Effect of  Traditional  Agronomic Practices on White Rust of Rapeseed – Mustard under Organic Farming System in Manipur

Introduction

Rapeseed – mustard is one of the most important cruciferous crops. This crop is basically cultivated for oils and vegetables during winter season in Manipur. This crop provides both   domestic consumption of oils and vegetables   to the marginal farmers. Pests and diseases are the major constraints which hamper the cultivation of this crop and   its  productivity. More than 30 diseases are known to occur on Brassica crops  including  rapeseed – mustard   in India.¹ The major   constraints   of rapeseed – mustard is fungal diseases ,  of which white rust is the most common . White rust caused by Albugo candida (Pers.) Kuntze which occurred various parts of the world causes  tremendous yield losses in mustard.² Management of pests and  diseases  through agronomic practices  includes  crop rotation, utilization of disease free seeds, burning of infected plant debris, soil solarization,  sowing date , intercropping , plant density etc.  These practices are widely followed in the traditional system of disease management in Manipur. Attempts have been made in the present investigation  to find out the suitable agronomic practices for the control of white rust on rapeseed- mustard because traditional agronomic practices are not only cost effective but also  sustainable,  subsistence in agriculture.   Keeping in view, the present investigation  was carried out  with the most important three traditional agronomic practices that include  intercropping ,  plant density and date of sowing in the management of white rust of rapeseed- mustard under organic farming.

Materials and Methods

Field Trials

Field  experiments  were conducted at Kakching , an agricultural hub of diverse crops,  located  in 24 29′ 30″ N latitude and 9359′ 30″ E longitude   at 45 Km away from  Imphal,  Manipur for two consecutive  winter seasons (2014  & 2015 ). The field has an earlier record of growing seasonal vegetables including  mustard .  Field experiments were conducted on two rapeseed varieties  [B. rapa (L.) var. M-27 (V₃) , Brassica rapa (L.) var. ragini (V₄) ], and two  local  mustard cultivars [ B. juncea (L.) Czern. & Coss. cv. Local Yella (V₁) and B. juncea (L.) Czern.& Coss. cv. Lamtachabi (V₂) ]. Seeds were sown in the last week of October  except for date of sowing ( DOS) experiment  in  plots [(2.2 X 1.3) m² ] keeping some border line with  three replications and raised under irrigated condition using farmyard manures (FYM)  as done by traditional farmers starting from September to November.  For DOS experiment seeds were sown  at  five different dates viz.,  D₁, D₂, D₃, D₄ and D₅ (30.09.14 , 15.10.14 , 30.10.14 , 14.11.14  and 29.11.14  ) by maintaining 15 days  interval.  A spacing of ( 30 x 10) cm²  row to row and plant to plant  distances were maintained except for the plant density  field experiment. For plant density  experiment   different spacing  viz., T₁= (20 X 5) cm², T₂ = (30 X 10)  cm² and T₃ = (40 X15 ) cm² were selected  to evaluate their  effect on white rust disease severity in  the experimental  varieties.  A ratio of 5:1 with rapeseed and 3:1 with mustard were maintained for observing intercropping effect with Pea (Pisum  sativum  L.) .  A weekly monitoring  was conducted 45 DAS ( Days After Sowing ) and  it extended  from November to February in each year. Data on disease severity  of rapeseed – mustard were rated using  0 – 6 scale.³

Data analysis

Disease severity data were statistically analyzed   using one way ANOVA and t – test  at 5% level of significance to evaluate any  variance of white rust severity among various treatments of agronomic practices . MS – Excel  was used for statistical computation of the data.

Isolation of the pathogen and identification  

White rust infected   leaves ( 5 for each variety)  were brought to the lab using sterile  poly-bags. The fungal pathogen was    isolated by following the method⁴ in the laboratory. The infected plant tissues along with unaffected tissue were cut into pieces ( size : 2- 5 mm ²).  With the help of sterilized forceps, the inoculants  were transferred to sterile petri – plates containing 0.1% mercuric chloride solution and later they were surface sterilized for   30  seconds.  The sterilized pieces @ 3 – 5 per plates were inoculated in BNPRA⁵ medium. The inoculated petri- plates  were incubated at 25 – 27  1 and observed after 5 days.

After the incubation period the growth of fungi was studied under microscope . By comparing the reproductive structures as revealed in microscopic observation  with  standard literature,⁶ the pathogen was identified.

Results and Discussion

Intercropping provides significant effects on  disease severity (DS ) of the crop than sole cropping (Table 1). It may be accounted that intercropping helps to avoid inter-crop competition and thus a higher number of crops can be grown per unit area at a time which enables efficient

Table 1: Effect of rapeseed-mustard and pea  intercropping  against white rust (DI and DS -pooled for two years i.e. rabi 2014 &  2015)

*Significant at 5% level of significance; DI = Disease Incidence, DS = Disease severity.

Table 2 : Effect of plant density against white rust of rapeseed –mustard  (DI and DS –pooled for two years i.e. rabi 2014 & 2015 )

*Significant at 5% level of significance.

Table 3: Effect of date of sowing against white rust of rapeseed –mustard ( DI and DS –pooled for two years i.e. rabi 2014 & 2015 )

*Significant at 5% level of significance.

Figure 1: White rust infection on Lamtachabi (V2)  Click here to View figure

Figure 2: Albugo candida  Click here to View figure

resource utilization and increased productivity probably by minimizing disease level. This finding corroborated with the findings⁷ who  reported that suitable intercropping systems were more favorable to control diseases without chemicals comparing with monoculture.  Similar findings in other crops were also reported.⁸

Plant density treatments  showed  significant effect on the experimental varieties used (Table 2).   Treatment, T₃ was found to be most effective where least disease severity  was encountered. By virtue of different spacing in plant density treatments viz., T₁ [(20X5) cm²], T₂   [(30×10)  cm²] and T₃  [(40X15 ) cm²] the number of plants per plot varies. DS values were found   increased in T₁ while reduced in T₃ than T₂ treatment.  It may be attributed  that  more nutrient uptake and  utilization for proper growth of the crop was facilitated by enough space availability around the crop.  Similar findings that reduction  in spacing between plants increased the incidence of seed borne infection in rice.⁹

Statistically significant variance was resulted among the treatments of sowing date (Table 3). The highest DS (18.08% ) was found in V₂ sown on D₅ ( 29.11.14) while  the least  DS (11.06%) in V₄ sown on  D₁ (30.09.14). Thus sowing of rapeseed- mustard varieties earlier than D₃ (30.10.14) resulted less DS even though there was some fluctuations in D₂ treatment if late higher DI and DS encountered. However, for rapeseed varieties DS values first increased and then reduced when sown late. These variations may be due to the fact that the rapeseed varieties mature earlier than mustard varieties hence congenial physiological stage of the crop was not found to infect in the former. Meantime they were susceptible for other diseases such as powdery mildew.  Early sown crops  on 30.09.14 (D₁) can  recede   the crop from damages caused by white rust. Various authors^{10, 11} also detected similar findings that  higher disease intensity under late sown conditions in rapeseed –mustard.  In an overall assessment the least DI( 22.59%)  & highest DI ( 50.80% )  were  detected in DOS treatments. The least DS ( 9.57%) was found in plant density followed by date of sowing (11.06% ) and intercropping (12.29%) experiments. Thus   among the agronomic practices evaluated   plant density was found to be most effective followed by date of sowing and intercropping.

Conclusion

Traditional agronomic practices  particularly the plant density were found to be effective in the   management of white rust under  organic farming system in Manipur’s agro-climatic condition. Thus the farmers  may adopt  these traditional agronomic practices to raise the crop successfully.

Acknowledgements              

The Author gratefully acknowledges  the receipt of  Manipur University  research fellowship and head,  Centre of Advanced Study in Life Sciences, Manipur University ,Canchipur,  Imphal for providing laboratory facilities.

References

1. Saharan  G..S.   Management of rapeseed – mustard diseases. In:  Kumar  D and  Rai M (eds.). Advances in oilseed research. Vol. 1 Rapeseed and Mustard  Scientific Pub. Jodhpur. 1992;155–188.
2. Bains  S.S  and  Jhooty J.S.  Mixed infections by Albugo candida and Peronospora parasitica on Brassica juncea inflorescence and their control. Indian Phytopathol. 1979;32:268-271.
3. Barbetti  M.J, Li C.X , Banga,  S.S,  Banga S.K , Sandhu P.S , Gurung  A.M and Salisbury P.A. High level resistance against white rust (Albugo candida) race 2V identified in Brassica juncea genotypes from China and Australia. 13^th International Rapeseed Congress June 5-9, Prague, Czech Republic. 2011.
4. Narayanasamy  P.  Microbial Plant Pathogens – Detection and Disease Diagnosis: Fungal Pathogens, vol. 1, Springer  Science & Business Media. 2010;9.
5. Masago  H, Yoshikawa  M,   Fukada M.  and   Nakanishi N.  Selective inhibition of Pythium spp. on a medium for direct isolation of Pytophthora spp. from soils and plants. Phtytopathol. 1977;67:425-428.
   CrossRef
6. Singh  R. S.  Plant Diseases, 9^th Edition. Oxford & IBH  Publishing Company Pvt. Ltd.  India, 2009;173-393.
7. Gomez- Rodriguez O ,   Zavaleta – Mejia E ,  Gonzalez-Her nandez V.A,  Livera-Munoz M and Cardenas-Soriano E. Allelopathy and microclimatic  modification of intercropping with marigold on tomato early blight disease development. Field Crop Res. 2003;83:27-34.
   CrossRef
8. Abdel-Monaim M.F and  Abo-Elyousr  K.A.M.  Effect of preceding and intercropping crops on suppression of lentil damping – off and root rot disease in New Valley – Egypt. Crop Prot. 2012;32:41- 46.
   CrossRef
9. Agarwal, V.K ,  Singh  O.V and   Modgal  S.C.   Influence of different doses of nitrogen and spacing  on seed- borne infection of rice. Indian Phytopathology. 1975;28:38-40.
10. Saharan  G.S.  A review on research on rapeseed-mustard pathology in India. Paper presented in the Annual Rabi Oilseed Workshop, held at Jaipur, 6-10 August. 1984.
11. Gupta K,  Saharan G.S  and Singh D. Assessment of white rust severity on Brassica juncea under genotype-environment interactions. J. Mycol and  Pl.  Path. 2002;32:106-109.