Seed discoloration in rice: Causes and their effect on seed quality
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Date
2019-07
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Rice not only constitutes the most important staple food for half of the world’s population, especially in Asia but is also an important export commodity. In India, rice crop is attacked by several bacterial, fungal, viral pathogens and pests. However, “grain discoloration” is a complex
disease due to infection by certain microorganisms on the glumes, kernels, or both. In the recent years, it is emerging as a potent threat to rice crops. Seed discoloration is considered to affect the grain quality, breaking of rice grains during milling, weight loss, exports, post-harvest losses, crop yield and ultimately badly affect the economy. The present investigation was undertaken to determine the nature of seed discoloration, causes and their effect on seed quality, seed transmission, detection and identification of different seed borne fungal pathogens associated with grain discoloration of rice. In the present study, seven types of seed discoloration namely; light to dark brown dot like spot, dark purple discoloration, light pink discoloration, eye shaped spots with ash grey center, ash grey discoloration marked by brown band and black discoloration were observed. However, light to dark brown dot like spots were found to be most predominant type of seed discoloration. Pant Basmati 1 variety exhibited maximum discoloration while, Pusa Basmati 1509 had minimum discoloration. Light pink discoloration was
present only in three varieties namely; Sarju-52, Pusa Sugandh-5 and Pant Basmati-1, while, eye shaped spots with ash grey center type of discoloration was not observed in varieties Govind, Pusa basmati-1509 and Pant Dhan -21. Twelve fungi namely; Alternaria alternata, F. oxysporum, F. verticillioides, Aspergillus niger, A. flavus, A. ochraceus, Nigrospora oryzae, Penicillium sp. Bipolaris tetramera, Curvularia lunata, Curvularia pallescens and Bipolaris oryzae. were found to be associated with different types of seed discoloration. Of the two incubation methods tested, agar plate method was found to be more efficient than standard blotter test. All types of seed discoloration reduced germinability, seedling vigor and resulted in increase in abnormal seedlings, seed rot and non-germinated seed. Lowest germination (33.00%) was recorded in the seeds showing ash grey discoloration marked by brown band while, highest percentage of abnormal seedlings (26.33%), seed rot (20.33%) and non-germinated seeds (24.33%) were recorded in the seeds showing black discoloration, light of dark brown dot like spots and dark purple discoloration, respectively. Of the thirteen fungi, four fungi namely; F. verticillioides, F. oxysporum, Bipolaris oryzae and B. tetramera were found to be transmitted from seed to seedlings. The study has shown that fungi associated with seed discoloration are major constraint in production of quality seeds of rice. Therefore, the farmers should be trained regarding production and post production activities for healthy, disease free quality seed and to minimize crop failure.
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