Evaluation of Maize Genotypes against Southern Leaf Blight ( Bipolaris Maydis ) During Summer Seasons at Rampur , Chitwan Tirtha

Maize genotypes were screened at research field of National Maize Research Program, Rampur, Chitwan on 20 maize genotypes during 2015 and 2016 summer season with the objective of identification of resistant genotypes against southern leaf blight caused by Bipolaris maydis. Field experiment was laid out in randomized complete block design with three replications. Disease scoring was done as percentage of leaf area infected using 1-5 rating scale. In both the years among the tested genotypes, disease severity and grain yield varies significantly. None of the genotypes reacted for resistant whereas four genotypes; 05SADVI, BGBYPOP, RAMS03F08 and RML-32/RML-17 were moderately resistant over the years. For grain yield most of the tested genotypes produced comparatively lower grain yield however RML-32/RML-17 was superior for grain yield (3.1 t/ha) over the years.


Introduction
Maize (Zea mays L.) is an important food and feed crop among cereal crops in the world.It is the second most important staple food crop in Nepal in terms of both area and production after rice.Maize is the world's widely grown cereal and primary staple food crop in many developing countries.It is the principle food crop in the hills and feed for terai of Nepal.Maize plays significant role in national economy and contributes 3.15% in national GDP and 9.5% in AGDP and 26.06% to total cereal crop production in the country (MoAC, 2013/14).Recently the area of this crop is increasing and establishing as a commercial commodity due to its higher yield potentiality among major crops and its ever increasing use in feed especially for poultry in terai regions of Nepal.It has a very high yield potential than any other cereals and is popularly known as 'queen of cereals' (Singh, 2002).The contribution of maize to food security in the hills and in accessible areas gradually becoming a commercial commodity due to increasing demand of feed for poultry and animal.The overall demand for maize has been estimated to grow up by 6-8% per annuam for the next two decades because of of increasing demand for food in hills and livestock feed in accessible areas of terai and inner-terai (Pathik, 2002).The productivity of maize in Nepal is more or less static at around 2500 kg -1 (ABPSD, 2007/08) while there is increased demand, estimated to grow by 6-8% per annum (NARC/CIMMYT, 2001).About 75% of maize is grown in

Research Article
the hills by small scale, resource-poor farmers as traditional crop for food, feed and fodder (Adhikari et al., 2002).The major constraints for maize production in South Asian region including Nepal are several biotic and abiotic factors.Among them, diseases are one of the major biotic constraints for successful maize production.Economically important diseases of Nepal are leaf blights (northern and southern), ear rot, stalk rot, rust, downy mildews, etc. (Khadka and Shah, 1967;Shah, 1968;Thapa, 1977;Manandhar, 1983;Batsa et al., 1989;Paudel et al., 1989).Southern leaf blight occurs worldwide and is important in regions of warm and humid climate with 20-30 o C temperature.In the United States, in 1970, this disease reached an epidemic level, resulting n estimated losses of one billion dollars (Ullstrup, 1972).The epidemic was caused by the race 'T' attacking to corn with Texas male sterile cytoplasm (T-cms), which comprised 85% of corn loss at that time.Race 'O' occurs mainly in sub-tropical and tropical areas , where it causes minor losses.Yield reduction up to 50% was recorded when race 'O' inoculated into susceptible line (Fisher et al., 1976;Gregory and Nelson, 1978).

Site Selection
The field experiment was conducted during summer season of 2015 and 2016 at National Maize Research Program (NMRP), Rampur, Chitwan, Nepal located between 84 o 19 ′ E longitude and 27 o 40 ′ latitudes and 282 m above the sea level.Climatically Rampur les in humid sub-tropical region with average annual rainfall of 1920 mm (Fig. 1).

Experimental Setup
The experiment was conducted in a randomized complete block design (RCBD) with 3 replications.Twenty maize genotypes including standard check (Rampur composite) and susceptible check (yellow popcorn) were screened under natural epidemic environment are shown in Table 1.Chemical fertilizers were applied at the rate of 120:60:0 kg ha -1 .The individual plot size was 6 m 2 (5 x 1.2 m 2 ).There were 2 rows of 5m length per plot spaced line to line 60 cm and plant to plant 25 cm apart.The susceptible check 'yellow popcorn' was sown in two rows around the whole experimental block to provide a uniform source of inoculums for the test entries.Intercultural operations as weeding, earthing-up, irrigation etc. were applied as per the rules of other experiments conducted at NMRP.

Disease Assessment and Data Analysis
Disease incidence was recorded at the peak time of disease prevalent on maize crop and disease scoring was carried out on the basis of modified 1 to 5 scales reported by ( 42) and was used to estimate percent leaf area diseased on individual plots as: 1 (Resistant, R))= plants with one or two to few scattered lesions on lower leaves, 2 (Moderately resistant, MR)= moderate number of lesions on leaves, affecting <25% of the leaf area, 3 (Moderately susceptible, MS)= abundant lesions on lower leaves, few on other leaves affecting 26-50% leaves, 4 (Susceptible, S)= lesions abundant on lower and mid leaves, extending to upper leaves affecting 51-75% leaf area and 5 (Highly susceptible, HS)= lesions abundant on almost all leaves, plants prematurely dried or killed with 76-100% of the leaf area affected.Grain yields were adjusted to 80% shelling recovery.Grain yield was estimated using formula adopted by Carangal et al. (1971) and Shrestha et al. (2015) by adjusting the grain moisture at 15% and converted to the grain yield kg per hectare.Data were analyzed through GENSTAT packages applying 5% significance level

Discussions
In the present research work, different maize genotypes were screened against Bipolaris maydis, the causal organism of southern leaf blight disease, a foliar blight of maize.Disease severity was taken as the leaves blighted on maize.This disease is considered as the most important creating a threat to successful maize cultivation in Nepal during summer season at terai and inner terai regions of Nepal.Disease severity is the intensity of disease prevalence based on specific scale of rating as described in the results of Lambert and White (1997) In another screening experiment against this disease out of 72 maize OPVs, SO1SIYQ, CotaxlaS9627, RampurS03F04, S03TLYq-02, Narayani, Sitala, Bangalore9745, RampurS03F02, Pop45C10, RampurS03F08, Across501, TakfaS9624, TakfaS9636, RampurS03F06, RampurS03F04 and S99TLYGHAB were identified moderately resistant (Paudel et al.,2007).Rijal et al., (2013) also evaluated 52 maize OPVs to identify source of resistant against southern leaf blight and identified 20 genotypes moderately resistant.Maize germplasms were evaluated for resistance to H. maydis had negative impact on grain yield was confirmed in numerous studies (Mubeen et al., 2017).

Conclusion
Disease severity and yield results showed significant effect of southern leaf blight on different maize genotypes.None of the genotypes evaluated against this disease showed complete resistance.However, from the result of two years, 05SADVI, RamS03F08, BGBYPOP and RML-32/RML-17 identified moderate level of resistance and can be recommended for end users after further trials under tropical and subtropical climatic conditions during summer season in Nepal as well as can be used as sources of resistance in maize breeding program.

Fig. 1 :
Fig. 1: Weather data of Rampur during the crop period

Table 1 :
Pedigree, origin and source of tested genotypes

Table 2 :
Response maize genotypes tested against southern leaf blight (SLB) disease 2015 and 2016 summer at Rampur