Fusarium spp. Verticillium wilt was negatively correlated with infections of potato feeder roots and stem-ends of potato tubers by F. equiseti. Exemplifying the effect of a green manure on fungal ecology, sudangrass treatments were shown to have lasting effects on Fusarium avenaceum populations with quantitative changes that extended 5 years beyond the time of soil incorporation with sudangrass.Resumen Los estudios demuestran que una vez que se ha establecido el efecto supresivo, es suficiente un tratamiento con abono verde por un ciclo de cultivo ya sea para mantener o re-establecer el control del marchitamiento por Verticillium en papa. El marchitamiento por verticillium, causado por Verticillium dahliae Kleb, fue controlado en los primeros años del cultivo de papa Russet Burbank siguiendo dos o tres años sucesivos de tratamientos con abono verde. Siguiendo este control, se aumentaron los rendimientos en el primer año del cultivo de la papa, pero se reducía durante el segundo año consecutivo de cultivo con papa. En el segundo año continuo del cultivo con Russet Burbank , se redujo el rendimiento total en un 10% y los tubérculos U.S. # 1 en 40%, y estas reducciones se acompañaron por el aumento en las poblaciones de V. dahliae en más de cinco veces. Pero con un tratamiento temprano de abono verde en un ciclo (por ejemplo, chícharo Australiano de invierno, pasto sudán, colza enana Essex, colza Bridger, avena, centeno, o maíz dulce), se controlaba nuevamente el marchitamiento por Verticillium y se aumentaban los rendimientos de Russet Burbank a niveles más altos o equivalentes a aquellos observados inicialmente sig...

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Three studies provided additional knowledge of beneficial effects of sudangrass for yield and quality increases of the Russet Burbank potato. Thro of these studies showed significant 'increases of both U.S. #1 and smooth tubers >280 g following green manures of sudangrass. These sudangrass (HS-33) effects did not differ from a sorghum-sudan hybrid . When a sudangrass green manure was compared with a fallow treatment, results of the first study showed mean yield increases of 36% for U.S. #1 tubers >280 g and yields of a second study by 34% for U.S. #1 tubers. This same sudangrass treatment outperformed green manures of either Austrian winter pea, barley, or sweet corn by increased U.S. #1 yields that ranged from 27% to 61%. By several lines of evidence, these benefits were found to extend beyond the effect of Verticillium suppression. Soil N was significantly increased following green manures of sudangrass, and these increases were in turn negatively correlated with wilt incidence and positively correlated with yields of both U.S. #1 tubers and tubers >280 g. Additional benefits also included significant increases of tuber grade percentages for marketable tubers and of smooth tubers >280 g. Benefits from sudangrass green manures beyond the effects of Verticillium suppression became further evident following a greenhouse study that involved field soil and sudangrass that had been grown in the same field. This study corAccepted for publication 7 June 2004. ADDITIONAL KEY WORDS: Fusarium spp., green manures, Verticilhum dahliae roborated both field experiments by showing increased yields with green manures of sudangrass that approximated 5.5 t ha-1 dry wt. As with the field studies, these yield benefits also extended beyond the effects of Verticillium suppression and were closely associated with significant increases of Fusarium equiseti, F. oxysporum, and F. solani. Throughout all studies, sudangrass green manures significantly increased microbial activities with increased populations of Fusarium spp. and increased concentrations in soil of mineralizable N, organic P, K, Mn, along with the percent soil organic matter -all factors that could have contributed to significant increases of yield and quality. RE SUMENSe obtuvo informaciOn adicional sobre los efectos beneficos del sorgo pars el increment° de rendimientos y calidad de papa Russet Burbank por medio de tres estudios. Dos de ellos mostraron un significativo increment° de U.S. #1 y tuberculos uniformes >280g despues de haber recibido sorgo como abono verde. Los efectos del sorgo (HS-33) no mostraron diferencias con el sorgo hibrido (Tridan-8). Cuando se comparO el abono verde de sorgo con un tratamiento de barbecho, los resultados del primer estudio mostraron un promedio de increment° del rendimiento de 36% para tuberculos U.S. #1 >280g y los del segundo estudio 34% para. tuberculos U.S. #1. El mismo tratamiento de sorgo, super° a los abonos verdes de alverjilla, cebada y maiz dulce con rendimientos de U.S. #1 que variaron entre 27 y 61%. Junto con est...