INTRODUCTION

Maize (Zea mays L.,), a staple food crop in many parts of the World. Maize is monocotyledonous plant that belongs to grass family (Poaceae). Maize (Zea mays L.) is the most versatile crop, adapted to different agro-ecological and climatic conditions. Maize the third most important cereal crops in the world’s agricultural economy had highest genetic yield potential and is commonly called as queen of cereals. One of the main deterrents to high grain yield in maize is its susceptibility to several diseases (Madhavi et al., 2018). It is the third most important cereal crop next to rice and wheat in India. It is one of the potential crop of  Telangana State  which has come up on large areas in different districts under rainfed areas and under irrigated command areas of Karimnagar, Nizambad, Siddipeta, Warangal, Khammam, Bhadradi kottagudemamu and  Kamareddy etc.. Maize is being affected by many diseases. Diseases  in maize decreasing the yield from 28% to 91%. Maize with a notable productive potential among the cereals, is the third most important grain crop after wheat and rice. At global level, maize is cultivated over an area of 197.20 million hectares with an annual production of about 1148.49 million tons with an average productivity of 5.8 tons per hectare (Anonymous, 2019). In Telangana, it is being cultivated on16.06 lakh acres area with an annual production of 40.78 lakh million tons and productivity of 2,539 kg acre^-1 (Anonymous B, 2019−2020). For existing biotic and abiotic stresses, the sustainability of the maize production to meet the future demand is debatable. Maize is affected by more than sixty diseases. Sixteen are major diseases among the sixty. Maize is attacked by many diseases in kharif and rabi seasons causing severe reduction in yield. Among all  the  foliar diseases which are affecting the maize, Turcicum leaf blight caused by Exserohilum turcicum (syn. Heliminthosporium turcicum Pass.), is considered a serious disease where climatic conditions are cool with high relative humidity. Maize grain yield loss varies from 25% to 90% in different parts of India depending upon the severity of turcicum leaf blight epiphytotics (Chenulu and Hora, 1962; Jha, 1993). Yield losses approached 50%, when the disease is severe at 2−3 weeks after pollination (Shurtleff, 1980, Dey et al., 2017). Turcicum leaf blight is considered a serious disease under agro ecologies of Telangana. Turcicum leaf blight affects the maize crop from the seedling stage to maturity. The symptoms first appear as grayish green small elliptical spots on the leaves with water soaked lesions parallel to leaf margins, finally attaining a spindle shape with long elliptical grayish or tan lesions. If the disease starts at an early stage, it causes the premature death of blighted leaves. As a result, the crop losses its nutritive value as fodder, have reduced germination capacity, vigor, grain yield and total sugar content (Ferguson and Carson, 2004), has restricted starch formation, chaffy kernels and infected plants are liable to infection with stalk rots (Cuq et al., 1993) .

Genetic resistance of crop plants against pathogen is economical and eco-friendly disease management strategy. The resistant varieties are not only environmental friendly but also suitable to adopt at farmers level. There is a need to identify new sources of resistance through artificial epiphytotics to cater the resistance breeding programs. The objective of this study was to assess the maize inbred lines and their hybrids for resistance to  turcicum leaf blight  disease under field conditions. Keeping in view the above points, the present study was carried out to screen the three hundred and two maize entries for identification of resistant sources against turcicum leaf blight disease.

MATERIALS AND METHODS

2.1.  Collection of diseased samples

Evaluate three hundred two maize entries for resistance against turcicum leaf blight (TLB) disease in Telangaana  State. The diseased leaf samples of affected maize plants showing typical symptoms of turcicum leaf blight having necrotic lesions were collected in paper poly bags from different maize growing areas of research station, Karimnagar  and Telangana districts   in rabi, 2019−2020 (12 lakh acres ) and kharif season, 2020 (20 lakh acres). The Agricultural Research Station, Karimnagar is situated at 18^o 30'N latitude, 79^o 15'E longitude and 259.15 m above mean sea level. Two hundred five entries for  rabi season, 2019−2020 and  ninety eight  entries for  kharif season, 2020. The pathogen Exserohilum turcicum was isolated from infected leaves using single spore isolation technique (Tuite, 1969).

2.2.  Layout of maize trial for field screening

For the identification of source of resistance to Exserohilum turcicum, a set of three hundred and two maize entries were evaluated in a randomized block design (RBD) along with a check CM-202 at Agricultural Research Station, Karimnagar field conditions  using 1 to 9 disease rating scale (Mitiku et al., 2014) . The test genotypes were planted in 2 rows of 3m length each with a plant spacing of 60×20 cm².

2.3.  Inoculum preparation and inoculation

Spore suspension of the Exserohilum turcicum from twenty days old cultures was prepared by washing the conidia with distilled water. Equal volume of spore suspension was mixed and sprayed in evening hours by using atomizer at three to four leaf stages of maize plants and humidity was maintained by spraying water. Check plants were also treated similarly with spore suspension.

2.4.  Disease assessment

Disease reaction was recorded by using 1 to 9 scale (Mituku et al., 2014 and Indian Institute of Maize Research, Ludhiana (Anonymous A, 2014) at 35 to 45 days after inoculation andassessed % diseased leaf area of TLB disease. The genotypes showing disease score /scale from 1.0 to 3.0 were considered as resistant (R), 4−5 as moderately resistant (MR), 6−7 as moderately susceptible (MS)and 8-9 as susceptible (S) (Table 1).

Table 1: Rating scale for maize turcicum leaf blight Disease (Mitiku et al., 2014 and Anonymous A. Indian Institute of Maize Research. Annexure A. 2014)

RESULTS AND DISCUSSION

Disease score of maize entries to turcicum leaf blight disease and artificially inoculated under field conditions during rabi, 2019−2020 and kharif, 2020 was observed. The performance of three hundred two germplasms along with susceptible check on the basis of disease reaction and 1-9 disease scale was classified into four groups (Table 2, 3 and 4 ).

Table 2: Per cent diseased leaf area of maize entries to turcicum leaf blight disease during rabi, 2019−2020

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Table 3: Per cent diseased leaf area of maize entries (hybrids) to turcicum leaf blight disease during rabi, 2019−2020

Table 3: Continue...

Table 4: Per cent diseased leaf area of maize entries (hybrids) to turcicum leaf blight disease during Kharif-2020

3.1.  Disease reaction during rabi, 2019-2020

Out of the two hundred five entries, five lines viz., IB-140, DHM-121, 17×605-1-2, 107×BML-7 and 186×BML-32 were identified with disease score 1, one hundred and nine lines with a score 2 and sixty one  lines with a score 3. Entries with disease scores 1, 2 and 3 were categorized as resistant. The % DLA for IB-140 and IB-78 was 7.5 and 30 respectively. Twenty eight with disease score 4  are moderately resistant. Two lines viz., IB-154-1 and IB-59 were moderately susceptible with a disease score 6. The % diseased leaf areafor IB-154-1 and IB-59 was 55.20 and 55.60 respectively. CM-202 recorded 74.30% diseased leaf area, severely affected by turcicum leaf blight and rated as susceptible (Tables 2 and 3).

3.2.  Disease reaction during kharif-2020

Ninety eight genotypes were screened against turcicum leaf blight disease. Out of them, forty one genotypes viz., 70531×CML156, 70530×BML45, 70530×11-2-1, 70425×BML6, 72554×50-2-1, 72555×BML7, 72343×50-2-1, 2336×11-2-1, 72336×CML156, 72343×BML45, 72603×66-1-1, 72513×CML156, 72343×66-1-1, 70531×BML45, 722603×CML-156, 72555×66-1-1, 72336×BML6, 70439×CML156, 70576×50-2-1, 72555×605-1-1, 72555×BML6, 72336×50-2-1, 72374×BML7, 72555×CML156, 72555×33-1-4, 70425×BML45, 72520×CML156, 72504×CML156, 70474×50-2-1, 72568×BML14, 72686×PFSR3, 72660×CML156, 66-1-1, 524-3-2, 31-2-4, 207-1-3, 244-1-2, 540-2-3, 388-2-1, KML225 and 186-4-3 were identified as disease score 1, fifty lines with a disease score 2 and  three  lines with a score 3, which were categorized as resistant.Two lines with disease score 4 and one line with disease score 5 were moderately resistant. In CM-202, the % diseased leaf area was 72.46%, which was also severely affected by turcicum leaf blight and rated as susceptible (Tables 4 and 5).

Table 5: per cent diseased leaf area of maize Inbreds to turcicum leaf blight disease during kharif , 2020

Similar results were reported by scientists:Shikari and Zafar (2009) reported that inbred NAI-147 and composite Girija expressed reisitance to Turcicum leaf blight. Kumar et al. (2011) identified twenty inbred lines as sources of resistance against Turcicum leaf blight of maize.Babita and Mani (2011) screened the temperate maize lines against northern corn leaf blight and found five inbreds resistant to disease.Shankara and Gowda (2011) identified 56 moderately resistant genotypes and two inbreds (NAI-125, NAI-137)showed mode rately resistant reaction. Ishfaq et al. (2014) carried out a disease reaction studies against turcicum leaf blight were done with two crosses viz., 15C (A) x I-318 (R) and I-401(A)×I-318(R) for all six generations with P1, P2, F1, F2, BC1 and BC2 and results revealed significant variability has been exhibited by fungus to infect different generations of a particular cross. In I-15C (A)×I-318(R) cross, F1 was moderately resistant to turcicum leaf blight but F1 of I-401(A)×I-318(R) cross was moderately susceptible to the disease. Mitiku et al. (2014)  results revealed that the variety BH660 was highly resistant with the incidence of 13.7% and variety BH543 was susceptible with the incidence of 52.3%. Out of 26 maize genotypes,8 genotypes viz., PS 39, CML 451, CML 470, CML 472, VL1030, VL 1018140, VL1018527 and SMI178-1 were found resistant and eight genotypes viz., PS45, CML165, CML459, VL1249, VL0536, SMC-5, SMC-3 and KDL 211 were found moderately resistant against E. turcicum with disease grade ranged from 2.1−2.5 (Ahangar et al., 2016). One hundred inbred lines each of early maturing (EM) and extra-early maturing (EEM) were tested against TLB disease and recorded average disease severity values ranged from 1.9−5.8 and 2.9−5.7 for the EM and EEM inbred lines, respectively (Baffour et al.,  2021). Out of 135 genotypes, 34 genotypes expressed moderately resistant reaction, 73 showed moderately susceptible reaction and 29 genotypes exhibited susceptibility reaction to TLB disease (Mallikarjuna et al., 2018). Wani et al., 2018% disease severity was recorded in two inbred lines, viz., NAI-112 and NAI-147 and one hybrid, viz., HQPM-1 was found resistant to turcicum leaf blight disease. Out of twenty six maize hybrids were evaluated along with check hybrids against turcicum leaf blight disease resistance, two hybrids viz., AH4158 and AH4142 were found to be resistant to turcicum leaf blight disease (Meghashri and Motagi, 2020). Out of 237, 41 inbred lines were found resistant (disease incidence <3.0), 181 inbred lines were moderately resistant (disease incidence 3.1−5.0) and 15 inbred lines were moderately susceptible (disease incidence 5.1−7.0) (Singh et al., 2018).

CONCLUSION

In rabi 2019−2020, out of two hundred five lines, 5 entries viz., IB-140, DHM-121, 17×605-1-2, 107×BML-7 and 186×BML-32 were identified with a disease score 1 and CM -202 recorded 74.30%  diseased leaf area and in kharif, 2020, out of ninety eight entries, forty one  entries were  noticed with a disease score 1, remaining were recorded with disease score from 2−7 and one line CM-202 was observed with high 72.46% diseased leaf area, severely affected by turcicum leaf  blight disease and rated as susceptible. Breeders use these identified resistant lines in crossing program to develop high yield turcicum leaf blight disease resistant hybrid  varieties.

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