predicting wheat grain number by photothermal quotient in anthesis stage

this study was conducted to examine effects photothermal quotient on grain number of four wheat cultivars under four planting dates and four replications. the experiment conducted at the sabzevar agricultural sciences research during 2007-2008 and 2008-2009. various responses functions were evaluated to quantify the response of grain number to influencing parameters (environmental and non- environmental- based factors). the best relationship was found between grain number and grain yield, thus we evaluated and modeled other influence parameters (photothermal quotient and temperature) on grain number. result indicated that the grain number per area with mean temperature (r=0.88) at stem elongation to anthesis stage the highest correlation coefficient and grain number reduced with increasing temperature, in first and second years,12150.3 and 1118.9 grain number /°c respectively. in 27 and 30 ° c mean temperature grain was not formed. qquadratic equation was obtained between grain number per unit area and photothermal quotient at stem elongation to anthesis stage and the highest grain number of wheat were observed in 0.55 photothermal quotient.