Screening of pink pigmented facultative methylotroph isolates for water stress tolerance and yield in paddy

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Date
2019
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Department of Agricultural Microbiology, College of Agriculture, Vellayani
Abstract
The study entitled “Screening of Pink Pigmented Facultative Methylotroph (PPFM) isolates for water stress tolerance and yield in paddy” was undertaken during 2017-2019, in the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram, with the objective to screen the Pink Pigmented Facultative Methylotroph (PPFM) isolates for water stress tolerance and yield in paddy. The study comprised an in vitro screening experiment and a pot culture experiment with rice variety Harsha. For in vitro screening of PPFM isolates for water stress tolerance, 20 isolates of PPFM from paddy were selected from the previous study of M.Sc. (Ag.) thesis work conducted in the Department of Agricultural Microbiology, Vellayani during 2015-2017 on the basis of carotenoid pigment production, IAA production, proline content, seedling vigour index and yield. These isolates were screened by paper towel method for water stress tolerance under in vitro conditions using mannitol for inducing osmotic stress. There were 21 isolates (20 KAU isolates of PPFM and one TNAU isolate) and four water stress levels (1%, 2%, 3% mannitol and control). The experiment was laid out in completely randomized block design with two replications. Osmotic stress was higher in 3 per cent mannitol treatment. Seeds treated with PPFM 26 recorded the highest germination percentage, shoot length and seedling vigour index. The highest root length and shoot dry weight were observed with the isolate PPFM 15 whereas the highest root dry weight was recorded with PPFM 9. Scoring was done to assess the best five isolates and those with higher ranks were selected for the subsequent experiment. Consequently, PPFM 26, PPFM 15, PPFM 38, PPFM 37 and PPFM 35 which secured ranks from 1 to 5 were selected for the pot culture experiment. The pot culture experiment was undertaken to study the effect of PPFM isolates on growth and yield of paddy under water stress. The experiment was laid out in CRD with 21 treatments and three replications, during summer 2019. The treatments comprised six PPFM isolates (5 KAU isolates of PPFM and one TNAU isolate) and three moisture levels (at field capacity, 75% available water and 50% AW) and three control treatments (0.5% methanol, AMS liquid medium supplemented with 0.5% methanol and absolute control). The treatments were given as seed treatment, seedling root dip and foliar application at 15 and 30 DAT. The study revealed that PPFM isolates had significant effect on biometric parameters, physiological parameters, yield and yield attributes of paddy under water stress. Maximum plant height and leaf area index was recorded with PPFM 38 at 30 DAT and 60 DAT whereas PPFM 37 recorded maximum number of tillers per hill at 60 DAT. Leaf rolling score and leaf drying score were found to be the lowest with PPFM 37 at 30 and 60 DAT. Cell membrane integrity, relative water content, chlorophyll stability index and root dry weight were the highest with PPFM 38 at 30 and 60 DAT. Rooting depth was the highest with PPFM 38 at 30 DAT and PPFM 37 at 60 DAT. Proline content (at all the three moisture levels) and super oxide dismutase (SOD) were significantly higher with PPFM 37 at 30 and 60 DAT. While at 60 DAT, PPFM 37 recorded significantly higher catalase activity at FC and 50% AW, PPFM 38 was found to be superior at 75% AW. Both these isolates were comparable at the different moisture levels. Crop treated with PPFM 37 also recorded the lowest drought susceptibility index. However, peroxidase activity was significantly higher with PPFM 38 at all moisture levels at 30 and 60 DAT. All the PPFM isolates had significant effect on yield attributes and yield of paddy under water stress. Maximum number of panicles per hill, number of grains per panicle (at all moisture levels), grain yield and the lowest relative percentage yield reduction was recorded with PPFM 37. While, PPFM 37 recorded significantly higher number of panicles per hill at FC and 75% AW, PPFM 38 was found to be superior at 50% AW. Both these isolates were comparable at different moisture levels. Though PPFM 37 recorded higher grain yield at all the moisture levels it was on par with PPFM 38. Considering the major drought tolerance parameters such as leaf rolling score, leaf drying score, rooting depth, proline content, SOD, catalase and peroxidase, PPFM 38 was ranked first among the PPFM isolates tested in the pot culture experiment. With respect to the yield attributes and yield of rice under water stress the effect of PPFM 37 and PPFM 38 were observed to be at par. The present study revealed that the isolates PPFM 37 and PPFM 38 (seed treatment 1% PPFM broth culture + seedling dip 2% PPFM broth culture + foliar spray 1% PPFM broth culture at 15 and 30 DAT) were effective in improving the growth, yield and drought tolerance characters of rice.
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