More than 3,000 durum wheats (Triticum turgidum L. durum group) from the USDA world wheat collection were grown in the field and classified for leaf sheath glossiness, glume pubescence and color, awn color, kernel color, and basal spike node fertility. The entries were grouped by geographic origin, and frequencies of the various phenotypes were examined. Variation for all characters was found, and usually within each geographic region. The number of entries in the collection was very small from some areas known to be important sources of germplasm, pointing to the importance of intensifying efforts in germplasm exploration and conservation. The Shannon‐Weaver diversity index (H') was used to examine overall genetic divergence on a country and regional basis. In collections of substantial size, Ethiopia and Portugal had the greatest diversity (H' = 0.87 and 0.86), and Turkey, Bulgaria, and the United States had significantly less diversity (H' = 0.50, 0.42, and 0.39). Based on the characters studied and the relatively small collection evaluated, the centers of diversity seem to be Ethiopia, the Mediterranean region, and India.
Interrelationships among production characters were determined both by simple correlation and path coefficient analyses, using ecogeographically diverse spring wheat genotypes . Simple correlation analysis indicated that kernel weight correlated positively with plant height and negatively with heading time. Also spike number and kernel weight showed highly positive and heading time highly negative correlations with grain yield . Path coefficient analysis was useful in that it revealed the true nature of cause-and-effect relationships of heading time, plant height, spike number and kernel weight with grain yield . Wherever feasible, path coefficient analysis should be conducted in addition to simple correlation analysis .
A method of choosing parents for hybridization (aiming at yield improvement) by quantitatively measuring the genetic divergence is described, with the use of data on several characters measured on 40 genotypes of wheat (Triticum aestivum) which had their origin in different ecogeographic regions of Australia. The genotypes were grouped into 12 gene constellations by this method. The method of formulating a crossing programme based on the information on statistical distance between different gene constellations is discussed briefly.
Triticum aestivum, wheat, pre-harvest sprouting, components of resistance to sprouting . complex resistance (RCP), a-amylase synthesis, GA3 response, wheat endosperm .
SUMMARYThe problem of pre-harvest sprouting in wheat is very intricate . New concepts in breeding for resistance to pre-harvest sprouting regard many components such as a-amylase production potential, response to gibberellic acid and inhibition in the bracts as important as dormancy . In the research work carried out at The University of Sydney's Plant Breeding Institute, we found varietal differences for each of these components. We also developed criteria for screening breeding material for these components. The implications of our findings in planning efficient breeding programmes to evolve varieties with multiple resistance to pre-harvest sprouting have been discussed briefly .
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