The effects of NaCl and mannitol iso-osmotic stresses on calli issued from sugarcane cultivars (cvs.) R570, CP59-73 and NCo310 were investigated in relation to callus growth, water content, ion and proline concentrations. Callus growth and water content decreased under both stresses with the highest reduction under mannitol-induced osmotic stress. The ion concentration was drastically affected after exposure to NaCl and mannitol. Salt stress induced an increase in Na + and Cl -accumulation and a decrease in K + and Ca 2+ concentrations. Under mannitol-induced osmotic stress, K + and Ca 2+ concentrations decreased significantly while Na + and Cl -concentrations remained unchanged. Free proline accumulation occurred under both stresses and was more marked in stress-sensitive cv. than in stress-resistant one. Our results indicated that the physiological mechanisms operating at the plant cell level in response to salt-and osmotic-induced stress in sugarcane cvs. are different. Among the cvs., we concluded that the stress resistance is closely related to the maintain of an adequate water status and a high level of K + and Ca 2+ under both stresses and a low level of Na + concentration in the presence of NaCl. Thus, sugarcane (Saccharum sp.) can be regarded as a Na + excluder. We also provided evidence that proline accumulation is a stress-sensitive trait rather than a stress resistance marker.
Stable callus cultures tolerant to NaCl (68 mM) were developed from salt-sensitive sugarcane cultivar CP65-357 by in vitro selection process. The accumulation of both inorganic (Na + , Cl -and K + ) and organic (proline and soluble sugars) solutes was determined in selected and non-selected calli after a NaCl shock in order to evaluate their implication in in vitro salt tolerance of the selected lines. Both salt-tolerant and non-selected calli showed similar relative fresh weight growth in the absence of NaCl. No growth reduction was observed in salt-tolerant calli while a significant reduction about 32% was observed in nonselected ones when both were cultivated on 68 mM NaCl. Accumulation of Na + was similar in both salt-tolerant and non-selected calli in the presence of NaCl. Accumulation of Cl -was lower in NaCl-tolerant than in non-selected calli while proline and soluble sugars were more accumulated in salt-tolerant than in non-selected calli when both were exposed to salt. K + level decreased more severely in non-selected calli than in NaCl-tolerant ones after NaCl shock. The results indicated that K + and Cl -may play a key role in in vitro salt-tolerance in sugarcance cell lines obtained by in vitro selection and that organic solutes could contribute mainly to counteract the negative water potential of the outside medium.
Dioscorea rotundata Poir. is mainly dioecious but it also produces monoecious individuals. Recently two genetic markers were proposed to determine the sex in this species. We tested them in 119 individuals from 101 different cultivars of the national collection of Benin to verify whether they can predict the sex observed in the field. Among the analyzed individuals, 72 were male, 37 were female, 7 were monoecious and 3 were non-flowering. Our results showed that the marker sp16, associated with the W allele (female allele), was present in all female individuals but also in more than 42% of male individuals. Thus, while the absence of sp16 confirmed the male sex of the individuals, its presence did not allow sex discrimination. The marker sp1 allowed the identification of four genotypes (AA, AB, BB and AC) in the analyzed individuals with AA and AB being the most represented. Although AA was observed in 62.16% of female individuals and AB in 83.33% of male individuals, we did not observe a clear correlation between sp1 genotypes and sex identity. We concluded that the tested markers did not allow a clear sex discrimination in Beninese Dioscorea rotundata cultivars. Our results also suggest that Beninese D. rotundata cultivars have adopted a male XX/XY heterogametic system that is undergoing reorganization.
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