Full Length Research Paper
ABSTRACT
Gray leaf spot is one of the major constraints of maize production in Ethiopia where warm humid environmental condition is prevailing. A field experiment was conducted in Gondar zuria district of western Ethiopia during 2016/17 and 2017/18 cropping season with the aim to evaluate effective maize varieties for the management of maize gray leaf spot disease. The experiment was laid out in Randomized Complete Block Design (RCBD) in three replications. Nine improved varieties, that is, SBRH, Gibie 2, Gibie 3, Argene, Jibat, BH-546, SPRH, Wonji, AMR-852 with one local maize were tested for GLS resistance. The genotype significantly varied and there were significant differences (P<0.05) in the overall mean of GLS incidence, severity, AUDPC%/day, yield and yield component among varieties. Data were analyzed using SAS version 9.2. The result indicated that the maximum disease incidence and area under disease progress curve (AUDPC), 58.8 and 214.83% per day respectively were recorded from local maize while the minimum incidence and AUDPC value, 22.7 and 150.49% per day, respectively were recorded from Gibie 2 maize variety. The maximum grain yield of 8611.7 kg/ha was recorded from Gibie 2 variety while the minimum grain yield of 4542.3 kg/ha was recorded from local maize. The study suggested that variety of Gibie 2 showed minimum grain yield loss which result to negligible loss of 1.47%, respectively and showed significant reduction of maize GLS incidence, with a corresponding increased grain yield of maize.
Key words: Cercospora zeae maydis, Maize varieties, area under disease progress curve (AUDPC), disease incidence, disease progress rate.
INTRODUCTION
Maize (Zea mays L) is one of the world’s most widely cultivated crops, providing food and animal feed as well as being a source of biofuel. In Ethiopia it is grown in the lowlands, the mid altitudes and the highland regions. It is an important field crop in terms of area coverage, production and utilization for food and feed purposes.
However, maize varieties mostly grown in the highlands of Ethiopia are local cultivars. They are low yielding, vulnerable to biotic and a biotic constraints (Berger et al., 2014). Currently the average national yield of maize is very low under small scale farmers of Ethiopia 3.7 t/ha (Duguma and Janssens, 2016). Foliar diseases of maze are the number one factors in contributing in the reduction of maize production and productivity across the world (Berger et al., 2014).
Gray leaf spot caused by Cercospora zeae maydis has become one of the major yield-limiting diseases of maize in eastern Africa including Ethiopia (Bekeko et al., 2018). This disease is most severe and damaging when periods of high relative humidity extended, slow-drying of dews and prolonged late-season fogs (Lyimo et al., 2013). Increased incidence of gray leaf spot in Ethiopia has been associated with cultural practices such as reduced tillage, continuous cultivation of maize, and use of susceptible maize cultivars (Wegary et al., 2008; Worku et al., 2012). Documented yield losses of maize attributed to gray leaf spot vary from 11 to 69% (Stromberg and Donahue, 2006) with estimated losses as high as 100% under severe epidemics. The loss of photosynthetic area, increased stalk lodging, and premature plant death (Poland et al., 2009) are observed due to GLS. The yield losses caused by the disease were estimated to reach 50% for moderately resistant and 65% for susceptible hybrid maize in South Africa (Alemu et al., 2016; Paul et al., 2011). In Ethiopia, reported that yield losses due to gray leaf spot on resistant, moderately resistant, and susceptible varieties were between 0-14.9%, 13.7-18.3% and 20.8-49.5%, respectively in Bako and its surrounding areas (Lyimo et al., 2013; Nega, et al., 2016).
Gray leaf spot was first reported in Ethiopia in 1997 in the border of west Wellega and Ilubabor zones, of western Ethiopia (Wegary et al., 2001). The survey report showed increased prevalence of gray leaf spot in the major maize producing regions of Western, Southern and Northwestern parts of Ethiopia (Nega et al., 2016; Wegary et al., 2001). According to the report, gray leaf spot has become the principal maize disease since 1998 in Ethiopia. In Ethiopia, however no commercial cultivars have been found to be resistant to gray leaf spot, but have identified high yielding hybrids that are less susceptible to the disease (Bekeko et al., 2018). However, presently gray leaf spot is becoming one of the major constraints of maize production in Ethiopia, genetic resistance is the most economic and effective means of reducing yield losses caused by this disease (Bekeko et al., 2018; Tilahun et al., 2012). In view of its expansion, seriousness, and potential destructiveness of this disease, it is necessary to develop resistant genotypes for resource poor farmers. Therefore, the main objective of this study was to evaluate the effective maize varieties resistance against maize gray leaf spot disease.
MATERIALS AND METHODS
Description of the study area
The experiment was conducted at Gondar zuria district, in central Gondar Zone, Amhara National Regional State, Ethiopia during the main cropping season (May to November) for two consecutive years in 2016/17 and 2017/18. The experimental site was located in the geographical location of between longitude 37°-48° E to W and latitudes 12°- 24° N to S. The experimental site lies at an altitude of about 2380 m.a.s.l and the mean annual rainfall is 992.5 mm. The soil type is black vertisol and characterized with 5.5 pH. tThe average annual maximum and minimum temperature are 28.5 and 13.5°C respectively (Tilahun et al., 2002).
Treatment and experimental design
The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. The size of the experimental plot was 4.5 m × 2.5 m (11.25 m2) with six rows in which four central rows were used for data collection. The path between plots and blocks were 1 m and 1.5 m, respectively. The seeds were planted at a spacing of 25 cm between plant and 75 cm between rows. Nine improved maize varieties, i.e., SBRH, Gibie 2, Gibie 3, Argene, Jibat, BH-546, SPRH, Wonji, AMR-852 and one local variety (check) were obtained from the Ethiopian National Maize Research Co-ordination Center, Bako and International Maize and Wheat Improvement Centre (CIMMYT) and used for this study to develop gray leaf spot resistant: Date of plating was the same for all trials. Planting was made at same seed rate. 100 kg/ha DAP were applied at planting time. Weeding and other agronomic practices were carried out as per recommendations.
Disease development
Appearance of the natural occurrence disease in the experimental plots was inspected 10 times every 7 days. Initial scoring for disease incidence was done when lesions were visible on the three to five basal leaves of the plants. Numbers of plants infected in the four middle rows were recorded and their means were converted into percentage as the total plant observation. Disease incidence on each plot was calculated in the following way:
Disease severity was recorded on ten randomly tagged plants per plot. It was assessed as the percentage of the total leaf surface covered with gray leaf spot lesions on each expanded leaflet separately at regular intervals using a 1-5 standard disease scoring scale recommended by Roane, et al., (1974)where 1 = No lesions; 2 = Lesions on some plants, usually not visible; 3 = A few scattered lesions, usually seen only after careful examination; 4 = Lesions and defoliation on some plants, not damaging and 5 = Abundant lesion on all leaves with most of leaves tissue being necrotic.
Area under progress curve (AUDPC) was calculated for each treatment from the assessment of disease incidence using the formula:
Where, xi is the cumulative disease severity expressed as a proportion at the ith observation, ti is the time (days after sowing) at the ith observation and n is total number of observations. AUDPC values were expressed in %- days (Madden and Bosch, 2007). AUDPC values were used in analysis of variance to compare amount of disease among plots with different variety. Relative yield losses were calculated separately for each of the treatments with different levels of disease using the formula of Madden et al., 2007.
Where, RYL = Relative yield loss (reduction of the yield and yield component), Y1= the yields which was obtained from plots with maximum protection) and Y2 = the yields which was obtained from plots with minimum protection).
Statistical Data analysis
Data on maize gray leaf spot incidence, severity, AUDPC, yield and yield components and all agronomic data from each assessment date were subjected to analysis of variance (ANOVA) according to the Duncan Multiple Range Test (DMRT) as suggested by Gomez et al., (1984) using SAS software programs; and least significance difference (LSD) was used for the mean comparison at 5% probability level.
RESULTS AND DISCUSSION
The two consecutive cropping seasons data were analyzed separately, but there were no showed significant difference among two season outputs in the experiments, so that, the two season data was combined and analyzed together.
Incidence of maize gray leaf spot
There was significant differences (p < 0.05) oin gray leaf spot incidence among the maize varieties. The highest incidence of 58.8% was on local maize varieties, whereas the lowest incidence of 22.7, 24.17 and 25.57% were recorded from Gibie 2, Jibat and BH-546 maize varieties, respectively (Table 1). The hybrid varieties used in this experiment reacted differently with regards to the onset of gray leaf spot . The result agrees with the work of Bekeko et al., (2018) in which differential response of these varieties to gray leaf spot was reported.
Severity of Maize Gray Leaf Spot
The analysis of variance on gray leaf spot severity were showed significant difference at p<0.05 among the main effects of maize varieties. The highest gray leaf spot severity were recorded from local maize (check) and AMR-852 hybrid variety which result of 2.47 (49.4%) and 2.41 (48.2%), respectively that were not showed significant different whereas the lowest gray leaf spot severity were recorded from Gibie 2 and Jibat varieties which result of 1.02 (20.4%) and 1.06 (21.2%), respectively and that were not showed significant different (Table 1).
Area under disease progress curve (AUDPC)
Analysis of variance revealed that there was significant difference at p<0.05 on AUDPC%/days among the main effects of maize hybrid varieties. The highest AUDPC%/days of 214.83%/days and 211.06%/days were calculated from local maize and AMR-85 hybrid variety. The lowest AUDPC%/days of 150.49%/days was calculated from Gibie 2 variety, followed by Jibat and BH-546 varieties resulting to 152.64%/days and 154.52/days, respectively and that did not show significant different (Table 1). Previous works at Bako indicated genotypes considered as susceptible variety had AUDPC values more than resistant genotypes (Tilahun et al., 2012). There was gray leaf spot pressure on the susceptible local maize and high inoculum pressure had major influence on disease development and reproduction in conformity with the findings of (Madden et al., 2007).
Gray Leaf Spot Disease Progress Rate
The disease progress rate did not exhibit significant difference at p<0.05 among the maize varieties. The faster gray leaf spot disease infection rate progressed rapidly on the susceptible local maize and AMR-852 variety varied from 0.0862 to 0.0844 units/day, respectively while slowest infection rate of 0.0315 units/day was recorded from Gibie 2, followed by Jibat and BH-546 maize varieties resulting to 0.0349 and 0.0368 units/day, respectively (Table 1). Disease progress rates of the resistant varieties, namely Gibie 2, Jibat, BH-546 and Hora showed little increase in rate starting from the time of disease onset onwards, whereas the susceptible varieties local maize (check) and AMR-852 showed variability in disease progress rates from time to time, i.e. progress rate increased over time. The use of genetically resistant maize varieties is the preferred means of controlling gray leaf spot (Tilahun et al., 2012).
Maize ear length, ear diameter and stand count
The analysis of variance for ear length and ear diameter showed significant difference at p<0.05 among the maize varieties. The longest ear length (25.28 cm) was recorded in Gibie 2, which is at par with Jibat. However, the shortest ear length (16.62 cm) was recorded in local maize, followed by AMR-852 and Argene maize varieties. The rear diameter (26.48cm cm) was recorded in Gibie 2 while the (15.65 cm) ear diameter was recorded in local, variety, AMR-852 and Argene maize varieties (Table 2). The result of analysis of variance indicated that there was no-significant difference among the variety on the stand count of maize. The stand count at harvest across the treatments ranged from 80.67 to 76.67 plants of maize per plot. This is because gray leaf spot did not predispose to stalk rots, resulting in no lodging.
Grain yield and thousand-kernel weight (TKW) of maize
Analysis of variance for grain yield and TKW showed significant difference at p<0.05 among the maize varieties. The variation in mean grain yield between the tested varieties was attributed to their genetic potential for yield and disease resistance. Accordingly, the maximum grain yield of 8611.7 kg/ha was obtained from Gibie 2 hybrid variety, followed by Jibat which resulted in grain yield of 8485.0 kg/ha. Minimum grain yield of 4542.3 and 4763.3 kg/ha were recorded from local maize and ARM-852 variety, respectively (Table 3).The maximum TKW of 430.61 g was obtained from Gibie 2, followed by Jibat (425.42 g) while the minimum TKW of 245.64 g was recorded from local maize (Table 3).
Losses in grain yield and thousand-kernel weight (TKW) of maize
In all maize varieties grown under the same condition, the highest grain yield losses of 47.25% was recorded in local maize, followed by AMR-852 maize hybrid variety which resulted in grain yield losses of 44.69% while the lowest grain yield losses was obtained from Gibie 2 resulting to negligible losses, followed by Jibat and BH-546 maize varieties resulting to 1.4 and 5.7%, respectively (Table 3). This result agrees with the finding of Eik and Hanway (1996) who reported reduction in grain yield due to increased disease pressure that was associated principally with increased blighting and premature death of photosynthetic tissues prior to grain filling.
CONCLUSION
The present study suggested that application of resistance varieties results in reduced gray leaf spot disease incidence, and loss of grain yield and thousand kernel weight, along with a correspondingly increased total grain yield . Based on the findings of this study, gray leaf spot is an important disease that calls for better attention in maize producing area in terms of economic management with resistant varieties. Based on collected data analysis, varieties Gibie 2, Jibat and BH-546 showed best performance resistance to maize gray leaf spot disease incidence and gave better grain yield.
CONFLICT OF INTERESTS
The authors have not declared any conflict of interests
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