Cryopreservation is a promising technique for long term conservation of sugarcane's genetic resources which could be used in breeding programs. Preculture is a key step for success this technique. The purpose of this study was to evaluate the effect of sucrose concentrations and preculture period on dessication tolerance of sugarcane tissue dehydrated to 30, 20 and 10 % moisture. Sugarcane shoot tips were encapsulated in sodium alginate and precultured in a liquid culture medium with 0.3, 0.5, and 0.75 M sucrose. Preculturing in 0.3 M sucrose was ideal to induce desiccation tolerance in tissue. This sucrose concentration reduced the percentage of electrolytic leakage. Shoot tips were sensitive to a sucrose concentration of 0.75 M, resulting in low survival rates after desiccation. Preculturing in 0.5 M sucrose resulted in a higher survival rate after drying for 5.7 and 7.45 h. The percentage of electrolytic leakage was high when shoot tips were desiccated after preculturing in 0.5 and 0.75 M sucrose.
The purpose of this study was to investigate and compare root morpho-anatomical traits and physiological responses of susceptible (SP81-3250) and resistant (H. Kawandang) sugarcane genotypes exposed to the attack by nymphs of spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae). Two experiments were conducted to compare the damage caused by spittlebug nymphs on fresh and dry biomass weight; lignin content in stalks; root anatomy; chlorophyll content; photosynthetic rate (A); carboxylation efficiency (A/Ci); stomatal conductance (gS) and transpiration rate (E) of these genotypes. SP81-3250 consistently obtained significantly higher damage scores than H. Kawandang in both experiments, confirming the previously observed level of resistance in each genotype. Attack by spittlebug nymphs had a much higher effect on both fresh and dry biomass weight, chlorophyll content, A, A/Ci, gs and E of SP81-3250, than that on H. Kawandang. Anatomical studies indicated the presence of aerenchyma tissue in the root cortex of SP81-3250, a feature which may facilitate penetration of the nymph's stylet into the vascular cylinder. In contrast, roots of H. Kawandang are characterized by having more dense and compact parenchyma cells. In addition, infested plants of this genotype contained an unidentified mucilaginous compound in the vascular cylinder of the roots. We conclude that resistance of H. Kawandang to spittlebug is related to the ability of this genotype to maintain normal chlorophyll content, as well as stomatal conductance and photosynthesis, thus, allowing for biomass accumulation under spittlebug attack, in contrast to SP81-3250. In addition, the presence of more compact and denser parenchymal cells, as well as that of an induced mucilaginous compound in the root's vascular cylinder, are likely to hinder host-feeding activity in nymphs, causing higher nymph mortality and therefore, reduced damage in plants of this genotype.
O presente trabalho teve por objetivo aplicar a teoria de modelos mistos para predizer os valores genotípicos e estimar os parâmetros de adaptabilidade e estabilidade de clones de cana-de-açúcar avaliados no delineamento de blocos aumentados em vários ambientes e, também, avaliar a correlação existente entre estes valores preditos e, ou estimados. Foram utilizadas as metodologias de Wricke (Wricke & Webber, 1986), Eberhart & Russell (1966) e Carneiro (1998). Os valores genotípicos preditos livres dos efeitos da interação genótipos x ambientes mostraram-se fortemente correlacionados com os parâmetros estimados pela metodologia de Carneiro, moderadamente correlacionados com os parâmetros de adaptabilidade ( ) do método de Eberhart and Russel e fracamente correlacionados com o parâmetro ωi (%) de Wricke e com o parâmetro R2i (%) de Eberhart and Russel. O parâmetro ωi (%) apresentou correlação significativa apenas com o parâmetro R2i (%) de Eberhart e Russell, indicando a semelhança de ambos em avaliar a estabilidade dos genótipos. Esses resultados revelam que os valores genotípicos preditos livres dos efeitos da interação genótipos x ambientes correlacionam-se mais com a adaptabilidade do que com a estabilidade.
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