Correlation between soil pH of collection site and the tolerance of wild genotypes of Lupinus angustifolius L. to neutral pH

Abstract

Summary. Lupinus angustifolius L. grows poorly on alkaline soils, and high pH appeared to be a major limiting factor. In this study, 30 wild genotypes of this species collected from soils with a wide range of pH (4.2–9.0) and texture (coarse sand–clay) were grown in nutrient solution for 22 days to examine their tolerance of pH 7. Cultivars of L. angustifolius, L. pilosus, L. luteus and Pisum sativum were included for comparison. Root length, nodule number, chlorophyll and iron concentrations in leaves were lower in almost all wild genotypes grown at pH 7.0 compared with those at pH 5.2. However, there was large variation in growth and nodulation in response to high pH among genotypes. Compared with the value at pH 5.2, shoot weight at pH 7.0 ranged from 41 to 120%, chlorophyll concentration from 8 to 75%, iron concentration from 22 to 70%, root weight from 27 to 109%, root elongation rate from 61 to 96% and nodule number from 0 to 86%. However, the tolerance (as assessed by growth and nodulation) of these wild genotypes to pH 7.0 was not correlated with soil pH or texture at collection site, but iron chlorosis at pH 7.0 was weakly correlated with collection site soil texture (r = –0.36, n = 30) and seed size (r = –0.45, n = 30), and early root elongation correlated with seed size (r = –0.55, n = 30). In addition, some wild genotypes appeared to be more tolerant to pH 7.0 than existing cultivars of L. angustifolius. The results confirm that soil pH at collection site (as recorded in the Agriculture Western Australia International Lupin Collection) is not a useful indicator for selecting high pH-tolerant genotypes of L. angustifolius.