Legume Genomics and Genetics 2016, Vol.7, No.1, 1-11
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3 Discussion
In India, temperature fluctuation during the grain
filling period causes drastic yield losses in cool-season
legumes. In chickpea, grain yields is estimated to
reduce by 53-301 kg/ha if mean temperature rises 1 ºC
(Kalra et al., 2008). Photoperiod and temperature are
the major factors affecting flowering initiation in crop
plants. Pulses are particularly sensitive to heat at
flowering and pod development stages. If the crop
encounters a few days of exposure to high
temperatures (30-35°C) at these stages, heavy yield
losses are reported due to flower drop and pod
abortion (Summerfield et al., 1985; Sarker et al., 1999;
Roberts et al., 1986; Gopesh et al., 2013). However,
this sensitivity varies from genotype to genotype. The
temperature during the reproductive stage in both
years of experimentation was above the threshold
level (>30°C; Figure 2), which suggested suitable
conditions for identification of heat tolerant genotypes
in lentil. Similar environmental conditions have also
been used earlier to screen heat tolerant genotypes in
chickpea (Krishnamurthy et al., 2011). Based on
flowering and podding under higher temperature, in
the present study, lentil genotypes were clearly
categorized into three main groups, (i) early flowering,
(ii) no flowering or rarely flowering and (iii) normal
flowering and pod setting. In the present study 174
genotypes flowered early and matured within 80-85
days after sowing. Because these genotypes escaped
from high temperature conditions and hence excluded
from screening studies conducted further in next year.
Earlier studies showed that heat stress delays
flowering and accelerates maturity (Krishnamurthy et
al., 2011) and hence probably due to this, 64
accessions in the present study did not flower or
flowered rarely. The degree of tolerance was studied
among 37 genotypes, which had filled and unfilled
pods on individual plant as well as on terminal branch.
The combined analysis of variance showed significant
genetic variability for heat tolerance among these
genotypes for filled pods/plant, unfilled pods/plant,
filled and unfilled pods on terminal branch, 50%
flowering and 100-SW. Similarly, genetic variation
for heat tolerance among chickpea genotypes was
reported (Krishnamurthy et al., 2011).
Heritability determines the proportion of parental
characters that is inherited to their off-springs and
hence it is an important parameter to study the
inheritance of quantitative characters (Allard, 1960).
A trait with high heritability suggests maximum
genetic gain in response of selection and can be used
reliably for screening the tolerant genotypes under
heat stress conditions. In the present investigation, we
observed high heritability for filled pods/plant and
filled pods on terminal branch. Therefore, these traits
could be useful to select tolerant genotypes at higher
temperature. Lucas et al. (2012) also used number of
pods per peduncle for identification of heat tolerance
in recombinant inbred lines population of cowpea. In
the present study, three genotypes, IG 3745, IG 4258
and IG 5146 were identified as heat tolerant because
these accessions had significantly more pods per plant
(>43 pods/plant) at higher temperature. On the basis
of the number of pods on the terminal branch at higher
temperature, FLIP2009-55L, IG2507 and IG4258
showed more number of pods on terminal branch and
thus highly heat tolerant. Though another genotype
(IG-3984) also showed more pod formation on
terminal branch, it was poor in total number of
effective pods per plant. We observed significantly
higher unfilled pods for some genotypes, indicating
the impacts of high temperature on pod formation. In
legumes high temperature during anthesis reduces
seed set due to impaired pollen tube growth and
fertilization (Gross and Kigel, 1994).
The present study showed instability in performance
of filled pods/plant over the years in most of the
genotypes. The combined analysis of variation for
filled pods/plant reflected that a large proportion of
total
phenotypic
variance
was
due
to
environmental factors. In pulses, environment and
genotype × environment interactions contribute >70%
of total phenotypic variance as reported earlier
(Kumar and Ali, 2006). However, two genotypes (i.e.
FLIP2009-55L and IG2507) that classified as highly
tolerant to heat showed stable performance over the
years as reflected by low s.e.m. These genotypes can
be used in lentil breeding program for developing
improved cultivars having tolerance to terminal heat.
In the present investigation, impacts of high
temperature were also observed on seed size, which
varied from 2.4% to 67.2% over the normal sown
conditions. However heat tolerant genotypes showed
5.7% to 28.3% reduction in seed size which is
