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Date palm trees (Phoenix dactylifera) were found to be infected with Chalara radicicola and Chalara (Thielaviopsis) paradoxa in 1992. Compared with healthy palms, most of the diseased palms appeared to be drought stressed and poorly maintained in landscape settings and nurseries. Water potential studies conducted in growth chambers with 5- to 6-leaf seedling plants subjected to water stress at -2.3 MPa had relatively larger necrotic lesions that developed into cankers, death of buds, and eventually plant death. Tissue necrosis was directly related to water potential. Histological studies showed many necrotic islands of parenchyma tissue in drought-stressed infected plants. Only a few inoculated plants in the growth chamber study died without developing extensive cankers, apparently due to the invasion of the crown or terminal bud by the pathogens. In vitro studies with potato dextrose agar amended with glycerol, NaCl, and KCl to decrease the osmotic matrix-based water potential of the media (-4.25 MPa) resulted in a decrease in the radial growth, biomass, and the sporulation of C. radicicola and T. paradoxa. Solute potential of -0.35 to -1.97 MPa, however, favored the growth of both fungi. Sodium chloride had the greatest effect on the growth characteristics of both fungal species. These studies indicate that in parts of Kuwait where drought and salinity prevail, opportunistic pathogens such as C. radicicola and T. paradoxa could become aggressive and cause serious damage to date palms.

Androgenesis of wheat genotypes was evaluated by pretreating anthers or embryo-like structures (ELS) with polyamines. Anthers of the genotype DH were pretreated with different concentrations of putrescine, spermidine, and spermine for 1, 3, and 6 h, and those of drought-tolerant International Center for Agricultural Research in the Dry Areas (ICARDA) wheat accessions were treated for 1 and 3 h. ELS of two genotypes were also treated for 30 and 60 min with the same polyamines and evaluated for green plant regeneration. The pretreatment of anthers with polyamines enhanced the development of ELS in all genotypes. The formation of ELS varied significantly with genotype. Pretreated anthers showed that four treatments improved significantly green plant regeneration with the genotype ICR 17. However, two treatments (1 mM putrescine or spermine for 1 h) significantly improved green plant regeneration per 100 ELS of only two ICAR-DA genotypes. ELS treated with polyamines for 30 min were greener and formed more adventitious roots. The chloroplasts of these greener ELS examined with a transmission electron microscope had agranal to grana thylakoids, while those of the control had plastids with mostly starch globules. Although exogenous application of polyamines to anthers improved the production of ELS and green plants, the effects of putrescine, spermidine, and spermine was dependent on genotype and the duration of pretreatment of anthers with the polyamines.

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