Effect of salinity on Echinochloa crus-galli germination as affected by herbicide resistance

Abstract

Salinity is one of the major abiotic stresses that may affect yield and quality of crops. Salinization, in combination with the presence of aggressive weeds, such as barnyard grass (Echinochloa spp.), can be considered one of the factors responsible for reducing yield in rice fields. The aims of the study were to evaluate the salt effect on germination and first seedling growth of six different Italian common barnyard grass (E. crus-galli) populations (three sensitive and three resistant to ALS-inhibitor herbicides) and to verify the presence of differences in salt response between populations sensitive and resistant to the ALS-inhibitor herbicides. Germination tests were conducted under nine different NaCl concentrations (from 0 mM to 400 mM). Significant differences in germination capacity were found between sensitive and resistant populations from 0 mM to 250 mM NaCl; in particular, germination capacity of the sensitive populations was higher (up to 90%) than that of the resistant ones (about 70%). The increase in salinity over 250 mM reduced progressively the germination capacity: from 300 mM onwards, no significant differences were found between sensitive and resistant populations and the germination resulted inhibited for two of them (one sensitive and one resistant). Speed of germination and root and shoot length of seedlings were also inversely related to salt concentration. Time required for achieving 50% of final germination capacity was extended from about three days at 0 mM NaCl up to about 10-12 days at 400 mM NaCl. Root length and shoot length ranged from 9.88 cm and 6.16 cm, at 0 mM NaCl, to 0.36 cm and 0.41 cm, at 400 mM NaCl. According to the results, there is no a clear evidence that response to saline conditions was related to resistance towards ALS-inhibitor herbicides, as in some cases significant differences were found between populations showing a similar herbicide sensitivity. Responses of barnyard grass to salinity are may play a role in the importance of this weed in future scenarios of salt intrusion: for example, a lower speed of germination at increasing salt levels could suggest a delayed emergence of this weed during crop establishment and first growth. To evaluate the real consequences in terms of competitions towards the crop, future studies are needed for assessing the response to salinity of the main rice varieties cultivated in the environment in which the E. crus-galli populations tested in this study were collected.

Sensitivity to salinity at the emergence and seedling stages of barnyardgrass (Echinochloa crus-galli), weedy rice (Oryza sativa), and rice with different tolerances to ALS-inhibiting herbicides

“…In this study, values of between 36% and 44% were observed for the emergence of sensitive populations for the highest salt level, while percentages lower than 20% were recorded for the resistant populations. Thus, emergence seems to be affected more by salinity than germination, as observed in the germination test conducted previously on the same populations; in addition, the emergence of herbicide-resistant populations was reduced to a great extent by high salt concentrations compared with the sensitive ones, as already observed for germination in a previous study (Serra et al 2018).…”

“…Reductions in plant height and in the biomass of E. crus-galli for increasing salinity levels were observed in previous studies (Chauhan et al 2013;Hakim et al 2011;Serra et al 2018). A study carried out on E. crus-galli seeds, collected in environments with different degrees of salinity, showed that the seeds were able to germinate up to 1.5% NaCl, while once they emerged, they only survived about 20 d at a concentration of about 1% NaCl (Rahman and Ungar 1990).…”

“…Although most plants can cope with salinity during germination, they are generally more sensitive at the emergence and early growth stages (Läuchli and Grattan 2007). A previous study conducted on Italian ALS inhibitor-resistant and ALS inhibitor-sensitive E. crus-galli populations found that germination occurred up to 400 mM NaCl, although with lower values, that is, about 13% (Serra et al 2018). Moreover, in the same study, values of up to 90% were recorded for the germination of sensitive populations for up to 250 mM NaCl, while an average germination of 70% was observed for resistant populations (Serra et al 2018).…”

“…According to some studies, E. crus-galli is considered to be able to cope with high-saline conditions, probably because this species is able to take up potassium more selectively than sodium (Wilson and Read 2006). The salt tolerance of E. crus-galli is generally higher than that of many other crops, such as rice, and other weeds, like O. sativa (Fogliatto et al 2019;Hakim et al 2011;Serra et al 2018). Echinochloa is also one of the genera most prone to developing herbicide resistance; it has been demonstrated that different populations of E. crus-galli have become resistant to eight site-ofaction herbicides used in rice throughout the world and, in particular, to acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors (Heap 2020).…”

Effect of Different Water Salinity Levels on the Germination of Imazamox-Resistant and Sensitive Weedy Rice and Cultivated Rice

“…A variable germination among weedy rice populations was found in previous studies even in non-saline conditions, and a correlation with other morphological traits (hull colouration, awn presence) has been demonstrated [4,16,52]. The variable response to salt has already been shown for other weed species, such as E. crus-galli, and it can be considered as an advantage for weeds that can easily adapt and infest rice in different environments [38,53].…”