Seed Discolouration in Rice- Discussed ! | Plant Diseases

In this article we will discuss about:- 1. Introduction to Rice 2. Damage Caused to Rice 3. Occurrence and Distribution 4. Predisposing Factors 5. Control of Diseases.

Introduction to Rice:

Rice (Oryza sativa L.) is one of the most important cereal crop of the world. About 90 per cent of rice produce in world is consumed only in Asia, while, China is the leading producer of rice (112.4 million tonnes per year) followed by India (87 million tonnes).

India has largest area under rice (44.6 million ha) cultivation in the world. It is the staple food crop and provides food security for its more than two-third population, and is a means of livelihood for millions of rural households.

The production of rice comprehended, 87 million tonnes during the year 2003-2004 from a cultivated area of 44.6 million hectares. It has ample cultivation in all the states under diversified agro-ecosystems, upto an altitude of 2200 m above mean sea level (a.m.s.l) in hilly tracks of north zone.

Over 3000 rice varieties are prevalent or under cultivation in various and perceptible parts of the country, which differ in their crop heritage comprised with maturation periods, grain quality and biotic stresses.

In the Jammu and Kashmir, rice is adopted and ascended as the most important cereal q»op as staple food of the people, especially for the people of Kashmir valley.

It occupies an area of about 0.259 million ha with a production of 0.495 tonnes, the annual contribution from Kashmir being 0.304 metric tonnes from an area of 0.143 million ha with an average production of 2.09 metric tones per hectare during 2003-2004 (Anonymous, 2004) which is far below the national productivity average.

Inspite of quite favourable adaphic and environmental conditions for rice cultivation in the valley, the yields have not been encouraging due to constraints in rice cultivation are essentially similar to those associated with conditions of temperate regions, such as low temperature, high altitude, short growing season, physiological disorder and biotic stresses.

Among biotic stresses diseases are major, abeyances in rice production. Many of them namely, blast (Pyricularia grisea), sheath blight (Rhizoctonia solani), brown spot (Helminthosporium oryaze) and glume discolouration are ascribed by Anwar, 2000, however, becoming as serious problem in rice cultivation that causes heavy losses in the quality and quantity of grains.

Several biotic and abiotic factors are responsible for discolouration of rice seeds. Glume discolouration is term for the alteration in colour of mature seed from its original colour and seeds possess series of problems in seed certification programme. The symptoms of false smut and bunt are distinctly clear and the seeds affected by them could be easily identified.

However, other abnormalities are caused by a number of fungi either singly or in association, invading seeds before or after harvest. All these maladies of rice seeds can be broadly termed as seed discolouration which are appeared externally on the glumes or internally in kernels or both.

In Jammu and Kashmir, the glume discolouration of paddy has perceived serious proportion both in grain and seed production programme in temperate ecosystem area, where it appears to be surpassing the importance of even previously known major constraints.

The appearance of glume discolouration by various organism before or after harvest the extent of which varies according to season and also within the season on short, medium and long duration rice cultivars grown under rice growing domain of Kashmir valley.

They produce different types of symptoms, depending upon the organism involved in the degree of infection. Sometimes there are distinct black dots usually caused by fungus fruiting bodies are other structures on normal or bleached areas of the glume.

In other cases there are brown or blackish blotches, which may be flecks, are large enough to cover the inter-glumes. Often the lesions are pale or greyish in the centre with a dark brown margin. About thirty three fungal species belonging to 2 genera are responsible to cause glume discolouration in India, which reduce yield and also affect the quality parameters.

It reduces germination, causes coleoptiles or radicle decay, or both, resulting in chaffy grain and ultimately causing low yield. The infected plants produce partially filled discoloured grains with reduced viability and quality.

Once it can be concluded the history of glume discolouration is difficult to trace because of involvement of complex of fungi. The pathogen on different parts of plant are lodged on the seeds through the agencies of winds, raindrop insects etc. where they remain either as contaminants or as infectants, producing either visible or non-visible symptoms depending upon environmental conditions.

These pathogens affect seed germination, quality and yield or rice. The grain discolouration caused by several micro-organisms had not been considered a severe problem. It is gaining importance in almost all rice growing areas of world in recent years.

Recent findings on the various aspects of disease i.e., occurrence, symptoms and effect, association of mycoflora with discoloured grain, inoculation techniques, scoring system, detection of mycoflora in discoloured grains, role in seed health, and management practices have been suggested by Biswal (2003).

Damage Caused to Rice:

These microorganisms have various effects on the grains. When infection is by field fungi, the main effect are reduced viability and grain quality; seedling blights and other diseases may occur when the seeds are planted. When infection is by storage mode, besides a reduction in viability and grain quality, these may also be production of toxins.

Uraguchi (1942) reported a toxin formed in yellowed rice due to Penicillium sp. Lizuka (1958) also found a toxin which was poisonous to rice. Tran-Vy (1958), however, reported that rice infected by P. citrinum was not toxic to rice. In view of present knowledge on the occurrence of mycotoxins in fungus infected cereal grains, the toxic aspect of fungus – infected rice grains should be further exposed.

Occurrence and Distribution of Rice:

The prevalence of microoganisms causing glume discolouration of paddy varies widely. Tullis in 1936 has isolated different fungi associated with discoloured grain from USA.

The most common were Alternaria spp, Curvularia lunata, Alternaria padwickii and Phoma spp. while Drechslera oryzae and Fusarium spp. were found rarely but Cladosporium herbarum, Helicoceras oryzae and Penicillium spp. were encountered occasionally.

Baldacci and Picco (1948) from Italy reported that out of 50-55 per cent discoloured rice grains, 13.4 per cent exhibited Alternaria spp. 23.4 per cent Cochliobolus miyabeanus, 1.2 per cent Fusarium spp. and 4.9 per cent Pencillium spp. whereas, 30.8 per cent grains were not found affected with any fungus.

Similarly, Padmanabhan (1949) reported Alternaria padwickii to be predominant over Cochliobolus miyabeanus, Curvularia lunata and Nigrospora sp. Subsequently, Rae and Salam (1954) found that sixty per cent of discoloured grain in Hyderabad, India yielded five species of Curvularia.

Besides, Shafait (2007) reported Helminthosporium oryzae, Curuvularia lunata, Alternaria oryzae, Rhizoctonia solani, Phyllosticta oryzae, Nigrospora sp. Fusarium moniliforme from discoloured grain with variable occurrence pre-harvest stage of rice cultivar in Kashmir, India.

Pavgi and Singh (1969) had been reported that Helminthosporium oryzae (Cochliobolus miyabeanus), Phaeosphaeria oryzae and Phyllosticta oryziae were frequently found as parasitic fungi on rice grains from Varansi. Vaidehi and Rama Rao (1974) has also been isolated 28 fungi from the grains of rice varieties namely IR-8, IN-1 and ADT-27.

The most dominant fungal species were Alternaria, Curvularia, Fusarium, Helminthosporium, Nigrospora, Pyricularia, and Rhizoctonia,. In Philippines, some fungi are found to penetrate the endosperm of rice grain such as Curvularia while as, Fusarium and Nigrospora. are mostly perpetuated on glume.

Ahuja (1980) advocated that grain spotting known as glume discolouration (GLD) or dirty panicles appeared sporadically in Haryana on Basmati-370, later emerging panicles of IR-8 and Jaya. They have further reported that 7 per cent discoloured grains were recorded in IR-8 and 31.5 per cent in Basmati-370.

Various species of mycoflora isolated from harvested grains viz., Trichoconis padwickii, Curvularia lunata, Drechslera oryzae which were found to be predominant over Fusarium sp., Phoma spp. and Pyricularia oryzae. Roy (1983) has recorded that twenty two fungi which were associated with about ninety three per cent of spotted paddy grains.

The common and prevalent fungi were, Alternaria padwickii, Drechslera oryzae, Curvularia lunata and Fusarium semitectum. Zakaria and Zaid (1983) have investigated that pericarp of seeds is affected by Pyricularia oryzae, Curvularia lunata and Drechslera oryzae whereas endosperm also contained all these three alongwith, Richoconis padwickii, whereas, Pyricularia oryzae.

Cochiliobolus miyabeanus and Nigrospora oryzae were isolated from rice embryo. Ahmad and Prasad (1985) have also been observed that Curvularia spp. is frequently associated with seed while Jhu and Prasad (1985) isolated Drechslera oryzae, Trichoconiella padwickii, Fusarium spp. Curvularia sp., Aspergillus sp. and Penicillium spp. from seeds of different rice cultivars.

Basak and Mridha (1985) have reported occurrence of Alternaria spp. Curvularia spp. Dreshslera oryzae, Fusarium moniliformae, Nigrospora oryzae which were also varied in prevalence with respect to variety and locations. Mishra and Dharamvir (1985) examined discoloured seeds of paddy from Bihar, Jammu, Hyderabad and Cuttack and total of 28 fungi were detected from the examined seed lots.

Drechslera oryzae and Curvularia lunata from Bihar, Dreschlera oryzae and Alternaria alternata from Jammu, Phoma spp. Curvularia lunata and Nigrospora oryzae from Hyderabad and Curvularia lunata from Cuttack were found dominant.

Overall, only Curvularia lunata was dominant in all samples collected from different states. Rodriguez (1988) have been found the incidence of Dreschlera oryzae (Cochliobolus miyabeanus) and Alternaria padwickii from grain discolouration in Venezuelan.

Ziegler and Alvarez (1989) surveyed and collected discoloured rice grains from Colombia and elsewhere in South America, non-fluorescent Pseudomonas spp. were associated with discoloured seeds. They further suggested and confirmed that Pseudomonas avenae can be eradicated from seeds samples with dry heat treatment of 65°C for 6 days.

Wu (1994) has also isolated a total of 25 fungi from major rice growing areas in Taiwan and reported that Phyllosticta glumarium is more frequent on rice seeds from Northern and Eastern Taiwan while Curvularia lunata and Alternaria padwickii were also more dominant on seeds from southern Taiwan.

Sachan and Agarwal (1995) have been observed Alternaria alternata and Helminthosporium oryzae caused ash grey and black discolouration in seed respectively, whereas, due to Curvularia lunata and Fusarium graminearum, Fusarium moniliforme, eye shaped and light pink discolouration appeared in seed coat, endosperm and embryo of seed respectively.

Vaid (1994) reported that glume discolouration is caused by complex of fungi with the species of Alternaria, Curvularia, Fusarium, Helminthosporium, Nigrospora, Phyllostic and Sclerotium. These fungal infection increased protein and decreased amylase content as well as decreased the hulling and milling quality of paddy.

Jaiswal (1996) observed highest incidence of Helminthosporium oryzae Alternaria tenuis, Curvularia lunata. Rhizoctonia solani, Dreschslera sp. and Fusarium moniliformae on seed of paddy collected from different parts of the Uttar Pradesh, India.

Sharma (1997) have been detected rice samples from various rice growth location in the districts of Himachal Pradesh viz., Bilaspur, Chambal, Hamirpur, Kangra, Kullu, Mandi, Sirmaur and Una and observed that the extent of grain discolouration varied from 4.35 to 79.32 per cent.

The fungi viz., Alternaria alternata, Aspergillus niger, Curvularia lunata, Fusarium spp. Helminthosporium oryzae, Nigrospora oryzae, Phyllosticta glumarium, Penicillium spp. and Sclerotium oryzae are attacked at booting, heading, milking and doughing stages of crop.

The heading stage is found to be most vulnerable to grain discolouration. Gutierrez (2002) have been used blotter test and identified sixteen fungi associated with rice grain under irrigated ecosystem in Argentina.

Picco (2004) isolated various species belonging to the genus Fusarium from discoloured grain of rice. They found that these fungal species are produced broad toxic compounds and some of these toxins such as deoxynivalend and fumonisins have been shown to possess phytotoxic activity and cause disease symptoms on the plants during the infection process.

Most of storage moulds are species of Aspergillus and Penicillium, Mucor and Rhizopus spp. are also found and occasionally species of Chaetomium, Dematium, Streptomyces and Verticillium have been reported.

Del Prado and Christensen 91952 found that Aspergillus glaucus, A. niger, A. terreus and Penicillium sp. were most common on samples from Lovisiana and Fusarium sp. A. niger and Hormodendrum sp. from Surinam.

Predisposing Factors of Rice:

Infection of grains by field fungi is greatly affected by climatic conditions, particularly moisture. It takes place from some considerable time before the grains mature up to the period just before storage. Tisdale (1922) stated that stackburn disease is likely to develop in a wet- season when the rice remains in the field and the stacks do not dry out.

Martyn (1936) recorded severe infection by Curvularia lunata during a wet season. Ito and Jwadare (1934) found red blotch of grains to be favoured by lodging of the plants, when the ears touch the ground. Much of the rice in Asia does not get threshed immediately after cutting but is piled or stacked for some time in the field. Moist weather at this period may induce discolouration of large number of grains.

In storage relative humidity and temperature greatly affect the development of saprophytic moulds. Ghosh (1951) found that the mould development depend more on the relative humidity of the storage atmosphere then the moisture content of the grain development and being fairly repeat on all samples exposed to 65-100 per cent relative humidity.

Naito (1953) found heavier infection by Penicillium and Aspergilus at 20°C than at 10 or 30°C, and a moisture content of 18-20 per cent of most conducive to mould growth. The moulds holds moisture and this in turn hastens deterioration of the rice. This was accompanied by more grain discolouration particularly at low rate of aeration.

Control of Diseases in Rice:

Prevention of mould infection on grains depends upon both pre-and post-harvest measures including those taken during cutting, threshing and drying. Condition for storage of rice in the USA has been reviewed by Dachtler (1959). Low moisture, aeration and avoidance of high temperatures are essential.

Higher moisture content together with high temperature is most conducive to mould development. Schroeder (1964) reported that the use of infrared drying and additional treatment with sodium propionate (500 ppm) reduced infection by field fungi.

Various research workers have also attempted the management of glumes discolouration caused by the use of fungitoxicants. Sinclair (1981) reported two sprays of benomyl 50 WP at the rate 0.1% at 15 days of interval can be reduced the infection of the glumes discolouration and increased the yield.

Arunyanart (1981) have been tested seven fungicides viz., carboxin, copper oxychloride, edifenphos, MBC + mancozeb, mancozeb, polyoxin Z and sisthane which were controlled seed discolouration of rice at heading stage and found that plants treated with polyoxin-Z gave the highest number of healthy seeds per panicle, followed by sisthane and edifenphos .

Duraisamy (1982) reported that discolouration caused by Helminthosporium oryzae, Alternaria padwickii and Curvularia lunata can be controlled by application of guazatine, IBP and mancozeb on panicles at the milk stage of crop.

Govindarajan and Kannaiyan (1982) observed that edifenphos and copper oxychloride are most effective fungicides against rice grain infection caused by seed borne pathogens viz., Helminthosporium oryzae, Nigrospora oryzae and Curvularia sp.

Singh and Chand (1996) reported that edifenphos (0.1%) and mancozeb (0.2%) remarkably controlled the seed discolouration. Zeigler (1987) have found highest efficacy of carbendazim (0.1-0.2%) in controlling grain discolouration. Ray (1988) established that mancozeb and bavistin efficiently controlled the grain discolouration in rice.

Rodriguez (1988) reported that a single chemical or in combination of different chemicals at 10 per cent panicle emergence viz., iprodione at the rate 1 kg/ha, iprodione + edifenphos at the rate 0.85 kg/ha + 1 lit/ha, iprodione + zineb at the rate 0.75 kg/ha + 2 kg/ha and edifenphos at the rate 1 lit/ha are reduced disease infection while crop treated with iprodione alone had the best and healthy appearance of panicles in relation to severity of glume discolouration.

Kapkoti and Pandey (1990) noted that dithane M-45, agronsan GN and dithane-Z- 78 are reduced the fungi causing glume discoluration but Aspergillus niger was only controlled by agrosan GN, which resulted in significant increase in seed germination of rice.

Mishra and Dharamvir (1991) reported that fungicidal seed treatment with agrosan GN, captan, vitavax (carboxin), bavistin (carbendazim) + thiram, carbendazim, thiram or thiophanate methyl provided protection to seed against fungi causing discolouration and improvement in seed germination.

Ahmad and Mir (1991) have recommended the foliar spray of edifenphos together with mancozeb and carbendazim as a seed dressing (0.1-0.2 g/kg seed) were found effective in reducing brown spot severity and discolouration of grain and also found remarkable increase in yield of paddy.

Geeta and Sivaprakasam (1993) reported that seed treatment with tubler of pyroquilon (0.25%), mancozeb (0.3%) or carbendazim (0.2%), most effective in controlling seed borne diseases. Ray Pritima (1993) revealed that carbendazim at the rate 0.1% was found effective in controlling the grain infection, even though there was significant variation in percentage of grain discolouration.

Viswanathan and Narayanaswamy (1993) found that tricyclazole at the rate 2 g/kg and carbendazim at the rate 4 g/kg were most effective than other fungicides viz., mancozeb, captan and thiram.

When seeds were treated by shaking method with these fungicides or by wet application (10 g seed + 1 ml water + fungicides), the seed germination increased by 64 per cent, while 68-90 per cent with wet application, moreover seed treated with these fungicides also improved growth and vigour of seedling.

Vaid (1994b) have tested six fungicides at the rate 2 g/kg of seed to improve the germinability of discoloured grain. They found that carbendazim was most effective, hence, increased germinability of discoloured grain by 20-30 per cent followed by triadimefon.

Deka (1996) found that application of fungicides at the boot leaf stage followed by spray with common salt (10%) 20 days after 50 per cent flowering is more effective in reducing grain discolouration that only fungicides at both stages. However, carbendazim (0.1%) followed by common salt is found most effective.

Ali and Deka (1996) articulated that bavistin at the rate 1g/kg seed was most effective treatment more than seventy per cent seed germination even after eight months of storage. Saifulla (1996) revealed that mancozeb and tricyclazole were significantly superior over all treatments in highly discoloured seeds of paddy.

Malavolta and Takada (1997) have been reported tubeconazole (125 g/ha), chlorothalonil (1250 g/ha), tricyclazole (187.5 g/ha), propiconazole (125 g/ha) and kasugamycin + stannic triphenyle acetate (20 ml + 100 g/ha) were proved tobe arsenic against rice grain discolouration.

Santos (2000) found that least incidence of grain spot of neck blast appeared by applying difenconazole and mancozeb followed by difenaconazole + tricyclazole.

Simultaneoulsy, Coutinho (2000) treated rice seeds with iprofione and thiram to evaluate the incidence of Cochliobolus miyabeanus and found that this treatment proved most effective against incidence of Cochliobolus miyabeanus in rice seed and also increased the seed germination and its vigour.

Tasleem-uz-Zaman (2000) found the control of glume discolouration in paddy by using as foliar sprays as well as seed treatments of topsin M (thiophanate methyl), anvil (hexaconazole) and benlate (benomyl).

Malavolta and Bedendo (2004) reported that seed borne infection by Bipolaris oryzae, Microdocliium oryzae and Phoma sorghina in rice, can be removed when procloraz is used for seed treatment. Subsequently chlorothalonil and imiricoctadine were also seen effective.

Pizzatti (2004), revealed the percentage of discoloured caused by Cochliobolus miyabeanus, Magnaporthe grisea and Sarocladium spp. decreased by delaying the date of sowing and fungicidal spray with carbendazim.

Shafait (2006) has been studied many fungi which cause glume discolouration of rice in Kashmir India and recommended two sprays of of carbendazim 50 WP (0.1%) bitertanol 25 WP (0.4%) or tricyclazole 75 WP (0.1%) to control the glume discolouration at pre harvesting stages of crop.