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Wheat Information Service
Number 86: 46-48 (1998)
Research information

Effect of delayed sowing on some parameters of photosynthesis in wheat (Triticum aestivum L.)

M. Yasin Ashraf and A. Saeed Bhatti

Nuclear Institute for Agriculture and Biology, P.O. Box No. 128, Jhang Road Faisalabad, Pakistan


Wheat is the staple food of the people of Pakistan and is cultivated on large area. However in the face of ever growing population, crop production in the country is limited and could be attributed among other factors to the forced late sowing because of delay in the harvesting of the preceding Kharif crops e.g. rice and cotton. As a result, the grain filling period (Mid March to first week of April) of the late sown wheat experiences higher temperature (35-45C) as well as a longer photoperiod. In addition the crop receives less total photosynthetically active radiant energy than its early sown counterparts resulting in a reduction in biomass and the grain yield (Panelia et al. 1993). The duration of grain filling period is relatively more affected than the period from sowing to anthesis and occasionally the crop is prematurely ripened.

Besides many other factors, productivity of a crop depends on the photosynthetic efficiency which is regulated by gaseous exchange capacity, leaf area and their chlorophyll contents (Ashraf, Azim et al. 1994; Ashraf, Khan et al. 1992). We, therefore, investigated the effect of three sowing times on the leaf area and chlorophyll contents of 16 wheat genotypes.

A field experiment was conducted during 1994-1995 season, to study the effect of different sowing times on chlorophyll contents and leaf area of six wheat genotypes. The experiment consisted of three treatments i.e. T1 (normal, 13-11-1994), T2 (1-12-1994) and T3 (15-12-1994) with five replications and 16 wheat genotypes. Fertilization was done @ 100 kg N/ha, 115 kg P205/ha and 5.3 kg K/ha and normal cultural practices were followed as and when required. Ninety days after sowing leaf area (LI-3100 Area meter, LI-COR, inc, USA) and chlorophyll content were determined (Arnon, 1949). At maturity grain yield per plant was determined. Analysis of variance was applied to determine the significance of differences among the treatments and/or genotypes. Differences compared by Duncan's Multiple Range Test (DMRT) at 5% probability (Steel and Torrie 1980).

Chlorophyll content in all genotypes decreased with late sowing (Fig.1). Under normal conditions, Mehran-89, Sarsabz form one group with the highest chlorophyll content, Soghat-90, PN-9086, PN-9041, PN-9005, SH-9044, SI- 9077, SP-89128, SH-8921, SH-8918, SI-8927 second group and PN-9111, PN-9083, SI-90157 and SP-89126 the third group with lowest chlorophyll content. Under T2 treatment, genotypes form four groups and PN-9005 having the highest chlorophyll content. Under T3 conditions Sarsabz competed to all genotypes (Fig.1 a).

Leaf area (LA) also decreased with late sowing (Fig.1 b) but the differences between T2 and
T3 were nonsignificant. Under normal conditions, genotype SH-8921 had the highest and SP-89128, PN-9005 and SI- 8927 had the lowest LA. Under T2 SH-8921 had the highest LA and SP-89128, SI-9077, SH-9044 and PN-9005 had the lowest LA. But under T3 Sarsabz was on the top and SI-9077 on the bottom of the list. Genotypic means showed that SH- 8921 had greater LA than all other genotypes.

Grain yield per plant in all genotypes was reduced due to late sowing (Fig.1 c). However, the differences between T1 and T2 are nonsignificant. Under T1 the highest grain yield per plant was recorded in SH-8918 while under late sowing it lost its top position. Under T2, Mehran had the maximum grain yield per plant which nonsignificantly differed from Sarsabz, PN-901 11, PN-9086, SI-90157 and SP-89126. But under T3, the maximum grain yield per plant was obtained in PN-90111 and SH-8918 and the second group with high grain yield per plant was formed by Sarsabz, Mehran-89, PN-9041, PN-9005, SI-9077 and SP-89128, while others remained beyond these. Genotypic means again showed that SH-8918 had the highest grain yield per plant (Fig.1 c). The correlations between grain yield per plant, chlorophyll contents and leaf area were positive but nonsignificant.

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