Some studies on the stem rot disease (Sclerotinia sclerotiorum ) of rapeseed / mustard in Rajasthan, India
Plant Pathology Department, Rajasthan Agricultural University Durgapura, Jaipur, India.
E-mail – Shivpuri@jp1.vsnl.net.in
Indian mustard (Brassica juncea) is the major oil seed crop of Rajasthan, occupying about 2.6 million hectares area in Rajasthan. The present investigation revealed that first symptoms of the stem rot appear in the field 65-70-day after sowing. Diseased plants can be identified by sudden drooping of leaves and finally drying of plants. For estimation of yield loss due to stem rot, diseased plants were tagged at 70, 80, 90, 100 and 110 days after sowing. Seed yield losses varied from 37.18 to 92.32 percent depending on the time of disease appearance. The highest yield loss (92.32%) resulted when disease started appearing at 70 days of crop and the least (37.18%) with the occurrence of disease at 110 days. Of the 70 genotypes ZYR-6, PCR-10, Cutlass (B. juncea); Westar (B. napus); Parkland, Tobin, Torch and Candle (B. campestris) were resistant. Rest all were susceptible.
Key words : Indian mustard, stem rot, yield loss, resistant genotypes.
Indian mustard is the major oilseed crop occupying about 2.6 million hectare area in Rajasthan state. In India, Brassica crop occupies second largest position after groundnut covering 6.2 million hectare of area with annual production of 5.5 million tonnes. A number of fungal diseases are known to infect rapeseed-mustard crop. Stem rot of mustard induced by Sclerotinia sclerotiorum) (Lib) de Bary has set its foot in this state appearing in patches and incidence ranging from 5-10% in different mustard growing areas. The aim of this study was to determine seed yield loss due to stem rot and evaluation of rapeseed mustard genotypes against Sclerotinia stem rot under field conditions.
MATERIALS AND METHODS
For screening of genotypes, seeds were sown in 5 meter rows in the first week of November 1997. Three week old culture of Sclerotinia multiplied on sterilized sorghum grains at 25oC ± 2oC was used as inoculum and mixed @ 100 g per 5 meter row at the time of sowing. Observation for severity of stem rot on main stems were recorded after 120 days of sowing using 0-4 scale (Sansford, 1995) (Assessment scale 0-4 where 0 = no disease, 1 = less than half stem girdled, 2 = more than half stem girdled, 3 = whole stem girdled and 4 = plant dead).
An experiment was laid out for estimation of yield loss due to stem rot in the field in 1997-98 winters. For this, two blocks each one of 75 m2 having 5 subplots (5x3 m size) sown in first week of November 97 using a susceptible Brassica variety T-59 of Indian mustard. One block was artificially inoculated with Sclerotinia inoculum multiplied on sterilized sorghum grains for 3 weeks. Whereas, in the second block, no inoculum was added. The inoculum was applied in furrows (3-5 cm deep) at the time of sowing @ 100 g per 5 m linear length of the row. In the present study, stem rot infected plants were tagged 70, 80, 90, 100 and 110 days after sowing, respectively, to find out the most vulnerable growth stage of the crop for the disease, yield of equal number of healthy and diseased (artificially inoculated) plants of each category was recorded after harvesting at 125 days of sowing.
RESULTS AND DISCUSSION
Screening of 70 genotypes under artificial inoculation conditions revealed that only 8 genotypes showed resistance against stem rot. These were ZYR-6, PCR-10, Cutlass (B. juncea) Westar (B. napus), Torch, Parkland, Tobin and Candle (B. campestris). Rest all were found susceptible. Sansford (1995) while working on stem rot reported that once the disease established within the plant it can not be effectively cured and will result in yield losses. Further work will be required to determine the nature of resistance in these 8 genotypes and possibilities to transfer this character for improvement of other genotypes.
Table 1 : Behaviour of different genotypes to stem rot under artificial inoculation during 1997-98
Rapeseed/ Mean Score Genotypes
B. juncea 0 Cutlass, ZYR-6, PCR-10
2 RH 9401, RNG 8006
3 PRO-Agro, PR-9622, RSM-22, PCR-T, R4-19-191,
RN-393, B10-53-93, PCR-28, RL-19-11, 45J-30,
HUM-9501, RK-9601, TKG-100, KM-999, RM-9506,
4 Vardhan, Vaibhav, NDR-9603, CSR-911, Varuna,
NDR-9601, BE-3121, CSR-703, Kranti, PRD-9505,
JGM, 9602, CSR-450, RK-9602, B10-322-93, VSL-6,
CSR-429, TKG-72, RAU-RD-95, JGM-9601, CSR-102,
JMWR-941-2, RSK-84, PBRA-2-5-2, RH-9324,
RSM-221, RW-8410, B-443, RC-154, RW-8410,
JMG-256, JMG-200, JMG-193, JMG-273, CSR-1206,
CSR-955, PSR-8, VMR 1-2, RAURD-101, RH 9303,
TM-28, JMM-915, B10-772, PR-9401
B. campestris 0 Parkland, Tobin, Torch, Candle
B. napus 0 Westar
It was observed that the earliest symptoms of the disease became visible 70 days after sowing. The distribution of infected plants was erratic. Most plants infected by stem rot died due to girdling of stem during or soon after flowering period which is a typical symptom of the disease throughout the world. Finally, crop was harvested 125 days after sowing and yield data were recorded. Data in Table 2 reveals that plants received early infection i.e. 70 days after sowing had exhibited the maximum loss in seed yield (92.32%). As the infection delayed the loss in yield were found to be reduced. The minimum yield loss of 37.18 per cent was noted when disease was visible 110 days after sowing.
Table 2 : Estimation of yield loss due to stem rot appeared at different growth stages of the crop.
Variety Time of Disease Seed yield Yield
appearance severity g/25 plants loss
of disease 120 DAS (%) (%)
70 100 284 92.32
T-59 80 100 1255 66.08
(B. juncea) 90 75 1627 56.02
100 62 2250 39.18
110 50 2324 37.18
125 (Healthy pts.) - 3700 -
Horning (1983) and Liu (1991) working on stem rot in Germany and China reported up to 50 per cent yield losses due to this disease. Disease appear at an early stage or at flowering stage can cause heavy yield losses ranging from 56 to 92 per cent. If disease appear after siliqua formation, yield losses reduced to 37.0 per cent. Hardwick et al. (1991) working on stem rot suggested that once you know the vulnerable stage of crop then timings of spray application should be aimed accordingly to control the disease. However, Davies (1986) suggested that neither changes in cultivars nor sowing dates could explain sudden increase or decrease in disease incidence, but wet weather during petal fall was the most conducive for disease development.
We are grateful to Dr. R.B.L. Gupta Associate Professor, Plant Pathology Department, for his guidance and the time spared by him to go through the manuscript.
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