Heterosis in lucerne testcrosses with Medicago arborea introgressions and Omani landraces and their performance in synthetics

Testcrosses were made with novel sources of lucerne germplasm. These were evaluated in the field in a subtropical environment to identify the lines which produced the highest yielding hybrids as a guide to future breeding efforts. The novel sources were derivatives of Medicago sativa × M. arborea partial (asymmetric) hybrids (termed sac) and very highly winter-active Omani landraces of M. sativa. As testers, 2 lines were used; a Colletotrichum trifolii race 2 resistant selection from the group 9 Australian-bred and adapted cultivar PacL 901 (selection hereafter termed 901) and the Omani landrace, Oman 2, collected at 17°N latitude, from Salalah, Oman. In the row experiment, substantial and significantly positive tester parent heterosis for overall yield (sum of 13 harvests) was observed in all of the sac × Oman 2 testcrosses, with the mean performance of the 11 testcrosses (1839 g/m row) significantly (P < 0.05) exceeding the mean performance of the sac × 901 testcrosses (1703 g/m row) evaluated. Where 901 was used as the tester, heterosis values relative to the tester for the same sac lines were negative for all testcrosses with 8 of the testcrosses being significantly negative. For the Omani landrace × 901 testcrosses, positive and negative heterosis values for total yield relative to the tester were observed, but none were significantly different from zero. The 901 tester yielded significantly (P < 0.05) more per se than the Oman 2 tester (1956 v. 1470 g/m row), although in an adjacent sward experiment Oman 2 yielded comparably to most of the standard commercial cultivars. The potential of the novel germplasm in the subtropics was verified in sward experiments with synthetics and/or strain crosses with yield increases of up to 42% over the benchmark synthetic Sequel. Further improvements can be expected following selection for disease and pest resistance within the lines and in the case of Oman 2 and sac, converging to maximise complementary gene action.