Agriculture Reference
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grain protein (11.84 %), and 1,000 grain weight (62 g) were higher for wheat plants
co-inoculated with Rhizobium and Bacillus . The increase in grain yield due to
co-inoculation of Rhizobium and Bacillus was calculated as 17.5 % increase over
control. In contrast, the single inoculation of Bacillus increased grain yield by
7.7 %. Phosphorus uptake by grains (25.29 kg ha 1 ) was maximum following
dual-culture application which was followed by sole application of Bacillus inoc-
ulation. Available P in soil after wheat harvest was 16.27 mg kg 1 which was
significantly higher than all other treatments. This field trial clearly demonstrated a
dramatic increase in the availability of P following dual application of Rhizobium
and Bacillus sp. which in effect exerted a strong positive effect on the growth and
yield of wheat plants. Similarly, in a trial conducted under both pot and field
environments, the biomass and total P of winter wheat was significantly increased
following sole application of Phosphobacterium strain 9320-SD. However, there
was no significant difference in height of the test plants (Chen et al. 2006 ). Simi-
larly, PSB ( Serratia marcescens ) isolated from cold temperature region, capable of
synthesizing IAA, HCN, and siderophore, profoundly enhanced the plant biomass
and nutrient uptake of wheat seedlings when grown in cold environment
(Selvakumar et al. 2008 ). In a follow-up study, wheat plants inoculated with
ACC deaminase-positive P. fluorescens and P. fluorescens biotype F had higher
growth, yield, and nutrient use efficiency, when grown in soil treated simulta-
neously with varying levels of three major nutrients like N, P, and K (at 0,
25, 50, 75, and 100 % of recommended doses). However, the overall growth of
inoculated wheat plants decreased both under pot and field trials with increasing
concentration of synthetic fertilizers. Hence, in most of the cases, significant
negative linear correlations were recorded between percentage increases in growth
and yield parameters of even inoculated wheat plants. The decline in growth and
yield of bacterized wheat plants when grown with increasing chemical fertilizers,
however, raised certain questions. For example, do the rates of fertilizers greater
than the recommended ones have any direct impact on composition and functional
activities of bacteria or do excessive rates have any inhibitory effect on plant
metabolism? In this context, it is speculated that low fertilizer application causes
reduction in the ACC deaminase activity of PS strains and thereby leads to
reduction in the synthesis of stress (nutrient)-induced inhibitory levels of ethylene
in the roots through ACC hydrolysis into NH 3 and
-ketobutyrate. Based on this
finding, it was suggested that pseudomonads could be used in combination with
appropriate doses of fertilizers for better plant growth and savings of fertilizers
(Shaharoona et al. 2008 ) as also observed by Kumari et al. ( 2009 ) and Maheshwari
et al. ( 2011 ). Such increase in cereal production following PSB such as
P. fluorescens 153, P. fluorescens 169, P. putida 4, and P. putida 108 application
has been attributed to both PSA of PSB and their ability to synthesize growth-
promoting substances (such as ACC deaminase and IAA-like products) in natural
soil ecosystem (Zabihi et al. 2011 ). Interestingly, P. putida 108 among the bacterial
cultures displayed enhanced P uptake (96 and 80 %) and grain yield (58 and 37 %)
in wheat under greenhouse and field conditions, respectively. Even though this
finding suggested that Pseudomonas sp. could serve as an alternative to expensive P
α
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