LIST OF ABBRIVIATIONS
2.3 Sowing time and variety
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growth and physiological attributes under heat stress applied at different phenological stages (Javedv et al., 2014).
Kumar et al., (2013) in Ranchi (Chhattisgarh) with two dates of sowing and five wheat varieties (Raj 4229, K 0906, K 0307, HD 2733 and DBW39) and found that grains/ear, grain yield, net returns and benefit: cost ratio was higher in K 0307 variety which was statistically at par with K 0906 and HD 2733 but significantly better than other two varieties of wheat.
Due to heat stress under late sown conditions (December 27), the highest yield reduction was observed in Sourav (46%) followed by Sufi (43%) and lowest reduction was in Shatabdi (27%) followed by Bijoy (32%) and Prodip (35%).
When the phenological, growth and yield attributes took into consideration, Shatabdi performed best under heat stress followed by Bijoy and Prodip, while Sourav and Sufi were sensitive to heat stress in Dinajpur, Bangladesh (Hossain et al., 2012).
Heat occured five days prior to anthesis caused grain number to decline by 0.21%
per °C increase in temperature above 32°C for variety Scout, for variety Yitpi, there was no effect of pre-anthesis heat on yield components, although there was a consistent trend of increasing kernel size across both varieties (Nuttall et al., 2015).
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yield at November 15 sowing as compared to all other sowing dates. Interaction effect of sowing date and varieties on grain yield of wheat showed that the highest grain yield (11.43 t ha-1) was with November 15 sowing date and the lowest grain yield (7.44 t ha-1) was with December 15 sowing date for Pishgam variety, however, for Pishtaz variety gave highest grain yield (9.97 t ha-1) when sown at October 31 and lowest grain yield (7.66 t ha-1) when sown at December 30(Lak et al., 2013).
Bahar variety in Lorestan province (Iran) gave the highest grain yield (10.89 t/ha) when sown at December 15 and lowest grain yield (8.64 t ha-1) when sown at November 30 and Sivand variety gave highest and lowest grain yield when sown at October 31and December 30 respectively (Lak et al., 2013).Basu et al. (2014) in Nadia (West Bengal) concluded that late sown wheat crop experienced highest canopy temperature, varieties of K 9107 and HW 2045 recorded lowest and highest canopy temperature at late sown conditions, respectively and grain yield reduced significantly which was negatively correlated with canopy temperature Wenda-Piesik et al., (2016) in Bydgoszcz (Poland) using four different varieties of wheat (OstkaSmolicka, Monsun, Bombona and Tybalt) under two sowing conditions (autumn and spring) and found that variety Bombona gave higher ear density m-2 in spring sowing than autumn sowing whereas kernels ear-1 and ear length of Tybalt variety was higher autumn sowing. Interaction for thousand grain weight and grain yield was non-significant.
Rascio et al., (2015) conducted an experiment at Italy using two old wheat varieties (Cappelli and Timila) and one new variety (Claudio) under two different sowing conditions (December 19 and March 3) and found that yield of Cappelli and Claudio varieties were decreased under late sown conditions but yield of variety Timila was not affected at all under both conditions. However Claudio variety performed significantly better than both old varieties under both the sowing conditions. Suleiman et al (2014) studied four dates of sowing of wheat (November 1, November 15, December 1 and December 15) on five wheat
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varieties (Al Nilein, Debiera, Imam, Sasaraib and Wadel Neil) at Bahri (Sudan) and found that variety Al Nilein performed better under November 1 sown conditions whereas Imam and Wadel Neil variety performed better under November 15 sown conditions.
In a similar experiment conducted by Hossain et al., (2011) in Bangladesh, using eight dates of sowing (November 8, November 15, November 22, November 29, December 6, December, December 20 and December 27) with eight wheat varieties (Sourav, Gourab, Shatabdi, Sufi, Bijoy, Prodip, BARI Gom 25 and BARI Gom 26) and concluded that the highest 1000-grain weight was recorded by Prodip variety sown under November 29, the highest grain yield was recorded by Shatabdi variety under November 29 and December 6 sown conditions whereas Bijoy and Prodip varieties showed highest grain yield under December 13 sowing.
In an experiment conducted by Costa et al., (2013) at two locations (Elvas and Beja of Portugal) with two dates of sowing (December 5 and December 21 for Elvas and October 26 and November 29 for Beja), two seeding rate and fifteen advanced wheat varieties and revealed that Nabao variety gave the highest test weight at both the dates of sowing, but the highest grain yield was given by Flycatcher at 5 December sowing and Ingenio at 21 December at Elvas, whereas at Beja highest test weight was given by Roxa and the highest grain yield was given by Nogal variety at both dates of sowing and at both seeding rate.
Yajam and Madani (2013) in Iran, in an experiment with four winter wheat varieties (Roshan, Alvand, Amirkabir and Shahriar) and six sowing dates (September 23, October 9, October 24, November 10, November 25 and December 11) and found that maximum grain yield for late sowing date was obtained by Shahriar variety (3.7 t ha-1). The maximum grain yield by 5.3 t ha-1 was obtain at September 23 sowing date by Shahriar variety. The results showed that the Roshan (0.9 t ha-1) and Alvand (1.1 t ha-1) varieties had lowest grain yield for delay in sowing time on December 24.
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Hossain et al., (2015) conducted an experiment at Bangladesh with three wheat varieties (BAW 1051, BARI Gom 27 and BARI Gom 28) with normal (November 25) and late sown (December 10, December 25 and January 10) conditions and concluded that in late sowing conditions, the grain yield was reduced by 4.5-17.8% in BARI Gom 28, 0.4-30.9 % in BARI Gom 27 and 5.8- 20.4% in BAW 1051. It was also observed that grain yield was found to be reduced by about by 8.6-12.6% in BARI Gom 28, 12.8-13.5% in BARI Gom 27and 13.6-15.8% in BAW 1051 from irrigated timely sowing condition for each 1°C rise in average mean air temperature during booting to maturity.
The above findings suggested that long duration varieties with lower ability to tolerate high thermal conditions performed better under early sowing conditions.
Medium duration varieties like PBW 550 were suitable for sowing in mid of the season, but sowing after that also result in reduction in yield of these varieties.
Variety with ability to tolerate thermal conditions also performs well under late sowing conditions.