Isolation and characterization of Ustilaginoidea virens and survey of false smut disease of rice in India

Abstract

The intensity of rice false smut disease in selected states of northwest and south India was studied. In northern Indian states as a whole, disease incidence (percentage of false smut-infected tillers) varied from 2% to 75%. In the state of Haryana, maximum infection was recorded on hybrids like PA 6444 and PA 6129 while in Punjab state, 10-20% disease incidence was recorded in popular inbred rice varieties like PR 114, PA 116 and PAU 201. In the southern state of Tamil Nadu, the disease incidence varied from 5% to 85%. A heavy incidence of the disease was noticed in variety BPT 5204 and due to this, the air above the infected field gave a black smoky appearance from a distance as a result of release of spore mass in the atmosphere. In severe cases the number of infected grains reached even more than 100 per panicle. The pathogen Ustilaginoidea virens was isolated in potato dextrose agar medium and was characterized by both pathogenicity test and molecular analysis. Under glasshouse conditions, when a conidial suspension of the pathogen was injected during boot leaf stage of the rice variety TN1, typical smut balls were observed. The identity of the pathogen was further confirmed through polymerase chain reaction (PCR) analysis using U. virens-specific internal transcribed spacer (ITS) primers. The primer pair US 1-5/US3-3 and US2-5/US4-3 amplified 380 bp and 232 bp product, respectively, which are typical for the U. virens fungus.

Isolation, Characterization and Pathogenesis of Ustilaginoidea virens Causing False Smut Disease in Rice (Oryza sativa L.)

“…In the culture medium the chlamydospore burst and appears after 30-40 days after incubation at 27 o C. The colour of the mycelium changed white to yellow and later greenish yellow resembling symptoms in the field. These results agreed with Ladhalakshmi et al, (2012) and Baite et al, (2015). In culture medium U. virens proliferated and produced creamy-white colony, flat or rose with slight undulations, mycelium fluffy, compact and leathery.…”

“…The pathogen was characterized based on its colony and spore morphology, which produced pure white coloured, raised, smooth colony margin and on continuous incubation, the colour converted to light yellow and in some cases green. Similar morphological characteristics of the pathogen were described by Hegde et al, (2000) and Ladhalakshmi et al, (2012) in rice. The isolates produced well defined colonies on potato sucrose agar medium with colony growth ranging from 3.47 to 5.57 cm after 30 days of incubation.…”

“…The disease was first reported from Tirunelveli district of Tamil Nadu State of India (Cooke, 1878). Historically being an uncommon and minor disease by occurring sporadically in certain regions (Ou, 1972;Dodan et al, 1996), now epidemics of the disease is being reported frequently (Rush et al, 2000;Singh and Pophaly, 2010;Ladhalakshmi et al, 2012). This disease is considered as farmer's friendly and locally known as "Lakshmi" (meaning wealth) disease because it is found associated with bumper yields.…”

“…However, the disease has been observed in severe form since 2001 due to widespread cultivation of high fertilizerresponsive cultivars and hybrids, heavy application of nitrogenous fertilizer and change in climate Sugha et al, 1993;Lu et al, 2009). In India the disease has been observed in major ricegrowing states viz., Haryana, Punjab, Uttar Pradesh, Uttaranchal, Tamil Nadu, Karnataka, Andhra Pradesh, Bihar, Jharkhand, Gujarat, Maharastra, Jammu and Kashmir and Puducherry (Dodan, 1996;Mandhare et al, 2008;Ladhalakshmi et al, 2012).…”

Rice false smut [Ustilaginoidea virens (Cooke) Takah.] in Paraguay

“…Disease was first reported in India (1878) and was considered as a secondary disease due to their sporadic occurrence (Ladhalakshmi et al 2012). In the 2014-2015 growing season disease survey was conducted in different rice producting areas of the country.…”