Morpho-physiological and some biochemical responses of sorghum (Sorghum bicolor (L.) Moench) landraces grown under different irrigation levels with special emphasis on post-flowering drought stress
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Date
2014-06
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Addis Ababa Universty
Abstract
Morpho-physiological and biochemical investigations were conducted on five selected
sorghum (Sorghum bicolor (L.) Moench) landraces (SorColl 60, SorColl 146, SorColl
163, SorColl 178 and SorColl 179) and three cultivars (Abshir, E 36-1 and B 35) to
evaluate and screen for drought resistant and stay green potential landraces. The main
objective of the study was to enrich parental lines with stay green trait. The study was
undertaken both at field (Melkassa Research Station, Melkassa) and greenhouse (College
of Natural Science, Addis Ababa University) conditions in 2011 and 2012. A split plot
and randomized complete block designs with three replications were used for the field
and greenhouse experiments, respectively. Irrigation levels 0%, 25%, 55%, 65% and
80% of total available water (TAW)at field and FC at green house during pre-flowering
and a post-flowering progressive drought stress during the field study were applied.
Results demonstrated that all sorghum varieties exhibited different values of the
phenotypic traits considered at non stress level except proline content analysis,
indicating genetic variation among landraces. Moreover, all traits examined were with
different varieties scoring highest value, and high performance at full irrigation had no
synchronization with stay green trait. Imposing different irrigation level at pre-flowering
resulted in delayed reproductive stage occurrence in the field study. Culm height was
more affected by pre-flowering drought stress than by post-flowering. Culm height was
relatively more resistant to pre-flowering drought effect in varieties E 36-1, SorColl 163
and Abshir. SorColl 60, E 36-1 and SorColl 163 demonstrated an improvement in culm
height over other varieties.Third leaf area, biomass, senescence rate, assimilation rate
responses were more sensitive to drought, but SPADR was not. SorColl 60, Abshir
followed by SorColl 163 third leaf area decreased least relative to other varieties.
Senescence rate evaluation after grain filling revealed an increasing rate with increasing drought stress. SorColl 163, SorColl 146 and E 36-1were with least senescence rate in
post grain filling stage. At 80% water deficit level, the maximum per cent shoot weight
loss from the controls was recorded for SorColl 179 (60%) followed by Abshir and E 36-
1. SorColl 146 had the lowest percent shoot weight loss (36%) as compared to other
varieties. Root biomass of E 36-1 and SorColl 163 increased at severe and mild drought
stress levels respectively, while root biomass of SorColl 60 and SorColl 179 went
diminishing with increasing water deficit levels. E 36-1, SorColl 178 and SorColl 163
demonstrated a sharp increase in root-shoot biomass ratio indicating relatively a higher
dry mater partitioning to roots, while SorColl 179 had the least. In all sorghum varieties
under non stress condition /full irrigation/, root length density (RLD) distribution was
skewed (greater than 50%) to the first two upper soil depths. The skewed RLD
distribution was improved with increasing drought stress from 70-60% in non stress
condition to 55-47.5% at 80% on the upper depth. High drought tolerance index (DTI)
value was recorded in Abshire, SorColl 178 and SorColl 60. Abshir had high DTI that
increased with increasing drought effect; while SorColl 179 demonstrated least index
value that further declined with increasing drought stress. Assimilation rate decreased
with increasing drought stress and at 55% water deficit level, SorColl 146 (48.4 mole
CO2/m2s), E 36-1(43.4 mole CO2/m2s) and SorColl 163 (40 mole CO2/m2s) maintained
rate of assimilation better than others and at both 65% and 80 % levels AN was
insignificantly affected by the drought stress.Yield in terms of seed weight per panicle
was observed highest in the check E 36-1 followed by SorColl 163 and SorColl 60
whereas SorColl 178 performed least. The study on interrupted drought in the phases of
the reproductive stage revealed that yield loss was due to different factors in the
reproductive phases considered. Higher yield loss was found due to drought imposed at
panicle initiation and seed filling. Loss in seed count had least contribution in E 36-1,
SorColl 146 and SorColl 163.Seedlings of Sorghum varieties were found decreasing in
height, biomass, assimilation rate but increasing in Chlorophyll a and b and proline
content with increasing drought stress. Sorghum landraces SorColl 146, SorColl163,
SorColl 60 relatively performed better, whereas SorColl 179, E 36-1, SorColl 178,
Abshir, and B 35 were negatively affected by the drought stress. Green house root-shoot ratio of SorColl 146, SorColl 178, SorColl 179 and SorColl 163 were higher than others
at the most severe drought stress (65%). Third Leaf area of SorColl 179, SorColl 163,
and E 36-1 SorColl 178 was less affected over other genotypes. Unlike the results from
the field condition, assimilation rate of SorColl 163 and SorColl 146 including the checks
were affected highest at seedling and greenhouse condition. A gentle increase in Chl a
and Chl b content was recorded with increasing drought but concentrations at 65% were
relatively lower than 25% and 55% irrigation levels. The highest reading of Chl a
content was recorded in B 35, SorColl 163 and SorColl 60 but SorColl 146 and SorColl
179 had least content and with a sharp decrease in Chl a. On the other hand, Chl b
content in SorColl 179, SorColl 146 and B 35 was highest but SorColl 146, SorColl 163,
E 36-1 had least and values decreased up to 55% field capacity. Proline content also
increased with increasing drought stress in the extracts of all the three organs from
control plants. In all organs, there was small amount (about 2-5 gm/gm) and
insignificant variation among the varieties (except SorColl 60 (14.17gm/gm) and
SorColl 146 (8.95gm/gm) in root) at non stress condition and slow induction in proline
was recorded in the mild drought stress. With increasing drought stress, proline content
increased sharply in the stem followed by root extract. E 36-1, SorColl 163, B 35 and
Abshir demonstrated the highest content in all the organs at the severe drought stress
levels, indicating that all the check varieties had active response. It is concluded that of
the grain sorghum landraces studied, SorColl 163 had a stay green trait that is found to
give high yield under both deficit irrigation before flowering and progressive drought
stress in post-flowering period. SorColl 146 performed in many traits next to SorColl 163
but with reduced yield. Thus, SorColl 146 may be described to have cosmetic stay green
trait under drought stress. SorColl 60 had inconsistent responses but had better yield
than SorColl 146 under severe drought stress. The study recomends that SorColl 163 be
used to transfer drought resistant traits to other sorghum lines along with the currently
used lines, B 35 and E 36-1.
Key words: grain sorghum, stay green, pre-flowering drought stress, post-flowering
drought stress, biomass, leaf area, senescence, photosynthesis, SPAD, RLD, yield,
proline, chlorophyll content, drought tolerance.
Description
Keywords
Grain sorghum, Stay green, Pre-flowering drought stress, Post-flowering drought stress, Biomass, Leaf area, Senescence, Photosynthesis, SPAD, RLD, Yield, Proline, Chlorophyll content, Drought tolerance