Biocontrol agents are beneficial for plant and soil health and are effective in controlling many plant diseases. These biocontrol agents in combination with fungicides at reduced doses can be more effective than using alone. Keeping this in view, an in vitro study was carried out to test the compatibility of commonly used fungicides viz., captan 50 WP, thiram 75% DS, tebuconazole 5.36% FS, carboxin 37.5% + thiram 37.5% DS, prochloraz 24.4% + tebuconazole 12.1% w/w EW and thiophanate methyl 450 g/l + pyraclostrobin 50 g/l with two fungal (Trichoderma asperellum and T.viride) and three bacterial biocontrol agents (Bacillus subtilis S4KB5, B. subtilis S8KB2 and B. subtilis B3). All the five fungicides were found to be compatible with all the biocontrol agents at 100ppm and 250ppm. All the fungicides except thiram, showed complete inhibition of T. asperellum at 1500ppm and 2000ppm and with T. viride, 100 per cent inhibition is shown by all the fungicides at 1500ppm and 2000ppm except carboxin + thiram. With biocontrol isolates, B. subtilis S4KB5, B. subtilis S8KB2 and B. subtilis B3, highest inhibition zone were recorded by prochloraz + tebuconazole (2000ppm), tebuconazole (2000ppm) and thiophanate methyl + pyraclostrobin (2000ppm). Present findings suggest that compatible fungicides can be used with biocontrol agents in an integrated disease management practices for the control of seed and soil borne pathogens.

The study was conducted in the Department of Plant Pathology, College of Agriculture, Rajendranagar, Professor Jayashankar Telangana State Agricultural University, Hyderabad, India to understand the histopathological mechanisms of initial interaction of Puccinia arachidis with six groundnut genotypes. Fully expanded quadrifoliate leaves were inoculated with P. arachidis using the detached leaf assay. Five-mm leaf discs were cut at 6 hours after inoculation (hai) and each day until 5 days after inoculation (dai) and examined for histopathological interactions. Germination of urediniospores was detected during 6–8 hai and continued until 24 hai. There were no differences in pre-penetration and penetration among all the six genotypes. Differences in post-penetration were observed among the genotypes during 3–5 dai. In genotypes TMV 2 and K 6, extensive hyphal colonization was observed in the intercellular spaces of mesophyll cells by 4–5 dai indicating compatible interaction and susceptibility to rust disease. Sparse hyphal growth and corresponding mesophyll cell death at 3–5 dai in genotypes ICGV 171015 and ICGV 13229 indicated defense response by the host and moderate resistance. In genotypes ICG 11426 and GPBD 4, complete arrest of hyphal growth by 4–5 dai due to extensive mesophyll necrosis suggested incompatible interaction and resistance to rust. This is the first documentation of the histopathological description of the initial infection strategies of P. arachidis in the selected groundnut genotypes.

Background Stem rot caused by Sclerotium rolfsii Sacc. is a major nuisance in groundnut production, causing substantial yield losses in almost all groundnut-growing areas around the world. Biological control is regarded as a sustainable choice over the currently popular management strategy i.e., chemical control, as later has a negative influence on the environment. The present study evaluated the antagonistic effect of native rhizosphere micro-flora against groundnut stem rot pathogen S. rolfsii. Results A total of 111 bacterial isolates and 9 Trichoderma isolates isolated from groundnut rhizosphere soil were evaluated for their antagonist activity against S. rolfsii in vitro. Eight isolates (seven bacterial and one Trichoderma) were chosen as prospective biocontrol candidates based on the findings of the dual culture assay. Molecular characterization of these isolates by 16S rDNA and ITS rDNA sequencing confirmed the identity of bacterial isolates as Bacillus spp. (six B. subtilis and one B. amyloliquefaciens) and fungal isolate as Trichoderma asperellum. Also, the selected seven bacterial isolates recorded favourable results for antagonism-promoting biochemical traits. Conclusion The results of the current study suggested that the native groundnut rhizosphere micro-flora can be exploited for biological control of groundnut stem rot pathogen S. rolfsii. Further research may enable the use of the isolated rhizosphere biocontrol agents as single organisms or in a consortium for sustainable management of the groundnut stem rot pathogen.