Screening of sesame plant against charcoal rot disease
Sesame (Sesamum indicum L.) is a crop which is considered to be an oldest oilseed crop probably originated from Africa (Bedigian 1985). It is known traditional crop worldwide as well as in Pakistan. Sesame covers an area of 71.7 thousand hectares with annual production of 35.5 thousand tones (Anonymous 2010) in Pakistan. Sesame oil which is mostly edible in nature have 47% oleic acid and 39% lenolinic acid. Its oil is used in the production of soap, perfumes, paints, pharmaceuticals as well as insecticides. Although it has been cultivated for a long period of time but enhanced yield level is not much impressive. This is just because of leaf blight (Alternaria sesame) and charcoal rot (Macrophomina phaseolina) disease in our country.
Charcoal rot which is also known as root and stem rot has become highly critical nowadays. Yield losses have been estimated up to 57% after about 40% infection (Abdou et al., 2001). Loss in yield at the rate of 1.79 kg/ha due to one percent increase in the incidence has been accounted (Khan et al., 2005). The pathogen mostly attacks at the base of the plant.
Most common symptom of this disease is the rapid wilting of host plant generally before or just after pollination. Symptoms do not appear early on infected plants, but they become pathetic and when become dry they show a appearance of black ash discoloration on the stem followed by entire plant. Black sclerotia appear in huge number on the affected part of plant. The pathogen lives as sclerotia in crop residue as well as in soil. It is known to be seed borne. Stress by moisture and extinsive temperature favors disease development (Shalaby et al., 1998). Disease intensity has aggravated in heavy and ill drained soils. Practically no field control is available by using chemicals (Abawi and Corrales 1989). Genetic resistance of sesame against Macrophomina phaseolinas in some sesame genotypes has been assumed (El-Deeb et al., 1989) in Egypt and (Dinakaran and Muhammad 2001) in India.
In the light of above discussion a research plan has been initiated to develop foundation stone for management and screening of all available varieties/lines in Ayub Agriculture Research Institute. Regarding screening of resistance in varieties/lines against charcoal rot, it helped out us to identify genotypes with handsome resistance, that can be used directly in hybridization programs for inducing resistance in agronomical suitable cultivars and also for a large scale cultivation. For management of charcoal rot disease, growth of Macrophomina phaseolina was examined under controlled condition by growing it on artificial media, in the stress of four fungicides. This was helpful in getting most suitable fungicide that inhibit growth and could be used in controlling of this disease in field.
SCREENING OF SEASAME
Collection of diseased samples
Current Research was conducted in Oil Seed Research Institute, Ayub Agriculture Research Faisalabad district. Sesame lines/varieties were grown in order to determine the reactions and the development of disease. Eight sesame genotypes (Black tills, 20011, 40009, TH-6, 87002, 87006, TS-3, 95002) were grown and data will be recorded. Information regarding disease incidence was recorded by given formula.
No. of infected plants
Disease incidence % = - -------------------------------- X 100
Total no. of plants
Diseased samples of infected tissues comprised of roots, twigs, stem (collar region) leaves and soil collected in polythene bags separately from sick field showing charcoal rot. Samples from healthy plants in the same field was also be collected. The collected samples were brought to the laboratory for the isolation of fungal pathogens.
The percent severity was evaluated by the following rating scale proposed by Dinkaran et'al., (2001).
Key/Scale Disease rating Description of symptoms Severity (%)
0 No disease No signs of disease 0.0
1 Very mildly diseased Less symptom on stem and branches 10.0
2 Mildly diseased Few branches became dry 25.0
3 Moderately diseased Up to 35% of the plant became dead 50.0
4 Highly diseased More than 35% of the plant became dead 75.0
5 Dead Mortality of whole plant 100.0
From the raw severity data, the severity index of charcoal rot of seasame was calculated by using the following formula.
Sum of all disease ratings
Disease severity index (%) = ---------------------------------------------------- x 100
No. of plants observed x Maximum disease grade