Recent Advances and Future Prospects on Practical Use of Salicylic Acid - Salicylic Acid: Plant Growth and Development - page 364

plant height, leaf area, crop growth rate and total dry matter production. Moreover,
and the cob yield of baby corn was the highest by the foliar application of SA.
Sujatha ( 2001 ) reported that foliar application of SA (100 ppm) on green gram at
75 days after sowing increased plant height, root length, number of leaves and leaf
area index. Authors also demonstrated that foliar application of SA increased
number of pods plant -1 , number of seeds pod -1 , seed weight plant -1 , 100 seed
weight and grain yield. In green gram, foliar application of SA at branching, flower
bud initiation stages increased the number of flowers, pods and seeds plant -1 and
seed yield (Singh et al. 1980 ). Treatment of mungbean with SA significantly
increased the pod number plant -1 and yield (Singh and Kaur 1981 ).
The quality parameters were also improved by SA treatment. Jeyakumar et al.
( 2008 ) reported that the highest seed protein content in black gram was recorded
by foliar application of SA (125 ppm). Hussein et al. ( 2007 ) indicated that in
maize hybrid, all determinated amino acids concentration such as tyrosine, lysine,
arginine, alanine, leucine, except methionine increased with the application of SA
(200 ppm). Proline concentration increased when using SA acid as foliar appli-
cation under salt stress condition. Sujatha ( 2001 ) revealed that foliar application of
SA (100 ppm) on green gram at 75 DAS increased seed protein and soluble
protein. Kalpana ( 1997 ) found that foliar spray of SA increased the soluble protein
in rice. Results indicated that seed imbibition with SA affected physiological
processes related to growth and development in cucumber plants. At lower con-
centrations, SA significantly increase rate of seed germination and plant dry mass
even if added NO 3 was 20 lM. Plants treated with 10 and 50 lM SA had higher
chlorophyll levels and NO 3 -assimilation through the induction of nitrate reductase
(NR) activity. However, 100 and 500 lM were detrimental to plant health.
Exogenous application of SA to cucumber plants improved their growth and
50 lM SA is the optimum physiological concentration that increased nitrogen use
efficiency during germination and seedling growth (Kumar et al. 2010 ).
Plant species vary widely in their tolerance to applications of SA and aspirin at
varying concentrations. Often at high concentrations, plant damage occurs.
However, relatively large concentrations are needed to induce resistance because
much of the SA become immobilized in the plant tissues that initially get contact
during application.
Plants make SA acid to trigger natural defenses against bacteria, fungi, and
viruses. However, plants often do not produce the acid quickly enough to prevent
injury when attacked by a microbe. Plants have always had some means to defend
themselves; it is just that some do not recognize their microbial attackers in time.
In 2009, Science News published a very interesting paper concerning how to
use SA and what are the benefits for farmers and for plants of increased level of
SA. The dilemma is that spraying SA puts plants defenses on high-alert against
future attacks. But a rise in SA levels also causes the plant to slow its growth,
perhaps saving its strength for the battle against the pathogen. That sets up a
challenging situation for both the plant-grow faster or protect myself better? and
farmers, who might view SA as a tool to protect their plants from disease. A plant
that makes high levels of SA all the time will be safe from infection but will grow