Identification of Resistant Genotypes and Integrated Management of Dry Root Rot of Chickpea

Dry root rot caused by Rhizoctonia bataticola is an important disease of chickpea causing significant yield losses. The farmers are facing the problem of disease in all states that grow the crop and it is particularly more in Karnataka. The recent reports indicated that dry root rot is an emerging as a potential threat to chickpea productivity and production (Ghosh et al., 2013).
       
The dependence on chemical control or any other single control method is not advisable to manage dry root rot. Although, growing of resistant cultivars for the management of disease is a cost effective, sustainable and ideally fit into integrated disease management, identification of sources of resistance against soil borne diseases is not easy and requires artificial epiphytotic conditions or sick plots as the pathogen, is a soil and seed borne and survives in the form of sclerotia for many years.
       
Since the disease is a major hindrance to chickpea production Karnataka, it was felt necessary to identify the sources of resistance and develop eco-friendly integrated disease management strategy to manage the emerging and destructive dry root rot of chickpea. Hence, the present studies aimed at identification of sources for resistance and integrated management of emerging dry root rot of disease of chickpea.

Isolation and purification of R. bataticola
 
Chickpea plants showing typical dry root rot symptoms were transferred to sterilized potato dextrose agar (PDA) medium in Petri dishes and incubated at 25±2°C to obtain mycelial growth. The pathogen was purified by hyphal tip technique.
 
Molecular detection of R. bataticola
 
The pathogen was detected molecularly using ITS-1 (5' CCTGTGCACCTGTGAGACAG-3') and ITS-4 (5'-TGTCC AAGTCAATGGACTAT-3') as reverse primer. For this, standard protocols were used for the isolation of DNA according to Liu et al., (2000) and  amplified products was sent for sequencing and identification of species to Eurofins, Bangalore.
 
Identification of dry root rot resistant sources of chickpea
 
Preliminary disease screening
 
One hundred germplasm lines chickpea germplasm entries obtained from  Indian Institute for pulses Research, Kanpur) were screened in ‘sick plot’ at Agricultural Research Station, Kalaburgi, Karnataka during rabi-2019 and rabi-2020. The crop was raised as per the recommended package of practices except the plant protection measures against dry root rot and observations were recorded. Disease incidence (%) was calculated using the following formula and genotypes were categorized (Khan et al., 2013) for their reaction (Table 1).
   
Advanced screening of promising entries by phenotyping technique
 
Nineteen promising (Resistant and moderately resistant) germplasm lines (Table 2) which were resistant/moderately resistant in preliminary disease screening were f further subjected for advanced screening using phenotyping technique during rabi-2021 (Bera et al., 2016). For this, nineteen germplasm lines were sown in block with 2 meter width bed with spacing of 0.5   meter between beds with spacing of 30 × 10 cm.


 
Integrated management of the disease
 
Field experiments were  conducted in randomized block design (RBD) during rabi-2019-20 and rabi-2020-21 at Agricultural Research Station, Kalaburgi, Karnataka by following recommended agronomical practices with highly susceptible variety Annigeri-1 with eight treatment combinations of bio-agents replicated thrice with plot size of 5 × 3 m² in sick pot along with untreated control plot. The observations on per cent disease, seed yield and test weight were recorded and benefit cost (B: C) ratio was also calculated as per standard methodologies. 

Isolation and identification of R. bataticola
 
The pathogen  produced black, brown to grey coloured mycelium and the young hyphae were thin, hyaline, septate and typical right angle branching of the mycelium and constriction of the branch near the point of origin. The sclerotia formed were black, smooth, varying from spherical through oblong to irregular shapes (Fig 1 and 2). The results are in line with Sharma et al., (2012) with respect to isolation and characters of R. bataticola.
 

 

 
Molecular detection of pathogen
 
Both ITS-1 and ITS-4 primers produced amplified product size of 500-650 bp and nucleotide sequencing was done for ITS region of 18S rRNA. The BLAST data results revealed that the R. bataticola matched with the reference strain and confirmed as Rhizoctonia bataticola and accession number (HQ649832.1) was obtained by depositing the sequence in NCBI GeneBank, Maryland, USA.

Preliminary disease screening
 
Fourteen were resistant (0-10 per cent disease incidence) and five moderately resistant (10.1-20 per cent) out of 100 germplasm lines screened against the disease. (Table 1,3 and Fig 3).The present findings are well supported by Saifulla et al., (2011) who screened chickpea entries for dry root rot pathogen under field condition and reported that  20 entries as resistant and 36 entries moderately resistant out of 196 genotypes screened in sick plot. Further, Nagamma and Saifulla (2012) out sixty four Kabuli genotypes against dry root rot of chickpea, six were resistant and nine showed moderately resistant reaction.
 



 
Advanced disease screening of promising lines by phenotyping technique
 
Four germplasm lines viz., IC83798, IC95135, IC83506 and IC83500 showed resistant reaction and five germplasm lines viz., IC83736, IC 83526, IC83358, IC83501 and IC83514 were moderately resistant (Table 2 and Fig 4). Similarly, Pande et al., (2004) tested 47 lines of chickpea against the dry root rot in advanced screening and reported that only ICC 14395 and ICCV 2 were resistant and the remaining 22 lines moderately resistant against dry root rot of chickpea. Similarly, Jayalakshmi et al., (2008) also tested 12 genotypes against dry root rot disease and found only four genotypes as resistant.
 

 
Integrated management of dry root rot of chickpea
 
The results on pooled data (Table 4 and Fig 5) indicated that the treatment combination, seed treatment with mancozeb 50% + carbendazim 25% WP @ 3.5 g/kg followed by soil drenching of mancozeb 50% + carbendazim 25% WP @ 3 g/lit water to infected and surrounding plants was highly effective and significantly superior in recording least disease incidence when compared to other treatments. The treatment recorded lowest pooled mean disease incidence of 7.97% with highest pooled mean yield (11.42 q/ha) and BC ratio (1:3.40). Khan et al., (2012) tested eight fungicides against dry root rot fungus, among them mancozeb, carbendazim, copper-oxy- chloride and benomyl completely inhibited the growth of the fungus compared to control. Further, in fungicidal trails on management of dry root rot of chickpea caused by R. bataticola, carbendazim (0.2 per cent) used as seed treatment, soil drenching and seed treatment plus soil drenching recorded lowest disease incidence of 15.6 per cent highest grain yield of 192 q/ha respectively (Vijay Mohan​ et al., 2006).
 

 

Preliminary screening of 100 germplasm lines resulted in the identification of fourteen resistant and five moderately resistant germplasm lines. Advanced screening of 19 genotypes under phenotyping technique yielded only four genotypes resistant and five moderately resistant genotypes. The integrated disease management, seed treatment with mancozeb 50% + carbendazim 25% WS @ 3.5 g/kg followed by soil drenching of mancozeb 50% + carbendazim 25% WS @ 3 g/l water to infected and surrounding plants was highly effective by recording least disease incidence of dry root rot with highest seed yield, test weight and highest benefit cost ratio.

The work has been undertaken as part of the doctoral research programme at Department of Plant Pathology, University of Agricultural Sciences, Raichur. The first author is thankful to the University for providing facilities to conduct the work. 

None.