OCCURRENCE, PATHOGENIC VARIABILITY AND MANAGEMENT OF TURCICUM LEAF BLIGHT OF MAIZE
Abstract
Survey in Guntur district revealed 29.03% (PDI) of Turcicum leaf blight incidence caused by Exserohilum turcicum. Severity in the surveyed mandals ranged from 26.84 to 30.41% PDI during rabi 2019-20.
Variability in cultural characters was assessed at 8 DAI on PDA. All the isolates showed considerable variation in terms of color, pigmentation, colony character, growth habit, nature and texture of mycelium. Six types of colony colours were observed in all the isolates viz. gray, dark grayish brown, very dark grayish brown, very dark gray, olive brown and greenish black. Dark olive brown, very dark grayish brown, black and greenish black were the four types of pigmentation observed in the test E. turcicum isolates where blackish pigmentation was found to be dominant. Circular, oval and irregular colony margins were observed. Aerial, aerial and submerged, and submerged were the types of growth habits observed. All the test E. turcicum isolates showed two different textures: cottony and flocculant. Average growth rate of each isolate also showed significant variation where a maximum growth rate was recorded in two isolates HMEt-20-02 and HMEt-20-16 with 0.46 mm h-1 followed by HMEt-20-01 at a growth rate of 0.45 mm h-1 while a minimum of 0.06 mm h-1 was recorded in the isolate HMEt-20-14.
Among all the isolates, the highest spore production was recorded in HMEt-20-19 and HMEt-20-02 each with 0.48 × 104 spores/mm2 followed by HMEt-20-04 and HMEt-20-13 with 0.47 × 104 spores/mm2 and 0.46 × 104 spores/mm2 respectively. The least sporulating isolate was found to be HMEt-20-03 with 0.01 ×
xv
104 spores/mm2. Conidiophore length and breadth varied from 106.67 ± 23.88 μm to 291.88 ± 52.25 μm and 4.17 ± 0.93 μm to 7.97 ± 0.45 μm respectively. Conidial size ranged from 42.26 ± 7.74 μm × 65.45 ± 14.35 μm × 6.94 ± 1.34 μm to 15.03 ± 2.00 μm while the number of septa varied from 4.65 ± 1.18 to 7.15 ± 1.39. Germination pattern was recorded in all the isolates and all of them showed unipolar germination which was the characteristic feature of E. turcicum.
Variability in molecular characters was analysed using eight arbitrary RAPD primers among different test E. turcicum isolates. A total of 58 bands were obtained from the four primers which showed 100% polymorphism and the band size ranged from 100 to 1300 bp. PIC (Polymorphic Information Content) values varied from 0.40 to 0.45. OPA-03 primer recorded the highest PIC (0.45) while the least PIC value (0.40) was observed in case of OPA-08 and an average PIC value of 0.45 was obtained. The coefficient of similarity varied from 0.43 to 1.00. The least similarity (0.43) was recorded between HM Et 20-04 & HM Et 20-09 and HM Et 20-05 & HM Et 20-16 while the highest similarity (0.81) was observed in case of HM Et 20-01 and HM Et 20-02. The dendrogram obtained showed two major clusters or groups. Of the two major clusters, 19 isolates belonged to one cluster while HM Et 20-18 isolate deviated to be a lone cluster. The lone cluster showed 54% dissimilarity when compared to the other major cluster. The highest similarity of 81% was observed between the isolates, HM Et 20-01 and HM Et 20-02 that belonged to the same mandal. Within the same mandal also variation existed, indicating the presence of different isolates. On the contrary, isolates from different mandals also found to be similar irrespective of geographic locations.
Under in vitro conditions, mancozeb @ 0.25%, zineb @0.25%, pyraclostrobin+epoxiconazole @ 0.5% and difenconazole @ 0.15% were found effective in inhibiting the mycelial growth of E. turcicum. From in vitro dual culture experiments, four biocontrol agents, HMP A 02, HMP Bc 03, HMP Pf 01 and T 19023 were found best in inhibiting radial growth of the pathogen.
Among the test treatments, at 14 days after second spray (64 DAS), difenconazole @0.15% recorded the lowest PDI (14.00%) and a minimum area under disease progress curve of 359.33 as against untreated control (873.32).
Maximum yield was recorded in treatment with difenconazole @0.15% (7448.81 kg ha-1) and mancozeb @0.25% (7328.57 kg ha-1). The benefit cost ratio varied from 1.49 to 2.54 with highest recorded BC ratio (2.54) in the treatment difenconazole @0.15% against unsprayed check (1.49).
Description
OCCURRENCE, PATHOGENIC VARIABILITY AND MANAGEMENT OF TURCICUM LEAF BLIGHT OF MAIZE