Management of Black Scurf (Rhizoctonia solani) of Potato through Organic Approaches

Black scurf (Rhizoctonia solani) disease of potato is becoming prominent in many potato growing districts of Gujarat state which reduce quality and market value of the produce, resulting in economic losses. The field experiment was conducted during rabi season of 2014-15 in naturally infested field with scurf pathogen at Potato Research Station, S.D. Agricultural University, Deesa (Gujarat) with the objective to find out suitable management strategies for black scurf through organic approaches (bio-agents and organic amendments). Among different bio-agents (Trichoderma viride, T. harzianum. Pseudomonas fluorescens and Bacillus subtilis) tested against black scurf, the tuber treatment with 2 per cent boric acid spray along with tuber treatment with T. viride @ 10 g/kg seed before sowing recorded the lowest disease incidence (15.33 %) and index (0.38) with highest total tuber yield (324.68 q/ha) with maximum income `2,57,414/ha. When price computed with healthy and diseased tuber yield among treatments, the maximum income variation was (`92,986/ha) recorded by the same treatment followed by the tuber treatment with 3 % boric acid spray before sowing (`68,440/ha). In case of various organic amendments tested, soil application of mustard cake @ 10 q/ha registered minimum disease incidence (37.33 %) and disease index (0.66) as compared to rest of the organic treatment with highest total tuber yield (`327.20 q/ha) with maximum income `2,65,010/ha. When price computed with healthy and diseased tuber yield among treatments, the maximum income variation was (`1,12,990/ha) recorded by the same treatment followed by the neem cake @ 10 q/ha (`56,660/ha). These organic treatments can provide an effective and economical management of black scurf of potato for cultivaters.

First Report of Potato Powdery Scab, Caused by Spongospora subterranea f. sp. subterranea, in North Dakota

Powdery scab is a serious disease of potatoes (Solanum tuberosum L.) that can cause extensive surface defects on susceptible potato cultivars. The pathogen, Spongospora subterranea (Wallr.) Lagerh. f. sp. subterranea J. A. Tomlinson, is an important concern in seed potato production because current seed certification standards in North Dakota have a zero tolerance for this pathogen. Powdery scab had not previously been identified in North Dakota. Until recently this disease was not thought to be present in U.S. commercial potato-producing areas. Powdery scab has now been shown to be more widely distributed than previously thought (1), having been identified in several locations in eastern and western North America. However, environmental conditions in North Dakota, including high soil pH, low rainfall, and high temperatures, are not considered favorable for powdery scab development. Diseased potatoes were found in a field from Griggs County, ND, in the fall of 1994 and characteristic cystosori were present in erumpent lesions on infected tubers. The field was an irrigated circle planted to three different cultivars. The cultivars Goldrush and Red Norland were symptomless, while cv. Red La-Soda was severely affected. Up to 30% of the tuber surfaces were diseased and disease incidence approached 25%. The infected crop was destroyed. Pathogenicity was confirmed by planting pieces of diseased tuber tissue adjacent to healthy seed pieces of Russet Burbank. Transmission of the obligate parasite occurred naturally by simulating conditions that were favorable for infection, acidic potting mix (Jiffy-Mix) maintained at a high water potential. Progeny plants were found to be infected on both tubers and roots after 60 days. Control plants that were not exposed to diseased tuber pieces were unaffected. North Dakota, a major seed-potato-producing state, ships seed to every other potato-producing area in the U.S. and much of Canada. Infected seed shipped to areas with a favorable environment for disease development may result in crops becoming diseased and unmarketable. The cooler temperatures and higher than normal rainfall during the 1992 to 1995 seasons may account for powdery scab development in North Dakota. Recent increases in irrigated agriculture and potato production in North Dakota could lead to the infestation of new areas, restricting the value of that land for potato production. Reference: (1) B. Christ et al. Am. Potato J. 65:583, 1988.

The Stem Eelworm, Tylenchus dipsaci (Kühn, 1858): Observations on its attacks on Potatoes and Mangolds with a Host-list of plants parasitized by it.

The nematode has been known as a serious parasite of potatoes for a number of years. The disease produced by it was first described in Germany by Kühn (1888) under the name of Wurmfäule. Shortly after this Ritzema Bos (1892) confirmed and amplified Kühn's account and carried out an experimental investigation on the disease. The present writer Goodey (1923) gave a short résumé of this earlier work and an account of the occurrence of the disease on potatoes in the Holbeach area of Lincolnshire. Buckhurst (1925) also reported the results of certain successful pot experiments in which potatoes were infected by growing in soil containing diseased tuber material. Finally, an important paper by Quanjer (1927) has appeared in which he deals with the occurrence of the disease on potatoes at Wageningen, Holland, and shows that the physiological race of worms attacking potatoes there occurs naturally on certain wild plants in the pastures and is capable of attacking a wide range of host plants both cultivated and wild. He also discusses the mode of entry of the parasite into the host and the nature of its action on the plant tissues.