Salt Effects on Emergence and Seedling Mortality of Guayule1

Abstract

AbstractEstablishment of guayule (Parthenium argentatumGray) by direct seeding has been unreliable due to poor seedling emergence and subsequent mortality. Laboratory germination, greenhouse and small field plot tests were performed for evaluating possible salinity interactions. Guayule seeds (593, 11591, and bulk collection) germinated 60 to 85% in petri dishes containing high saline solutions (EC = 22 dSm−1). Yet, emergence from well‐watered sandy soils was reduced sharply with increasing salinity, e.g., less than 10% emergence at irrigation water salinity of 4.5 dSm−1in field plots irrigated twice a day. Seedling mortality was negligible when irrigated with distilled or low salt water, but increased with increasing salinity. Both emergence and seedling survival rates were highly correlated (r = −0.94) with the salinity of surface (0 to 1 cm depth) soil samples. Salts introduced through irrigation water accumulated mostly in the surface 0.5 cm of soils with concentrations ranging from 4 to 22 dSm−1in soil saturation extract. Salt concentrations at seeding depths (0.5 to 0.8 cm) were, however, low enough to allow seed germination. Low emergence and high seedling mortality observed here appeared to be related to hypocotyl and seedling damage by salts accumulated on soil surfaces. Such damage can occur in soils classified as nonsaline when irrigated with water having salinity as low as 1 dSm−1.