Colonization of Potato Roots and Stolons by Colletotrichum coccodes from Tuberborne Inoculum

Abstract

The rate of colonization by Colletotrichum coccodes was quantified on roots and stolons of the potato cultivar Russet Burbank. Greenhouse grown plants arising from seed-tubers infected with C. coccodes were observed. The distance that C. coccodes colonized potato roots was measured from the seed tuber to the distal edge of microsclerotial development along the roots starting at 21 days after plant emergence and continued at 14 day intervals until crop death. Visual assessment of disease progress was confirmed by isolation from diseased and non-diseased tissues onto nutrient agar. Expansion of C. coccodes foci along the roots in two independent trials resulted in a linear growth model of 1 mm/day (Trial 1 P<0.011, R 2 =0.84; Trial 2 P<0.007, R 2 =0.87). Colonization radiated from the seedtuber to form compact foci of infected tissue that was rotationally symmetrical; no secondary foci were observed. The results suggested that C. coccodes expanded linearly from an inoculum source and that for multiple disease foci to develop on a root system, multiple primary infections must occur from sclerotia in the soil.Resumen Se cuantificó el nivel de colonización por Colletotrichum coccodes en raíces y estolones del cultivar Russet Burbank de papa. Se observaron las plantas cultivadas en el invernadero que emergieron de la semilla tubérculo infectada con C. coccodes. Se midió la distancia en que C. coccodes colonizó a las raíces de papa desde el tubérculo semilla a la orilla distal del desarrollo del microesclerocio a lo largo de las raíces, empezando 21 días después de la emergencia de la planta y continuando a intervalos de 14 días hasta la muerte del cultivo. Se confirmó el análisis visual del progreso de la enfermedad mediante el aislamiento de los tejidos enfermos y sanos a agar nutritivo. La expansión del foci de C. coccodes a lo largo de la raíz en dos ensayos independientes dio como resultado un modelo de crecimiento lineal de 1 mm/día (ensayo 1, P<0.011, R 2 =0.84; Trial 2 P<0.007, R 2 =0.87). La colonización fue radial desde la semilla tubérculo para formar foci compactos de tejido infectado que fue rotacionalmente simétrico; no se observaron foci secundarios. Los resultados sugieren que C. coccodes se expandió linealmente desde una fuente de inoculo y que para que se desarrollen múltiples foci de la enfermedad en un sistema radical, se deben presentar infecciones múltiples primarias de los esclerocios en el suelo.

Impact of Seed Lot Infection on the Development of Black Dot and Verticillium Wilt of Potato in Washington

“…Infected seed tubers likely played a major role in promoting colonization of roots and increased progeny tuber infection by C coccodes in the long potato rotation field in 2008. In previous studies, tuberbome inoculum of C. coccodes was demonstrated to contribute to progeny tuber infecfion and the pathogen had been shown to spread from infected seed along roots and stolons at a rate of 1 mm/day (1,15,32). Mean root disease sevedty values in the 2008 long potato rotation field were 0.2 to 0.8, which is equivalent to 1 to 25% of total root colonization by the pathogen according to the disease severity index used in this study.…”

Response of Colletotrichum Coccodes to Selected Fungicides Using a Plant Inoculation Assay and Efficacy of Azoxystrobin Applied by Chemigation

“…Small (150 to 230 um in diameter), black sclerotia of the fungus develop on infected roots, stolons, stems and tubers. C. coccodes can colonize below ground stems, stolons, roots and tubers from infected seed pieces at a rate of 1 mm/day (Ingram and Johnson 2010) however, soilborne inoculum of C. coccodes has the potential to cause more severe disease than tuber borne inoculum (Nitzan et al 2005;Nitzan et al 2008). Infections of the tuber periderm result in gray to brown blemishes in which sclerotia may develop.…”

Effect of Extended Crop Rotations on Incidence of Black Dot, Silver Scurf, and Verticillium Wilt of Potato

“…The fungus was isolated from yellow mustard, spring canola, soybean, alfalfa, and oat, with sig nificantly lower frequencies obtained from alfalfa and oat than yellow mustard, spring canola, or soybean in a previous study (34). The assay of the stolon end of tubers would have been a measure of both tuberbome and soilborne inocula, while the assay of the periderm would have been a measure of mostly soilborne inoculum (22). Weeds such as S. nigrum (black nightshade) and 5. triflorum (cutleaf nightshade) can be common in potato fields and may serve as alternative hosts for C. coccodes.…”

“…Inoculum of C. coccodes originates from soil, seed tubers, and water splashed and windblown plants (14,22,25,27,30,32). C. coc codes was detected in soil from a majority of commercial fields in a survey in Idaho in 1988, but it was not detected in native vegeta tion areas (2).…”