EFFECT OF WEATHER PARAMETERS ON GRAIN MOLD OF SORGHUM
SUJATA N. DANDALE1 ; S.T.INGLE2 AND G.F.VYAVHARE3
Department of Plant Pathology,Dr. Panjabrao Deshmukh Krishi Vidyapeeth,
Akola- 444 10(Maharashtra)
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ABSTRACT: The major constraint for sorghum cultivation in kharif season is grain mold. It is an air borne disease, severe during moist condition and wet weather. An experiment was carried out on different genotype to assess the severity of grain mold of sorghum and effect of weather parameters on grain mold at different seed developmental stages. Weekly observations on incidence of grain mold and association of grain mold fungi were recorded from flowering to maturity. FGMR, TGMR, per cent association of fungi on threshed seeds and glumes, germination per cent, grain hardness and electrical conductivity were also recorded. Grain mold fungi were observed at flowering to maturity stage of sorghum. Among the genotype tested CSH-14 showed highest FGMR and TGMR rating (6.59 and 6.80), lowest germination per cent (46.91%), grain hardness (6.10 kg/cm2) and electrical conductivity (0.20 dsm-1) than resistant check B-58586.
Keywords: Grain mold, Sorghum, Meteorological week, weather parameters, FGMR
INTRODUCTION:
Sorghum (Sorghum bicolor (L) Moench) is the world’s fifth most important cereal crop cultivated widely throughout tropical, subtropical and temperate region, commonly known as “Jowar / Camel Crop / Great millet”.Which provide staple food for human consumption and fodder for livestock. Grain mold, the most important and widespread disease of sorghum, is a major constraint to sorghum productivity. Grain mold development is particularly severe in the short-duration hybrid cultivars and varieties that are grown during the rainy season under warm and humid conditions. Grain mold causes a severe damage resulting from infection of developing grain by one or more fungal species under moist climate. Weather parameters play an important role in the development of grain mold. Hence, keeping this view; the study on weather parameters responsible for the development of grain mold was studied in year 2013. Fusarium and Curvularia are the two most important and predominant fungal genera causing grain discoloration and reduction in variability of seed. During the study weekly meteorological data were recorded and observations on development of grain mold was recorded on two variety, two hybrids, one check and one restorer line.
MATERIAL AND METHODS
Present study was conducted at Department of Plant Pathology and in field of Sorghum Research Unit, Dr. PDKV, Akola with different sorghum genotypes viz., Sorghum hybrids (CSH-9, CSH-14), varieties (SPV -669, PVK-809), Sorghum AKR Line (AKR-150) and Sorghum resistance check (B-58586).
METEOROLOGICAL DATA
The meteorological data in respect of maximum and minimum temperature, relative humidity (RH-I and RH-II), rainfall, rainfall, bright sunshine hours (BSH) and wind speed etc. recorded at Meteorological Observatory Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola was used. The total rainfall received during 24th to 43rd meteorological weak at Akola was 860.7 mm, which was sufficient as against the average rainfall of 694.2 mm. Precipitation received during flowering to grain maturity period i.e. 36th MW to 43rd MW was 238.2 mm which was more as against the average rainfall of 153.9 mm. Morning and evening relative humidity (%) during this critical period were around 86.70% and 50.70% respectively and it was on higher side as compared to normal (81.20% and 47.70%) respectively. Maximum and minimum temperature was around 32.00C and 22.00C respectively. This weather condition was favored for mold development.
Detection of per cent grain mold fungi on glumes
At physiological maturity stage, correspondent glumes of seed taken for detection of association of grain mold fungi on glumes. To detect per cent fungal mycoflora, standard blotter plate method (SBM) of ISTA (1985) was used throughout the study. Sterile 200 glumes of correspondent seeds were detected by placing twenty five glumes at equidistant on sterile three layer blotting paper discs presoaked in sterile distilled water in each plate. The plates were kept for incubation at 27°C ± 2°C for seven days. Fungi on incubated glumes were detected by stereoscopic binocular microscope. Research microscope was used for detailed observations.
Field Grain Mold Rating (FGMR)
Infection percentage was measured on randomly selected five panicle from genotypes of each replication at physiological maturity on the basis of moldiness rating i.e. disease scoring scale (percentage/1-9)
Threshed grain mold rating (TGMR)
FGMR labeled five panicles from each genotypes of each replication were harvested. Harvested panicles were threshed separately and bulk of each panicle was evaluated for grain mold severity. TGMR estimate on the basis of percentage of molded grain surface area.
Grain hardness (kg/cm2)
A manually operated `Kiya’ hardness tester (Kiya Seisakusho Ltd. Japan) with bar type probe (0.5 cm diameter) was used with a maximum permissible load of 20 kg/cm2 for the determination of hardness of single grain. Randomly selected 100 grains from each 5 panicles from each genotypes of each replication were tested for hardness and mean was calculated.
Seed germination
The Ragdoll’s (rolled paper towel) method (ISTA, 1985) was used for germination studies. In rolled paper towel 100 seeds were placed at equidistant on two layers of moist paper towel (48 x 25 cm). Seeded paper towel were incubated for 10 days at room temperature (270C+20C). The rolled paper was then unrolled after removing rubber bands, gently upper cover paper was removed and germinated seeds were counted. Unless otherwise mentioned the test was based on 500 seeds per treatment of each replication.
Electrical conductivity (dsm-1)
Electrical conductivity of the grain leachates was measured using the method of Hendricks and Tylorson (1976).Three grams of seed sample of each genotype under study was washed twice with the glass distilled water and placed in clean corning glass test tube and 12 ml of glass distilled water was added to each tube. After four hours of soaking at 25oC, the supernatant liquid was used for measuring the electrical conductivity. ‘YSI model 32’ conductance meter of scientific division, Yellow Spring Instrument Co. INC., was used. The electrical conductivity was expressed in dSm-1.
RESULTS AND DISCUSSION:
Effect of weather parameters on the incidence of grain mold.
Grain mold is the problem of early maturing sorghum in a region where flowering and grain filling occurs during period of high relative humidity and warm temperatures. Effect of weather parameters on incidence of grain mold was studied and environmental parameters were correlated with grain mold incidence and occurrence of different mold flora on sorghum. The results where furnished in table 1 and 1a.
Initiation of grain mold incidence on CSH-9 sorghum genotype was observed during 34th meteorological week (21st August, 2013) with 27.50 per cent, when maximum and minimum temperature was 25.10C and 22.80C, relative humidity ranged between morning 95.0 per cent (RH-I) to evening (RH-II) 69.0 per cent along with rainfall 47.9mm, wind speed 11.6 km/h and zero hours sunshine respectively. Later on disease incidence on same genotype was at increasing trend and the maximum incidence 70.50 per cent was recorded in 41st (09th August, 2013) meteorological week there was drastic increase i.e. 27.50% to 70.50% grain mold in September and October was due to relative humidity and high maximum temperature during growth of the crop. The role of maximum temperature, high relative humidity and continuous rains (number of rainy days) might be responsible for increase in disease incidence.
Correlation of grain mold on sorghum hybrid CSH-9 with weather parameters
It is seen from results depicted in table 1a that significant and positive correlation exhibited between mean temperature, relative humidity (RH-I and RH-II) and incidence of grain mold. Wind speed was also positively significant at both (1% and 5%) levels of significance; the development of grain mold and bright sunshine hours (BSH) was positive with significant.
Total rainfall received during 24th to 43rd meteorological week at experimental field was 860.7 mm. Precipitation during flowering to grain maturity period i.e.34th MW (20th – 26th August, 2013) to 43rd MW (22nd to 28th October, 2013) was 238.2mm. Weather conditions during this period were most favorable for mold infection and mold development.
Consistent rains were received at Akola region during 20th August to 28th October, 2013. Similarly morning and evening relative humidity (%) during this critical period were around 86.7% and 50.7% respectively and it was on higher side compare to normal during this period. Further, during this period, maximum temperature was around 320C and minimum temperature was around 220C. This condition favored the alternate drying and wetting of grains which ultimately promoted mold development.
Narnaware et al. (2006) showed that grain mold intensity was high due to continuous rain at physiological maturity of sorghum crop. Somani et al. (1992) reported that relative humidity 75 per cent or more and maximum temperature in between 28 -350C favours disease development, however rain was the only important factor for disease development. Grain mold infection was promoted by prolonged period of humid (85 to 90% relative humidity) and or rainy weather and temperature of 25 to 350C throughout grain development, both before after physiological maturity (Garud et al., 2000 and Tarekegn et al.,2006).
Field Grain Mold Rating (FGMR)
Grain mold infection percentage was measured in the field on the basis of moldiness rating i.e. disease scoring scale (percentage/1-9). From the table 2, it was inferred that, on the basis of field grain mold rating B-58586 and PVK-809 were found resistant it recorded 2.33 and 2.72 Score. Maximum FGMR was recorded in CSH-14 (6.59) followed by CSH-9 (6.19), SPV-669 (4.19), and AKR-150 (4.29) respectively.Narnaware et al. (2006) recorded that field grain mold rating of MS-296B variety was 26-50 per cent using disease scoring scale. Thakur et al. (2006) reported that the FGMR and TGMR of variety CSH-9 is 3 and 2.8 grades respectively.
Threshed Grain Mold Rating (TGMR)
Per cent grain mold was measured from threshed grain on the basis of moldiness rating scale (percentage/ 1-9). Data in table 2 revealed that, on the basis of threshed grain mold rating (TGMR) B-58586 and PVK-809 were found as resistant as it recorded 2.52 and 2.66 grade TGMR respectively. The highest TGMR was recorded in CSH-14 (6.80) followed by CSH-9 (6.79), SPV-669 (4.75) and AKR-150(4.09). Garud et al. (1998) reported that field and threshed grain mold ratings increased significantly and progressively as harvesting was delayed in all the tested sorghum genotypes. Reddy et al. (2000) studied threshed grain mold rating (TGMR) using 1–5 scale, where 1 indicates no mold and 5 represents >50% of threshed grain surface were found molded. Viral (2011) studied TGMR of 18 sorghum genotypes, CSH-14(41.53%) hybrid showed highest TGMR than resistant check i.e. B-58586(8.46%) respectively.
Per cent Germination
The germination of different sorghum genotypes were tested by (Rogdoll’s) towel paper method. It is observed from the table 2, the lowest germination was recorded in CSH-14(46.91%) followed by CSH-9(50.79%), SPV-669(51.16%) and AKR-150(55.50%). The highest germination was found in B-58586(62.07%), followed by PVK-809(60.46%). Narasimhan and Rangaswami (1969) found a viability reduction of 40 to 80% when healthy sorghum seeds were treated with mold isolates. Bhatnagar (1971) and Castor (1977) noticed that fungus infected seeds often exhibited a reduction in germination and emergence, which caused poor stand in the farmers fields.
Grain Hardness (Kg/cm2)
Grain hardiness was measured with the help of “KIYA HARDNESS TESTER” using randomly selected 20 grains from each cob. Data given in table 2 showed that, the grain hardness was observed in the range of 6.10 to 8.65 kg/cm2. As per the scale all the genotypes grouped under intermediate hardness scale (6 to 8.99 kg /cm2). The lowest grain hardness was noticed in the CSH-14 (6.10 kg/m2) followed by CSH-9 (6.25 kg/m2) and B-58586 exhibited highest grain hardness (8.65 kg/cm2). Abedelrahman and Hosney (1984) showed that cross-link prolamin may be advantageous as it confers hardness to grain. Rana et al. (1984) reported that hardness and rate of absorption of water are predominant additive character offering resistance to grain deteriorates while in white sorghum without test, grain hardness contributes positively to mold resistance. Mukuru (1992) suggested that for sorghum lines to be mold-resistant, their grain must remain hard and vitreous in the field under wet and warm conditions, the ideal environment for grain mold development.
Electrical Conductivity (dsm-1)
Electrical conductivity was measured with help of “YSI model 32’ conductance meter” using three grams of seed sample of each genotype. Electrical Conductivity was (table 2) ranged from 0.20 - 0.29 dsm-1 the lowest E.C was observed in the genotype CSH-14 (0.20 dsm-1) followed by CSH-9 (0.22 dsm-1), AKR-150 (0.23 dsm-1) and highest E.C. was observed in genotype of B-58586 (0.29 dsm-1) and PVK-809(0.27dsm-1). Electrical conductivity of seed leachates was more in susceptible cultivars (Somani, 1992). Conductivities of flour suspension were lower than of corresponding extracts due to the electrolyte displacement (Clements, 1975). Effect of different seed lots on electrical conductivity for measuring viability and seedling vigour in wheat which showed Significant differences among selected seed lots in most of the parameters of seed quality (Tajbakhsh, 2000).
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