Evaluation of CIMMYT conventional and synthetic spring wheat germplasm in rainfed sub-tropical environments. I. Grain yield

Hexaploid spring wheat (Triticum aestivum L) germplasm from CIMMYT's breeding program in Mexico has assisted wheat improvement in Australia, particularly in the north-eastern region where terminal drought frequently reduces grain yield. A total of 273 conventional hexaploid and derived synthetic hexaploid spring wheats from CIMMYT, along with 15 locally adapted Australian cultivars (Oz lines), were evaluated for grain yield over four years in a total of 27 environments in Australia's north-eastern wheat region. The CIMMYT conventional spring wheats were from a Seri/Babax recombinant inbred line population (SB lines), elite entries from an International Adaptation Trial (IAT lines) introduced to Australia between 1999 and 2004 and from CIMMYT screening nurseries introduced to Australia in 2004-2005 (SW lines). Synthetic wheats (SYN lines) were also from these nurseries as well as from a separate program of synthetic wheat introductions to Australia over 2001-2004. Across all environments SB lines were the highest yielding, with 16 broadly adapted SB lines having advantages of 6-10% over seven broadly adapted Oz lines. In a subset of high yielding environments broadly adapted SB, SW and IAT lines were the highest yielding classes, with advantages of 3-8% over these broadly adapted Oz lines. Relative to older CIMMYT spring wheats in the IAT class, the more recent CIMMYT SW lines were better adapted to low yielding environments, with yield advantages of 5% over broadly adapted Oz lines, but they also had the capacity to respond to more favourable conditions. SYN lines were specifically adapted to a subset of lower yielding environments where yields of the broadly adapted synthetics were 5% higher, and up to 13% for individual lines, than that of the broadly adapted Oz lines. Our results support CIMMYT's use of synthetic wheats to improve adaptation to drier environments, and CIMMYT's current breeding strategy of sequential selection under water-stress and irrigation to improve adaptation in drier environments while retaining capacity to respond to more favourable conditions. CIMMYT germplasm has been identified that would be useful as parents in Australian breeding programs targeting rainfed environments with high probabilities of water deficit during the grain filling period. This germplasm should also be adapted globally to similar non-irrigated regions within CIMMYT's mega-environments ME1, ME4c and semi-arid to arid regions of ME5. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.