Yellow lupin (Lupinus luteus) tolerates waterlogging better than narrow-leafed lupin (L-angustifolius) - IV. Root genotype is more important than shoot genotype

To understand how yellow lupin tolerates waterlogging better than narrow-le afed lupin, we investigated the roles of the roots and the shoots of these species. Reciprocal- and self-grafted combinations (scion = shoot/rootstock ) of yellow and narrow-leafed lupin were made at the 2-leaf stage and water logged 45 days later (8-10 leaf stage). Responses to waterlogging were exam ined at the end of waterlogging and following a recovery period of 14 days. Waterlogging of reciprocal and self-grafted plants reduced total plant dry weight by 15-58% compared with non-waterlogged controls. These reductions w ere greater when the rootstock was narrow-leafed rather than yellow lupin, and were similar for the roots and shoots. Waterlogging increased dry weigh t of hypocotyl roots in most grafting combinations (by 2-19-fold), but graf ts with narrow-leafed lupin scions produced almost twice the hypocotyl root length of grafts with yellow lupin scions. During the waterlogging period, leaf gas exchange decreased by 16-74% in all grafting combinations except in narrow-leafed lupin scion/yellow lupin rootstock where it increased by 1 7-30%. During waterlogging, stem water potential decreased and leaf osmotic pressure increased. These changes compensated one another and consequently there was no effect on bulk leaf turgor. After 14 days recovery, water rel ations returned to initial values. Tolerance of the whole plant to waterlogging was influenced more by the roo t genotype than the shoot genotype. However, production of hypocotyl roots in response to waterlogging was related to the shoot genotype rather than t he root genotype.