Development of black dot disease (Colletotrichum coccodes (Wallr.) Hughes) and its effects on the growth and yield of potato plants

Abstract

SummarySeed tubers of cvs Désirée and Pentland Crown with different severities of black dot were planted in 1988 and 1989 at Rothamsted in fields in 4– or 7‐course rotations, respectively. Tubers treated with prochloraz (1988) or imazalil (1989) were planted in some plots, and in others Colletotrichum coccodes inoculum was added to the soil at planting. In further experiments at Mepal, Cambridgeshire in 1989 and 1990 and at Rothamsted in 1990 on sites where potatoes had not been grown for more than 15 years, large amounts of inoculum were added to the soil around disease‐free seed tubers of two (1989) or three (1990) cultivars at planting. In all experiments plants were sampled during the season and the effects of treatments on disease development, growth and yield were recorded.Disease on roots, stem bases and tubers was found early in the season and was more severe on Désirée than on Pentland Crown plants from fields in 4– or 7‐course rotations. Severity increased throughout the season and with increasing amounts of disease on the seed tubers, especially with Desiree. Disease was also found on plants from disease‐free tubers and was more severe in 1988 than 1989. At harvest, black dot on tubers was significantly more severe from severely affected than from disease‐free seed, and was most severe where inoculum, especially large amounts, had been added at planting. Fungicide treatment decreased disease early in the season but had no effect on tuber infection at harvest. In 1989 the weight loss of seed tubers during sprouting increased with increasing amounts of black dot, but the disease had little effect on plant size through the season. At harvest the yield of ware tubers (>50 mm) decreased with severe disease but total tuber yields were not significantly affected. However, at harvest in 1988 severely affected seed yielded significantly less than healthy seed.Plants grown from mini‐tubers were free from disease on sites where potatoes had not been grown for at least 15 years. Inoculum applied at planting caused severe disease on all cultivars in both years, whereas disease was slight on uninoculated plants. Inoculated plants senesced early at Mepal in 1990, but there were no significant differences in total tuber yield in any experiment. However, yields of ware tubers (>50 mm) were sometimes decreased and the total tuber number per plant increased.

Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black‐dot fungus Colletotrichum coccodes

“…Although Schmiedeknecht (1956) reported that C. coccodes was not able to infect green leaves, but could infect chlorotic leaf tissue, isolate 91·22g, shown here to be highly pathogenic to roots and to a lesser extent to stolons and tubers, is also pathogenic to both wounded and unwounded potato leaves (Guérin & Andrivon, unpublished data). Since foliage infections have been shown to cause yield losses (Barkdoll & Davies, 1992), and because tuber symptoms are responsible for a decrease in market value of the crop (Jellis & Taylor, 1974;Read & Hide, 1995), a single test might allow for a global assessment of the economic impact of black dot in the event of a significant correlation between pathogenicity to above-and below-ground organs. Such a correlation, if it exists, would also make the identification of resistance sources and breeding of black dot resistant germplasm an easier prospect.…”

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

“…However, a significant yield increase, when compared with a nonfungicide treated control, only occurred 1 of 3 years when azoxystrobin was applied multiple times to foliage during the growing season (Nitzan et al 2005). In furrow applications at planting had no measurable effect on black dot severity and seed treatments have not been effective when soil borne inoculum is present (Denner et al 1997;Read and Hide 1995).…”

“…coccodes frequently infects potato stems and other tissues early in the growing season but symptoms which include foliar chlorosis and necrosis, and signs of the pathogen in the form of sclerotia are often not expressed until relatively late in the growing season (Andrivon et al 1998;Johnson and Miliczky 1993;Pasche et al 2010). Potato yield and tuber quality can be reduced by C. coccodes (Hunger and McIntyre 1979;Johnson 1994;Mohan et al 1992;Pasche et al 2010;Stevenson et al 1976;Tsror et al 1999); however, the effect on yield is variable and yield losses are not always evident (Kotcon et al 1985;Read and Hide 1995;Pasche et al 2010;Scholte et al 1985). Even though yield losses are not always observed, C. coccodes is a serious threat to potato production (Pasche et al 2010).…”

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

“…Colletotrichum coccodes can be isolated relatively early in the development of potato and tomato in commercial fields (Dillard and Cobb 1997;Johnson and Miliczky 1993b;Read and Hide 1995;Tsror et al 1999). A long interval between infection and crop maturity could attribute to significant root colonization that can be observed in commercial fields.…”