Breeding for increased nodule tissue in white clover (Trifolium repens L.)

Summary The results of progeny tests of families of F1 and F2 selections derived from S 100 white clover are reported. The selection criterion was a high total nodule mass per plant coupled with an effective symbiosis with a known effective strain of Rhizobium trifolii. Selection for increased nodule volume produced a correlated increase in nodule number. F1 and F2 had significantly higher means than S 100 but F2 was not significantly higher than F1. Scores for nodule mass showed a significant increase in F1 and a smaller but insignificant increase in F2. An estimate of the efficiency of nitrogen fixation on a unit-nodule basis indicated that as nodule size increased efficiency decreased.