The role of the phytotoxin coronatine in the virulence of Pseudomonas syringae pv. tomato in Arabidopsis thaliana was evaluated by comparing symptom development, in planta bacterial multiplication, and the induction of defense-related genes in Arabidopsis plants inoculated with the coronatine-producing (Cor+) P. s. pv. tomato strain DC3000 and the coronatine-defective (Cor-) strain DC3661 by either infiltration or dipping methods. The Cor+ strain, P. s. pv. tomato DC3000, caused severe disease symptoms and multiplied by 4-6 logs after inoculation by either infiltration or dipping. P. s. pv. tomato DC3661 failed to produce any disease symptoms and multiplied by only 1-1.5 logs in dipped plants, whereas it caused mild symptoms and multiplied 6 logs over the 4-day experimental period in plants inoculated by infiltration. Parallel experiments using a natural host, tomato, yielded similar results. Analysis of the accumulation of mRNAs encoded by several distinct defense-related genes in Arabidopsis leaves infiltrated with either DC3000 or DC3661 demonstrated that the Cor- strain consistently induced higher levels of these transcripts. These results demonstrate that coronatine production is required under more natural inoculation conditions for the successful infection of Arabidopsis by DC3000, and that coronatine may play a critical role during the early stages of infection by suppressing the activation of defense-related genes.

The role of the phytotoxin coronatine in the virulence of Pseudomonas syringae pv. tomato in Arabidopsis thaliana was evaluated by comparing symptom development, in planta bacterial multiplication, and the induction of defense-related genes in Arabidopsis plants inoculated with the coronatine-producing (Cor+ ) P. s. pv. tomato strain DC3000 and the coronatine-defective (Cor-) strain DC3661 by either infiltration or dipping methods. The Cor+ strain, P. s. pv. tomato DC3000, caused severe disease symptoms and multiplied by 4-6 logs after inoculation by either infiltration or dipping. P. s. pv. tomato DC3661 failed to produce any disease symptoms and multiplied by only 1-1.5 logs in dipped plants, whereas it caused mild symptoms and multiplied 6 logs over the 4-day experimental period in plants inoculated by infiltration. Parallel experiments using a natural host, tomato, yielded similar results. Analysis of the accumulation of mRNAs encoded by several distinct defense-related genes in Arabidopsis leaves infiltrated with either DC3000 or DC3661 demonstrated that the Cor- strain consistently induced higher levels of these transcripts. These results demonstrate that coronatine production is required under more natural inoculation conditions for the successful infection of Arabidopsis by DC3000, and that coronatine may play a critical role during the early stages of infection by suppressing the activation of defense-related genes.

Glucose oxidase (GOD) produced by a strain of Penicillium (Penicillium variabile P16) was employed, in a model system, to control the activities of tomato lipoxygenase (LPO), polyphenoloxidase (PPO), and peroxidase (POD). GOD inhibited all three enzymes, at the typical pH of tomato fruit (4.3), i.e., the LPO was inhibited up to ca. 88%, the PPO up to ca. 63% and the POD up to ca. 50%. GOD also prevented beta-carotene bleaching caused by these enzymes.

Sandofan-M and Ridomil mz-72 Gave good control of Phytophthora infestans under laboratory conditions as well as in the field while Captan-50 WP, Daconil and Dithane M-45 were less effective. Among twelve varieties/lines, Paceter, Riogeranali and L.T. 1991 showed better performance. However, none of the varieties was found to be immune to the pathogen.

The efficacy of flourescent Pseudomonas to control tomato damping-off caused by Rhizoctonia solani was evaluated under laboratory and screenhouse conditions. In vitro tests showed that flourescent Pseudomonas at 25, 45, 50, and 55 percent transmittance which corresponded to 294 x 10 to the eighth power, 283 x 10 to the sixth power, 251 x 10 to the sixth power colony forming units (cfu)/ml inhibited the mycelial growth of R. solani, with 294 x 10 to the eighth power cfu/ml causing the highest inhibition. Screenhouse test showed treatment of flourescent Pseudomonas during transplanting gave the lowest percent wilting of tomato plants of 20 and 40 percent, with correponding 77.3 and 57.4 percent control, for 294 x 10 to the eighth power and 251 x 10 to the sixth power cfu/ml, respectively. Lowest control was observed when treatment was done 14 days after transplanting. The results implied that flourescent Pseudomonas can be an effective biocontrol agent against tomato damping-off if applied in tomato plants during transplanting

We have isolated a novel mutation that caused variegated leaf color in a tomato plant which had multiple maize Ac transposable elements and the tomato Xa allele. Xa is a previously characterized semi-dominant mutation that causes tomato leaves to be bright yellow when heterozygous (Xa/xa+). The mutation responsible for the new phenotype was named Mox (Modifier of Xa). The Mox mutation modified the Xa/xa+ yellow leaf phenotype in two ways: it compensated for the Xa allele resulting in a plant with a wildtype green color, and it caused somatic variegation which appeared as white and yellow sectors on the green background. Somatic variegation was visible only if the plant contained both the Mox and Xa loci. Genetic studies indicated that the Mox locus was linked in repulsion to Xa and that the Mox locus was genetically transmitted at a reduced frequency through the male gamete. Molecular characterization of the Ac elements in lines segregating for Mox identified an Ac insertion that appeared to cosegregate with Mox variegation. We propose a model in which the Mox mutation consists of a duplication of the xa+ allele and subsequent AC-induced breakage of the duplicated region causes variegation.

We have isolated a novel mutation that caused variegated leaf color in a tomato plant which had multiple maize Ac transposable elements and the tomato Xa allele. Xa is a previously characterized semi-dominant mutation that causes tomato leaves to be bright yellow when heterozygous (Xa/xa+). The mutation responsible for the new phenotype was named Mox (Modifier of Xa). The Mox mutation modified the Xa/xa+ yellow leaf phenotype in two ways: it compensated for the Xa allele resulting in a plant with a wildtype green color, and it caused somatic variegation which appeared as white and yellow sectors on the green background. Somatic variegation was visible only if the plant contained both the Mox and Xa loci. Genetic studies indicated that the Mox locus was linked in repulsion to Xa and that the Mox locus was genetically transmitted at a reduced frequency through the male gamete. Molecular characterization of the Ac elements in lines segregating for Mox identified an Ac insertion that appeared to cosegregate with Mox variegation. We propose a model in which the Mox mutation consists of a duplication of the xa+ allele and subsequent AC-induced breakage of the duplicated region causes variegation.

A pressure-flux approach was used to evaluate the effects of HgCl2 on water transport in tomato (Lycopersicon esculentum) roots. Addition of HgCl2 to a root-bathing solution caused a large and rapid reduction in pressure-induced root water flux; the inhibition was largely reversible upon addition of beta-mercaptoethanol. Root system hydraulic conductivity was reduced by 57%. There was no difference between treatments in the K+ concentration in xylem exudate. The results are consistent with the presence of a protein-mediated path for transmembrane water flow in tomato roots.

The joint action of metribuzin and tridiphane was investigated in metribuzin-tolerant (T) and metribuzin-susceptible (S) soybean and tomato cultivars within species, respectively, under growth room studies. Maple Arrow (T) and Maple Amber (S) exhibited similar tolerance to tridiphane applied at soybean emergence. Vision (T) tomato was more sensitive to tridiphane than was Springset (S) tomato, the reverse of the relative tolerance to metribuzin. A phytotoxic interaction was demonstrated following application of tridiphane and metribuzin at the respective rates (kg ai ha-1) of 0.1 and 1.1 in Maple Arrow (T) soybeans, 0.05 and 0.25 in Maple Amber (S) soybeans, and 0.25 and 0.2 in Springset (S) tomato. Tridiphane applied 1 or 4 h before metribuzin caused the greatest phytotoxicity in Maple Amber (S) soybeans. Soybean field results generally supported those of growth-room studies. Foliar spray pretreatment with tridiphane increased total radioactivity in Springset (S), decreased the total root radioactivity and increased total shoot radioactivity in both Vision (T) and Springset (S) and decreased metabolism of metribuzin to water soluble conjugates in Springset (S) roots over 24 h following 14C-metribuzin application to roots of intact tomato seedlings. The increased uptake, translocation to the shoots, and decreased root metabolism of metribuzin in Springset when pretreated with tridiphane could explain the phytotoxic interaction (which was unexpected, based only on the glucose detoxification pathway of metribuzin in tomato).

Tomato plants overexpressing a prosystemin gene that encodes the precursor of a mobile wound signal called systemin have been shown previously to constitutively synthesize extraordinarily high levels of two defensive proteinase inhibitor proteins in leaves in the absence of wounding. We herein report that leaves of these transgenic plants possess enhanced levels of another defensive protein, polyphenol oxidase (PPO) at levels that are up to 70-fold higher than levels found in leaves of wild-type plants. Supplying young wild type tomato plants with systemin through cut stems induced PPO activity in leaves, and wounding lower leaves of young tomato plants induced PPO activity in both wounded and unwounded leaves to levels equal to those induced by systemin. Exposing young tomato plants to methyl jasmonate vapor caused an increase in PPO activity equivalent to levels found in plants overexpressing the prosystemin gene. The data indicate that PPO and proteinase inhibitor genes are coactivated systemically by wounding via the octadecanoid signal transduction pathway and that systemin has a much broader role in signaling plant defensive genes than was previously known.