Determination of Marginal Effects of Climatic and Phenotypic Factors on Risk and Average Yield of Irrigated Wheat Lines in Breeding Research

Document Type : Research Paper

Authors

1 Assistant Professor of socio-economic researches office, Seed and Plant Improvement Institute(SPII), Agricultural Research, Education and Extension Organization (AREEO ), Karaj, Iran

2 Associate Professor in Economic, Faculty of Management and Economics, University of Sistan and Baluchestan, Zahedan ,Iran

3 Associate Professor in Economic, Faculty of Management and Economics, University of Sistan and Baluchestan, Zahedan ,Iran.

4 Professor in Agricultural Economic, Faculty of Agriculture, Ferdowsi University of Mashhad, Iran.

5 Principal Scientist, International Maize and Wheat Research Center (CIMMYT) in Iran, Karaj,

Abstract

Introduction
One of the important and effective economic activities in the field of agricultural economic is release varieties or crop improvement technology. This is done to increase the yield and production of various products and to increase food security, self-reliance and reduce dependency (Aghaei & Asadi, 2010 ). Historically, breeders have focused more on increasing of yield varieties, However, reducing variability and instability in yield of varieties at different locationa and times is considered on important breeding goal (Byerlee & Moya, 1993). A lot of factors especially phenotype factors effect on the mean and risk of lines yield in wheat breeding. The one of important models for determine mutual effect on both mean and risk of lines yield is Just and Pope production function. One of the basic requirement of the Just and Pope model is that there be no a priori restrictions on the marginal risk effects so that an factor could be either risk-increasing or risk-decreasing.(Just and Pope, 1979). The objectives of this research were to determine the direct and indirect marginal effects of environmental and phenotypic factors, variety release year as breeders’ efforts in genetic improvement, location and time trend factors on the mean ans variance of grain yield of irrigated bread wheat lines.

Materials and methods
In this study, the required panel data were collected from 23 agricultural locations during 1995-2014 in Iran. The methodolgy of this study was partial equilibrium method and the marginal effects of the variables on the mean and variance of wheat grain yield were assessed using stochastic production function of Just and Pope and spatial durbin models(SDMs). Just and Pope production function was estimated with linear functions in three steps as follows:


Yht =β 0+ β 1 trend + β 2 DHE + β 3 DMA+ β 4 TGW+ β 5 GFD+ β 6 MTem+ Ɓ7S9Rain + Ɓ8 PH + λ RLyear + ɓ1DLoc1 …+ ɓ23DLoc23 + ϵht
Step 1
Ln (ei) 2 = Φ0+ Φ1 trend + Φ2 DHE+ Φ3 DMA+ Φ4 TGW+ Φ5 GFD + Φ6MTem + Φ7 S9Rain + Φ8 PH + Ə RLyear + + ϵh
Step 2
Yht =α0+ α 1 trend + α 2 DHE + α 3 DMA+ α 4 TGW+ α 5 GFD+ α 6 MTem+ α 7S9Rain + α 8 PH + λ RLyear + weight + ϵht
Step 3
Where; Yht: mean yield of bread wheat lines (kg/ha) in year t, trend: time trend, Ln (ei) 2 : yield risk for bread wheat lines in year t,, DHE: days to heading in year t, DMA: days to physiological maturity, GFD: mean of grain filling duration in year t, TGW: thousand grain weight (TGW) (g)
, MTem: mean of annual temperature ( MTem ) (0C), S9Rain: sum of rainfall during cropping season ( S9Rain ) (mm), pH , DLoch: Dummy variables of locations,
RLyear(h=1, 2, …..23): variety release year, Φ.β: δ, ɑ: models parameters and ϵht:, residuals
Results and Discussion
According to the regression results, the study of spatial spillover effects using spatial durbin models (SDM) shwoed that the direct marginal effects of all the phenotypic factors( mean of days to heading, mean of days to physiological maturity, mean of grain filling duration and mean of thousand grain weight) and climatic factors (mean of annual temperature and sum of rainfall during cropping season) on the mean and variance of grain yield of irrigated bread wheat lines were statistically significant. The direct marginal effect of time trend and variety release year on the mean and variance of grain yield of irrigated bread wheat lines was positive but not statistically significant . The annual direct marginal effect of variety release year on the mean of grain yield of irrigated bread wheat lines was estimated to be 69.5 kg/ha in the period of 1995-2014. Adjusted R2 of the model was estimated at 78.4 %.
Conclusion
In general, the direct marginal effects of all the phenotypic factors on the mean of grain yield of irrigated bread wheat lines was satistically significant. The direct marginal effect of time trend and variety release year on on the mean of grain yield of irrigated bread wheat lines was positive.

Keywords

References

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Applied Field Crops Research
Volume 33, Issue 02 - Serial Number 127
papers
July 2020
Pages 1-23

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