Embryogenic calli derived from anther cultures of the two-rowed winter barley cultivar 'Igri' were plated on solid L3 medium containing the proline analogue hydroxyproline (Hyp), 10-20 mmol l −1 . Exposure to Hyp caused severe degeneration of most of the calli. Hyp resistant calli, distinguishable by their lighter colour and higher growth rate, and control calli not exposed to Hyp were plated on L3 regeneration medium. From 22,500 anthers exposed to Hyp 46 Hyp resistant regenerates were obtained, which were transferred to soil. After cultivation for 5-10 weeks at normal growth conditions they were cold hardened at 2 • C under short day conditions together with control regenerates. Frost tolerance assays with segments of fully grown leaves of unhardened and cold hardened plants revealed that Hyp resistant regenerants were significantly more frost tolerant than the control regenerants. Improved frost tolerance was found also in the progenies R 1 to R 9 , and genotypic segregation in the R 1 generation in a 1:2:1 ratio was indicated. Increased proline content was observed in the R 2 generation and in subsequent generations and was significantly (P ≤ 0.001) correlated with increased frost tolerance in the Hyp lines. Comparative studies of R 9 progenies from homozygous R 2 plants with the wild type 'Igri' under field conditions in winter at three locations in Europe as well as crossing experiments confirmed the heritable improvement of frost tolerance and winter survival, respectively, in the Hyp lines. The results support the hypothesis that proline accumulation in cold acclimated winter barley plants is causally related to the acquisition of frost tolerance. Moreover, the described biotechnological procedure may be applicable in breeding programs for improved winter hardiness and possibly also for other stress tolerances.

Five hundred hydroxyproline‐resistant cell lines were selected from cell cultures of wheat (Triticum aestivum L. cv. Koga II) after plating on 10 to 30 mM hydroxyproline (Hyp) containing solid Gamborg B 5 medium. All selected cell lines from 30 mM Hyp‐medium contained increased (up to 17‐fold) levels of free proline. Seventy‐four cell lines were transferred to Hyp‐free medium and subcultivated 25 times, for 12 months altogether, after which 80% still had increased proline levels. Fourteen cell lines with increased proline levels were further investigated in liquid media with regard to their frost tolerance, which was measured by means of electrolyte leakage. Ten of them showed increased fros tolerance, with LT 50 values as low as 2.7°C below that of the wild type (‐4.7°C). Besides increased proline levels and increased percentage dry weight, the Hyp‐resistant cell lines had lower osmotic potentials. Osmotic potentials correlated better than levels of free proline with the increase in frost tolerance.

A new form of disease called Ôdie-backÕ has been established in Dalbergia sissoo trees. This disease has reached epidemic proportions in Bangladesh as well as in other countries of South Asia and is characterized by browning of the leaves, signs of wilting, and trunk lesions with gum flow. The trees die within a few months. In order to investigate the causes of this dieback disease, samples were taken for a first trial in the Rajshahi division at two sites around Sherpur. For the isolation of bacteria, surface-sterilized plant material (leaves, twigs and trunk bark) from diseased trees was transferred to LB medium and incubated. After isolation of single colonies, various bacteria species could be identified by polymerase chain reaction analysis with two primers specific for highly conserved sequence regions in the bacterial 16S rDNA and by sequencing. First indications for the presence of bacteria with phytopathogenic potential were found.

The causal agent(s) of dieback of sissoo (Dalbergia sissoo Roxb. ) have not yet been identified unequivocally. Putative microbial pathogens (fungi and bacteria) were studied in dieback affected sissoo trees collected from Bangladesh, using plant pathological techniques combined with molecular tools. DNA based characterization showed the presence of heterogeneous patterns of various fungi (mostly saprophytic). It did not support the hypothesis of Fusarium solani being the cause of sissoo dieback. In contrast, isolation and molecular characterisation of bacteria from dieback affected sissoo revealed the presence of Pseudomonas in 83% of the samples. Sequencing the gene of 16S ribosomal RNA, the rpoD-gene, the gacAgene and the rnpB-gene strongly suggested that these isolates belong most probably to a still unassigned Pseudomonas species. Hypersensitivity response assays and infection studies using sissoo seedlings demonstrated their pathogenic potential.

The possible role of bacteria as pathogens in dieback affected Dalbergia sissoo Roxb. (sissoo) trees in Bangladesh has been investigated. Among the high diversity of bacterial genera detected by 16S rDNA sequences, several plant pathogenic Pseudomonas strains were identified and classified by AFLP analysis. Three isolates produced significant symptoms on D. sissoo seedlings after mechanical inoculation in vivo, suggesting that Pseudomonas should be considered as a potential cause for the dieback disease. DOI: http://dx.doi.org/10.3329/bjb.v42i1.15710 Bangladesh J. Bot. 42(1): 1-16, 2013 (June)