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A study was conducted on the “Evaluation of abiotic stress tolerant PGPR and Trichoderma sp. for growth and disease management in black pepper (Piper nigrum L.)” at the Department of Agricultural Microbiology, College of Horticulture, Vellanikkara during May 2015 to July 2016. The objective of the study were to screen Azospirillum sp., Micrococcus sp., Burkholderia sp., Pseudomonas fluorescens and Trichoderma sp., for abiotic stress tolerance under in vitro and also evaluate the abiotic stress tolerant isolates for growth and disease management in black pepper under stress (polyhouse) and without stress (natural) conditions.
Rhizosphere soil samples were collected from ten different black pepper growing areas of Thrissur district for isolation of Azospirillum sp., Micrococcus sp., Burkholderia sp., Pseudomonas fluorescens and Trichoderma sp. The isolates obtained were screened for PGPR activities, abiotic stress tolerance and screening for antagonistic activity against P. capsici. The most promising isolate from each type of microorganism were selected for pot culture experiment to evaluate the selected abiotic stress tolerant isolates for growth promotion and disease management in black pepper.
Azopsirillum sp. was not recorded in the black pepper rhizosphere soil collected from Thrissur district. In the case of Micrococcus sp., the highest population was recorded in Pazhayannur (45×104 cfu g-1). In the case of Burkholderia sp., was highest in Kannara (116.5×104 cfu g-1). In the case of Fluorescent pseudomonads, the highest population was recorded in Chellakkara (55×104 cfu g-1). And Trichoderma sp., was highest in Mupliyam (96.5×103 cfu g-1).
A total of 34 obtained different microbial isolates were screened for PGPR activities (IAA production, % P - solubilisation, Ammonia production and HCN production) and abiotic stress tolerance (temperature tolerance 280C, 370C, 410C and 500C, acidity tolerance and drought tolerance). Based on the PGPR activities
and abiotic stress tolerance, the most promising isolates selected for pot culture experiment were Micrococcus sp. - VKM isolate (410C, pH 5.5 and -0.15 M Pa osmotic stress) Burkholderia sp. - PAB isolate (410C, pH 5.5 and -0.15 M Pa osmotic stress), fluorescent pseudomonads - PAP isolate (410C, pH 5.5 and -0.15 M Pa osmotic stress) and Trichoderma sp. - CKT isolate (370C, pH 5.5 and -0.15 M Pa osmotic stress). The maximum Per cent inhibition (64.75 %) was recorded in the case of Burkholderia sp. (KKB) and in the case Trichoderma sp. the maximum per cent inhibition (66.95 %) was recorded with CKT isolate.
The isolates were further screened under pot culture experiment. There were two pot culture experiments with polyhouse condition (with elevated temperature as stress) and natural condition (without stress). Under polyhouse condition (with elevated temperature as stress), T5 (Trichoderma sp. - CKT isolate) and T6 was the most efficient isolates for enhancing the growth of black pepper. However, T4 (Pseudomonas fluorescens - PAP isolate) and T5 (Trichoderma sp. - CKT isolate) were the most promising treatments for Phytophthora disease management.
Under natural condition (without stress), T8 (PGPR Mix - II - KAU ref. culture) and T4 (Pseudomonas fluorescens - PAP isolate) were the most efficient isolates for enhancing the growth of black pepper under natural condition (without stress). However, T3 (Burkholderia sp. - PAB isolate), T4 (Pseudomonas fluorescens - PAP isolate) and T5 (Trichoderma sp. - CKT isolate) were the most promising isolates for Phytophthora disease management.
Among the isolates obtained in the present studies, the most promising abiotic stress tolerant isolate for growth promotion and disease management in black pepper under polyhouse condition was Trichoderma harzianum (T5 - CKT isolate), whereas Pseudomonas fluorescens (T4 - PAP isolate) was the most promising abiotic stress tolerant isolate under natural conditions.
Most promising abiotic stress tolerant isolate for abiotic stress tolerance, growth promotion and Phytophthora disease management in black pepper nursery under both polyhouse and natural conditions was Trichoderma harzianum (T5 - CKT isolate). However, further studies are needed to confirm the results.