ABSTRACT

1. MOLECULAR MAPPING OF LEAF CUTICULAR WAXES IN WHEATS. MONDAL, R.E. MASON, F. BEECHER AND D.B.HAYS TEXAS A& M UNIVERSITY, DEPT. OF SOIL & CROP SCIENCES, COLLEGE STATION, TX-77845 ABSTRACT Leaf cuticular waxes in plants provide protective barrier to biotic and abiotic stresses. The objective of this study was to identify quantitative trait loci (QTL) associated with leaf waxes in wheat. A RIL population was derived from a cross of Halberd and Karl 92 was grown in the greenhouse. Plants were grown in the greenhouse at 25C/ 20C day/night temperatures respectively. Leaf wax was collected at 10 DAP from the flag leaf. Flag leaf temperature and leaf width was measured in the greenhouse. The RIL population was evaluated for yield and yield components.  190 SSR markers were polymorphic between the parent lines. Preliminary QTL analysis identifies QTLs associated with leaf wax on chromosome 2A, 5D and 4 A. INTRODUCTION Plant cuticular layer is a thin hydrophobic layer that covers the primary aerial plant surfaces and protects from biotic and abiotic stresses. The cuticular layer is composed of cutin and waxes. Cutin forms the framework of the cuticular matrix with the waxes embedded ( intracuticular wax) and also deposited on the surface ( epicuticular wax). Leaf cuticular waxes affect stomatal conductance, leaf temperatures and surface reflectance. In wheat leaf epicuticular wax increases under drought stress. Studies by Johnson et al (1983) reported significant associations of wheat leaf waxes with reduced leaf temperatures and yield. Various genes controlling wax production and movement have been identified in Arabidopsis, maize, barley and rice. In wheat no genes or molecular markers associated with leaf cuticular waxes have been reported. This study aims at identification of regions in wheat chromosomes that may be associated with flag leaf wax content. RESULTS HALBERD KARL92 Figure 1. SEM images of flag leaf surface of the parent lines Karl92 and Halberd Figure 3. Relationship between flag leaf wax content (mg/dm2)and temperature depression °C (ambient temperature – leaf temperature) DISCUSSION Significant difference in wax content between the parent lines (α = 0.05) Leaf temperature depression positively correlated to leaf wax content ( R=0.4695, α = 0.05) 3 QTLs identified from the parent Halberd. A QTL on 5D is in the same region in both years. 1 QTL on 1B from the parent Karl92 is present in both years of greenhouse study • OBJECTIVE • Map QTLs associated with flag leaf wax content in wheat • Define the interaction between QTLs for leaf wax content and phenotypic and physiological traits Figure 2. Flag leaf wax content of the parent lines Karl92 and Halberd in Year1 2008 and Year2 2009 FURTHER WORK RIL population will be grown in the field in multiple locations to check the validity of the QTLs observed Analysis of the phenotypic data and physiological data to define the interaction with leaf wax content Table 1. Preliminary mapping result of flag leaf wax content in year 2008 and year 2009 • MATERIALS & METHODS • A 120 Recombinant Inbred Lines (RIL) population was developed from a cross of Halberd and Karl 92 wheat lines. The population was grown in the greenhouse at 25°C/20°C day and night temperature respectively • Leaf wax was extracted and quantified by colorimetric technique (Ebercon 1977) at 10DAP • Leaf waxes were visualized by SEM imaging (TAMU-MIC) using Au-Pd sputter coating method. • Leaf temperature was recorded with a infra-red thermometer and porometer respectively • Phenotypic data such as kernel number, kernel weight etc was collected • A genetic linkage map has been developed for the RIL population ( Mason et al 2009. in prep). Single marker analysis and composite interval mapping were performed in QTL Cartographer REFERENCES Ebercon, A.., Blum A. and Jordan W.R. 1977. A rapid colorimetric method for epicuticular wax content of sorghum leaves. Crop Science. 17: 179-180 Johnson, D.A., R.A. Richards, and N.C. Turner.1983. Yield, water relations, gas- exchange, and surface reflectances of near-isogenic wheat lines differing in glaucousness. Crop Sci. 23: 318–325