Abstract
Herbicides are an important component of weed management in wheat, particularly in the southeastern US where weeds actively compete with wheat throughout the winter for nutrients and reduce tillering and ultimately the yield of the crop. Some wheat varieties are sensitive to metribuzin, a low-cost non-selective herbicide, leading to leaf chlorosis, stand loss, and decreased yield. Knowledge of the genetics of herbicide tolerance in wheat is very limited and most new varieties have not been screened for metribuzin tolerance. The identification of genes associated with metribuzin tolerance will lead to the development of molecular markers for use in screening breeding lines for metribuzin tolerance. AGS 2035 and AGS 2060 were identified as resistant and sensitive to metribuzin in several previous field screening experiments as well as controlled condition screening of nine varieties in the present study. Genome-wide transcriptome profiling of the genes in AGS 2035 and AGS 2060 through microarray analysis identified 169 and 127 genes to be significantly (2-fold, P>0.01) up- and down-regulated, respectively in response to metribuzin. Functional annotation revealed that genes involved in cell wall biosynthesis, photosynthesis and sucrose metabolism were highly responsive to metribuzin application. (Semi)quantitative RT-PCR of seven selected differentially expressed genes (DEGs) indicated that a gene coding for alkaline alpha-galactosidase 2 (AAG2) was specifically expressed in resistant varieties only after one and two weeks of metribuzin application. Integration of the DEGs into our ongoing mapping effort and identification of the genes within the QTL region showing significant association with resistance in future will aid in development of functional markers for metribuzin resistance.
Highlights
Weed control in wheat (Triticum aestivum) is an important aspect of crop management, in the southeastern US where wheat and weeds actively grow throughout the winter
Pio 26R87 was moderately sensitive while Progeny 125, AGS 2060, Harrison and USG 3555 were highly sensitive with maximum damage to foliar growth and photosystem II (Fig 2)
Previous greenhouse and field-based screening showed that AGS 2035 possessed high levels of resistance to metribuzin whereas AGS 2060 was highly sensitive with severe foliar damage, and tiller death and reduction in growth
Summary
Weed control in wheat (Triticum aestivum) is an important aspect of crop management, in the southeastern US where wheat and weeds actively grow throughout the winter. Some non-selective herbicides, such as metribuzin, are advantageous over selective herbicides because of the flexibility of their use as pre- and postemergent, and these are less labor-intensive with less or no tillage requirement, and most importantly cost-effectiveness as a single application can kill many types of weeds in the field. Despite their advantages, non-selective herbicide resistance has not been widely targeted in breeding field crops becasue they may not discriminate between the weed and the crop. The inheritance of tolerance to metribuzin was complex and under the control of multiple alleles This was supported by the observation that physiological processes, such as uptake, translocation and metabolism/detoxification modified the amount of herbicide reaching the target site [5]. We report on identification of candidate genes associated with the tolerance of wheat to metribuzin using the 44K wheat gene-chips
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