An Integrated Approach to the Management of Lentil Rust | Plant Diseases

In this article we will discuss about:- 1. Introduction to Lentil Rust 2. Disease Outbreak and Yield Loss of Lentil Rust 3. Symptomatology 4. Causal Organism 5. Host Range 6. Epidemiological Studies 7. Scoring Method 8. Host Resistance 9. Biochemical Basis of Resistance 10. Cultural Management 11. Chemical Control 12. Botanical Control 13. Biological Control 14. Integrated Management.

Contents:

1. Introduction to Lentil Rust
2. Disease Outbreak and Yield Loss of Lentil Rust
3. Symptomatology of Lentil Rust
4. Causal Organism of Lentil Rust
5. Host Range of Lentil Rust
6. Epidemiological Studies of Lentil Rust
7. Scoring Method of Lentil Rust
8. Host Resistance of Lentil Rust
9. Biochemical Basis of Resistance of Lentil Rust
10. Cultural Management of Lentil Rust
11. Chemical Control of Lentil Rust
12. Botanical Control of Lentil Rust
13. Biological Control of Lentil Rust
14. Integrated Management of Lentil Rust

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1. Introduction to Lentil Rust:

Rust of lentil (Lens culinaris Med.) caused by Uromyces fabae (Pers.) de Bary has now become one of the major biotic constraints in realising the potential yield. U. fabae is a very widely distributed fungus parasitizing large number of crop plants throughout the world. U. fabae was first reported from India by Butler (1918) on lentil, pea, sweet pea and broad bean in the Indo-Gangetic plain.

Later the disease has been reported from several countries viz., Cyprus, Morocco, Sicily, Palestine, Portugal, Bulgaria, Turkey, Iran, Israel, Chile, Hungary, Syria, Bangladesh and Nepal.

2. Disease Outbreak and Yield Loss of Lentil Rust:

Severe outbreak of occurred in Larnaca district of Cyprus which destroyed the lentil crop completely over a large area. Heavy loss due to lentil rust was also reported from Sicily. Epiphytotics of lentil rust were common in Chile, Ecuador, Ethiopia, Morocco and Pakistan. Sepulveda (1985) observed upto 70 per cent reduction in the yield of lentil due to rust attack.

In India, severe outbreak of lentil rust was reported from Delhi during 1945-47. The rust appeared in epiphytotic form in the Narmada valley of Madhya Pradesh in 1978 when as much as 100 per cent losses were recorded in some fields of lentils. Naraian and Diwakar (1983) observed an outbreak of lentil rust (Uromyces fabae) in Bihar during rabi season of 1982-83.

Singh (1986) studied the effect of lentil rust on yield and found a highly negative correlation between yield and disease indices. Beniwal (1993) reported complete failure of the crop although yield losses on a plot basis varied from 30-60 per cent depending upon cultivar and disease severity.

Recently, rust appeared in epiphytotic form on lentil in Mokama Tal Area of Bihar during 1999-2000 and rust severity ranged from 10-70 per cent in different fields.

3. Symptomatology of Lentil Rust:

Prasad and Verma (1948) observed pycnia and aecia of U. fabae on lentil leaves and stems in the month of February. The earliest symptoms of the rust of lentil were characterized by the development of aecia in February or even later.

Aecial formation was preceded by slight yellowing which gradually turned brown. The aecia appeared as spots either singly or in round or elongated clusters. Uredosori were formed on both leaf surfaces.

They could be seen on stems and petioles and even on pods. Khare and Agrawal (1978) reported all three stages simultaneously i.e. aecia, uredia and telia in the centre of the patch. Uredia and aecia in the middle circle and mostly aecia on the border plants of the patch. Teleutosori were dark brown or almost black in colour smaller in size and found oftenly on the stem.

In severe cases of infection plants become stunted and showed burnt appearance. Seed size in severely infected crop was reduced appreciably. Agrawal and Prasad (1997) reported appearance of pycnia on both surface of the leaves followed by yellowish white aecia on lower surface of leaves and also on pods.

Aecia are borne singly or arranged in circular manner as small groups on leaflets. The aecia gradually turned light brown. Later, brown uredia developed on both surfaces of the leaves. Uredia were oval to circular in shape and upto 1 mm in size. In severe cases of infection leaves may shed and plants dried completely even before seed formation.

4. Causal Organism of Lentil Rust:

Uromyces fabae, the rust fungus of lentil/pea was first reported by Persoon (1801). It was then termed Uromyces fabae Pers. But de Bary (1866) changed the genus and renamed it as Uromyces fabae (Pers.) de Bary. He was the first person to make successful culture experiments of Uromyces fabae, introducing modern methods.

He sowed teliospores of Faba vulgaris on seedlings of that species and Pisum sativum and produced aecia on both hosts.

In India, Bulter (1918) reported the occurrence of rust Uromyces fabae on lentil, pea, sweet pea and broad bean and several weeds from Indo-Gangetic plain of Bihar. Prasad and Verma (1948) also reported the occurrence of U. fabae on lentil crops during the year 1945-46 and 1946-47 in Delhi. Hiratsuka (1933) reported several forms of U. fabae which were differentiated on the basis of their selective host range.

Uromyces fabae is an autoecious and heterothallic fungus forming all spore forms on lentil. Pycnia and aecia are formed mostly mixed. The details of different stages in sequence are:

Form ‘O’:

It represents pycnia (spermogonia) and the spore form pycniospore (spermatia). Pycnia were small, flask shaped and produced on the upper as well as lower surface of leaves and possess flexuous hyphae and nectar drop at the mouth. Pycnia were first reported, described and illustrated in as early as 1800 ADwhile their function was explained by Craige (1927).

Form I:

Designates aecia (aecidia) with aecisopores. Agrawal and Prasad (1997) reported that aecia were formed after diploidization by fertilization of pycnia through pycniospores or joining of pycnia of two sexes when formed side by side.

The pycnia formed on both surfaces of leaves were functional and capable of fertilization. Aeciospores were borne in the aecial cups. Aeciospores were round to angular or elliptical with fine warts, yellowish in colour and 14-22 m in diameter. The O and I spore forms were designated as cluster cup stage.

Form II:

The red rusts stage, as it is referred, have the spore fruit uredinia (uredia) with uredospores. Uredospores were light brown, spiny, elliptical, single called, pedicillate, 20-30 x 18-26 mm and possess 3-4 germ pores.

Form III:

It represents telia with teliospores in it. It is referred as black rust stage. Teleutospores were subglobose, ovate or elliptical, single called, pedicillate, thick walled with flattened apex and 25-38 x 18-27 mm in diameter. They were light brown with papillate apex.

Form IV:

Represents basidia with basidiospores. The teleutospore germinates and forms a 4-celled basidium on which four, single celled hyaline basidiospores were formed. On germination basidiospores infect the host and produced pycnia of different sexes.

Chauhan and Singh (1995) while studying morphological variation in teliospores of Uromyces viciae fabae reported that aeciospores and uredospores of isolates collected from pea, lentil, faba bean, Vicia hirsuta, V. tetrasperma, showed little variation in morphology, colour or size whereas teliospores markedly differed in size and shape.

5. Host Range of Lentil Rust:

Uromyces fabae has a wide host range and includes all the leguminous crops and many allied genera. Bilgrami (1979) and Butler (1918) have reported occurrence of this pathogen on various host species like pea, sweetpea and broad bean.

Prasad and Verma (1948) observed several species of Vicia, Lathyrus, Pisum and Lens culinaris to be susceptible to U. fabae in India and abroad. Kapooria and Sinha (1963, 1966 and 1971) noticed natural infection on Vicia sativa L. and V. hirsuta Gray, the most common weeds in the fields of lentil near Agra.

The most common weeds (Fumari parviflora; Lathyrus sp., Meliolota alba, Circicum arvense, etc.) in the fields of lentil were also found infected. They also determined the susceptibility of Vicia sp. under green house conditions.

Conner and Bernier (1982) observed that isolates from native spp. of Vicia and Lathyrus infected broad beans, pea and lentil. They assorted that the native plant spp. may have an important role in the epidemiology of rust on these crops.

Artificial epiphytotics of lentil rust in the field was created by Kramm and Juan-Tay (1984). Chauhan and Singh (1995) observed that isolates of Uromyces viciae-fabae from crops and wild Vicia spp. were cross pathogenic and did not show variability with regard to virulence. Wild hosts may serve as primary or secondary foci of infection.

Lai (2007) studied the cross infectivity of Uromyces fabae (Pers.) de Bary on different hosts. The results clearly revealed that strain of U. fabae present at Dholi was infective to lentil and faba bean only and did not show infection on other hosts such as Lathyrus odoratus, Pisum sativum and Melilotus alba under field conditions.

6. Epidemiological Studies of Lentil Rust:

The formation of uredia or secondary aecia in U. fabae is governed by environmental conditions. The optimum temperature for the germination of uredospores of U. fabae was reported to be between 16-22°C and there was no germination at 28-29°C. Temperature plays an important role in the formation of aecia and uredia.

Infection of host by aeciospores was reported to occur at relatively low temperature of 17-22°C and infection came to halt at 30°C. They also reported that aeciospores were incapable of retaining their viability from one crop season to the next. At 26-30°C, no infection was observed by uredospores.

Srivastava (1985) studied the relationship of bio-meteorological variables with disease severity under artificial epiphytotics of leaf rust of wheat using computerised multiple regression programme and observed that previous level of disease severity had constantly got highest correlation with severity. Maximum temperature and relative humidity were the next variables.

The green leaf area was negatively correlated with the disease. High humidity, cloudy and drizzling weather with 20-22°C temperature was found to be favourable for disease development and there were no infection above 30°C. Bakr (1991) reported high humidity, gloomy weather and slightly higher night temperature (20 + 2°C) to be congenial for disease development.

Broad bean and Lathyrus were found to play an important role in epidemiology of the disease. Disease progress curve was described using Gompertz and Logistic transformation for the estimation of epidemic rate, projection of future disease severity and determination of initial disease.

Environment based prediction models to predict rust a week before the actual appearance of the disease were also calculated using logistic and Gompertz equation and the variables used were temperature, relative humidity, sunshine hours, etc. in groundnut rust.

Mittal (1997) reported that atmospheric temperature around 20°C (maximum) and 5°C (minimum) with high RH (60-70% mean weekly) and light shower or drizzle favour the development and spread of rust in lentil.

Saxena (1998) reported that cloudy and drizzling weather with 20-22°C favoured disease development in lentil rust. Lentil plants were more susceptible to rust at flowering stage. Aeciospores repeated its cycle and produced aeciospores between 17-22°C temperature.

Lal (2008) studied the effect of weather variables on the severity and progress of rust on lentil cultivar Sehore 74-3 during two consecutive Rabi seasons. The symptoms appeared in the field on Feb 5, with disease severity (<2%) when the crop was 10 week old and then progressed fast between Feb 12 to March 11 to reach upto 83 per cent.

During this period of disease development minimum temperature varied from 7.7-13.0°C maximum from 23.8-28.0°C, R.H 81.0-97.0 per cent and minimum from 31.0-45.0 per cent and cloud cover at 0700 h from 0- 3.0 okta to 0-2.8 okta at 1400 h.

Thereafter, the rust showed a decline in the rate of progress. Linearization in sigmoid disease progress curve was effectively done by transforming the percent disease severity data into Logits and Gompits. Logits effectively linearized un-transformed data set in the range of-4.306 to 2.623.

These data sets were further used to calculate and compare infection rates (r and k). Regression analysis revealed that minimum temperature, maximum RH and maximum cloud cover had significant and positive effects on rust progress while maximum temperature and minimum RH exhibited significant and negative effect on disease progress.

Progress of rust in relation to weather variables revealed that logistic equation best fitted the regression model followed by Gompertz and untransformed equations. Disease severity values calculated from the equation derived from the Logit transformations were very close to the observed values.

7. Scoring Method of Lentil Rust:

Agrawal (1976b) used the modified cobb’s scale which was based on leaf area covered by the disease and recommended for wheat rust.

Khare (1978) recommended a five point scale for scoring rust of lentil as given below:

From the numerical ratings, Disease Index (DI) is calculated as given below:

Based on the Disease Index, the test lines are then grouped as follows:

Singh and Sokhi (1980) used a scale for grading host varieties based on reaction of the host tissues against the pathogen as follows:

i = No symptoms

0 = Chlorosis/necrosis, no pustules formed

1 = Chlorosis and/or necrosis, few small pustules formed

2 = Chlorosis, little or no necrosis, few small pustules formed

3 = Chlorosis, many large and abundantly sporulating pustules formed

4 = No chlorosis, many large abundantly sporulating pustules formed.

Mishra (1985) used 1-9 point scale for grading, adopted from Ascochyta blight, of chickpea as follows:

1 = No pustules visible

3 = Few scattered pustules usually seen after careful search

5 = Pustules common on leaves and readily observed but causing no apparent damage

7 = Pustules very common and damaging but not observed on petioles and stems

9 = Pustules extensive on all parts, seen on leaves, petioles and stems and kill leaves and other plant parts

Subba Rao (1991) devised a 9-point scale for scoring infection of groundnut (Arachis hypogea) by rust (Puccinia arachidis) given below:

8. Host Resistance of Lentil Rust:

A -large number of lentil lines/genotypes have been scored for resistance to rust (Uromyces fabae) in India and abroad. The entries exhibited resistant reaction in different countries are presented in Table 9.1.

9. Biochemical Basis of Resistance of Lentil Rust:

Reddy and Khare (1984a, b) studied the effect of rust infection on biochemical parameters of resistant and susceptible varieties of lentil and reported that chlorophyll content decreased after inoculation while quantity of sugars, total phenols, orthodihydric phenol and free amino acids increased after inoculation.

They also reported that resistant cultivars had more phenol P, K, S, Zn, Fe and Cu whereas susceptible cultivars had greater content of free amino acids, N, protein sugar and Mn. There were higher levels of reducing and non reducing sugars, N and Zn in susceptible cultivars.

Singh (1998) while working on biochemical changes in safflower leaves infected by rust reported higher amount of chlorophyll, amino acids and orthodihydric phenols in the tolerant cultivars whereas total soluble and non reducing sugars were more in susceptible cultivars.

They also reported that total chlorophyll, chlorophyll “a” and “b”, total amino acids and soluble sugar declined whereas total and orthodihydric phenol content increased after rust infection.

Mathar and Vidyasekaran (1978) made an attempt to assess the biochemical factors responsible for resistance to rust in sunflower caused by Puccinia helianthi and reported that resistant varieties had more total phenol, total soluble sugar whereas susceptible varieties had more reducing and non reducing sugar.

They also reported that reducing sugar, non reducing sugar and total sugar decreased in infected leaves while apparently healthy leaves showed increased level of reducing, non reducing and total sugar whereas no significant reduction was observed in infected leaves.

Vidyasekaran (1974) studied the possible role of sugars in rust resistance in Italian millet and reported that susceptible varieties had more glucose, sucrose and total sugar than the resistant varieties. They also reported that glucose, fructose and sucrose contents increased in both susceptible and resistant varieties due to infection. The increase was more marked in the infected susceptible varieties.

Pozsar (1966) reported increased level of total nitrogen and protein content of the rust infected bean leaves in bean Uromyces phaseoli pathogen host complexes.

Nitrogen fraction of the leaves was considerably higher at the infection centre than in non infected parts of the leaf, an indication of intensified protein synthesis in the diseased parts which might be due principally to protein synthesis of the pathogen rather than the host.

They showed that tritium labelled glycine fed to infected leaves was incorporated mainly into the fungal mycelia and uredospores of Uromyces phaseoli.

Lal (2008) studied biochemical and nutritional changes in lentil leaves infected by Uromyces fabae and reported that the amount of reducing and total sugar content were significantly higher in leaves of resistant than in susceptible varieties. The increased level of reducing and total sugar content in the infected leaves was observed in all the varieties.

Rust infected leaves of lentil recorded lower level of total phenol than healthy leaves. Per cent nitrogen in dried rust infected leaves of lentil showed higher level as compared to healthy leaves while lower percentage of phosphorus and potassium were recorded in infected leaves.

10. Cultural Management of Lentil Rust:

Prasad and Verma (1948) recommended destruction of the crop refuse after the harvest irrespective of the host. Singh and Dhingra (1980) reported that early sowing (November) caused high disease severity compared to late sowing (December). Shukla and Amin (1991) reported increase in rust intensity on susceptible variety (Lens 830) with delayed sowing.

Mittal (1997) studied the effect of date of sowing on disease occurrence and yield of lentil and reported that disease incidence gradually declined from the first to last sowing dates.

The rust was started in mid-March and was observed more in early sown (9th and 19th October) sole crop of lentil. Khare (2000) reported that rust lentil (Uromyces fabae) survived as telial stage on diseased plant parts which got mixed with the seed.

The teleutospores germinated under favourable conditions and the aecial stage appeared on the foliage. Lai (2006) studied the effect of date of sowing and spacing on rust severity and yield of lentil and reported that 15^th October sown crops recorded maximum disease severity (51%) and lowest grain yield (533 kg/ha) whereas maximum disease severity (47%) was recorded in 15 cm spacing.

11. Chemical Control of Lentil Rust:

Prasad and Verma (1948) reported the control of lentil rust by treating the seeds with Agrosan GN which eliminated the inoculum from the seeds. Singh (1985) studied the effect of seed treatment on lentil rust (Uromyces fabae) development and reported that seeds treated with Vigil (Diclobutrazole) remained free from rust infection upto 60 days of sowing while Bayleton (Triademefon) gave light disease reaction 50 days after sowing.

The import of seeds of lentil from South American countries was prohibited in USA due to seed transmitted nature of the disease. Agrawal (1976a) found Hexaferb and Dithane M-45 at 2500 ppm each to be very effective in checking the disease and increasing the yield of lentil.

Singh (1985) studied the relative efficacy of fungicides against lentil rust and reported Dithane M-45 to be most effective as spray against U. fabae. Out of the seven fungicides evaluated against lentil rust, Wettasul (0.3%) gave the excellent result in controlling the disease and increased yield closely followed by Dithane M-45 which significantly increased the yield and reduced the disease index.

Calixin gave the phytotoxic effect while laird variety showed sensitivity reaction towards Bayleton and Plantvax, yielding less in the treated than in the untreated plots.

Sepulveda and Alvarez (1989) studied the effect of fungicides against lentil rust in Chile and reported that a mixture of Triadimefon and Propineb when applied as foliar spray at the rate of 0.5 + 2.0 kg/ha at pre-bloom, full-bloom and pod maturity stages resulted in the best disease control and the highest yield.

Pandey (1995) treated lentil cv. PL 406 with 8 fungicides to control Uromyces fabae and found that Triademorph (Calixin) gave the best control followed by Metiram (Campogram) and Benomyl (Benlate).

Ayub (1996) assessed 6 fungicides for their ability to control Uromyces fabae in lentil and reported that Tilt 100 EC (0.05%) gave the best control, reducing the disease intensity and increasing the pod yield. Folicur (Tebuconazole) (0.1%) and Calixin (0.1%) (Tridemorph) were also effective against the pathogen.

Singh and Singh (1997) studied the effect of chemicals on pea rust caused by Uromyces fabae and reported that all the fungicide Topsin M, Calixin, Benlate, Bavistin, Indofil M- 45, Indofil Z-78, Ridomil and PP 450 significantly reduced the disease and increased grain yield of pea but PP 450 was the most effective fungicides giving 74.7 per cent disease control and recommended 3 sprays at 10 days intervals of PP 450 at the rate 0.1%, or Calixin at the rate 0.06 per cent.

Lal (2006) studied the effect of fungicides both as seed treatment and as foliar spray against rust of lentil under field conditions and reported that seed treatment with propiconazole at the rate 1.0 ml/kg seed) showed minimum disease severity.

Seed treatment minimized the initial inoculum of the pathogen and prevented the crop up to 70 days from infection. Foliar spray of propiconazole at the rate 0.1% was the most effective fungicide in reducing the disease (18.15%) and increasing the yield of lentil (1089 kg/ha).

12. Botanical Control of Lentil Rust:

Disease management through plant products is gaining importance in view of their selective properties, low cost and safety to ecosystem. Many plant products have been identified to be effective in the control of plant diseases. Among 5280 plant species tested, 346 plant species possessed fungicidal, 92 bactericidal, 90 antiviral properties.

Ganpathy and Narayansamy (1994) tested 53 plant products to control rust (Puccinia arachidis Speg.) disease of groundnut under laboratory conditions and reported that water extracts of neem (Azadirachta indica) leaf, neem cake and neem oil one percent inhibited the disease. Neem oil caused deformation of rust uredospores.

There was no germination of uredospores of Puccinia arachidis on groundnut leaves sprayed with extracts of neem seed,-young neem leaf, eucalyptus, red periwinkle, nerium, coir pith and fungicides carbendazim and mancozeb.

Amaresh and Nargund (2001) studied the effect of plant extracts on Puccinia helianthi, causing rust of sunflower and reported that plant extracts of Allium cepa, Allium sativum, Pongamia glabra, Nerium oleander and Melia azadirach were effective in inhibiting the uredospore germination of P. helianthi.

Lai (2006) studied the effect of botanicals as foliar spray against rust of lentil under field conditions and reported that neemol at the rate 0.2% showed least disease severity (39.0%), the best disease control (52%) and grain yield (844 kg/ha).

13. Biological Control of Lentil Rust:

Biological control is a promising alternative over fungicide application but it is normally not as effective as chemical control when used in the same ways to prevent germination of and infection by Sclerotinia sclerotiorum at its infection court. Carrion (1999) compared the use of agrochemical package versus the application of Verticillium lecanii as a biocontrol agent against bean rust (Uromyces appendiculatus).

They observed final incidence and severity for biocontrol (BC) plots as 56 per cent and 17 per cent, respectively whereas agrochemical plots showed 98 per cent and 85 per cent incidence and severity, respectively.

Verticillium lecanii proved to be more effective than agrochemicals and significantly reduced the incidence and severity of attack by rust. Carrion (1999) also reported the first use of V. lecanii as biocontrol agent of bean rust under plantation conditions.

Information concerning use of bioagents for management of lentil rust is not available in literature. Lai (2006) studied the effect of biocontrol agents as foliar spray against rust of lentil under field conditions and reported that foliar spray of T. viride or Gliocladium virens formulations resulted in low disease severity (41- 43%) and maximum disease control (43-45%).

14. Integrated Management of Lentil Rust:

Lal (2006) conducted field trial on integrated disease management against lentil rust and reported that a combination of delayed sowing (15 days later than normal sowing), seed treatment with propiconazole (at the rate1.0 ml/kg seed) and two spraying (at the rate 0.1%) gave the highest disease control (83.0%) and yield (1233 kg/ha).