EVALUATION OF MAIZE GENOTYPES FOR RESISTANCE AGAINST GRAY LEAF SPOT IN HILLS OF NEPAL

Maize crop is affected by several diseases, but Gray leaf spot (GLS), is the major disease that threat maize production in every year in midhills and high-hills of Nepal. To identify the source of resistant on gray leaf spot disease maize genotypes were screened/evaluated under hot spots during 2013 and 2014 summer seasons across the hill environment of Nepal. In the screening nursery both exotic(CIMMYT China) and NMRP developed genotypes were included and screened at Pakhribas, Dhungkharka, Supping and Salyan during 2013 & 2014 summer seasons under replicated conditions. The genotypes identified resistant and high yielding at Dhungkharka in 2013 were YML58/(CML226/CATETO//CML226/CATETO)F2-B-1-2-B,YML32/(P147-F2-108-S7/P45-C8-76-S5)-F2-B-30-1-3, YML32/Cel FSRYS9956-B-3-2-4-B and YML58/(G34/36/G33TSR)-F2-B-4-1-B. In case of Salyan none of the genotypes showed resistant reaction against GLS but eight genotypes namely; YML23/P502-C2-58-1-1-2-5-B, YML23/P502-C2-185-3-4-1-3-B-1-B, YML23/P502-C3-F2-10-8-1-1-B, YML23/GLSI01P502-B-25-2-B, YML23/MBR-C5W-F108-2-3-1-B, YS12Q-189, YS12Q-33 and YS12Q-189 reacted MR reaction. At Pakhribas two genotypes reacted resistant (R) reaction namely; YML23/GLS101HGA-B-4-1-B and YS12Q-189 and other ten genotypes responded MR reaction. None of the tested entries at Suping responded resistant reaction but four genotypes ZM-401, 07SADVI, ZM-627 and BGBYPOP responded MR reaction against GLS. During 2014 summer season a total of 20 genotypes both exotic (CIMMYT India) and NMRP developed were screened against GLS across the hill regions of Pakhribas, Dhungkharka and Salyan. From the result of Pakhribas the genotype P501SRCO/P502SRCO was recorded for resistant (1.3) reaction and three genotypes 05SADVI, Entry # 36 and Entry # 27 were responded for MR reaction. In case of Dhungkharka nine genotypes namely; ZM-401, ZM-627, 05SADVI, 07SADVI, TLBRSO7F16, ENTRY#33, ENTRY#24, ENTRY#32 and ENTRY#21 were recorded for MR reaction. The tested genotypes at Salyan revealed that six genotypes namely; 05SADVI, 07SADVI, ACROSS-9942/ACROSS-9944, BGBYPOP, ENTRY # 24 and ENTRY# 32 were reacted resistant reaction and the genotype 07SADVI produced significantly highest grain yield (8638 kg/ha).


Introduction
Maize is staple food of hill people and seventy percent of maize is produced in mid hills region (900-1500 masl) and a further eight percent is produced in high hills (1500-2200 masl) and remaining 22 % is produced in Terai and inner terai (<900 masl). Of the several maize diseases Gray leaf spot ( GLS) caused by Cercospora zea-maydis Tehon and Daniels, on maize is recognized as one of the most yieldlimiting diseases of maize in the mid hills and high hills of Nepal. It is estimated to be spreading at a rate of 80-160 km each year. It is an important new record disease in Nepal. The disease was recorded from hill districts like Lalitpur, Kavrepalanchowk, Tehrathum, Khotang Bhojpur and Dhankuta within the country. Grain loss of 80% was estimated in farmer's field due to this disease (Manandhar et al., 2009). Since, the problem of the disease is realized in many districts there need of resistant variety to combat the disease. The disease was first identified and reported in Nepal in 2006 (Tiwari and Ferrara, 2007). The disease has been observed spreading over the years in 22 districts in the eastern, central and mid-western regions of the country (Manandhar et al., 2009).
GLS is evident on plants as small spots first on lower leaves of plants at tassel initiation. The disease moves upwards and spots change into long characteristics lesions within a month turning plants into a diseased field. The disease is significant since it rapidly destroys foliage when the plant is near at grain maturity..The disease has been reported from America, Africa Europe and Asia. Gray leaf spot is becoming very economically important disease at the Research Article present upper eight or nine leaves which contribute 75-90% of the photo syntheses for grain fill (Ward et al., 1999).Leaves of susceptible varieties become severely blighted or killed as early as 30days prior to physiological maturity.
The impact of Grey leaf spot on yield production greatly realized. With objective to observe and measure reactions of maize to GLS, maize genotypes were screened across the hill environments of Nepal to identify the source of resistance for general cultivation for the resource poor farmers in the hills.

Study site Description
Field experiments were conducted to identify the sources of resistance for gray leaf spot in maize genotypes during 2013 and 2014 summer seasons across the mid hill environments. Maize genotypes requested from CIMMYT China and NMRP developed were evaluated in disease hot spots in hilly regions. The experimental site ware Pakhribas, Dhungkharka, Supping and Salyan.

Experimental Design and Crop Husbandry
Experiments were laid out in replicated conditions in randomized complete block design with natural epidemic condition. The plot size was 4.5 m 2 (2 rows of 3 m long) with spacing 75cm × 25cm. (row to row and plant to plant), respectively. Assessment of disease severity was done by using 1-5 disease rating scales (Maroof et al., 1993)

Data Analysis
Analysis of variance for grain yield and other ancillary characters of maize were analyzed using the statistical package MSTAT-C (Russel and Eisensmith, 1983). Treatments (genotypes) were compared using the "F-test" and any significant differences between treatments were compared by Least Significant Difference (LSD) at 5% level of probability.

Results and Discussion
The disease began to appear on plants in mid-July in most of the tested sites and first symptoms seen in farmer's variety and started infected in other tested genotypes. The result from Chinese genotypes screened at Dhungkharka during 2013 showed that the severity ranged from resistant to susceptible reaction. The resistant and high yielding genotypes were YML58/ ( genotypes were screened against GLS during 2013 and the result showed that genotypes reacted resistant reactions were YML23/GLS101HGA-B-4-1-B and YS12Q-189 and the severity level of other ten genotypes were 2.0 which reacted MR level of disease reaction. The yield was significantly differences among the tested genotypes and highest yield was produced by YML23/P502-C2-185-3-4-1-3-B-1-B (7080 kg/ha) with MR reaction. At Suping, Makawanpur, one of the hot spot of GLS, NMRP set was screened including 11 genotypes in farmer's field with farmer as replications in three farmer's field. For favorable environmental conditions the farmers local (Suping local) is severely infected by GLS and yield reduction up to 50-60% in this location. Of the tested entries none of genotypes showed resistant reaction but four genotypes namely; ZM-401, 07SADVI, ZM-627 and BGBYPO reacted MR reaction against GLS. The yield of tested entries was found significantly difference. During 2014 summer season a total of 20 genotypes both exotic (CIMMYT India) and NMRP developed were screened against GLS across the hill regions of Pakhribas, Dhungkharka and Salyan. From the result of Pakhribas the genotype P501SRCO/P502SRCO was reacted for resistant reaction and three genotypes 05SADVI, Entry # 36 and Entry # 27 were reacted as MR reaction and rest of the genotypes were recorded as MS reaction. In case of yield non-significant difference was observed among the tested genotypes. In case of Dhungkharka nine genotypes namely; ZM-401, ZM-627, 05SADVI, 07SADVI, TLBRSO7F16, ENTRY#33, ENTRY#24, ENTRY#32 and ENTRY#21 were recorded for MR reaction. For grain yield production the genotype ZM-627 produced significantly highest grain yield of 6932 kg/ha among the tested entries. The tested genotypes at Salyan revealed that six genotypes namely; 05SADVI, 07SADVI, ACROSS-9942/ACROSS-9944, BGBYPOP,ENTRY # 24 and ENTRY# 32 were reacted resistant reaction and the genotype 07SADVI produced significantly highest grain yield (8638 kg/ha). Host resistance for this worldwide important disease of maize has been reported on several hybrids and inbred lines (Hilty et al., 1979;Ward et al., 1999). Details of results are given in Table 2 -8.