ANGULAR LEAF SPOT OF SESAME (Sesamum indicum L.) CAUSED BY Cercoseptoria sesami (HANSF.) DEIGHTON AND ITS MANAGEMENT
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Date
1992
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AAU, Anand
Abstract
Sesame (Sesamum indicum L,) is an important oil seed crop, also suffers from angular leaf spot , caused by Cercoseptoria sesami (Hansf.) Deighton which produced brown coloured spots (5-25 mm), enlarged , coaiesced and the blighted leaves were finally defoliated Capsules and stem remained free from infection, Isolated culture (on PDA) with proven pathogenicity lost the sporlation on 5th transfer, irrespective of virulence, Sclerotia, acervuli / stomata and the spores were produced on host. Hyaline 2-3 septate conidiophores (21.5 x 3.3µm) were produced with 3-8 septate hyaline conidia (118 x 3.8µm) on the host and the germinating sclerotia , Conidia remained viable upto 40 days and carry over of pathogen through the sclerotia which confined only in plant debris. Ten and 20 days old leaves had very few spots (1-5/leaf) on the lower leaves as compared to 70 days old leaves (70.2 % disease intensity ). Perfect stage- Mycosphaere1la sesamicola Sivanesan of this pathogenic fungus Cercoseptorla sesami (Hansf.) Deighton and the seed borne (internal or external) infection was not observed in Gujarat, In infected sesame leaves, total phenols increased by 22.20 per cent and decreased total amino acids, total chlorophyll, chlorophyll 'a' chlorophyll 'b' and nitrogen by 26.00, 35.63, 30.26, 30.64 and 20,18 per cent, respectively. In host range and growth t e s t studies, this fungus girew only on the sesame leaves and i t was found highly host specific. Maximum fungal growth was observed on PDA and Richard's solution at pH 6.5 (30 C temperature). Starch and glucose (carbon sources), L-aspartic acid (organic nitrogen source) and ammonium dihydrogen orthophosphate (as inorganic nitrogen source)yielded significantly more dry mycelial mat. Trichoderma spp, overgrew the Cercoseptorla sesami (Hansf,) Deighton and i t was also inhibited by Pseudomonas sp. (A) by 66.6 per cent. Milk bacteria found promising against C. sesami (showed 33.3% inhibition ) . Leaf extract of Datura stramonium L. and the botanical products viz., repelin, neemark and neem o i l inhibited this pathogen upto 100 %, during laboratory studies. Hormone-indole butyric acid(lBA) at 750 ppm, insecticides viz. triazophos (hostathion) and phosalone(zolone) each at 500 and 350 ppm; herbicides viz. alachlor (lasso) isoproturon (Kanak); diuron (Karmex) and benthiocarb(saturn) at V2 to the normal recommended dose also completely inhibited this fungus ini vitro. Pre and post emergence application of alachlor (herbicide) d) 1 kg a.i./ha found promising in suppressing angular leaf spot upto 75 days after sowing, Both carbendazim (0.05 %) and chlorothalonil (0.2 %) were found most promising during laboratory as well as field screening. These two fungicides gave significantly highest grain and dry stem yield and found significantly best in the control of the leaf spots. During comparative studies with proven findings., carbendazim and chlorothalonil reduced the disease upto 61.19 and 54.47 per cent, respectively and proved superior to the antagonists (best fungal and bacterial) used. Yield loss was estimated upto 56.78 per cent during kharif 1990 and 1991. None of the sesame varieties released and under pre-released stage were found immune/ resistant during (artificial inoculation) field screening.
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Plant Pathology, Agriculture, A Study