Effect of salt stress on growth, Na+ accumulation and proline metabolism in potato (Solanum tuberosum) cultivars.

Potato (Solanum tuberosum) is a major crop world-wide and the productivity of currently used cultivars is strongly reduced at high soil salt levels. We compared the response of six potato cultivars to increased root NaCl concentrations. Cuttings were grown hydroponically and treated with 0 mM, 60 mM and 180 mM NaCl for one week. Growth reduction on salt was strongest for the cultivars Mozart and Mona Lisa with a severe senescence response at 180 mM NaCl and Mozart barely survived the treatment. The cultivars Desiree and Russett Burbank were more tolerant showing no senescence after salt treatment. A clear difference in Na(+) homeostasis was observed between sensitive and tolerant cultivars. The salt sensitive cultivar Mozart combined low Na(+) levels in root and stem with the highest leaf Na(+) concentration of all cultivars, resulting in a high Na(+) shoot distribution index (SDI) for Mozart as compared to Desiree. Overall, a positive correlation between salt tolerance and stem Na(+) accumulation was found and the SDI for Na(+) points to a role of stem Na(+) accumulation in tolerance. In stem tissue, Mozart accumulated more H2O2 and less proline compared to the tolerant cultivars. Analysis of the expression of proline biosynthesis genes in Mozart and Desiree showed a clear reduction in proline dehydrogenase (PDH) expression in both cultivars and an increase in pyrroline-5-carboxylate synthetase 1 (P5CS1) gene expression in Desiree, but not in Mozart. Taken together, current day commercial cultivars show promising differences in salt tolerance and the results suggest that mechanisms of tolerance reside in the capacity of Na(+) accumulation in stem tissue, resulting in reduced Na(+) transport to the leaves.

Transmission of wild-type and recombinant HaSNPV among larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) on cotton.

Horizontal transmission of insect viruses is a key factor in their cycling in agro-ecosystems. Here we study the transmission of the baculovirus HaSNPV among larvae of Helicoverpa armigera (Hübner) in cotton. Transmission of three HaSNPV genotypes was studied from larvae infected with a single virus genotype and from larvae infected with two different genotypes. Genotypes included a wild-type virus, an ecdysteroid UDP-glucosyltransferase (egt) deletion mutant (HaSNPV-LM2) with slightly enhanced speed of kill, and an egt-negative genotype that expresses a neurotoxin gene derived from the scorpion Androctonus australis Hector (HaSNPV-4A). The latter genotype has a substantially increased speed of kill. In three field experiments, the wild-type and egt deletion virus variants and a mixture of the two had similar rates of transmission. Transmission increased with density of infector insects and decreased with time lapsed since the inoculation of the infector larvae. Transmission of the neurotoxin expressing virus was lower than that of the other two genotypes in a glasshouse experiment. The studied genotypes of HaSNPV have significant differences in time to kill and virus yield, but we found no significant differences in rates of virus transmission at the crop level in the case of the egt deletion variant HaSNPV-LM2. Transmission of the transgenic virus genotype HaSNPV-4A was significantly reduced. Overall, differences in transmission between virus genotypes were subtler, and more difficult to detect with statistical significance, than effects of other factors, such as density of infectors and time delay between release of infectors and recipient caterpillars on the plant.