Screening of Mustard Varieties and Temperature Effect on White Rust and Alternaria Blight

Mustard (Brassica juncea L.) Czern. and Cosson is an important oilseed crop which occupies about 80 per cent of the total cropped area under oilseed crops in India. Total global area under rapeseed and mustard is about 26.09 m ha with total output of 571,880 tonnes of mustard at an average yield of 1-1.5 tons ha^-1 (FAO, 2016). India is the fourth producer of mustard contributing to around 11% of world’s total production. It accounted for an estimated production of 32.10 MT with 26.21 thousand hectare of area and 1224 kg/ha in 2016-17 (Anonymous, 2017) and production of edible oils was about 7.05 Mt (Jha, 2017). Rapeseed and mustard yields were lower in India compared to other rapeseed and mustard producing countries such as Germany (3811 kg/ha), France (3240 kg/ha), China (1834 kg/ha) and Canada (1769 kg/ha) as well as the world average (1849 kg/ha) (Kaur and Grover 2020). In India, although rapeseed and mustard is cultivated in 13 states, production in Rajasthan, Uttar Pradesh, Haryana and West-Bengal with their respective share of 45, 13, 11 and 8 per cent accounts for 77 per cent of the total production of rapeseed and mustard in the country (Kaur, 2017). Mustard crop requires about 18-25°C temperature, low humidity, practically no rains especially at the time of flowering.
       
Many biotic and abiotic stresses are responsible for reducing the production of mustard. White rust caused by Albugo candida Kuntze and Alternaria blight caused by Alternaria brassicae (Berk.) Sacc. have been reported to be most wide spread and destructive fungal diseases of rapeseed mustard throughout the world (Kolte, 1985). In India, both these diseases are quite common, while, combined infection of downy mildew and white rust on mustard have been observed rarely because of dry cool weather in this region. Yield losses from 23 to 54.5% due to both phases (leaf and stag head) of white rust and 17-48% due to Alternaria blight have been reported from India (Saharan et al., 1984 and Saharan, 1991). Hence, the present study was taken up to identify the sources of white rust and Alternaria resistance in different mustard cultivars that can be utilized in the breeding programmers.

Sixteen mustard varieties viz., Jagannath, Radhika, Hybrid-805, Dev-142, Nandi bull, Araurali, 45L46 Lohiya, Kranti, Pusa Mahal, PusaVijya, PM-31, Rh-149, PT-305, PM-44, Kanchan and MYSL-203 were screened at the Research Farm, Amar Singh (PG) College, Lakhaoti, Bulandshahr during rabi crop season of 2021-22 for check the disease severity of white rust and Alternaria blight disease. All mustard varieties were raised in triplicate in rows. Seeds of mustard varieties were supplied by local markets of Meerut and Bulandshahr. Seeds were sowed on 15^th November 2021. Randomly ten plants from each row were selected and tagged for taking observations for initial appearance of disease symptoms and the disease severity. Data collection was started at 35 days after sowing. All the data were collected once in a week.
 
White rust disease severity
 
Leaf area infected was observed randomly from each plot. Ten plants per row were randomly selected for the observations. Based on infected area, leaves of each plant were rated as per rating scale (0-9) (Table 1) and the disease severity was calculated by using the following formulae:     
 
Alternaria blight disease severity
 
Leaf area infected was observed randomly from ten plants per row under different varieties by using disease rating scale (0-5) (Table 2) and per cent disease index was calculated on the basis of following formulae:                           

Symptomology of white rust
 
One of the most identifiable symptoms of white rust is the white blistering on the undersides of infected leaves (Fig 1). Other disease symptoms include chlorosis, necrosis, defoliation, swelling and distortion of flowers, stunted growth and leaf curling. If the disease becomes systemic, an infected plant may form swollen, twisted floral parts called “stagheads.” If a plant is infected through the soil or seed, stagheads will most likely appear later in the plant’s life (Fig 2). The symptoms of rapeseed-mustard white rust observed in present studies were also reported earlier by Armstrong in 2007.
 

 

 
Symptomology of Alternaria blight
 
Symptoms of the Alternaria blight were characterized by evolution of spots on leaves, stem and siliquae. It first symptoms are appear on the lower leaves in the form of small light brown to blackish in color, circular or irregular lesions, which later on turns black due to the appearance of spore masses with disease evolution symptoms are show on the upper leaves, stem and siliquae of plant (Fig 3). These spots enlarged and combine forming large sized spots. In some cases, centre of these spots light brown dot surrounded by the number of dark alternating concentric rings. The symptoms of rapeseed-mustard Alternaria blight observed in present studies were also reported earlier by Nayyar et al., (2014).
 

 
Varietal response against white rust
 
Among the disease management approaches, the use of resistant varieties is considered to be the best and cheapest method of managing the plant disease. The present study was therefore, carried out for finding out the source of resistance against white blister of mustard caused by Albugo candida, under field conditions and results are presented Table 3. It was observed that seven varieties viz., Jagannath, Radhika, Hybrid-805, Nandi bull, Kranti, Pusa Mahal and PM-31 were observed to be highly susceptible to the disease. Five mustard varieties viz., Dev-142, Arauvali, 45L46 Lohiya, PusaVijya and RH-149 were observed susceptible to be white rust disease. Remaining four varieties viz., PT-305, PM-44, Kanchan and MYSL-203 were found as resistant (Immune). It was also observed that appearance of white rust symptoms on the leaves started from 05th January. Temperature on 05^th January was range minimum 7°C to maximum 19°C. The highest incidence of white rust on leaves was observed from 16^th January to 08^thFebruary. Temperature from 16^th January to 08^th  February was ranging minimum 8-10°C and maximum 20-22°C. ‘Staghead’ stage on floral parts of infected plants was appeared after 10^th February. In earlier studies different researchers evaluated different Brassica germplasms and reported few germplasms as a resistant source. Meena et al., (2011) reported PBC 9221 and EC 414299 brassica lines as resistant to white rust. Yadav and Sharma (2004) also found that genotypes EC399301 and EC-399299 were resistant to white rust under field conditions. Mukherjee et al., (2011) have reported that most commercial Indian mustard (B. juncea) varieties are highly susceptible to white rust.
 

 
Varietal response against alternaria blight
 
The present study was therefore, carried out for finding out the source of resistance against Alternaria blight of rapeseed-mustard caused by Alternaria brasicae under field conditions and results are presented in Table 4. The area of the plant part affected was observed visually and the results were expressed in percentage of the plant part affected. It is clear that out of 16 mustard varieties were tested, none was found free to this disease. Appearance of Alternaria blight symptoms on plants was start from 10^th January. On the date 25^th January disease symptoms was appear in all mustard varieties. Mustard varieties like Radhika and Dev-142 were showed with disease index of 5.6 and 6.4 per cent respectively. Remaining mustard varieties were recorded with below to 5 per cent disease index. On date 25^th February, disease symptom of alternaria blight was observed in all mustard varieties. Mustard varieties viz., Radhika, Dev-142, Kranti and RH-149 were observed with highly susceptible to the Alternaria blight. Mustard varieties like Jagannath, PT-305, PM-44, Kanchan and MYSL-203 were observed with moderately resistant to the disease. It is well established fact that every pathogen requires specific weather conditions for its occurrence, development and spread. The severity of mustard diseases is highly dependent on different meteorological parameters and different growing environments. Temperature, relative humidity and rainfall have been identified as most significant meteorological parameters in addition to the causal agent and host. Earlier similar work has been reported by many researchers. Meena et al., (2011) reported that the incidence of alternaria blight in rapeseed-mustard fields is influenced by air temperature, relative humidity, soil conditions at the time of sowing, splashing rain, wind velocity, leaf wetness and inoculum density available in the soil. Bharti et al., (2016) also observed the highest disease intensity of 53.60 per cent from Kalyanpur (Kanpur) and lowest intensity (37.60%) was recorded from Bagha (Kanpur) during their survey of various locations.
 

Sixteen varieties of mustard were screened for their susceptibility against white rust and Alternaria blight. Among the tested sixteen mustard varieties, four mustard varieties like PT-305, PM-44, Kanchan and MYSL-203 were shown resistant against white rust. Whereas, mustard varieties like Jagannath, Radhika, Hybrid-805, Dev-142, Nandi bull, Araurali, 45L46 Lohiya, Kranti, Pusa Mahal, PusaVijya, PM-31 and Rh-149 were susceptible to white rust. Infection of alternaria blight was observed in all tested mustard varieties. Postules of white rust were starting appear after 5^th January (Temperature min. 7°C to max. 19°C). The highest incidence of white rust on leaves was observed from 16^th January to 08^th February (Temperature range min. 8-10°C and max. 20-22°C).Variety, PT-305, PM-44, Kanchan and MYSL-203 were shown resistant against white rust and may be recommended for commercial cultivation and for breeding purpose.

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